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  • 1. Aung, S. H.
    et al.
    Zhao, L.
    Nonomura, K.
    Oo, T. Z.
    Zakeeruddin, S. M.
    Vlachopoulos, N.
    Sloboda, Tamara
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Svanström, S.
    Cappel, Ute B.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Hagfeldt, A.
    Grätzel, M.
    Toward an alternative approach for the preparation of low-temperature titanium dioxide blocking underlayers for perovskite solar cells2019In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 7, no 17, p. 10729-10738Article in journal (Refereed)
    Abstract [en]

    The anodic electrodeposition method is investigated as an alternative technique for the preparation of a titanium oxide (TiO 2 ) blocking underlayer (UL) for perovskite solar cells (PSCs). Extremely thin Ti IV -based films are grown from aqueous acidic titanium(iii) chloride in an electrochemical cell at room temperature. This precursor layer is converted to the UL (ED-UL), in a suitable state for PSC applications, by undertaking a sintering step at 450 °C for half an hour. PSCs with the composition of the light-absorbing material FA 0.85 MA 0.10 Cs 0.05 Pb(I 0.87 Br 0.13 ) 3 (FA and MA denote the formamidinium and methylammonium cations, respectively) based on the ED-UL are compared with PSCs with the UL of a standard type prepared by the spray-pyrolysis method at 450 °C from titanium diisopropoxide bis(acetylacetonate) (SP-UL). We obtain power conversion efficiencies (PCEs) of over 20% for mesoscopic perovskite devices employing both ED-ULs and SP-ULs. Slightly higher fill factor values are observed for ED-UL-based devices. In addition, ED-ULs prepared by the same method have also been applied in planar PSCs, resulting in a PCE exceeding 17%, which is comparable to that for similar PSCs with an SP-UL. The preparation of ED-ULs with a lower sintering temperature, 150 °C, has also been examined. The efficiency of a planar PSC incorporating this underlayer was 14%. These results point out to the possibility of applying ED-ULs in flexible planar PSCs in the future.

  • 2. Cappel, U. B.
    et al.
    Gibson, E. A.
    Hagfeldt, Anders
    KTH, School of Chemical Science and Engineering (CHE), Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. Uppsala University, Sweden.
    Boschloo, G.
    Dye regeneration by Spiro-MeOTAD in solid state dye-sensitized solar cells studied by photoinduced absorption spectroscopy and spectroelectrochemistry2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 15, p. 6275-6281Article in journal (Refereed)
    Abstract [en]

    Photoinduced absorption (PIA) spectroscopy is presented as a tool for the systematic study of dye regeneration and pore filling in solid state dye-sensitized solar cells (DSC). Oxidation potentials and extinction coefficients for oxidized species of the perylene dye, ID28, on TiO(2) and of the hole conductor, 2,2'7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-MeOTAD), were determined by spectroelectrochemistry. The onset of oxidation of a solid film of spiro-MeOTAD was found to be 0.15 V versus Fc/Fc(+) and extinction coefficients of spiro-MeOTAD(+) were found to be 33 000 M(-1) cm(-1) at 507 nm and 8500 M(-1) cm-' at 690 nm. Electrons in TiO(2) films were shown to alter the ground-state absorption spectra of ID28 attached to TiO(2)-PIA measurements indicated a good contact between ID28 and spiro-MeOTAD for different spiro-MeOTAD concentrations for both 2- and 6-mu m thick TiO(2) films. We discuss the possibility of estimating the quality of pore filling from the positions of absorption peaks. Results suggested that with a spiro-MeOTAD concentration of 300 mg mL(-1) in chlorobenzene, a uniform distribution of spiro-MeOTAD in the pores of the 6-mu m thick TiO(2) film could be achieved.

  • 3. Cappel, Ute B
    et al.
    Bell, Ian M
    Pickard, Laura K
    Removing cosmic ray features from Raman map data by a refined nearest neighbor comparison method as a precursor for chemometric analysis.2010In: Applied Spectroscopy, ISSN 0003-7028, E-ISSN 1943-3530, Vol. 64, no 2, p. 195-200Article in journal (Refereed)
    Abstract [en]

    An algorithm to remove cosmic ray (CR) features from Raman spectra collected in mapping experiments using a charge-coupled device (CCD) is presented. Each spectrum is compared to spectra collected from adjacent points in space using correlation values. The most similar neighbor (MSN) spectrum is selected, offset, and used for identification of CRs. The offset values are defined in terms of the noise level for data with a low signal-to-noise ratio and in terms of the peak height for data with a high signal-to-noise ratio. Scaled intensity values of the MSN spectra are used for replacement of contaminated pixels, allowing for full recovery of underlying spectral features. The algorithm is applicable for any Raman map where the particle sizes within the analyzed mixture are larger than the sampling size or to any other data where the sampling is more frequent than the variation, e.g., time series or temperature profiles. Its application to several maps of pharmaceutical samples is discussed here. With an appropriate offset value for the MSN spectra, no misdetections occur, and all CRs more intense than the offset are removed, which includes the CRs that would have hampered subsequent chemometric analysis by methods such as principal component analysis (PCA).

  • 4. Cappel, Ute B
    et al.
    Daeneke, Torben
    Bach, Udo
    Oxygen-induced doping of spiro-MeOTAD in solid-state dye-sensitized solar cells and its impact on device performance.2012In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 12, no 9, p. 4925-31Article in journal (Refereed)
    Abstract [en]

    Solid state dye-sensitized solar cells (sDSCs) employing the hole conductor 2,2'7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene (spiro-MeOTAD) require the presence of oxygen during fabrication and storage. In this paper, we determine the concentrations of oxidized spiro-MeOTAD within devices under different operating and storage conditions by UV-vis spectroscopy. Relative concentrations of spiro-MeOTAD(+) were found to be greater than 10% after illumination for standard sDSCs, where no chemical dopant had been used in the solar cell fabrication but oxygen and lithium ions were present. We suggest that oxidized spiro-MeOTAD is created as a byproduct of oxygen reduction at the TiO(2) surface during cell illumination. Furthermore, we studied the effect of light soaking under different conditions and associated changes in spiro-MeOTAD(+) concentration on the solar cell measurements. Our findings give insights to photochemical reactions occurring within sDSCs and provide guidelines for which doping levels should be used in device fabrication in absence of oxygen.

  • 5. Cappel, Ute B
    et al.
    Dowland, Simon A
    Reynolds, Luke X
    Dimitrov, Stoichko
    Haque, Saif A
    Charge Generation Dynamics in CdS: P3HT Blends for Hybrid Solar Cells.2013In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 4, no 24, p. 4253-7Article in journal (Refereed)
    Abstract [en]

    Development of design rules for hybrid inorganic-organic solar cells through understanding charge generation and recombination dynamics is an important pathway for the improvement of solar cell conversion efficiencies. In this Letter, we study the dynamics of charge generation in CdS:polymer blends by transient absorption spectroscopy. We show that charge generation following excitation of the inorganic component is highly efficient and can occur up to a few nanoseconds after excitation, allowing for diffusion of charges within the inorganic component to an interface. In contrast, charge generation following excitation of the organic component occurs on subpicosecond time scales but suffers from two loss processes, incomplete exciton dissociation and geminate recombination.

  • 6. Cappel, Ute B
    et al.
    Feldt, Sandra M
    Schöneboom, Jan
    Hagfeldt, Anders
    Boschloo, Gerrit
    The influence of local electric fields on photoinduced absorption in dye-sensitized solar cells.2010In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 132, no 26, p. 9096-101Article in journal (Refereed)
    Abstract [en]

    The dye-sensitized solar cell (DSC) challenges conventional photovoltaics with its potential for low-cost production and its flexibility in terms of color and design. Transient absorption spectroscopy is widely used to unravel the working mechanism of DSCs. A surprising, unexplained feature observed in these studies is an apparent bleach of the ground-state absorption of the dye, under conditions where the dye is in the ground state. Here, we demonstrate that this feature can be attributed to a change of the local electric field affecting the absorption spectrum of the dye, an effect related to the Stark effect first reported in 1913. We present a method for measuring the effect of an externally applied electric field on the absorption of dye monolayers adsorbed on flat TiO(2) substrates. The measured signal has the shape of the first derivative of the absorption spectra of the dyes and reverses sign along with the reversion of the direction of the change in dipole moment upon excitation relative to the TiO(2) surface. A very similar signal is observed in photoinduced absorption spectra of dye-sensitized TiO(2) electrodes under solar cell conditions, demonstrating that the electric field across the dye molecules changes upon illumination. This result has important implications for the analysis of transient absorption spectra of DSCs and other molecular optoelectronic devices and challenges the interpretation of many previously published results.

  • 7. Cappel, Ute B.
    et al.
    Karlsson, Martin H.
    Pschirer, Neil G.
    Eickemeyer, Felix
    Schoeneboom, Jan
    Erk, Peter
    Boschloo, Gerrit
    Hagfeldt, Anders
    A Broadly Absorbing Perylene Dye for Solid-State Dye-Sensitized Solar Cells2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 33, p. 14595-14597Article in journal (Refereed)
    Abstract [en]

    We present a new perylene sensitizer, ID 176, for dye-sensitized solar cells (DSCs). The dye has the capability for very high photocurrents due to strong absorption from 400 to over 700 rim. Photocurrents Of LIP to 9 mA cm(-2) were achieved in solid-state DSCs employing the hole conductor 2,2’7,7’-tetrakis-(NN-di-p-methoxyphenylamine)-9,9’-spirobifluorene (spiro-MeOTAD), with a conversion efficiency of 3.2%. In contrast, the sensitizer did not perform well in conjunction with liquid iodide/tri-iodide electrolytes, suggesting a difference in the injection and regeneration mechanisms in these two types of dye-sensitized solar cells.

  • 8.
    Cappel, Ute B.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Liu, Peng
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Johansson, Fredrik O. L.
    Uppsala Univ, Div Mol & Condensed Matter Phys, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Philippe, Bertrand
    Uppsala Univ, Div Mol & Condensed Matter Phys, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Giangrisostomi, Erika
    Helmholtz Zentrum Berlin GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Ovsyannikov, Ruslan
    Helmholtz Zentrum Berlin GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Lindblad, Andreas
    Uppsala Univ, Div Mol & Condensed Matter Phys, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Gardner, James M.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Rensmo, Hakan
    Uppsala Univ, Div Mol & Condensed Matter Phys, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Electronic Structure Characterization of Cross-Linked Sulfur Polymers2018In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 19, no 9, p. 1041-1047Article in journal (Refereed)
    Abstract [en]

    Cross-linked polymers of elemental sulfur are of potential interest for electronic applications as they enable facile thin-film processing of an abundant and inexpensive starting material. Here, we characterize the electronic structure of a cross-linked sulfur/diisopropenyl benzene (DIB) polymer by a combination of soft and hard X-ray photoelectron spectroscopy (SOXPES and HAXPES). Two different approaches for enhancing the conductivity of the polymer are compared: the addition of selenium in the polymer synthesis and the addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) during film preparation. For the former, we observe the incorporation of Se into the polymer structure resulting in a changed valence-band structure. For the latter, a Fermi level shift in agreement with p-type doping of the polymer is observed and also the formation of a surface layer consisting mostly of TFSI anions.

  • 9. Cappel, Ute B
    et al.
    Moia, Davide
    Bruno, Annalisa
    Vaissier, Valerie
    Haque, Saif A
    Barnes, Piers R F
    Evidence for photo-induced charge separation between dye molecules adsorbed to aluminium oxide surfaces.2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 21276Article in journal (Refereed)
    Abstract [en]

    Excited state dynamics and photo-induced charge transfer of dye molecules have been widely studied due to their relevance for organic and dye-sensitised solar cells. Herein, we present a femtosecond transient absorption spectroscopy study of the indolene dye D131 when adsorbed to inert Al2O3 substrates for different surface concentration of the dye. Surprisingly, we find that at high surface concentrations, the first singlet excited state of the dye is converted into a new state with an efficiency of about 80%. We assign the absorption features of this state to the oxidised dye and discuss the possibility of photo-induced charge separation between neighboring dye molecules. Our study is the first to show that this process can be highly efficient without the use of donor and acceptor molecules of different chemical structures.

  • 10. Cappel, Ute B
    et al.
    Plogmaker, Stefan
    Johansson, Erik M J
    Hagfeldt, Anders
    Boschloo, Gerrit
    Rensmo, Håkan
    Energy alignment and surface dipoles of rylene dyes adsorbed to TiO2 nanoparticles.2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 32, p. 14767-74Article in journal (Refereed)
    Abstract [en]

    The energy loss in dye-sensitized solar cells calculated from the energy difference between the lowest electronic transition of the dye and the obtained open-circuit voltage is often 1 eV or even more. To minimize this loss, it is important to accurately determine the energy alignment at the TiO(2)/dye/redox-mediator interface. In this study, we compared the results from electrochemistry and photoelectron spectroscopy for determining the energy alignment of three rylene dyes, two of which absorb relatively far in the red. The trends observed with the methods were different, as in the former, the energy alignment is measured relative to an external reference and includes contributions from solvent reorganization energies, while in the latter, it is measured relative to the energetics of the TiO(2) and is lacking such contributions. The influence of the dyes' dipole moments on the energetics of the TiO(2) was also measured and explained some of the differences in trends. Finally, we compared the injection efficiencies of the two red-absorbing dyes and found that the differences in injection efficiencies can be better explained using the energy alignment determined from photoelectron spectroscopy. This shows that the method for measuring the energetics of a DSC should be chosen according to what process one intends to study.

  • 11. Cappel, Ute B
    et al.
    Plogmaker, Stefan
    Terschlüsen, Joachim A
    Leitner, Torsten
    Johansson, Erik M J
    Edvinsson, Tomas
    Sandell, Anders
    Karis, Olof
    Siegbahn, Hans
    Svensson, Svante
    Mårtensson, Nils
    Rensmo, Håkan
    Söderström, Johan
    Electronic structure dynamics in a low bandgap polymer studied by time-resolved photoelectron spectroscopy.2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 31, p. 21921-9Article in journal (Refereed)
    Abstract [en]

    Means to measure the temporal evolution following a photo-excitation in conjugated polymers are a key for the understanding and optimization of their function in applications such as organic solar cells. In this paper we study the electronic structure dynamics by direct pump-probe measurements of the excited electrons in such materials. Specifically, we carried out a time-resolved photoelectron spectroscopy (TRPES) study of the polymer PCPDTBT by combining an extreme ultraviolet (XUV) high harmonic generation source with a time-of-flight spectrometer. After excitation to either the 1st excited state or to a higher excited state, we follow how the electronic structure develops and relaxes on the electron binding energy scale. Specifically, we follow a less than 50 fs relaxation of the higher exited state and a 10 times slower relaxation of the 1st excited state. We corroborate the results using DFT calculations. Our study demonstrates the power of TRPES for studying photo-excited electron energetics and dynamics of solar cell materials.

  • 12. Cappel, Ute B.
    et al.
    Smeigh, Amanda L.
    Plogmaker, Stefan
    Johansson, Erik M. J.
    Rensmo, Hakan
    Hammarstrom, Leif
    Hagfeldt, Anders
    Boschloo, Gerrit
    Characterization of the Interface Properties and Processes in Solid State Dye-Sensitized Solar Cells Employing a Perylene Sensitizer2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 10, p. 4345-4358Article in journal (Refereed)
    Abstract [en]

    We recently reported on a perylene sensitizer, ID176, which performs much better in solid state dye-sensitized solar cells than in those using liquid electrolytes with iodide/tri-iodide as the redox couple (J. Phys. Chem. C 2009, 113, 14595-14597). Here, we present a characterization of the sensitizer and of the TiO2/dye interface by UV-visible absorption and fluorescence spectroscopy, spectroelectrochemistry, photoelectron spectroscopy, electroabsorption spectroscopy, photoinduced absorption spectroscopy, and femtosecond transient absorption measurements. We report that the absorption spectrum of the sensitizer is red-shifted by addition of lithium ions to the surface due to a downward shift of the excited state level of the sensitizer, which is of the same order of magnitude as the downward shift of the titanium dioxide conduction band edge. Results from photoelectron spectroscopy and electrochemistry suggest that the excited state is largely located below the conduction band edge of TiO2 but that there are states in the band gap of TiO2 which might be available for photoinduced electron injection. The sensitizer was able to efficiently inject into TiO2, when a lithium salt was present on the surface, while injection was much less effective in the absence of lithium ions or in the presence of solvent. In the presence of the hole conductor 2,2’,7,7’-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9’-spirobifluorene (spiro-MeOTAD) and LiTFSI, charge separation was monitored by the emergence of a Stark shift of the dye in transient absorption spectra, and both injection and regeneration appear to be completed within 1 ps. Regeneration by spiro-MeOTAD is therefore several orders of magnitude faster than regeneration by iodide, and ID176 can even be photoreduced by spiro-MeOTAD.

  • 13. Cappel, Ute B
    et al.
    Svanström, Sebastian
    Lanzilotto, Valeria
    Johansson, Fredrik O L
    Aitola, Kerttu
    Philippe, Bertrand
    Giangrisostomi, Erika
    Ovsyannikov, Ruslan
    Leitner, Torsten
    Föhlisch, Alexander
    Svensson, Svante
    Mårtensson, Nils
    Boschloo, Gerrit
    Lindblad, Andreas
    Rensmo, Håkan
    Partially Reversible Photoinduced Chemical Changes in a Mixed-Ion Perovskite Material for Solar Cells.2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 40, p. 34970-34978Article in journal (Refereed)
    Abstract [en]

    ) with the element specificity and chemical sensitivity of core-level photoelectron spectroscopy. By carrying out measurements at a synchrotron beamline optimized for low X-ray fluxes, we are able to avoid sample changes due to X-ray illumination and are therefore able to monitor what sample changes are induced by visible illumination only. We find that laser illumination causes partially reversible chemistry in the surface region, including enrichment of bromide at the surface, which could be related to a phase separation into bromide- and iodide-rich phases. We also observe a partially reversible formation of metallic lead in the perovskite structure. These processes occur on the time scale of minutes during illumination. The presented methodology has a large potential for understanding light-induced chemistry in photoactive materials and could specifically be extended to systematically study the impact of morphology and composition on the photostability of metal halide perovskites.

  • 14. 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, p. 33470-33477Article 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.

  • 15. Dowland, Simon A.
    et al.
    Reynolds, Luke X.
    MacLachlan, Andrew
    Cappel, Ute B.
    Haque, Saif A.
    Photoinduced electron and hole transfer in CdS:P3HT nanocomposite films: effect of nanomorphology on charge separation yield and solar cell performance2013In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 1, no 44, p. 13896-13901Article in journal (Refereed)
    Abstract [en]

    The influence of morphology on the photophysical properties of blend films containing in situ grown CdS and poly(3-hexylthiophene-2,5-diyl) (P3HT), fabricated utilising a metal xanthate single source precursor, is reported. A combination of transient absorption spectroscopy (TAS), transmission electron microscopy (TEM) and photovoltaic device measurements are employed to study the relationship between the efficiency of charge separation, photocurrent generation and thin film morphology. We identify that a significant proportion of the extractable charge originates from the direct excitation of CdS followed by hole-transfer to the P3HT polymer. The yield of this hole-transfer step from the inorganic CdS to the organic polymer is largely unaffected by the film’s nanomorphology, while the dissociation of P3HT excitons into free charges at the CdS:P3HT interface is found to be strongly dependent on this parameter with high yields of charge transfer only being achieved at high CdS loadings. The present study elucidates design rules for the optimization of hybrid inorganic-organic solar energy conversion devices.

  • 16. Feldt, Sandra M.
    et al.
    Cappel, Ute B.
    Johansson, Erik M. J.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Characterization of Surface Passivation by Poly(methylsiloxane) for Dye-Sensitized Solar Cells Employing the Ferrocene Redox Couple2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 23, p. 10551-10558Article in journal (Refereed)
    Abstract [en]

    One-electron outer-sphere redox couples, such as ferrocene/ferrocenium, are an interesting alternative to the iodide/triiodide redox couple that is normally employed in dye-sensitized solar cells (DSCs) because they should reduce the driving force needed to regenerate the dye. Unfortunately, one-electron redox couples also show enhanced recombination with photoinjected electrons, and methods to inhibit this recombination are needed for functioning DSCs. In this study, dye-sensitized titanium dioxide surfaces were passivated by a trichloromethylsilane reaction in order to decrease the fast recombination rates when using the ferrocene redox couple. The formation and binding of poly(methylsiloxane) on the dye-sensitized TiO(2) surface was verified with infrared spectroscopy and photoelectron spectroscopy. Photoelectrochemical characterization of the silanization method showed that the treatment decreased the recombination rate of photoinjected electrons with ferrocenium and thereby improved the efficiency of the DSC. Transient absorption spectroscopy revealed, however, that the poly(methylsiloxane) coatings slowed down the regeneration of the oxidized dye by the ferrocene and prevented the regeneration of some of the dye molecules.

  • 17. Giangrisostomi, Erika
    et al.
    Ovsyannikov, Ruslan
    Sorgenfrei, Florian
    Zhang, Teng
    Lindblad, Andreas
    Sassa, Yasmine
    Cappel, Ute B.
    Leitner, Torsten
    Mitzner, Rolf
    Svensson, Svante
    Martensson, Nils
    Foehlisch, Alexander
    Low Dose Photoelectron Spectroscopy at BESSY II: Electronic structure of matter in its native state2018In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 224, no SI, p. 68-78Article in journal (Refereed)
    Abstract [en]

    The implementation of a high-transmission, angular-resolved time-of-Right electron spectrometer with a 1.25 MHz pulse selector at the PM4 soft X-ray dipole beamline of the synchrotron BESSY II creates unique capabilities to inquire electronic structure via photoelectron spectroscopy with a minimum of radiation dose. Solid-state samples can be prepared and characterized with standard UHV techniques and rapidly transferred from various preparation chambers to a 4-axis temperature-controlled measurement stage. A synchronized MHz laser system enables excited-state characterization and dynamical studies starting from the picosecond timescale. This article introduces the principal characteristics of the PM4 beamline and LowDosePES end-station. Recent results from graphene, an organic hole transport material for solar cells and the transition metal dichalcogenide MoS2 are presented to demonstrate the instrument performances. (C) 2017 The Authors. Published by Elsevier B.V.

  • 18. Hagfeldt, A.
    et al.
    Cappel, U. B.
    Boschloo, G.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Pettersson, H.
    Gibson, E. A.
    Mesoporous dye-sensitized solar cells2012In: Reference Module in Earth Systems and Environmental Sciences, Elsevier, 2012, Vol. 1, p. 481-496Chapter in book (Other academic)
    Abstract [en]

    Photovoltaics, or solar cells, are fast growing both with regards to industrialization and research. Globally, the total PV installation is around 40 GW and an annual growth rate of 45% has been experienced over recent years. In the comparison between different photovoltaic technologies a figure of merit is the production cost per peak watt of solar electricity produced. For so called second generation thin film solar cells production costs down to and even below 1 $/W-1 peak are reported. To be competitive with conventional energy sources for large-scale electricity production new PV technologies need to aim at production costs below 0.5 $/W-1 peak. The dye-sensitized solar cell (DSC) is a molecular solar cell technology which have the potential to achieve production costs below 0.5 $/W-1 peak. DSC is based on molecular and nanometer-scale components. Record cell efficiencies of 12%, promising stability data and means of energy efficient production methods have been accomplished. As selling points for the DSC technology the prospect of low-cost investments and fabrication are key features. DSCs offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. This chapter describes the basic principles of the operation of DSC, the state-of-the-art, the materials development that is currently taking place as well as the potentials for future development.

  • 19. Hagfeldt, Anders
    et al.
    Cappel, U.B.
    Boschloo, G.
    Sun, L.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Pettersson, H.
    Gibson, E.A.
    Dye-sensitized Photoelectrochemical Cells2012In: Practical Handbook of Photovoltaics Findamentals and Applications, 2nd Edition / [ed] A. McEvoy, T. Markvart, L.Castaner, Oxford: Academic Press, 2012, 2, p. 479-542Chapter in book (Refereed)
    Abstract [en]

    As part of the growing sustainable and renewable energy movement, the design, manufacture and use of photovoltaic devices is increasing in pace and frequency. The Handbook of Photovoltaics will be a 'benchmark' publication for those involved in the design, manufacture and use of these devices. The Handbook covers the principles of solar cell function, the raw materials, photovoltaic systems, standards, calibration, testing, economics and case studies. The editors have assembled a cast of internationally-respected contributors from industry and academia. The report is essential reading for: Physicists, electronic engineers, designers of systems, installers, architects, policy-makers relating to photovoltaics.

  • 20.
    Jacobsson, T. Jesper
    et al.
    Uppsala Univ, Dept Chem, Box 538, S-75121 Uppsala, Sweden..
    Svanström, Sebastian
    Uppsala Univ, Dept Phys & Astron, Box 5516, S-75120 Uppsala, Sweden..
    Andrei, Virgil
    Univ Cambridge, Dept Chem, Lensfield Rd, Cambridge CB2 1EW, England..
    Rivett, Jasmine P. H.
    Univ Cambridge, Dept Phys, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 0HE, England..
    Kornienko, Nikolay
    Univ Cambridge, Dept Chem, Lensfield Rd, Cambridge CB2 1EW, England..
    Philippe, Bertrand
    Uppsala Univ, Dept Phys & Astron, Box 5516, S-75120 Uppsala, Sweden..
    Cappel, Ute B.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry.
    Rensmo, Håkan
    Uppsala Univ, Dept Phys & Astron, Box 5516, S-75120 Uppsala, Sweden..
    Deschler, Felix
    Univ Cambridge, Dept Phys, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 0HE, England..
    Boschloo, Gerrit
    Uppsala Univ, Dept Chem, Box 538, S-75121 Uppsala, Sweden..
    Extending the Compositional Space of Mixed Lead Halide Perovskites by Cs, Rb, K, and Na Doping2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 25, p. 13548-13557Article in journal (Refereed)
    Abstract [en]

    A trend in high performing lead halide perovskite solar cell devices has been increasing compositional complexity by successively introducing more elements, dopants, and additives into the structure; and some of the latest top efficiencies have been achieved with a quadruple cation mixed halide perovskite Cs(x)FA(y)MA(z)Rb(1-x-y-z)PbBr(q)I(3-9). This paper continues this trend by exploring doping of mixed lead halide perovskites, FA(0.83)MA(0.17)PbBr(0.51)I(2.49), with an extended set of alkali cations, i.e., Cs+, Rb+, K+, and Na+, as well as combinations of them. The doped perovskites were investigated with X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, hard X-ray photoelectron spectroscopy, UV-vis, steady state fluorescence, and ultrafast transient absorption spectroscopy. Solar cell devices were made as well. Cs+ can replace the organic cations in the perovskite structure, but Rb+, K+, and Na+ do not appear to do that. Despite this, samples doped with K and Na have substantially longer fluorescence lifetimes, which potentially could be beneficial for device performance.

  • 21.
    Johansson, F. O. L.
    et al.
    Uppsala Univ, Dept Phys & Astron, Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Ivanovic, M.
    Univ Tubingen, Inst Phys & Theoret Chem, Morgenstelle 18, D-72076 Tubingen, Germany..
    Svanstrom, S.
    Uppsala Univ, Dept Phys & Astron, Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Cappel, Ute B.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. Uppsala Univ, Dept Phys & Astron, Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden.
    Peisert, H.
    Univ Tubingen, Inst Phys & Theoret Chem, Morgenstelle 18, D-72076 Tubingen, Germany..
    Chasse, T.
    Univ Tubingen, Inst Phys & Theoret Chem, Morgenstelle 18, D-72076 Tubingen, Germany..
    Lindblad, A.
    Uppsala Univ, Dept Phys & Astron, Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Femtosecond and Attosecond Electron-Transfer Dynamics in PCPDTBT:PCBM Bulk Heterojunctions2018In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 24, p. 12605-12614Article in journal (Refereed)
    Abstract [en]

    Charge separation efficiency is a crucial parameter for photovoltaic devices-polymers consisting of alternating electron-rich and electron-deficient parts can achieve high such efficiencies, for instance, together with a fullerene electron acceptor. This offers a viable path toward solar cells with organic bulk heterojunctions. Here, we measured the charge-transfer times in the femtosecond and attosecond regimes via the decay of sulfur is X-ray core excited states (with the core-hole clock method) in blends of a low-band gap polymer {PCPDTBT [poly[2,6-(4,4-bis (2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-1/1 dithiophene)-alt-4,7- (2,1,3-benzothiadiazole)]]} consisting of a cyclopentadithiophene electron-rich part and a benzothiadiazole electron-deficient part. The constituting parts of the bulk heterojunction were varied by adding the fullerene derivative PCBM ([6,6]-phenyl-C-61-butyric acid methyl ester) (weight ratio of polymer/PCBM as 1:0, 1:1, 1:2, and 1:3). For low-energy excitations, the charge-transfer time varies to the largest extent for the thiophene donor part. The charge-transfer time in the 1:2 blend is reduced by 86% compared to that of pristine PCPDTBT. At higher energy excitations, the charge-transfer time does not vary with the chemical environment, as this regime is dominated by intramolecular conduction that yields ultrafast charge-transfer times for all blends, approaching 170 as. We thus demonstrate that the core-hole clock method applied to a series with changing composition can give information about local electron dynamics (with chemical specificity) at interfaces between the constituting parts the crucial part of a bulk heterojunction where the initial charge separation occurs.

  • 22. Lee, George P
    et al.
    Shi, Yichao
    Lavoie, Ellen
    Daeneke, Torben
    Reineck, Philipp
    Cappel, Ute B
    Huang, David M
    Bach, Udo
    Light-driven transformation processes of anisotropic silver nanoparticles.2013In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 7, no 7, p. 5911-21Article in journal (Refereed)
    Abstract [en]

    The photoinduced formation of silver nanoprisms from smaller silver seed particles in the presence of citrate anions is a classic example of a photomorphic reaction. In this case, light is used as a convenient tool to dynamically manipulate the shape of metal nanoparticles. To date, very little is known about the prevailing reaction mechanism of this type of photoreaction. Here we provide a detailed study of the shape transformation dynamics as a function of a range of different process parameters, such as photon energy and photon flux. For the first time, we provide direct evidence that the photochemical synthesis of silver nanoprisms from spherical seed nanoparticles proceeds via a light-activated two-dimensional coalescence mechanism. On the other hand, we could show that Ostwald ripening becomes the dominant reaction mechanism when larger silver nanoprisms are grown from photochemically synthesized smaller nanoprisms. This two-step reaction proceeds significantly faster and yields more uniform, sharper nanoprisms than the classical one-step photodevelopment process from seeds. The ability to dynamically control nanoparticle shapes and properties with light opens up novel synthesis avenues but also, more importantly, allows one to conceive new applications that exploit the nonstatic character of these nanoparticles and the ability to control and adjust their properties at will in a highly dynamic fashion.

  • 23. Lindblad, Rebecka
    et al.
    Cappel, Ute B
    O'Mahony, Flannan T F
    Siegbahn, Hans
    Johansson, Erik M J
    Haque, Saif A
    Rensmo, Håkan
    Energy level alignment in TiO2/metal sulfide/polymer interfaces for solar cell applications.2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 32, p. 17099-107Article in journal (Refereed)
    Abstract [en]

    Semiconductor sensitized solar cell interfaces have been studied with photoelectron spectroscopy to understand the interfacial electronic structures. In particular, the experimental energy level alignment has been determined for complete TiO2/metal sulfide/polymer interfaces. For the metal sulfides CdS, Sb2S3 and Bi2S3 deposited from single source metal xanthate precursors, it was shown that both driving forces for electron injection into TiO2 and hole transfer to the polymer decrease for narrower bandgaps. The energy level alignment results were used in the discussion of the function of solar cells with the same metal sulfides as light absorbers. For example Sb2S3 showed the most favourable energy level alignment with 0.3 eV driving force for electron injection and 0.4 eV driving force for hole transfer and also the most efficient solar cells due to high photocurrent generation. The energy level alignment of the TiO2/Bi2S3 interface on the other hand showed no driving force for electron injection to TiO2, and the performance of the corresponding solar cell was very low.

  • 24. MacLachlan, Andrew J
    et al.
    Rath, Thomas
    Cappel, Ute B
    Dowland, Simon A
    Amenitsch, Heinz
    Knall, Astrid-Caroline
    Buchmaier, Christine
    Trimmel, Gregor
    Nelson, Jenny
    Haque, Saif A
    Polymer/Nanocrystal Hybrid Solar Cells: Influence of Molecular Precursor Design on Film Nanomorphology, Charge Generation and Device Performance.2015In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 25, no 3, p. 409-420Article in journal (Refereed)
    Abstract [en]

    In this work, molecular tuning of metal xanthate precursors is shown to have a marked effect on the heterojunction morphology of hybrid poly(3-hexylthiophene-2,5-diyl) (P3HT)/CdS blends and, as a result, the photochemical processes and overall performance of in situ fabricated hybrid solar cells. A series of cadmium xanthate complexes is synthesized for use as in situ precursors to cadmium sulfide nanoparticles in hybrid P3HT/CdS solar cells. The formation of CdS domains is studied by simultaneous GIWAXS (grazing incidence wide-angle X-ray scattering) and GISAXS (grazing incidence small-angle X-ray scattering), revealing knowledge about crystal growth and the formation of different morphologies observed using TEM (transmission electron microscopy). These measurements show that there is a strong relationship between precursor structure and heterojunction nanomorphology. A combination of TAS (transient absorption spectroscopy) and photovoltaic device performance measurements is used to show the intricate balance required between charge photogeneration and percolated domains in order to effectively extract charges to maximize device power conversion efficiencies. This study presents a strong case for xanthate complexes as a useful route to designing optimal heterojunction morphologies for use in the emerging field of hybrid organic/inorganic solar cells, due to the fact that the nanomorphology can be tuned via careful design of these precursor materials.

  • 25. Moia, Davide
    et al.
    Cappel, Ute B.
    Leijtens, Tomas
    Li, Xiaoe
    Telford, Andrew M.
    Snaith, Henry J.
    O’Regan, Brian C.
    Nelson, Jenny
    Barnes, Piers R. F.
    The Role of Hole Transport between Dyes in Solid-State Dye-Sensitized Solar Cells2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 33, p. 18975-18985Article in journal (Refereed)
    Abstract [en]

    In dye-sensitized solar cells (DSSCs) photo-generated positive charges are normally considered to be carried away from the dyes by a separate phase of hole-transporting material (HTM). We show that there can also be significant transport within the dye monolayer itself before the hole reaches the HTM. We quantify the fraction of dye regeneration in solid-state DSSCs that can be attributed to this process. By using cyclic voltammetry and transient anisotropy spectroscopy, we demonstrate that the rate of interdye hole transport is prevented both on micrometer and nanometer length scales by reducing the dye loading on the TiO2 surface. The dye regeneration yield is quantified for films with high and low dye loadings (with and without hole percolation in the dye monolayer) infiltrated with varying levels of HTM. Interdye hole transport can account for >50% of the overall dye regeneration with low HTM pore filling. This is reduced to about 5% when the infiltration of the HTM in the pores is optimized in 2 mu m thick films. Finally, we use hole transport in the dye monolayer to characterize the spatial distribution of the HTM phase in the pores of the dyed mesoporous TiO2.

  • 26. O'Mahony, Flannan T. F.
    et al.
    Cappel, Ute B.
    Imperial College London, UK.
    Tokmoldin, Nurlan
    Lutz, Thierry
    Lindblad, Rebecka
    Rensmo, Håkan
    Haque, Saif A.
    Low-temperature solution processing of mesoporous metal-sulfide semiconductors as light-harvesting photoanodes.2013In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 52, no 46, p. 12047-51Article in journal (Refereed)
    Abstract [en]

    Structured absorbers: Mesoporous films of highly crystalline Sb 2S3 are prepared from a doctor-bladed precursor paste that is thermally annealed. This facile and versatile processing route allows for control of the pore size through variation of the annealing temperature. The resulting high surface area allows for efficient charge transfer to a polymeric hole acceptor; hence, such films could form the basis of a novel hybrid organic-inorganic photovoltaic device.

  • 27. Pazoki, Meysam
    et al.
    Cappel, Ute B.
    Uppsala University, Sweden.
    Johansson, Erik M. J.
    Hagfeldt, Anders
    Boschloo, Gerrit
    Characterization techniques for dye-sensitized solar cells2017In: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 10, no 3, p. 672-709Article in journal (Refereed)
    Abstract [en]

    Dye-sensitized solar cells (DSCs) have been widely studied in the last two decades and start to be commercialized in the photovoltaic market. Comprehensive characterization is needed to fully understand and optimize the device performance and stability. In this review, we summarize different characterization methods for dye-sensitized solar cells with liquid redox electrolytes or solid state hole transporting materials, most of which can also be used for similar devices such as perovskite based thin film solar cells. Limitations and advantages of relevant methods for studying the energy levels and time scales involved in charge transfer processes as well as charge transport related characteristic lengths are discussed. A summary of recent developments in DSCs and the importance of measured parameters for the device optimization procedure are mentioned at the end.

  • 28. Philippe, Bertrand
    et al.
    Jacobsson, T. Jesper
    Correa-Baena, Juan-Pablo
    Jena, Naresh K.
    Banerjee, Amitava
    Chakraborty, Sudip
    Cappel, Ute B.
    Uppsala University, Sweden.
    Ahuja, Rajeev
    Hagfeldt, Anders
    Odelius, Michael
    Rensmo, Håkan
    Valence Level Character in a Mixed Perovskite Material and Determination of the Valence Band Maximum from Photoelectron Spectroscopy: Variation with Photon Energy2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 48, p. 26655-26666Article in journal (Refereed)
    Abstract [en]

    A better understanding of the electronic structure of perovskite materials used in photovoltaic devices is essential for their development and optimization. In this investigation, synchrotron-based photoelectron spectroscopy (PES) was used to experimentally delineate the character and energy position of the valence band structures of a mixed perovskite. The valence band was measured using PES with photon energies ranging from ultraviolet photoelectron spectroscopy (21.2 eV) to hard X-rays (up to 4000 eV), and by taking the variation of the photoionization cross sections into account, we could experimentally determine the inorganic and organic contributions. The experiments were compared to theoretical calculations to further distinguish the role of the different anions in the electronic structure. This work also includes a thorough study of the valence band maximum and its position in relation to the Fermi level, which is crucial for the design and optimization of complete solar cells and their functional properties.

  • 29. Philippe, Bertrand
    et al.
    Saliba, Michael
    Correa-Baena, Juan-Pablo
    Cappel, Ute B.
    Uppsala University, Sweden.
    Turren-Cruz, Silver-Hamill
    Gratzel, Michael
    Hagfeldt, Anders
    Rensmo, Hakan
    Chemical Distribution of Multiple Cation (Rb+, Cs+, MA(+), and FA(+)) Perovskite Materials by Photoelectron Spectroscopy2017In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 29, no 8, p. 3589-3596Article in journal (Refereed)
    Abstract [en]

    Lead-based mixed perovskite materials have emerged in the last couple of years as promising photovoltaic materials. Recently, it was shown that improved material stability can be achieved by incorporating small amounts of inorganic cations (Cs+ and Rb+), partially replacing the more common organic cations (e.g., methylammonium, MA, and formamidinium, FA). Especially, a mixed cation composition containing Rb+, Cs+, MA(+), and FA(+) was recently shown to have beneficial optoelectronic properties and was stable at elevated temperature. This work focuses on the composition of this material using synchrotron-based photoelectron spectroscopy. Different probing depths were considered by changing the photon energy of the X-ray source providing insights on the chemical composition and the chemical distribution near the surface of the samples. Perovskite materials containing two, three, or four monovalent cations were analyzed and compared. The presence of Cs and Rb was observed both at the sample surface and toward the bulk, and we found that in the presence of three or four cations, less unreacted PbI2 remains in the sample. Interestingly, Rb and Cs appear to act jointly resulting in a different cation depth profile compared to that of the triple counterparts. Our findings provide significant understanding of the intricate depth-dependent chemical composition in perovskite materials using the common practice of cation mixing.

  • 30. Plogmaker, S.
    et al.
    Terschlusen, J. A.
    Krebs, N.
    Svanqvist, M.
    Forsberg, J.
    Cappel, Ute
    Uppsala University, Sweden.
    Rubensson, J. -E
    Siegbahn, H.
    Soderstrom, J.
    HELIOS-A laboratory based on high-order harmonic generation of extreme ultraviolet photons for time-resolved spectroscopy2015In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 86, no 12, article id 123107Article in journal (Refereed)
    Abstract [en]

    In this paper, we present the HELIOS (High Energy Laser Induced Overtone Source) laboratory, an in-house high-order harmonic generation facility which generates extreme ultraviolet (XUV) photon pulses in the range of 15-70 eV with monochromatized XUV pulse lengths below 35 fs. HELIOS is a source for time-resolved pump-probe/two-color spectroscopy in the sub-50 fs range, which can be operated at 5 kHz or 10 kHz. An optical parametric amplifier is available for pump-probe experiments with wavelengths ranging from 240 nm to 20 000 nm. The produced XUV radiation is monochromatized by a grating in the so-called off-plane mount. Together with overall design parameters, first monochromatized spectra are shown with an intensity of 2 . 10(10) photons/s (at 5 kHz) in the 29th harmonic, after the monochromator. The XUV pulse duration is measured to be <25 fs after monochromatization.

  • 31. Sage, Rebecca S.
    et al.
    Cappel, Ute B.
    University of Bristol, UK.
    Ashfold, Michael N. R.
    Walker, Nicholas R.
    Quadrupole mass spectrometry and time-of-flight analysis of ions resulting from 532 nm pulsed laser ablation of Ni, Al, and ZnO targets2008In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 103, no 9, article id 093301Article in journal (Refereed)
    Abstract [en]

    This work describes the design and validation of an instrument to measure the kinetic energies of ions ejected by the pulsed laser ablation (PLA) of a solid target. Mass spectra show that the PLA of Ni, Al, and ZnO targets, in vacuum, using the second harmonic of a Nd:YAG laser (532 nm, pulse duration similar to 10 ns) generates abundant X(n+) ions (n <= 3 for Ni, <= 2 for Al, <= 3 and <= 2 for Zn and O respectively from ZnO). Ions are selected by their mass/charge (m/z) ratio prior to the determination of their times of flight. PLA of Ni has been studied in most detail. The mean velocities of ablated Ni(n+) ions are shown to follow the trend v(Ni(3+))>v(Ni(2+))>v(Ni(+)). Data from Ni(2+) and Ni(3+) are fitted to shifted Maxwellian functions and agree well with a model which assumes both thermal and Coulombic contributions to ion velocities. The dependence of ion velocities on laser pulse energy (and fluence) is investigated, and the high energy data are shown to be consistent with an effective accelerating voltage of similar to 90 V within the plume. The distribution of velocities associated with Ni(3+) indicates a population at cooler temperature than Ni(2+).

  • 32.
    Saki, Zahra
    et al.
    Sharif Univ Technol, Phys Dept, Tehran 14588, Iran.;Uppsala Univ, Dept Chem, Angstrom Lab, Phys Chem, Box 523, S-75120 Uppsala, Sweden..
    Aitola, Kerttu
    Uppsala Univ, Dept Chem, Angstrom Lab, Phys Chem, Box 523, S-75120 Uppsala, Sweden.;Aalto Univ Sch Sci, New Energy Technol Grp, Dept Appl Phys, POB 15100, Aalto 00076, Finland..
    Sveinbjornsson, Kari
    Uppsala Univ, Dept Chem, Angstrom Lab, Phys Chem, Box 523, S-75120 Uppsala, Sweden..
    Yang, Wenxing
    Uppsala Univ, Dept Chem, Angstrom Lab, Phys Chem, Box 523, S-75120 Uppsala, Sweden..
    Svanstrom, Sebastian
    Uppsala Univ, Dept Phys & Astron Mol & Condensed Matter Phys, Box 516, S-75120 Uppsala, Sweden..
    Cappel, Ute B.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. Uppsala Univ, Dept Phys & Astron Mol & Condensed Matter Phys, Box 516, S-75120 Uppsala, Sweden.;.
    Rensmo, Hakan
    Uppsala Univ, Dept Phys & Astron Mol & Condensed Matter Phys, Box 516, S-75120 Uppsala, Sweden..
    Johansson, Erik M. J.
    Uppsala Univ, Dept Chem, Angstrom Lab, Phys Chem, Box 523, S-75120 Uppsala, Sweden..
    Taghavinia, Nima
    Sharif Univ Technol, Phys Dept, Tehran 14588, Iran.;Sharif Univ Technol, Inst Nanosci & Nanotechnol, Tehran 14588, Iran..
    Boschloo, Gerrit
    Uppsala Univ, Dept Chem, Angstrom Lab, Phys Chem, Box 523, S-75120 Uppsala, Sweden..
    The synergistic effect of dimethyl sulfoxide vapor treatment and C-60 electron transporting layer towards enhancing current collection in mixed-ion inverted perovskite solar cells2018In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 405, p. 70-79Article in journal (Refereed)
    Abstract [en]

    Inverted perovskite solar cells (PSCs) have been introduced as better candidate for roll-to-roll printing and scaleup than their conventional configuration counterparts, while their fabrication is technically more demanding. The common light absorbing layer in inverted PSCs is the single cation methylammonium lead iodide (MAPbI(3)) perovskite, whereas mixed-ion perovskites are chemically more stable. In mixed-ion perovskites, where FA (formamidinium) is the main replacement for MA, the electron affinity is larger than in MAPbI3 perovskites, leading to possible barriers against photoelectron collection by the electron transporting layer (ETL). In this paper we report on a mixed-ion (FAPbI(3))(0.83)(MAPbBr(3))(0.17) inverted PSC with improved photocurrent through using a dimethyl sulfoxide vapor treatment of perovskite layer and replacing the conventional [6,6]-phenyl-C-71 butyric acid methyl ester (PC70BM) with C-60/bathocuproine (BCP) as more effective ETL. The treatment of perovskite layer results in reduction of impurity phases of 8-FAPbI(3) and Pbl(2). Photoluminescence and open circuit voltage decay data demonstrate better charge carrier collection by the C-60/BCP compared to the PC70BM ETL, and an electron barrier for the back flow of electrons from ETL to perovskite. Our improvements in perovskite crystalization and electron transfer layer simultaneously lead to increasing the current density from 10 to 21 mA cm(-2).

  • 33.
    Schaefer, A.
    et al.
    Lund Univ, Dept Synchrotron Radiat Res, POB 118, SE-22100 Lund, Sweden.;Chalmers Univ Technol, Competence Ctr Catalysis, S-41296 Gothenburg, Sweden..
    Lanzilotto, V.
    Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden..
    Cappel, Ute B.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden.
    Uvdal, P.
    Lund Univ, Dept Chem, Chem Phys, POB 124, SE-22100 Lund, Sweden..
    Borg, A.
    NTNU Norwegian Univ Sci & Technol, Dept Phys, NO-07491 Trondheim, Norway..
    Sandell, A.
    Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden..
    First layer water phases on anatase TiO2(101)2018In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 674, p. 25-31Article in journal (Refereed)
    Abstract [en]

    The anatase TiO2(101) surface and its interaction with water is an important topic in oxide surface chemistry. Firstly, it benchmarks the properties of the majority facet of TiO2 nanoparticles and, secondly, there is a controversy as to whether the water molecule adsorbs intact or deprotonates. We have addressed the adsorption of water on anatase TiO2(101) by synchrotron radiation photoelectron spectroscopy. Three two-dimensional water structures are found during growth at different temperatures: at 100 K, a metastable structure forms with no hydrogen bonding between the water molecules. In accord with prior literature, we assign this phase to chains of disordered molecules. Growth 160 K results in a metastable structure with expressed hydrogen bonding between the water molecules. At 190 K, the water molecules become disordered as the thermal energy is too high and hence the hydrogen bonds break. The result is a structure with isolated monomers. Partial dissociation is observed for all three growths, with the molecular state only slightly favored in energy (20-40 meV) over the dissociated state. Heating of a thick film leads to more dissociation compared to a bilayer, when formed at 100 K. Thus, extending the water network facilitates proton transport and hence dissociation. The results reconcile apparent conflicting experimental results previously obtained by scanning tunneling microscopy (STM) and core level photoelectron spectroscopy.

  • 34.
    Schaefer, A.
    et al.
    Chalmers Univ Technol, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Competence Ctr Catalysis, S-41296 Gothenburg, Sweden..
    Lanzilotto, V.
    Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden..
    Cappel, Ute
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry. Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden.
    Uvdal, P.
    Lund Univ, Dept Chem, Chem Phys, POB 124, SE-22100 Lund, Sweden..
    Borg, A.
    NTNU Norwegian Univ Sci & Technol, Dept Phys, NO-7491 Trondheim, Norway..
    Sandell, A.
    Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden..
    Defect-Induced Water Bilayer Growth on Anatase TiO2(101)2018In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 34, no 37, p. 10856-10864Article in journal (Refereed)
    Abstract [en]

    Preparing an anatase TiO2(101) surface with a high density of oxygen vacancies and associated reduced Ti species in the near-surface region results in drastic changes in the water adsorption chemistry compared to adsorption on a highly stoichiometric surface. Using synchrotron radiation excited photoelectron spectroscopy, we observe a change in the water growth mode, from layer-by-layer growth on the highly stoichiometric surface to bilayer growth on the reduced surface. Furthermore, we have been able to observe enrichment at the surface upon water adsorption. The Ti3+ enrichment occurs concomitant with effective water dissociation into hydroxyls with a very high thermal stability. The water bilayer on the reduced surface is thermally more stable than that on the stoichiometric surface, and it is more efficient in promoting further water dissociation upon heating. The results thus show how the presence of subsurface defects can alter the wetting mechanism of an oxide surface.

  • 35.
    Svanström, Sebastian
    et al.
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Jacobsson, T. Jesper
    Uppsala Univ, Dept Chem, Angstrom Lab, Box 538, S-75121 Uppsala, Sweden..
    Sloboda, Tamara
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Giangrisostomi, Erika
    Helmholtz Zentrum Berlin GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Ovsyannikov, Ruslan
    Helmholtz Zentrum Berlin GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Rensmo, Hakan
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Cappel, Ute B.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Effect of halide ratio and Cs+ addition on the photochemical stability of lead halide perovskites2018In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 44, p. 22134-22144Article in journal (Refereed)
    Abstract [en]

    Lead halide perovskite solar cells with multi-cation/mixed halide materials now give power conversion efficiencies of more than 20%. The stability of these mixed materials has been significantly improved through the addition of Cs+ compared to the original methylammonium lead iodide. However, it remains one of the most significant challenges for commercialisation. In this study, we use photoelectron spectroscopy (PES) in combination with visible laser illumination to study the photo-stability of perovskite films with different compositions. These include Br : I ratios of 50 : 50 and 17 : 83 and compositions with and without Cs+. For the samples without Cs and the 50 : 50 samples, we found that the surface was enriched in Br and depleted in I during illumination and that some of the perovskite decomposed into Pb-0, organic halide salts, and iodine. After illumination, both of these reactions were partially reversible. Furthermore, the surfaces of the films were enriched in organic halide salts indicating that the cations were not degraded into volatile products. With the addition of Cs+ to the samples, photo-induced changes were significantly suppressed for a 50 : 50 bromide to iodide ratio and completely suppressed for perovskites with a 17 : 83 ratio at light intensities exceeding 1 sun equivalent.

  • 36. Sveinbjornsson, Kari
    et al.
    Thein, Nan Kyi Kyi
    Saki, Zahra
    Svanstrom, Sebastian
    Yang, Wenxing
    Cappel, Ute B.
    Uppsala University, Sweden.
    Rensmo, Hakan
    Boschloo, Gerrit
    Aitola, Kerttu
    Johansson, Erik M. J.
    Preparation of mixed-ion and inorganic perovskite films using water and isopropanol as solvents for solar cell applications2018In: Sustainable Energy & Fuels, ISSN 2398-4902, Vol. 2, no 3, p. 606-615Article in journal (Refereed)
    Abstract [en]

    Presently, the most efficient lead halide perovskite solar cells are manufactured by using high-boiling point organic solvents to dissolve the perovskite precursor materials prior to the perovskite formation. Previously, efforts have been made to exchange the said solvents for water with some success. Herein, we build on that work to develop a procedure for synthesising perovskite absorbers using only water and isopropanol as solvents. Our technique can be utilised for fabricating many different perovskite compositions, organic and inorganic. The technique is based on the high solubility of metal nitrates, such as lead(ii) nitrate and caesium(i) nitrate, in water and, respectively, their poor solubilities in isopropanol. The inclusion of CsNO3 to Pb(NO3)(2) films does not result in a phase separation of the perovskite material as one would expect when using lead(ii) halide precursor films. Using the perovskite composition Cs(0.1)FA(0.9)Pb(I0.83Br0.17)(3) we were able to reach an average solar cell power conversion efficiency of 13.0%. Furthermore, the technique can be applied to many different perovskite compositions making it appealing for large-scale manufacturing of perovskite solar cells.

  • 37. Yang, Lei
    et al.
    Cappel, Ute B.
    Unger, Eva L.
    Karlsson, Martin
    Karlsson, Karl Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    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
    Johansson, Erik M. J.
    Comparing spiro-OMeTAD and P3HT hole conductors in efficient solid state dye-sensitized solar cells2012In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 2, p. 779-789Article in journal (Refereed)
    Abstract [en]

    Two hole conductor materials, spiro-OMeTAD and P3HT, were compared in solid-state dye-sensitized solar cells. Two organic dyes containing one anchor unit (D35) or two anchor units (M3) were used in the comparison. Absorbed photon to current conversion efficiency close to unity was obtained for the devices with spiro-OMeTAD. Energy conversion efficiencies of 4.7% and 4.9% were measured for the devices with spiro-OMeTAD and the dyes D35 and M3, respectively. For the devices using the P3HT hole conductor the results were rather different comparing the two dye molecules, with energy conversion efficiencies of 3.2% and 0.5% for D35 and M3, respectively. Photo-induced absorption measurements suggest that the regeneration of the dyes, and the polymer infiltration, is not complete using P3HT, while spiro-OMeTAD regenerates the dyes efficiently. However, the TiO(2)/D35/P3HT system shows rather high energy conversion efficiency and electrochemical oxidation of the dyes on TiO(2) indicates that D35 have a more efficient dye to dye hole conduction than M3, which thereby might explain the higher performance. The dye hole conduction may therefore be of significant importance for optimizing the energy conversion in such hybrid TiO(2)/dye/polymer systems.

  • 38.
    Zhang, Xiaoliang
    et al.
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Cappel, Ute B.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Jia, Donglin
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Zhou, Qisen
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Du, Juan
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Sloboda, Tamara
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Svanström, Sebastian
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Johansson, Fredrik O. L.
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Lindblad, Andreas
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Giangrisostomi, Erika
    Helmholtz Zentrum Berlin GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Ovsyannikov, Ruslan
    Helmholtz Zentrum Berlin GmbH, Inst Methods & Instrumentat Synchrotron Radiat Re, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Liu, Jianhua
    Beihang Univ, Sch Mat Sci & Engn, Beijing 100191, Peoples R China..
    Rensmo, Håkan
    Uppsala Univ, Dept Phys & Astron, Div Mol & Condensed Matter Phys, Box 516, SE-75120 Uppsala, Sweden..
    Gardner, James M.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Applied Physical Chemistry.
    Johansson, Erik M. J.
    Uppsala Univ, Phys Chem, Dept Chem Angstrom, S-75120 Uppsala, Sweden..
    Probing and Controlling Surface Passivation of PbS Quantum Dot Solid for Improved Performance of Infrared Absorbing Solar Cells2019In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 31, no 11, p. 4081-4091Article in journal (Refereed)
    Abstract [en]

    Surface properties of colloidal quantum dots (CQDs) are critical for the transportation and recombination of the photoinduced charge carrier in CQD solar cells, therefore dominating the photovoltaic performance. Herein, PbS CQD passivated using liquid-state ligand exchange (LSLX) and solid-state ligand exchange (SSLX) strategies are in detail investigated using photoelectron spectroscopy (PES), and solar cell devices are prepared to understand the link between the CQD surface properties and the solar cell function. PES using different energies in the soft and hard Xray regime is applied to study the surface and bulk properties of the CQDs, and the results show more effective surface passivation of the CQDs prepared with the LSLX strategy and less formation of lead-oxide. The CQD solar cells prepared with LSLX strategy show higher performance, and the photoelectric measurements suggest that the recombination of photoinduced charges is reduced for the solar cell prepared with the LSLX approach. Meanwhile, the fabricated solar cells exhibit good stability. This work provides important insights into how to fine-tune the CQD surface properties by improving the CQD passivation, and how this is linked to further improvements of the device photovoltaic performance.

  • 39. Zhang, Xiaoliang
    et al.
    Zhang, Jindan
    Phuyal, Dibya
    Du, Juan
    Tian, Lei
    Oberg, Viktor A.
    Johansson, Malin B.
    Cappel, Ute B.
    Uppsala University, Sweden.
    Karis, Olof
    Liu, Jianhua
    Rensmo, Hakan
    Boschloo, Gerrit
    Johansson, Erik M. J.
    Inorganic CsPbI3 Perovskite Coating on PbS Quantum Dot for Highly Efficient and Stable Infrared Light Converting Solar Cells2018In: Advanced Energy Materials, ISSN 1614-6832, Vol. 8, no 6, article id 1702049Article in journal (Refereed)
    Abstract [en]

    Solution-processed colloidal quantum dot (CQD) solar cells harvesting the infrared part of the solar spectrum are especially interesting for future use in semitransparent windows or multilayer solar cells. To improve the device power conversion efficiency (PCE) and stability of the solar cells, surface passivation of the quantum dots is vital in the research of CQD solar cells. Herein, inorganic CsPbI3 perovskite (CsPbI3-P) coating on PbS CQDs with a low-temperature, solution-processed approach is reported. The PbS CQD solar cell with CsPbI3-P coating gives a high PCE of 10.5% and exhibits remarkable stability both under long-term constant illumination and storage under ambient conditions. Detailed characterization and analysis reveal improved passivation of the PbS CQDs with the CsPbI3-P coating, and the results suggest that the lattice coherence between CsPbI3-P and PbS results in epitaxial induced growth of the CsPbI3-P coating. The improved passivation significantly diminishes the sub-bandgap trap-state assisted recombination, leading to improved charge collection and therefore higher photovoltaic performance. This work therefore provides important insight to improve the CQD passivation by coating with an inorganic perovskite ligand for photovoltaics or other optoelectronic applications.

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