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  • 1. Agrell, H. G.
    et al.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Conductivity studies of nanostructured TiO2 films permeated with electrolyte2004In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 108, no 33, 12388-12396 p.Article in journal (Refereed)
    Abstract [en]

    Charge transport in nanostructured TiO2 films permeated with an electrolyte was studied, using temperature-dependent conductivity and electron accumulation measurements. Two regions for charge transport were distinguished from the relationship between conductivity and electron concentration. In the first region (similar to1-20 electrons per TiO2 particle), the effective electron mobility is dependent on the electron concentration and values between 7 x 10(-4) and 78 x 10(-4) cm(2) V-1 s(-1) were determined. The activation energy of the mobility was similar to0.3 eV. The charge transport can be described with a trapping/detrapping model that involves localized band-gap states. In the second region (> 20 electrons per TiO2 particle), the effective electron mobility is independent of electron concentration and values of similar to150 x 10(-4) cm(2) V-1 s(-1) are calculated. The activation energy of mobility is in the range of 0-0.15 eV, depending on the electrolyte. Transport of electrons in the conduction band seems to be the most applicable model.

  • 2. Alarcon, H.
    et al.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Mendoza, P.
    Solis, J. L.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Dye-sensitized solar cells based on nanocrystalline TiO2 films surface treated with Al3+ ions: Photovoltage and electron transport studies2005In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 109, no 39, 18483-18490 p.Article in journal (Refereed)
    Abstract [en]

    Nanocrystalline TiO2 films, surface modified with Al3+, were manufactured by depositing a TiO2 suspension containing small amounts of aluminum nitrate or aluminum chloride onto conducting glass substrates, followed by drying, compression, and finally heating to 530 degrees C. Electrodes prepared with TiO2 nanoparticles coated with less than 0.3 wt % aluminum oxide with respect to TiO2 improved the efficiency of the dye sensitized solar cell. This amount corresponds to less than a monolayer of aluminum oxide. Thus, the Al ions terminate the TiO2 surface rather than form a distinct aluminum oxide layer. The aluminum ion surface treatment affects the solar cell in different ways: the potential of the conduction band is shifted, the electron lifetime is increased, and the electron transport is slower when aluminum ions are present between interconnected TiO2 particles.

  • 3. Alarcon, Hugo
    et al.
    Hedlund, Maria
    Johansson, Erik M. J.
    Rensmo, Hakan
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Modification of nanostructured TiO2 electrodes by electrochemical Al3+ insertion: Effects on dye-sensitized solar cell performance2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 35, 13267-13274 p.Article in journal (Refereed)
    Abstract [en]

    Nanostructured TiO2 films were modified by insertion with aluminum ions using an electrochemical process. After heat treatment these films were found suitable as electrodes in dye-sensitized solar cells. By means of a catechol adsorption test, as well as photoelectron spectroscopy (PES), it was demonstrated that the density of Ti atoms at the metal oxide/electrolyte interface is reduced after Al modification. There is, however, not a complete coverage of aluminum oxide onto the TiO2, but the results rather suggest either the formation of a mixed Al-Ti oxide surface layer or formation of a partial aluminum oxide coating. No new phase could, however, be detected. In solar cells incorporating Al-modified TiO2 electrodes, both electron lifetimes and electron transport times were increased. At high concentrations of inserted aluminum ions, the quantum efficiency for electron injection was significantly decreased. Results are discussed at the hand of different models: A multiple trapping model, which can explain slower kinetics by the creation of additional traps during Al insertion, and a surface layer model, which can explain the reduced recombination rate, as well as the reduced injection efficiency, by the formation of a blocking layer.

  • 4. Bauer, C.
    et al.
    Boschloo, Gerrit
    Mukhtar, E.
    Hagfeldt, A.
    Electron injection and recombination in Ru(dcbpy)(2)(NCS)(2) sensitized nanostructured ZnO2001In: Journal of Physical Chemistry B, ISSN 1089-5647, Vol. 105, no 24, 5585-5588 p.Article in journal (Refereed)
    Abstract [en]

    The dynamics of electron-transfer processes between bis(tetrabutylammonium) cis-bis(thiocyanato)bis(2,2'-bypiridine-4,4'-dicarboxylato)ruthenium(II) (called N719) and nanostructured ZnO films have been investigated by femtosecond and nanosecond spectroscopy. The incident photon to current conversion efficiency (IPCE) for these dye-sensitized electrodes was 36% in the maximum of 530 nm, corresponding to a quantum efficiency of 80%. The highest: IPCE values were obtained when the electrodes were prepared under conditions where formation of dye aggregates in the pores of the nanostructured films is avoided. For such films, the electron injection time was in the subpicosecond regime (< 300 fs), which is comparable to the N719-TiO2 system. The back electron-transfer kinetics between conduction band electrons and oxidized dye molecules were biexponential with time constants of 300 mus and 2.6 us. Variation of the light intensity did not affect the time constants, but only their relative weights. The kinetics of back electron transfer in the N719-ZnO and N719-TiO2 systems were found to be identical.

  • 5. Bauer, C.
    et al.
    Boschloo, Gerrit
    Mukhtar, E.
    Hagfeldt, A.
    Interfacial electron-transfer dynamics in Ru(tcterpy)(NCS)(3)-sensitized TiO2 nanocrystalline solar cells2002In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 106, no 49, 12693-12704 p.Article in journal (Refereed)
    Abstract [en]

    The anchoring of the ruthenium dye {(C4H9)(4)N}[Ru(Htcterpy)(NCS)(3)] (with tcterpy = 4,4',4-tricarboxy2,2':6',2-terpyridine), the so-called black dye, onto nanocrystalline TiO2 films has been characterized by UV-vis and FT-IR spectroscopies. FT-IR spectroscopy data suggest that dye molecules are bound to the surface by a bidentate binuclear coordination mode. The interfacial electron-transfer (ET) dynamics has been investigated by femtosecond pump-probe transient absorption spectroscopy and nanosecond laser flash photolysis. The electron-injection process from the dye excited state into the TiO2 conduction band is biexponential with a fast component (200 +/- 50 fs) and a slow component (20 ps). These two components can be attributed to the electron injection from the initially formed and the relaxed dye excited states, respectively. Nanosecond kinetic data suggest the existence of two distinguishable regimes (I and II) for the rates of reactions between injected electrons and oxidized dye molecules or oxidized redox species (D+ or I-2(.-)). The frontier between these two regimes is defined by the number of injected electrons per particle (Ne), which was determined to be about 1. The present kinetic study was undertaken within regime I (N-e > 1). Under these conditions, the back-electron-transfer kinetics is comparable to that in systems with other ruthenium complexes adsorbed onto TiO2. The reduction of oxidized dye molecules by iodide results in the formation of I-2(.-) on a very fast time scale (<20 ns). Within regime 1, the decay of I-2(.-) occurs in similar to100 ns via reaction with injected electrons (I-2(.-) + e(-) --> 2I(-)). In regime II (N-e less than or equal to 1), which corresponds to the normal operating conditions of dye-sensitized solar cells, the decay of I-2(.-) is very slow and likely occurs via the dismutation reaction (2I(2)(.-) --> I- + I-3(-)). Our results predict that, under high light intensity (N-e > 1), the quantum efficiency losses in dye-sensitized solar cells will be important because of the dramatic acceleration of the reaction between I-2(.-) and injected electrons. Mechanisms for the ET reactions involving injected electrons are proposed. The relevance of the present kinetic studies for dye-sensitized nanocrystalline solar cells is discussed.

  • 6. Bauer, C.
    et al.
    Boschloo, Gerrit
    Mukhtar, E.
    Hagfeldt, A.
    Ultrafast relaxation dynamics of charge carriers relaxation in ZnO nanocrystalline thin films2004In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 387, no 03-jan, 176-181 p.Article in journal (Refereed)
    Abstract [en]

    Ultrafast spectroscopy has been used to study the relaxation processes of charge carriers in ZnO nanocrystalline thin films. A broad red-IR absorption band linked to shallowly trapped electrons was observed by spectroelectrochemical measurements. Femtosecond transient absorption data revealed multiexponential decays of the charge carriers with time constants ranging from 1 to 400 ps. The decay profile of the signal shows a probe wavelength dependence. This effect is assigned to the trapping (localisation) of nonequilibrium charge carriers which occurs on a time scale of similar to1 ps. The recombination of shallowly trapped electrons with deeply trapped holes, determined by single-photon counting, mainly occurs in 400 ps.

  • 7. Bauer, C.
    et al.
    Boschloo, Gerrit
    Mukhtar, E.
    Hagfeldt, A.
    Ultrafast studies of electron injection in Ru dye sensitized SnO2 nanocrystalline thin film2002In: International Journal of Photoenergy (Online), ISSN 1110-662X, E-ISSN 1687-529X, Vol. 4, no 1, 17-20 p.Article in journal (Refereed)
    Abstract [en]

    By using two-color femtosecond transient absorption spectroscopy, we have measured the electron injection rate for bis(tetrabutylammonium) cis di(thiocyanato) bis (2,2-bypiridine-4,4 carboxylic acid) Ruthenium (II) dye ( called N719) into SnO2 nanocrystalline thin films. The electron injection rate has been measured by monitoring the formation of the dye oxidized state and the arrival of electrons in the conduction band. Dynamics of electron injection are multiexponential (0.2, 4 and 130 ps) and are therefore slower than the N719-ZnO or N719-TiO2 systems. The photocurrent action spectrum of N719-SnO2 shows a quantum efficiency of 0.65 at 530 nm proving that efficient charge separation can take place despite of the relatively slow electron injection rate.

  • 8. Beermann, N.
    et al.
    Boschloo, Gerrit
    Hagfeldt, A.
    Trapping of electrons in nanostructured TiO2 studied by photocurrent transients2002In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 152, no 03-jan, 213-218 p.Article in journal (Refereed)
    Abstract [en]

    The electron transport in nanostructured TiO2 has been investigated in an electrochemical system using laser flash induced photocurrent transient measurements with additional continuous monochromatic bias light. Significant effects are found on the photocurrent transient depending on the wavelength of the bias light (360-480 nm). The electron transport time is shorter and the total collected charge is higher when the bias light is in the UV region, while increased transport times and a decreased charge is found with visible light bias. These effects can be explained by trap filling by the UV bias light in the first case and by emptying of traps by visible bias light in the latter.

  • 9. Borgstrom, M.
    et al.
    Blart, E.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Mukhtar, E.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Hammarstrom, L.
    Odobel, F.
    Sensitized hole injection of phosphorus porphyrin into NiO: Toward new photovoltaic devices2005In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 109, no 48, 22928-22934 p.Article in journal (Refereed)
    Abstract [en]

    This paper describes the preparation and the characterization of a photovoltaic cell based on the sensitization of a wide band gap p-type semiconductor (NiO) with a phosphorus porphyrin. A photophysical study with femtosecond transient absorption spectroscopy showed that light excitation of the phosphorus porphyrin chemisorbed on NiO particles induces a very rapid interfacial hole injection into the valence band of NiO, occurring mainly on the 2-20 ps time scale. This is followed by a recombination in which ca. 80% of the ground-state reactants are regenerated within 1 ns. A photoelectrochernical device, prepared with a nanocrystalline NiO electrode coated with the phosphorus porphyrin, yields a cathodic photocurrent indicating that electrons indeed flow from the NiO electrode toward the solution. The low incident-to-photocurrent efficiency (IPCE) can be rationalized by the rapid back recombination reaction between the reduced sensitizer and the injected hole which prevents an efficient regeneration of the sensitizer ground state from the iodide/triiodide redox mediator. To the best of our knowledge, this work represents the first example of a photovoltaic cell in which a mechanism of hole photoinjection has been characterized.

  • 10. Boschloo, Gerrit
    et al.
    Fitzmaurice, D.
    Electron accumulation in nanostructured TiO2 (anatase) electrodes2000In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 147, no 3, 1117-1123 p.Article in journal (Refereed)
    Abstract [en]

    The potential-dependent optical-absorption spectroscopy of nanostructured TiO2 (anatase) is most fully accounted for by two processes, band-filling and intercalation. Under weak-accumulation conditions, occupation of surface and conduction-band states by electrons dominates with the accumulated charge being compensated by adsorbed protons or cations. Under strong-accumulation conditions, however, intercalation of protons or cations may take place with a fraction of the accumulated electrons being localized at Ti-IV sites.

  • 11. Boschloo, Gerrit
    et al.
    Hagfeldt, A.
    Photoinduced absorption spectroscopy of dye-sensitized nanostructured TiO22003In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 370, no 04-mar, 381-386 p.Article in journal (Refereed)
    Abstract [en]

    Photoinduced absorption (PIA) spectroscopy was used to investigate dye-sensitized electrodes and solar cells under illumination conditions comparable to sunlight. In the absence of redox electrolyte, cis-Ru (dcbpy)(2)(NCS)(2)-sensitized nanostructured TiO2 films show a long-lived photoinduced charge-separation (oxidized dye molecules/injected electrons in TiO2), with a lifetime of about 10(-3) s under full sun illumination. The PIA spectrum of a complete dye-sensitized cell is due to electrons in TiO2 and iodine radicals (12) in the electrolyte. The lifetime of this charge-separated state at open-circuit conditions was determined to be 0.15 s (0.27 sun illumination).

  • 12. Boschloo, Gerrit
    et al.
    Hagfeldt, A.
    Spectroelectrochemistry of nanostructured NiO2001In: Journal of Physical Chemistry B, ISSN 1089-5647, Vol. 105, no 15, 3039-3044 p.Article in journal (Refereed)
    Abstract [en]

    Transparent nanostructured NiO electrodes have been prepared by heating Ni(OH)(2) sol-gel films at a temperature of 300-320 degreesC. Nanostructured NiO (bunsenite) behaves as a p-type semiconductor and has an indirect band gap of 3.55 eV. It shows a strong anodic electrochromic effect, as it changes color from transparent to brown-black upon application of positive potentials. This effect is caused by oxidation of Ni atoms located at the NiO/electrolyte interface. Electrochemical oxidation reactions are highly reversible in both aqueous and nonaqueous electrolytes. In aqueous electrolyte, the half-potentials show a Nernstian pH dependence, whereas in nonaqueous electrolytes, the type of cation present determines the shape and position of the cyclic voltammogram.

  • 13.
    Boschloo, Gerrit
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Activation energy of electron transport in dye-sensitized TiO2 solar cells2005In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 109, no 24, 12093-12098 p.Article in journal (Refereed)
    Abstract [en]

    Various characteristics of dye-sensitized nanostructured TiO2 solar cells, such as electron transport and electron lifetime, were studied in detail using monochromatic illumination conditions. The electron transport was found to be a thermally activated process with activation energies in the range of 0.10-0.15 eV for light intensities that varied 2 orders of magnitude. Electron lifetimes were determined using a new method and found to be significantly larger (> 1 s) than previously determined. An average potential was determined for electrons in the nanostructured TiO2 under illumination in short-circuit conditions. This potential is about 0.2 V lower than the open-circuit potential at the same light intensity. The electron transport time varies exponentially with the internal potential at short-circuit conditions, indicating that the gradient in the electrochemical potential is the driving force for electron transport in the nanostructured TiO2 film. The applicability of the conventionally used trapping/detrapping model is critically analyzed. Although experimental results can be fitted using a trapping/detrapping model with an exponential distribution of traps, the distribution parameters differ significantly between different types of experiment. Furthermore, the experimental activation energies for electron transport are smaller than those expected in a trapping/detrapping model.

  • 14.
    Boschloo, Gerrit
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Photoinduced absorption spectroscopy as a tool in the study of dye-sensitized solar cells2008In: Inorganica Chimica Acta, ISSN 0020-1693, E-ISSN 1873-3255, Vol. 361, no 3, 729-734 p.Article in journal (Refereed)
    Abstract [en]

    Photoinduced absorption (PIA) spectroscopy, where the excitation is provided by a square-wave modulated (on/off) monochromatic light source, is a versatile tool in the study of dye-sensitized solar cells. Spectra of transient species, such as the oxidized dye, can easily be obtained and their kinetics can be explored using frequency or time-resolved techniques. Experimental PIA conditions can be kept close to typical solar cell operating conditions, allowing extraction of relevant time constants. PIA is also a suitable method to study the quality of pore filling in case of solid hole conductors. Dye molecules that are not in direct contact with the hole conductor will have long lifetimes in their oxidized state and appear clearly in the PIA spectrum. The basic principles of PIA are explained using the example of electron injection and recombination in dye-sensitized TiO2 in the absence of redox electrolyte.

  • 15.
    Boschloo, Gerrit
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Haggman, L.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Quantification of the effect of 4-tert-butylpyridine addition to I-/I-3(-) redox electrolytes in dye-sensitized nanostructured TiO2 solar cells2006In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 26, 13144-13150 p.Article in journal (Refereed)
    Abstract [en]

    Addition of 4-tert-butylpyridine (4TBP) to redox electrolytes used in dye- sensitized TiO2 solar cells has a large effect on their performance. In an electrolyte containing 0.7 M LiI and 0.05 M I-2 in 3-methoxypropionitrile, addition of 0.5 M 4TBP gave an increase of the open-circuit potential of 260 mV. Using charge extraction and electron lifetime measurements, this increases could be attributed to a shift of the TiO2 band edge toward negative potentials (responsible for 60% of the voltage increase) and to an increase of the electron lifetime (40%). At a lower 4TBP concentration the shift of the band edge was similar, but the effect on the electron lifetime was less pronounced. The working mechanism of 4TBP can be summarized as follows: (1) 4TBP affects the surface charge of TiO2 by decreasing the amount of adsorbed protons and/or Li+ ions. ( 2) It decreases the recombination of electrons in TiO2 with triiodide in the electrolyte by preventing triiodide access to the TiO2 surface and/or by complexation with iodine in the electrolyte.

  • 16.
    Boschloo, Gerrit K.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630). KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Edvinsson, Tomas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630). KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630). KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Dye-Sensitized Nanostructured ZnO Electrodes for Solar Cell Applications2006In: Nanostructured Materials for Solar Energy Conversion, Elsevier, 2006, 227-254 p.Chapter in book (Other academic)
    Abstract [en]

    This chapter describes dye-sensitized nanostructured ZnO electrodes for solar cell applications. Dye-sensitized nanostructured solar cells (DNSCs) based on nanostructured metal oxide films have attracted much attention in recent years. This chapter explains the schematic representation of the DNSC. The performance of dye-sensitized ZnO solar cells in terms of solar-to-electrical energy conversion efficiencies is so far significantly lower than that of TiO2, reaching currently about 4-5%. An analysis of the energetics and kinetics of ZnO-based DNSCs suggests that this is mainly because of the lesser degree of optimization in case of ZnO compared to TiO2-based DNSCs. A large potential exists to improve on the performance of dye-sensitized ZnO solar cells by learning how to use new types of anchoring groups and controlling the chemistry at the oxide/dye/electrolyte interface. This, in combination with the possibilities to tailor-make ZnO materials, manifests the opportunities for future research and development of these devices.

  • 17. Boschloo, Gerrit
    et al.
    Lindström, J.
    Magnusson, E.
    Holmberg, A.
    Hagfeldt, A.
    Optimization of dye-sensitized solar cells prepared by compression method2002In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 148, no 03-jan, 11-15 p.Article in journal (Refereed)
    Abstract [en]

    Nanostructured TiO2 films have been deposited onto conducting glass and on flexible conducting plastic substrates using a compression technique. Dye-sensitized solar cells prepared from Degussa P25 TiO2 powder, red dye (Ru(dcbpy)(2)(SCN)(2)) or black dye (Ru(tcterpy)(SCN)(3)) and an electrolyte containing LiI and I-2 in 3-methoxypropionitrile were tested using standard photoelectrochemical techniques. The average overall efficiency of small open cells sensitized with the red dye on plastic substrates was 4.5% (100W m(-2)). In a direct comparison, red and black dye gave about the same efficiencies. For both dyes, addition of 4-tert-butylpyridine to the electrolyte resulted in a decreased IPCE response in the whole spectral range, with a specific decrease in the red region, which is attributed to a shift in the conduction band edge of the nano structured TiO2.

  • 18. Colodrero, Silvia
    et al.
    Mihi, Agustin
    Häggman, Leif
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Ocana, Manuel
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Miguez, Hernan
    Porous One-Dimensional Photonic Crystals Improve the Power-Conversion Efficiency of Dye-Sensitized Solar Cells2009In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 21, no 7, 764-+ p.Article in journal (Refereed)
    Abstract [en]

    The solar-to-electric power-conversion efficiency (71) of dye-sensitized solar cells can be greatly enhanced by integrating a mesoporous, nanoparticle-based, 1D photonic crystal as a coherent scattering layer in the device. The photogenerated current is greatly improved without altering the open-circuit voltage of the cell, while keeping the transparency of the cell intact. Improved average 77 values between 15% and 30% are attained.

  • 19. Cummins, D.
    et al.
    Boschloo, Gerrit
    Ryan, M.
    Corr, D.
    Rao, S. N.
    Fitzmaurice, D.
    Ultrafast electrochromic windows based on redox-chromophore modified nanostructured semiconducting and conducting films2000In: Journal of Physical Chemistry B, ISSN 1089-5647, Vol. 104, no 48, 11449-11459 p.Article in journal (Refereed)
    Abstract [en]

    Described is the construction of an ultrafast electrochromic window. One electrode of this window is based on a transparent nanostructured TiO2 (anatase) film (4.0 mum. thick) supported on conducting glass (F-doped tin oxide, 10 Ohm cm(-2), 0.5 mum thick) and modified by chemisorption of a monolayer of the redox chromophore bis(2-phosphonoethyl)-4,4'-bipyridinium dichloride. The other electrode is based on a transparent nanostructured SnO2 film (3.0 mum thick) supported on conducting glass (F-doped tin oxide, 10 Ohm cm-2, 0.5 mum thick) and modified by chemisorption of a monolayer of the redox chromophore [beta-(10-phenothiazyl)propoxy]phosphonic acid. The electrolyte used is LiClO4 (0.2 mol dm(-3)) in gamma -butyrolactone. The excellent performance of a 2.5 cm x 2.5 cm window over 10 000 electrochromic test cycles-switching times (coloring and bleaching) of less than 250 ms, coloration efficiency of 270 cm(2) C-1, steady-state currents (colored and bleached) of less than 6 muA cm(-2), and memory of greater than 600 s (time required for low end transmittance to increase by 5%)-suggest a practical technology.

  • 20. D'Amario, Luca
    et al.
    Jiang, Roger
    Cappel, Ute B.
    Gibson, Elizabeth A.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Rensmo, Hakan
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Hammarstrom, Leif
    Tian, Haining
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Chemical and Physical Reduction of High Valence Ni States in Mesoporous NiO Film for Solar Cell Application2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 39, 33470-33477 p.Article in journal (Refereed)
    Abstract [en]

    The most common material for dye-sensitized photocathodes is mesoporous NiO. We transformed the usual brownish NiO to be more transparent by reducing high valence Ni impurities. Two pretreatment methods have been used: chemical reduction by NaBH4 and thermal reduction by heating. The power conversion efficiency of the cell was increased by 33% through chemical treatment, and an increase in open-circuit voltage from 105 to 225 mV was obtained upon heat treatment. By optical spectroelectrochemistry, we could identify two species with characteristically different spectra assigned to Ni3+ and Ni4+. We suggest that the reduction of surface Ni3+ and Ni (4+) to Ni (2+) decreases the recombination reaction between holes on the NiO surface with the electrolyte. It also keeps the dye firmly on the surface, building a barrier for electrolyte recombination. This causes an increase in open-circuit photovoltage for the treated film.

  • 21. Edvinsson, Tomas
    et al.
    Li, Chen
    Pschirer, Neil
    Schoeneboom, Jan
    Eickemeyer, Felix
    Sens, Ruediger
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Herrmann, Andreas
    Muellen, Klaus
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Intramolecular charge-transfer tuning of perylenes: Spectroscopic features and performance in Dye-sensitized solar cells2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 42, 15137-15140 p.Article in journal (Refereed)
    Abstract [en]

    Five novel perylene molecules with different intramolecular charge-transfer (ICT) characters have been synthesized. The relation between the ICT character for different donating groups and the results for their electro- and photochemical properties as well as their performance in nanostructured dye-sensitized solar cells (nDSC) are reported. With the stronger donors, we obtain a shift of the lowest unoccupied molecular orbital (LUMO) to more negative potential versus normal hydrogen electrode (NHE) as well as an increase the charge separation in the dye upon excitation. Ab initio calculations were used to analyze the effects on orbital energies and electron distribution with the different donors. Incorporating the dyes in nDSCs, we see a drastical improvement in the performance for the more polar dyes. In particular, we find a much improved photovoltage because of higher LUMO levels, allowing conduction band tuning in the TiO2 as well as a contribution from the permanent dipoles in the dyes. The photocurrent improves remarkably with increasing ICT character of the dyes. The external quantum efficiency reached over 70%, and the overall solar-to-electrical energy conversion efficiency was improved to almost 4% for the dye with highest ICT character, which can be compared with devices with the standard N719 dye (Ru(dcbPY)(2)(NCS)(2)) showing 6% under similar conditions. The performance is a significant improvement compared to previous reports for perylenes and lifts the performance from modest to promising. Initial stability tests show that the dye with the highest performance was spectrally stable after more than 2000 h of irradiation in a solar-cell device.

  • 22. Edvinsson, Tomas
    et al.
    Pschirer, Neil
    Schoneboom, Jan
    Eickemeyer, Felix
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Photoinduced electron transfer from a terrylene dye to TiO2: Quantification of band edge shift effects2009In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 357, no 1-3, 124-131 p.Article in journal (Refereed)
    Abstract [en]

    A terrylene chromophore exhibiting a high extinction coefficient has been developed as a sensitizer for photovoltaic applications. The photophysical and photochemical properties of the dye were analyzed both experimentally and theoretically. Terrylene-sensitized nanocrystalline TiO2 solar cells yielded good photocurrents providing more than 60% in external quantum efficiency. The photoinduced electron transfer from the dye to TiO2 was found to be very sensitive to conduction band edge shifts in TiO2 induced, either by changes in the composition of the redox electrolyte or by UV-illumination. This sensitivity was observed in quantum efficiencies for photocurrent generation of terrylene-sensitized solar cells and in photoinduced absorption experiments. The conduction band shifts were quantified using charge extraction methods. The observed sensitivity of the injection efficiency suggests that photoinduced electron transfer occurs from the relaxed excited state, possibly due to poor electronic coupling between TMIMA excited states and TiO2 conduction band states.

  • 23. Edwards, M. O. M.
    et al.
    Boschloo, Gerrit
    Gruszecki, T.
    Pettersson, H.
    Sohlberg, R.
    Hagfeldt, A.
    'Electric-paint displays' with carbon counter electrodes2001In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 46, no 13-14, 2187-2193 p.Article in journal (Refereed)
    Abstract [en]

    'Electric-paint displays' are electrochromic displays with dyed nanostructured metal-oxide electrodes, e.g. viologen-derivatized nanostructured titanium dioxide electrodes. Such displays are particularly promising for applications with low switch frequency, large segment areas, and high demands on colours, background brightness, and large viewing-angles. The concept is simple and well suited for inexpensive industrial production methods. We present blue-on-white electric-paint displays with porous carbon counter electrodes. The initial results with laboratory prototypes are promising. The switch time is about 1/2 s and the reflectance in the bleached state is as high as 40-55% in the visible region. Furthermore, the display prototypes sustain more than 100 000 switching cycles without severe degradation. The results from spectroelectrochemical measurements on the assembled displays are presented.

  • 24. Fabregat-Santiago, F.
    et al.
    Bisquert, J.
    Garcia-Belmonte, G.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Influence of electrolyte in transport and recombination in dye-sensitized solar cells studied by impedance spectroscopy2005In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 87, no 04-jan, 117-131 p.Article in journal (Refereed)
    Abstract [en]

    The main features of the characteristic impedance spectra of dye-sensitized solar cells are described in a wide range of potential conditions: from open to short circuit. An equivalent circuit model has been proposed to describe the parameters of electron transport, recombination, accumulation and other interfacial effects separately. These parameters were determined in the presence of three different electrolytes, both in the dark and under illumination. Shift in the conduction band edge due to the electrolyte composition was monitored in terms of the changes in transport resistance and charge accumulation in TiO2. The interpretation of the current-potential curve characteristics, fill factor, open-circuit photopotential and efficiency in the different conditions, was correlated with this shift and the features of the recombination resistance.

  • 25. Feldt, Sandra M.
    et al.
    Gibson, Elizabeth A.
    Gabrielsson, Erik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Design of Organic Dyes and Cobalt Polypyridine Redox Mediators for High-Efficiency Dye-Sensitized Solar Cells2010In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 46, 16714-16724 p.Article in journal (Refereed)
    Abstract [en]

    Dye-sensitized solar cells (DSCs) with cobalt-based mediators with efficiencies surpassing the record for DSCs with iodide-free electrolytes were developed by selecting a suitable combination of a cobalt polypyridine complex and an organic sensitizer. The effect of the steric properties of two triphenylamine-based organic sensitizers and a series of cobalt polypyridine redox mediators on the overall device performance in DSCs as well as on transport and recombination processes in these devices was compared. The recombination and mass-transport limitations that, previously, have been found to limit the performance of these mediators were avoided by matching the properties of the dye and the cobalt redox mediator. Organic dyes with higher extinction coefficients than the standard ruthenium sensitizers were employed in DSCs in combination with outer-sphere redox mediators, enabling thinner TiO2 films to be used. Recombination was reduced further by introducing insulating butoxyl chains on the dye rather than on the cobalt redox mediator, enabling redox couples with higher diffusion coefficients and more suitable redox potential to be used, simultaneously improving the photocurrent and photovoltage of the device. Optimization of DSCs sensitized with a triphenylamine-based organic dye in combination with tris(2,2'-bipyridyl)cobalt(II/III) yielded solar cells with overall conversion efficiencies of 6.7% and open-circuit potentials of more than 0.9 V under 1000 W m(-2) AM1.5 G illumination. Excellent performance was also found under low light intensity indoor conditions.

  • 26.
    Fischer, Andreas
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Pettersson, Henrik
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Kloo, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Gorlov, Mikhail
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Crystal formation involving 1-methylbenzimidazole in iodide/triiodide electrolytes for dye-sensitized solar cells2007In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 91, no 12, 1062-1065 p.Article in journal (Refereed)
    Abstract [en]

    Nitrogen heterocyclic compounds, such as N-methylbenzimidazole (MBI), are commonly used as additives to electrolytes for dye-sensitized solar cells (DSCs), but the chemical transformation of additives in electrolyte solutions remains poorly understood. Solid crystalline compound (MBI)(6)(MBI-H+)(2)(I-)(I-3(-)) (1) was isolated from different electrolytes for DSCs containing MBI as additive. The crystal structure of I was determined by single-crystal X-ray diffraction. In the crystal structure, 1 contains neutral and protonated MBI fragments; iodide and triiodide anions form infinite chains along the crystallographic a-axis. The role of the solvent and additives in the crystallization process in electrolytes is discussed.

  • 27.
    Fredin, Kristofer
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Gorlov, M.
    IVF Industrial Research and Development Corporation, Mölndal.
    Pettersson, Henrik
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    On the influence of anions in binary ionic liquid electrolytes for monolithic dye-sensitized solar cells2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 35, 13261-13266 p.Article in journal (Refereed)
    Abstract [en]

    Five ion c liquids (ILs) of the general formula Im(+)A(-), where Im(+) = I -methyl-3-n-butyl-imidazolium, A(-) = I- (1), BF4- (2), SCN- (3), CF3CO2- (4), and CF(3)S0(3)(-) (5), were used in electrolytes for dye-sensitized monolithic solar cells. The properties of the electrolytes and various characteristics of the solar cell performance, such as electron transport and electron lifetime, were studied. The composition of the binary electrolytes, i.e., the different anions, have a significant effect on the viscosity, but only a modest effect of the measured diffusior. coefficient for triiodide. No significant effect of the electrolyte composition on the electron transport time in the mesoporous TiO2 film was found, while there was a pronounced effect on the electron lifetime. Monolithic solar cells with thiocyanate, IL 3, showed overall light-to-electricity conversion efficiency up to 5.6% in 250 W m(-2) simulated sunlight and have promising stability.

  • 28.
    Fredin, Kristofer
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Häggman, Leif
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Influence of TiOs film thickness and illumination wavelength on electron transport in dye-sensitized solar cellsManuscript (Other academic)
  • 29.
    Fredin, Kristofer
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Nissfolk, Jarl
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    The influence of cations on charge accumulation in dye-sensitized solar cell2007In: Journal of Electroanalytical Chemistry, ISSN 0022-0728, E-ISSN 1873-2569, Vol. 609, no 2, 55-60 p.Article in journal (Refereed)
    Abstract [en]

    The relation between open-circuit voltage, VOC, light intensity, , and accumulated charge, Q, has been studied for dye-sensitized solar cells (DSCs) containing different counterions to the iodide/triiodide redox couple. At higher light intensities, VOC scaled in the order Cs+ > K+ > Na+ > Li+, which was caused in part by shifts in the conduction band edge. The relation between VOC and Q was fitted to an exponential trap model. It was found that inclusion of a capacitive term improved the fit significantly. The determined values of C were found to be relatively large, up to 75 μF cm−2, and dependent of cation. Physically, the largest fraction of C could be ascribed to the TiO2 bulk or TiO2/dye/electrolyte interface. The interpretation of the trap distribution broadening parameter, β, was found to be dependent of fitting model. Using the model including the linear CVOC term, β was independent of cation and could be viewed as a TiO2 material parameter, while in the model excluding CVOC, β was dependent of cation. Voltage decay experiments were performed to study the cationic influence on recombination. Electron lifetimes were calculated from the voltage decay curves and it was found that the DSC containing Li+ yielded by far the shortest lifetime followed by the DSCs containing Na+, K+ and Cs+. Voltage decay curves include the effect of TiO2 conduction band shifts in the comparison of electron lifetimes with different cations. We therefore suggest that the electron lifetimes should be calculated from the corresponding charge decay curves. From such a comparison, it was found that the DSC containing Li+ yielded the shortest lifetime whereas the DSCs containing Na+, K+ or Cs+ showed approximately identical lifetimes.

  • 30. Galoppini, Elena
    et al.
    Rochford, Jonathan
    Chen, Hanhong
    Saraf, Gaurav
    Lu, Yicheng
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Fast electron transport in metal organic vapor deposition grown dye-sensitized ZnO nanorod solar cells2006In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 33, 16159-16161 p.Article in journal (Refereed)
    Abstract [en]

    The electron transport in dye-sensitized solar cells with a MOCVD (metal organic vapor deposition)-grown ZnO nanorod array (ZnO-N) or a mesoporous film prepared from ZnO colloids (ZnO-C) as the working electrode was compared. The electrodes were of similar thickness (2 Am) and sensitized with zinc(II) mesotetrakis(3-carboxyphenyl) porphyrin, while the electrolyte was I-/I-3-in 3-methoxypropionitrile. Electron transport in the ZnO-C cells was comparable with that found for colloidal TiO2 films (transport time similar to 10 ms) and was light intensity dependent. Electron transport in solar cells with ZnO-N electrodes was about 2 orders of magnitude faster (similar to 30 mu s). Thus, the morphology of the working ZnO electrode plays a key role for the electron transport properties.

  • 31. Gibson, Elizabeth A.
    et al.
    Le Pleux, Loic
    Fortage, Jerome
    Pellegrin, Yann
    Blart, Errol
    Odobel, Fabrice
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Boschloo, Gerrit
    Uppsala University.
    Role of the Triiodide/Iodide Redox Couple in Dye Regeneration in p-Type Dye-Sensitized Solar Cells2012In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 15, 6485-6493 p.Article in journal (Refereed)
    Abstract [en]

    A series of perylene dyes with different optical and electronic properties have been used as photosensitizers in NiO-based p-type dye-sensitized solar cells. A key target is to develop dyes that absorb light in the red to near-infrared region of the solar spectrum in order to match photoanodes optically in tandem devices; however, the photocurrent produced was found to decrease dramatically as the absorption maxima of the dye used was varied from 517 to 565 nm and varied strongly with the electrolyte solvent (acetonitrile, propionitrile, or propylene carbonate). To determine the limitations of the energy properties of the dye molecules and to provide guidelines for future sensitizer design, we have determined the redox potentials of the duodide radical intermediate involved in the charge-transfer reactions in different solvents using photomodulated voltammetry. E degrees(I-3(-)/I-2(center dot-)) (V vs Fe(Cp)(2)(+/0)) = -0.64 for propylene carbonate, -0.82 for acetonitrile, and -0.87 for propionitrile. Inefficient regeneration of the sensitizer appears to be the efficiency-limiting step in the device, and the values presented here will be used to design more efficient dyes, with more cathodic reduction potentials, for photocathodes in tandem dye-sensitized solar cells.

  • 32. Gibson, Elizabeth A.
    et al.
    Smeigh, Amanda L.
    Le Pleux, Loic
    Fortage, Jerome
    Boschloo, Gerrit
    Blart, Errol
    Pellegrin, Yann
    Odobel, Fabrice
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hammarstrom, Leif
    A p-Type NiO-Based Dye-Sensitized Solar Cell with an Open-Circuit Voltage of 0.35 V2009In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 48, no 24, 4402-4405 p.Article in journal (Refereed)
  • 33.
    Hagberg, Daniel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Marinado, Tannia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630).
    Edvinsson, Tomas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630).
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630).
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630).
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630).
    Rhodanine Dyes for Dye Sensitized Solar Cells: Spectroscopy, Energy Levels and Photovoltaic Performance2009In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, 133-141 p.Article in journal (Refereed)
    Abstract [en]

    Three new sensitizers for photoelectrochemical solar cells were synthesized consisting of a triphenylamine donor, a rhodanine-3-acetic acid acceptor and a polyene connection. The conjugation length was systematically increased, which resulted in two effects: first, it led to a red-shift of the optical absorption of the dyes, resulting in an improved spectral overlap with the solar spectrum. Secondly, the oxidation potential decreased systematically. The excited state levels were, however, calculated to be nearly stationary. The experimental trends were in excellent agreement with density functional theory (DFT) computations. The photovoltaic performance of this set of dyes as sensitizers in mesoporous TiO2 solar cells was investigated using electrolytes containing the iodide/triiodide redox couple. The dye with the best absorption characteristics showed the poorest solar cell efficiency, due to losses by recombination of electrons in TiO2 with triiodide. Addition of 4-tert butylpyridine to the electrolyte led to a strongly reduced photocurrent for all dyes due to a reduced electron injection efficiency, caused by a 0.15 V negative shift of the TiO2 conduction band potential.

  • 34.
    Hagberg, Daniel P.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Edvinsson, Tomas
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Marinado, Tannia
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    A novel organic chromophore for dye-sensitized nanostructured solar cells2006In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 21, 2245-2247 p.Article in journal (Refereed)
    Abstract [en]

    A novel and efficient polyene-diphenylaniline dye for dye-sensitized solar cells has been synthesized. The dye has a short synthesis route and is readily adsorbed on TiO2 under a variety of dye-bath conditions. The overall solar-to-energy conversion efficiency is over 5% in the preliminary tests, in comparison with the conventional N719 dye which gives 6% under the same conditions. The dye is designed for future use also in solid state devices, with triarylamine based hole conductors.

  • 35.
    Hagberg, Daniel P.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Marinado, Tannia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Karlsson, Karl Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Nonomura, Kazeteru
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Qin, Peng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Tuning the HOMO and LUMO Energy Levels of Organic Chromophores For Dye Sensitized Solar Cells2007In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, no 72, 9550-9556 p.Article in journal (Refereed)
    Abstract [en]

    A series of organic chromophores have been synthesized in order to approach optimal energy level composition in the TiO2-dye-iodide/triiodide system in the dye-sensitized solar cells. HOMO and LUMO energy level tuning is achieved by varying the conjugation between the triphenylamine donor and the cyanoacetic acid acceptor. This is supported by spectral and electrochemical experiments and TDDFT calculations. These results show that energetic tuning of the chromophores was successful and fulfilled the thermodynamic criteria for dye-sensitized solar cells, electrical losses depending on the size and orientation of the chromophores were observed.

  • 36. Hagfeldt, A.
    et al.
    Boschloo, Gerrit
    Lindström, H.
    Figgemeier, E.
    Holmberg, A.
    Aranyos, V.
    Magnusson, E.
    Malmqvist, L.
    A system approach to molecular solar cells2004In: Coordination chemistry reviews, ISSN 0010-8545, E-ISSN 1873-3840, Vol. 248, no 13-14, 1501-1509 p.Article, review/survey (Refereed)
    Abstract [en]

    This paper gives an overview of the research and development of dye-sensitized solar cells (DSC) within the Swedish research program 'Angstrom Solar Center'. A path towards low production cost is the development of a continuous process, which allows the production of solar cells in large volumes and with a high productivity. We have developed a deposition method for the production of the mesoporous TiO2, electrode layer that is based on compression of a powder film at room temperature. This technique allows us to use flexible substrates-a prerequisite fora continuous process. A novel interconnect technology, compatible with a continuous production process, is described. Stability data of plastic DSC, exposed to indoor light for more than 10,000 h, demonstrates the possibility for the technology to be explored for various types of indoor applications. Optimization of the DSC is a challenging task as it is a complex highly interacting molecular system. A system approach is proposed, where the complete DSC is investigated with a series of measurement techniques ('toolbox') that allows the study of the internal processes under relevant conditions. Two examples of such techniques are given.

  • 37.
    Hagfeldt, Anders
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630).
    Boschloo, Gerrit
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry (closed 20110630).
    Pettersson, Henrik
    Dye-Sensitized Solar Cells2010In: Chemical Reviews, ISSN 0009-2665, E-ISSN 1520-6890, Vol. 110, no 11, 6595-6663 p.Article, review/survey (Refereed)
  • 38. Halme, Janne
    et al.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Lund, Peter
    Spectral characteristics of light harvesting, electron injection, and steady-state charge collection in pressed TiO2 dye solar cells2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 14, 5623-5637 p.Article in journal (Refereed)
    Abstract [en]

    The factors that limit photocurrent in dye solar cells (DSC) were studied by incident-photon-to-collected-electron efficiency (eta(IPCE)), optical, and photovoltaic measurements. Nanostructured TiO2 photoelectrodes were prepared by compression technique on glass substrates, and half of them were given an additional heat treatment at 450 degrees C. The spectral absorbed-photon-to-collected-electron efficiency (eta(APCE)) of the cells was determined as a function of the photoelectrode film thickness (d) and direction of illumination and analyzed in terms of electron injection (eta(INJ)) and collection (eta(COL)) efficiency. The cells with pressed-only photoelectrodes gave significantly lower photocurrents yet their eta(APCE), and thus eta(COL), increased significantly with increasing d. To analyze this result quantitatively, methods were formulated based on the standard diffusion model of electron transport in nanostructured photoelectrodes for the factorization of experimental eta(APCF) data into eta(INJ) and eta(COL) parts and subsequent estimation of the effective steady-state electron diffusion length (L). Consistent decoupling of eta(INJ) and eta(COL) was reached in a spectral region where electron generation rate was independent of d. eta(INJ) was low and strongly wavelength-dependent, which was attributed to a poor energetic matching between dye excited states and TiO2 acceptor states due to unfavorable electrolyte composition. L increased systematically with d in both types of cells. Consistent with the increase of eta(IPCE) with light intensity, the result was attributed qualitatively to the electron concentration dependence of L and for a small part to decrease of film porosity with d. The diffusion model and its predictions were reviewed, and its validity in the present case was discussed critically.

  • 39.
    Jiang, Xiao
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Karlsson, Karl Martin
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Gabrielsson, Erik
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Johansson, Erik M. J.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Quintana, Maria
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Karlsson, Martin
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Highly Efficient Solid-State Dye-Sensitized Solar Cells Based on Triphenylamine Dyes2011In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 21, no 15, 2944-2952 p.Article in journal (Refereed)
    Abstract [en]

    Two triphenylamine-based metal-free organic sensitizers, D35 with a single anchor group and M14 with two anchor groups, have been applied in dye-sensitized solar cells (DSCs) with a solid hole transporting material or liquid iodide/triiodide based electrolyte. Using the molecular hole conductor 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene (spiro-OMeTAD), good overall conversion efficiencies of 4.5% for D35 and 4.4% for M14 were obtained under standard AM 1.5G illumination (100 mW cm(-2)). Although M14 has a higher molar extinction coefficient (by similar to 60%) and a slightly broader absorption spectrum compared to D35, the latter performs slightly better due to longer lifetime of electrons in the TiO(2), which can be attributed to differences in the molecular structure. In iodide/triiodide electrolyte-based DSCs, D35 outperforms M14 to a much greater extent, due to a very large increase in electron lifetime. This can be explained by both the greater blocking capability of the D35 monolayer and the smaller degree of interaction of triiodide (iodine) with D35 compared to M14. The present work gives some insight into how the molecular structure of sensitizer affects the performance in solid-state and iodide/triiodide-based DSCs.

  • 40. Johansson, E. M. J.
    et al.
    Sandell, A.
    Siegbahn, H.
    Rensmo, H.
    Mahrov, B.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Figgemeier, E.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Jonsson, S. K. M.
    Fahlman, M.
    Interfacial properties of photovoltaic TiO2/dye/PEDOT-PSS heterojunctions2005In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 149, no 03-feb, 157-167 p.Article in journal (Refereed)
    Abstract [en]

    Systems comprising a dense TiO2 film electrode, a ruthenium polypyridine dye and a PEDOT-PSS (poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulphonate)) film were prepared. The heterojunctions were shown to have photovoltaic properties, with the dye absorbing the light, the TiO2 acting as an electron conducting material and PEDOT-PSS acting as a hole transport material. A series of dyes was used to investigate their influence on the photocurrent and the photovoltage characteristics of the heterojunction. These results were compared to a photoelectrochemical system in which the PEDOT-PSS was replaced by a liquid electrolyte containing triiodide/iodide redox-couple. Photoelectron spectroscopy (PES) was used to monitor the interfacial properties of the heterojunction and the investigation points out effects of importance when assembling the materials together to a functional unit. Specifically, it was concluded that the interaction with the dye clearly affects the structure of PEDOT-PSS, both with respect to the surface composition of PSS relative to PEDOT and with respect to the chemical state of the sulphur in the polymers. Moreover, a comparison of the Ru3d and the valence band spectra of the two different interfaces (dye/TiO2 and dye/PEDOT-PSS) indicates that the energy level structure of the dyes compared to the substrate is different for the two surfaces. Thus, in the combined energy level picture under dark conditions, the energy levels in TiO2 relative to the energy levels in PEDOT-PSS depend on the dye.

  • 41. Keis, K.
    et al.
    Bauer, C.
    Boschloo, Gerrit
    Hagfeldt, A.
    Westermark, K.
    Rensmo, H.
    Siegbahn, H.
    Nanostructured ZnO electrodes for dye-sensitized solar cell applications2002In: Journal of Photochemistry and Photobiology A: Chemistry, ISSN 1010-6030, E-ISSN 1873-2666, Vol. 148, no 03-jan, 57-64 p.Article in journal (Refereed)
    Abstract [en]

    Dye-sensitized photoelectrochemical solar cells constitute a promising candidate in the search for cost-effective and environment-friendly solar cells. The most extensively studied, and to date the most efficient systems are based on titanium dioxide. In this paper, the possibilities to use nanostructured ZnO electrodes in photoelectrochemical solar cells are investigated. Various experimental techniques (e.g. infrared, photoelectron, femtosecond and nanosecond laser spectroscopies, laser flash induced photocurrent transient measurements, two and three-electrode photoelectrochemical measurements) show that the thermodynamics, kinetics and charge transport properties are comparable for ZnO and TiO2. The preparation techniques of ZnO provide more possibilities of varying the particle size and shape compared to TiO2. However, the dye-sensitization process is more complex in case of ZnO and care needs to be taken to achieve an optimal performance of the solar cell.

  • 42. Koehorst, R. B. M.
    et al.
    Boschloo, Gerrit
    Savenije, T. J.
    Goossens, A.
    Schaafsma, T. J.
    Spectral sensitization of TiO2 substrates by monolayers of porphyrin heterodimers2000In: Journal of Physical Chemistry B, ISSN 1089-5647, Vol. 104, no 10, 2371-2377 p.Article in journal (Refereed)
    Abstract [en]

    Photoelectrochemical cells have been constructed by depositing monolayers of oriented covalently linked zinc/free base porphyrin heterodimers onto similar to 30 nm nonporous layers of TiO2 on ITO, deposited by metalorganic chemical vapor deposition (MO-CVD), and onto similar to 100 nm porous, nanostructured TiO2 layers, spin-coated from a suspension of P25 (Degussa) on ITO. Fluorescence quenching of the dyes on both types of TiO2 substrates is compared with that of dilute solutions of the dyes and with that of dye-coated, porous ZrO2 (Degussa) substrates. By functionalizing one of the porphyrin dimer components with carboxylic substituents, which bind to the TiO2 or ZrO2 substrate surface, either the zinc porphyrin (ZnP) or the free base porphyrin (H2P) component of the dimer can be made to be in diner contact with the substrate. These dimer-substrate arrangements are denoted ZnP-H2P- -TiO2 (dimer 1) and H2P-ZnP- -TiO2 (dimer 2), respectively, where - - denotes binding of the carboxyl-substituted porphyrin in the heterodimer to the substrate surface. In solution as well as deposited on ZrO2, in contact with the solvent without a redox couple, both types of dimers show efficient internal ZnP to H2P energy transfer. Deposited on TiO2, in the presence of the solvent, monolayers of both types of dimers show less efficient energy transfer than the dimers on ZrO2, For a ZnP-H2P- -TiO2 electrochemical cell the photocurrent action spectrum reproduces the absorption spectrum, i.e., contains contributions of both the ZnP and H2P moieties. By contrast, for H2P-ZnP- -TiO2 cells mainly the ZnP dimer component contributes to the photocurrent, demonstrating that in H2P-ZnP- -TiO2 cells electron transfer from the ZnP into the TiO2 substrate is faster than energy transfer to the adjacent free base porphyrin. The photocurrent action spectrum of the ZnP-H2P- -TiO2 cell also demonstrates that energy transfer in monolayers of this dimer results in sensitization of the semiconductor substrate, since the spectral response of a cell is enhanced with respect to that of a cell with a monolayer of a monomeric sensitizer. These results are relevant for the construction of a solar cell containing a supramolecular, light-collecting antenna.

  • 43. Lana-Villarreal, Teresa
    et al.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Nanostructured zinc stannate as semiconductor working electrodes for dye-sensitized solar cells2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 14, 5549-5556 p.Article in journal (Refereed)
    Abstract [en]

    Zinc stannate (Zn2SnO4) particles with 27-nm size were synthesized by hydrothermal treatment. Nanoporous Zn2SnO4 thin films were prepared on conducting glass substrates and used as working electrodes in dye-sensitized solar cells, DSSC. Their behavior was compared with standard TiO2 cells, using (TBA)(2)-cis-Ru(Hdcbpy)(2)(NCS)(2) (known as N719) as a dye and an electrolyte containing 0.7 M LiI and 0.05 M I-2 in 3-methoxypropionitrile. Under the same working conditions, Zn2SnO4 DSSC showed higher open-circuit potential, but their overall efficiency was lower due to their lower incident photon-to-current conversion efficiency. The properties of electrons in DSSC have been studied by measuring their transport time and lifetime by photocurrent and photovoltage transient measurements, respectively. The electron diffusion length is similar in both oxides, demonstrating the possible use of Zn2SnO4 as an electron collector in DSSC applications. On the other hand, photoinduced absorption measurements reveal problems in the electron injection from the dye to Zn2SnO4, owing to the higher position of its conduction band, in agreement with the higher open-circuit potential measured. Zinc stannate will be an interesting mesoporous material for DSSC, provided the use of dyes with a higher position of the LUMO compared to that of N719, as it will permit attaining higher photovoltages without affecting the photocurrent.

  • 44. Mahrov, B.
    et al.
    Boschloo, Gerrit
    Hagfeldt, A.
    Dloczik, L.
    Dittrich, T.
    Photovoltage study of charge injection from dye molecules into transparent hole and electron conductors2004In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 84, no 26, 5455-5457 p.Article in journal (Refereed)
    Abstract [en]

    Transient and spectral photovoltage (PV) have been investigated for charge injection from a dye [Ru(dcbpyH(2))(2)(NCS)(2)] into transparent hole ( CuSCN, CuI, CuAlO2) and electron ( TiO2, SnO2:F) conductors. The PV signal rises to a maximum within 10 ns to 10 mus, depending on the transparent hole or electron conductor and on the mechanism of charge separation. The efficiency of hole and electron injection is of the same order while the effective lifetimes of injected charge vary between several mus and 1 ms for the samples used. The thresholds for charge injection from the dye range between 1.6 and 1.8 eV depending on the material on which the dye is adsorbed.

  • 45. Mahrov, B.
    et al.
    Boschloo, Gerrit
    Hagfeldt, A.
    Siegbahn, H.
    Rensmo, H.
    Photoelectron spectroscopy studies of Ru(dcbpyH(2))(2)(NCS)(2)/CuI and Ru(dcbpyH(2))(2)(NCS)(2)/CuSCN interfaces for solar cell applications2004In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 108, no 31, 11604-11610 p.Article in journal (Refereed)
    Abstract [en]

    In this work, the electronic structure of the wide band gap hole conductors Cut and CuSCN in contact with an organic dye (Ru(dcbpyH(2))(2)(NCS)(2), cis-bis(4,4'-dicarboxy-2,2-bipyridine)bis(isothiocyanato)ruthenium(II)) were investigated by means of photoelectron spectroscopy. The experiments show specific interaction between the NCS groups of the dye molecules and the Cut and CuSCN surfaces. For Cut there are strong indications that the dye molecules interact with Cut through both NCS ligands. Also, one of the carboxylic groups is affected by the surface adsorption on the CuI substrate. For the CuSCN surface the results indicate that about half of the molecules interact with the surface through both NCS ligands, that about half of the molecules interact with the surface through one NCS ligand, and that there is no specific interaction with the carboxylic groups. The measurements also reveal changes in the electronic structure of the dye molecule when adsorbed onto the substrates. In particular, changes in the upper valence electronic structure, important for the function of this material combination in a solar cell device, are discussed.

  • 46. Mahrov, B.
    et al.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Lenzmann, F.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Comparison of charge accumulation and transport in nanostructured dye-sensitized solar cells with electrolyte or CuSCN as hole conductor2005In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 88, no 4, 351-362 p.Article in journal (Refereed)
    Abstract [en]

    The charge transport properties of the dye-sensitized solar cells consisting of Ru(dcbpyH(2))(2)(NCS)(2)-sensitized nanostructured TiO2 with either redox electrolyte or CuSCN as hole conductor have been compared. The electron transport time and the electron charge in the TiO2 varies in a similar way with the incident light intensity for both hole conductors: electron transport becomes faster and electron accumulation increases with increasing light intensity. Electron transport in the CuSCN-based cells is significantly faster than in electrolyte cells under conditions where the accumulated charge is equal. An ultra-thin aluminum oxide layer on the nanocrystalline titanium oxide has a beneficial effect as it reduces the recombination and increases the open-circuit potential.

  • 47.
    Marinado, Tannia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Edvinsson, Tomas
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Influence of π-Conjugation Units in Organic Dyes for Dye-Sensitized Solar Cells2007In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 4, 1853-1860 p.Article in journal (Refereed)
    Abstract [en]

    Two organic dyes with the general structure donor-conjugated chain-acceptor (D-pi-A) have been investigated as sensitizers for nanocrystalline TiO2 solar cells. The electron donor and acceptor groups were pyrrolidine and cyano acrylic acid, respectively. The conjugated chain of 2-cyano-3-{5-[2-(4-pyrrolidin-1-ylphenyl)vinyl]thiophen-2-yl}acrylic acid contains one phenyl ring and a thiophene unit and is therefore denoted PT, while for 2-cyano-3-{5 -[2-(5-pyrrolidin-1-ylthiophen-2-yl)vinyl]thiophen-2-yl}acrylic acid the phenyl ring is replaced by a second thiophene unit (TT). Solar-to-electrical energy conversion efficiencies under simulated AM 1.5 irradiation (1000 W m(-2)) of 2.3% were obtained for solar cells based on PT but of less than 0.05% for those based on TT. The reasons for the dramatic difference of the efficiencies were analyzed. Photoinduced absorption measurements revealed that the TT dye was not properly regenerated by redox electrolyte after electron injection. This sluggish regeneration is probably due to the 0.3 V less positive HOMO level for TT dye compared to the PT dye, resulting in a lower driving force for regeneration of the oxidized dye by iodide in the electrolyte. In addition, regeneration of the oxidized TT dye and electron injection from the excited TT dye may be poor due to formation of dye aggregates/complexes, as FT-IR measurements show an excess of not properly and/or unidentate bound TT dye molecules instead of bidentate bound PT dye molecules. The results highlight that small structural change of dyes results in significant changes in redox energies and binding features, affecting dramatically the performance of these dyes in dye-sensitized solar cells.

  • 48.
    Marinado, Tannia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagberg, Daniel P.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Edvinsson, Tomas
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Brinck, Tore
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Tian, Haining
    Yang, Xixhuan
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Energy level tuning of organic dyes for fundamental studies of the oxide/dye/electrolyte interface in solar cellsManuscript (Other academic)
  • 49. Morandeira, A.
    et al.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Hammarstrom, L.
    Photoinduced ultrafast dynamics of comnarin 343 sensitized p-type-nanostructured NiO films2005In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 109, no 41, 19403-19410 p.Article in journal (Refereed)
    Abstract [en]

    Photoinduced electron transfer from the valence band of nanocrystalline NiO, a p-type semiconductor, to an excited bound dye, coumarin 343, and the subsequent recombination have been measured by femtosecond transient absorbance spectroscopy probing with white light. It was found that both processes are nonexponential. The photoinduced electron transfer from the semiconductor to the excited bound dye has an ultrafast component (similar to 200 fs), which is comparable to the time constants measured for photoinduced electron injection in C343-TiO2 colloid solutions. The process is very efficient and constitutes the main path of deactivation of the excited dye. Back electron transfer is also remarkably fast, with the main part of the recombination process happening with a time constant of similar to 20 ps. Dye-sensitized nanostructured p-type semiconductors are attractive materials due to their potential use as photocathodes in dye-sensitized solar cells and solid electrolytes in solid-state dye-sensitized solar cells. To our knowledge, this is the first time that the photoinduced electron-transfer kinetics of a sensitized p-type semiconductor has been studied.

  • 50. Morandeira, Ana
    et al.
    Boschloo, Gerrit
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Hammarstrom, Leif
    Coumarin 343-NiO films as nanostructured photocathodes in dye-sensitized solar cells: Ultrafast electron transfer, effect of the I-3(-)/I- redox couple and mechanism of photocurrent generation2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 25, 9530-9537 p.Article in journal (Refereed)
    Abstract [en]

    Nanoporous, p-type NiO films were sensitized with coumarin 343 (C343), and the photoinduced electron transfer dynamics was studied in the presence of different concentrations of electrolyte (I-3(-)/I- in propylene carbonate). Electron transfer from the valence band of NiO to the excited C343 is very fast, occurring on time scales from hundreds of femtoseconds to a few picoseconds, but also the subsequent recombination is quite rapid, on the time scale of tens of picoseconds. Nevertheless, formation of an intermediate, attributed to I2-I NiO(+), was observed on the picosecond time scale. Simultaneously the reduced dye was converted back to the C343 ground state, indicating that recombination could be intercepted by 13 reduction. Consistent with that interpretation, we observed oxidized NiO and depletion Of 13 persisting on the millisecond time scale. Complete dye-sensitized solar cells (DSSCs) with these films as photocathode gave up to 10-11% incident photon to current conversion efficiency at the C343 visible absorption maximum, which is the highest value reported for a p-type DSSC. Our results elucidate the main mechanism for photocurrent generation in this p-type DSSC, which is important for the understanding and development of these rarely studied counterpart of conventional n-type "Gratzel cells".

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