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Photoelectrochemical studies of dye-sensitized solar cells using organic dyes
KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD. (Centre of Molecular Devices)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The dye-sensitized solar cell (DSC) is a promising efficient low-cost molecular photovoltaic device. One of the key components in DSCs is the dye, as it is responsible for the capture of sunlight.

State-of-the-art DSC devices, based on ruthenium dyes, show record efficiencies of 10-12 %. During the last decade, metal-free organic dyes have been extensively explored as sensitizers for DSC application. The use of organic dyes is particularly attractive as it enables easy structural modifications, due to fairly short synthetic routes and reduced material cost. Novel dye should in addition to the light-harvesting properties also be compatible with the DSC components.

In this thesis, a series of new organic dyes are investigated, both when integrated in the DSC device and as individual components. The evaluation methods consisted of different electrochemical and photoelectrochemical techniques. Whereas the light-harvesting properties of the dyes were fairly easily improved, the behavior of the dye integrated in the DSC showed less predictable photovoltaic results.

The dye series studied in Papers II and IV revealed that their dye energetics limited vital electron-transfer processes, the dye regeneration (Paper II) and injection quantum yield (Paper IV). Further, in Papers III-VI, it was observed that different dye structures seemed to alter the interfacial electron recombination with the electrolyte. In addition to the dye structure sterics, some organic dyes appear to enhance the interfacial recombination, possibly due to specific dye-redox acceptor interaction (Paper V).

The impact of dye sterical modifications versus the use of coadsorbent was explored in Paper VI. The dye layer properties in the presence and absence of various coadsorbents were further investigated in Paper VII.

The core of this thesis is the identification of the processes and properties limiting the performance of the DSC device, aiming at an overall understanding of the compatibility between the DSC components and novel organic dyes.

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , 84 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009 : 50
Keyword [en]
additive, charge recombination, coadsorbent, conduction band shift, dye-sensitized, electron lifetime, electron-transfer, organic dye, photoelectrochemical, photovoltaic, sensitizer, semiconductor, solar cell, solar cell efficiency, titanium dioxide
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-11248ISBN: 978-91-7415-461-0 (print)OAI: oai:DiVA.org:kth-11248DiVA: diva2:253350
Public defence
2009-10-30, F3, Lindstedtsvägen 26, KTH, Stcokholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100730Available from: 2009-10-14 Created: 2009-10-09 Last updated: 2010-07-30Bibliographically approved
List of papers
1. A novel organic chromophore for dye-sensitized nanostructured solar cells
Open this publication in new window or tab >>A novel organic chromophore for dye-sensitized nanostructured solar cells
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2006 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 21, 2245-2247 p.Article in journal (Refereed) Published
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.

Keyword
nanocrystalline tio2 electrodes, charge-transfer, conversion
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-7881 (URN)10.1039/b603002e (DOI)000237715800011 ()2-s2.0-33744465236 (Scopus ID)
Note
QC 20100716Available from: 2008-01-09 Created: 2008-01-09 Last updated: 2017-12-14Bibliographically approved
2. Influence of π-Conjugation Units in Organic Dyes for Dye-Sensitized Solar Cells
Open this publication in new window or tab >>Influence of π-Conjugation Units in Organic Dyes for Dye-Sensitized Solar Cells
2007 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 111, no 4, 1853-1860 p.Article in journal (Refereed) Published
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.

Keyword
density-functional thermochemistry; tio2 electrodes; conversion; efficiency; electricity; potentials; absorption; complexes; exchange; light
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-11294 (URN)10.1021/jp065550j (DOI)000245005500044 ()2-s2.0-33847351205 (Scopus ID)
Note
QC 20100730Available from: 2009-10-14 Created: 2009-10-14 Last updated: 2017-12-12Bibliographically approved
3. Tuning the HOMO and LUMO Energy Levels of Organic Chromophores For Dye Sensitized Solar Cells
Open this publication in new window or tab >>Tuning the HOMO and LUMO Energy Levels of Organic Chromophores For Dye Sensitized Solar Cells
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2007 (English)In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, no 72, 9550-9556 p.Article in journal (Refereed) Published
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.

Keyword
high-efficiency, coumarin dyes, tio2, acid, performance, derivatives, design, light
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-7882 (URN)10.1021/jo701592x (DOI)000251313600017 ()
Note
QC 20100716Available from: 2008-01-09 Created: 2008-01-09 Last updated: 2017-12-14Bibliographically approved
4. Rhodanine Dyes for Dye Sensitized Solar Cells: Spectroscopy, Energy Levels and Photovoltaic Performance
Open this publication in new window or tab >>Rhodanine Dyes for Dye Sensitized Solar Cells: Spectroscopy, Energy Levels and Photovoltaic Performance
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2009 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, 133-141 p.Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Cambridge: RSC Publishing, 2009
Keyword
Solar Cells
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-10529 (URN)10.1039/b812154k (DOI)000263278900011 ()2-s2.0-57449121558 (Scopus ID)
Note

QC 20150724

Available from: 2009-05-25 Created: 2009-05-25 Last updated: 2017-12-13Bibliographically approved
5. How the Nature of Triphenylamine-Polyene Dyes in Dye-Sensitized Solar Cells Affects the Open-Circuit Voltage and Electron Lifetimes
Open this publication in new window or tab >>How the Nature of Triphenylamine-Polyene Dyes in Dye-Sensitized Solar Cells Affects the Open-Circuit Voltage and Electron Lifetimes
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2010 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 4, 2592-2598 p.Article in journal (Refereed) Published
Abstract [en]

Three donor-linker-acceptor triphenylamine-based cyanoacrylic acid organic dyes used For dye-sensitized solar cells (DSCs) have been examined with respect to their effect on the open-circuit voltage (V-oc). Our previous study showed a decrease in V-oc for DSCs based oil dyes with increased molecular size (increased linker conjugation). In the present study, we investigate the origin of V-oc with respect to (i) conduction band (E-CB) positions of TiO2 and (ii) degree of recombination between electrons in TiO2 and electrolyte acceptor species at the interface. These parameters were Studied its it function of dye structure, dye load, and I-2 concentration. Two types of behavior were identified: the smaller polyene dyes show a surface-protecting effect preventing recombination upon increased dye loading, whereas the larger dyes enhance the recombination. How the different dye structures affect the recombination is discussed in terms of dye surface blocking and intermolecular interactions between dyes and electrolyte acceptor species.

Keyword
efficient molecular photovoltaics; nanocrystalline tio2 electrodes; organic-dyes; conversion-efficiency; interfacial transfer; coumarin dyes; energy-levels; performance; recombination; thiophene
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-14288 (URN)10.1021/la902897z (DOI)000274342200061 ()2-s2.0-77149163036 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note
QC 20110126Available from: 2010-07-30 Created: 2010-07-30 Last updated: 2017-12-12Bibliographically approved
6. Structural Modification of Organic Dyes for Efficient Coadsorbent-Free Dye-Sensitized Solar Cells
Open this publication in new window or tab >>Structural Modification of Organic Dyes for Efficient Coadsorbent-Free Dye-Sensitized Solar Cells
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2010 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 6, 2799-2805 p.Article in journal (Refereed) Published
Abstract [en]

Three triphenylamine-based organic sensitizers with different electron-donating substituents (butoxyl chains or dimethylamine groups) were examined to investigate the effect of bulky alkoxy donor substituents on the photovoltaic performances of dye-sensitized solar cells (DSCs) in the presence and absence of the coadsorbent chenodeoxycholic acid (CDCA) in dye-bath solutions. The study showed that, using the D29 dye without bulky alkoxy substituents, the power conversion efficiency of DSC was significantly increased by about 84% in the presence of CDCA as compared to that in the absence of CDCA addition during the sensitization. However, the photovoltaic performance of D35-sensitized DSC having four bulky butoxyl substituents was not dependent on CDCA at all, probably due to the inherent structural nature of the D35 molecule. The DSC based on the D37 sensitizer with only two bulky butoxyl chains displayed an expected medium performance as compared to D29 and D35. The inclusion of bulky alkoxy electron-donating substituents in dye molecules for efficient DSCs suppressed the electron recombination and reduced the interactions between dye molecules. This emphasizes the importance of designing novel dyes including functional groups that incorporate the properties normally needed from an external coadsorbent. The development of a coadsorbent free system is in particular important for the future economization and simplification of the DSCs' assembly process.

Keyword
nanocrystalline tio2 films; interfacial electron-transfer; near-ir sensitization; open-circuit voltage; highly efficient; molecular photovoltaics; conversion-efficiency; energy conversion; coumarin dyes; tetrahydroquinoline dyes
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-14289 (URN)10.1021/jp908552t (DOI)000274354800059 ()2-s2.0-77249111942 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note
QC 20110124Available from: 2010-07-30 Created: 2010-07-30 Last updated: 2017-12-12Bibliographically approved
7. Surface Molecular Quantification and Photoelectrochemical Characterization of Mixed Organic Dye and Coadsorbent Layers on TiO2 for Dye-Sensitized Solar Cells
Open this publication in new window or tab >>Surface Molecular Quantification and Photoelectrochemical Characterization of Mixed Organic Dye and Coadsorbent Layers on TiO2 for Dye-Sensitized Solar Cells
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2010 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 27, 11903-11910 p.Article in journal (Refereed) Published
Abstract [en]

Different molecular layers on TiO2 were prepared by using the p-dimethylaniline triphenylamine based organic dye, D29, together with the coadsorbents decylphosphonic acid (DPA), dineohexyl bis(3,3-dimethylbutyl)phosphinic acid (DINHOP), and chenodeoxycholic acid (CDCA). The surface molecular structure of dye and coadsorbent layers on TiO2 was investigated by photoelectron spectroscopy (PES). A focus was to determine the surface molecular concentrations using characteristic photoelectron core levels. Dye-sensitized solar cells (DSCs) were prepared from the same substrate and were further characterized by photoelectrochemical methods. Together the investigation gives information on the arrangement of the mixed molecular layer and a first insight to the extent to which the coadsorbents exchange with dye molecules on the TiO2 surface for the examined conditions.

Keyword
interfacial properties, charge-transfer, photovoltaic performance, conversion efficiency, coumarin dyes, acid, spectroscopy, complexes, light, heterojunctions
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-14290 (URN)10.1021/jp102381x (DOI)000279507900031 ()2-s2.0-77955330856 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note
QC 20100730Available from: 2010-07-30 Created: 2010-07-30 Last updated: 2017-12-12Bibliographically approved

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