%0 Journal Article %1 Karthikeyan2008 %A Karthikeyan, Chedarampet S. %A Thelakkat, Mukundan %C PO BOX 564, 1001 LAUSANNE, SWITZERLAND %D 2008 %I ELSEVIER SCIENCE SA %J INORGANICA CHIMICA ACTA %K cells cells; conductors; donor-antenna dye-sensitized dyes; hole hybrid organic solar solid-state tetraphenylbenzidines; %N 3 %P 635-655 %R 10.1016/j.ica.2007.04.033 %T Key aspects of individual layers in solid-state dye-sensitized solar cells and novel concepts to improve their performance %V 361 %X In this feature article, we discuss the key aspects of solid-state dye-sensitized solar cells (SDSC) and propose different concepts based on extensive studies carried out in our group to improve their performance. The influence of compact TiO2 layer, novel donor-antenna sensitizing dyes, nature of nanocrystalline-TiO2 layers and solid-state organic hole conductors on the performance of SDSC is discussed in this article. Both preparation and thickness of the compact TiO2 layer were optimized using spray pyrolysis. The studies revealed that an optimum film thickness of 120-150 nm of compact TiO2 yielded the best rectifying behavior and SDSC performance. The influence of three different mesoporous titania films, obtained from three different titania nanocrystals, prepared by sol-gel, thermal, and colloidal-microwave process, was also studied and discussed here. The TiO2 layer with the optimum pore volume and pore diameter (similar to 44 nm) displayed the highest efficiency and IPCE in SDSC. The importance of pore size rather than high surface area for filling the mesoporous layer with solid-state hole conductor became evident from this study. A series of heteroleptic Ru(II) complexes carrying donor antenna moieties, namely, triphenylamine (TPA) or N, N'-bis(phenyl)-N, N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), were synthesized and applied in SDSC. These novel donor-antenna dyes revealed spectacular performances of power conversion efficiencies in the range 1.5-3.4\%, as measured under AM 1.5 spectral conditions. This was attributed to highly efficient light harvesting of these novel dyes and the improved charge-transfer dynamics at TiO2-dye and dye-hole conductor interfaces. Different low molecular weight and polymeric triphenyldiamines were synthesized and utilized as hole-transporting layers (HTL) in SDSC. Different studies showed that low molecular TPDs displayed better efficiency than polymeric counterparts due to their improved filling into the pores of nc-TiO2 layer. Another interesting study revealed that an optimum driving force in terms of HOMO-level difference between the dye and HTL decides charge carrier generation efficiency. Recently, novel hole conductors with spiro-bifluorene-triphenylamine core for transporting holes and tetraethylene glycol side chains for binding lithium ions were synthesized and applied in SDSC. This work clearly emphasizes that Li+-salt is required at the TiO2/dye interface as well as in the bulk of HTL. It was also found that the addition of about 5-20\% of these Li+-binding hole conductors and higher Li-salt (N-lithiotrifluoromethane sulfonamide) concentrations improved the SDSC performance. An improvement of about 120\% in the solar cell efficiency as compared to the reference cells was achieved with an optimum composition of Li+-binding hole conductor and Li-salt. (c) 2007 Elsevier B. V. All rights reserved.

@article{Karthikeyan2008, abstract = {In this feature article, we discuss the key aspects of solid-state dye-sensitized solar cells (SDSC) and propose different concepts based on extensive studies carried out in our group to improve their performance. The influence of compact TiO2 layer, novel donor-antenna sensitizing dyes, nature of nanocrystalline-TiO2 layers and solid-state organic hole conductors on the performance of SDSC is discussed in this article. Both preparation and thickness of the compact TiO2 layer were optimized using spray pyrolysis. The studies revealed that an optimum film thickness of 120-150 nm of compact TiO2 yielded the best rectifying behavior and SDSC performance. The influence of three different mesoporous titania films, obtained from three different titania nanocrystals, prepared by sol-gel, thermal, and colloidal-microwave process, was also studied and discussed here. The TiO2 layer with the optimum pore volume and pore diameter (similar to 44 nm) displayed the highest efficiency and IPCE in SDSC. The importance of pore size rather than high surface area for filling the mesoporous layer with solid-state hole conductor became evident from this study. A series of heteroleptic Ru(II) complexes carrying donor antenna moieties, namely, triphenylamine (TPA) or N, N'-bis(phenyl)-N, N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), were synthesized and applied in SDSC. These novel donor-antenna dyes revealed spectacular performances of power conversion efficiencies in the range 1.5-3.4\%, as measured under AM 1.5 spectral conditions. This was attributed to highly efficient light harvesting of these novel dyes and the improved charge-transfer dynamics at TiO2-dye and dye-hole conductor interfaces. Different low molecular weight and polymeric triphenyldiamines were synthesized and utilized as hole-transporting layers (HTL) in SDSC. Different studies showed that low molecular TPDs displayed better efficiency than polymeric counterparts due to their improved filling into the pores of nc-TiO2 layer. Another interesting study revealed that an optimum driving force in terms of HOMO-level difference between the dye and HTL decides charge carrier generation efficiency. Recently, novel hole conductors with spiro-bifluorene-triphenylamine core for transporting holes and tetraethylene glycol side chains for binding lithium ions were synthesized and applied in SDSC. This work clearly emphasizes that Li+-salt is required at the TiO2/dye interface as well as in the bulk of HTL. It was also found that the addition of about 5-20\% of these Li+-binding hole conductors and higher Li-salt (N-lithiotrifluoromethane sulfonamide) concentrations improved the SDSC performance. An improvement of about 120\% in the solar cell efficiency as compared to the reference cells was achieved with an optimum composition of Li+-binding hole conductor and Li-salt. (c) 2007 Elsevier B. V. All rights reserved.}, added-at = {2009-02-13T13:09:53.000+0100}, address = {PO BOX 564, 1001 LAUSANNE, SWITZERLAND}, affiliation = {Thelakkat, M (Reprint Author), Univ Bayreuth, Angew Funkt Polymere, Lab Solarenergieforsch, POB 101251, D-95440 Bayreuth, Germany. {[}Karthikeyan, Chedarampet S.; Thelakkat, Mukundan] Univ Bayreuth, Angew Funkt Polymere, Lab Solarenergieforsch, D-95440 Bayreuth, Germany.}, author = {Karthikeyan, Chedarampet S. and Thelakkat, Mukundan}, author-email = {Mukundan.Thelakkat@uni-bayreuth.de}, biburl = {https://www.bibsonomy.org/bibtex/2fd874478b1566b11e5488f7855537c83/almailer}, cited-references = {ARGAZZI R, 1995, J AM CHEM SOC, V117, P11815. BACH U, 1998, NATURE, V395, P583. BANDARA J, 2005, SOL ENERG MAT SOL C, V85, P385, DOI 10.1016/j.solmat.2004.05.010. 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WANG P, 2003, NAT MATER, V2, P402, DOI 10.1038/nmat904.}, description = {Initial Import}, doi = {10.1016/j.ica.2007.04.033}, file = {ScienceDirect full text PDF:Karthikeyan2008.pdf:PDF}, interhash = {59ce9cadb44d770a5a557b96d16a76ab}, intrahash = {fd874478b1566b11e5488f7855537c83}, issn = {0020-1693}, journal = {INORGANICA CHIMICA ACTA}, keywords = {cells cells; conductors; donor-antenna dye-sensitized dyes; hole hybrid organic solar solid-state tetraphenylbenzidines;}, keywords-plus = {NANOCRYSTALLINE TIO2 ELECTRODES; DONOR-ANTENNA DYES; CHARGE-TRANSFER; ELECTROLUMINESCENT DEVICES; HOLE CONDUCTOR; SEMICONDUCTOR ELECTRODES; FUNCTIONAL MATERIALS; THIN-FILM; DEPOSITION; TRANSPORT}, month = {FEB 15}, number = 3, owner = {s0346678}, pages = {635-655}, publisher = {ELSEVIER SCIENCE SA}, review = {Review on solid state dye-sensitized solar cells (solid TiO2 layer and solid hole transport layer). Interesting description of each layer (blocking layer, mesoporous layer, htl etc.) and the desired characteristics of each. P25 anatase studied. Importance of pore size over surface area (both measured by BET) highlighted. "The following are the requirements of a hole conductor in order to function efficiently in SDSC: (i) high hole transport mobility, (ii) good film forming capacity, (iii) low tendency towards crystallization and (iv) excellent pore filling in mesoporous TiO2 layer. The driving force for hole transfer from dye to hole conductor depends on the HOMO energy value offset." (stated without references)}, times-cited = {1}, timestamp = {2009-02-13T13:09:54.000+0100}, title = {Key aspects of individual layers in solid-state dye-sensitized solar cells and novel concepts to improve their performance}, type = {Article}, unique-id = {ISI:000254426600010}, volume = 361, year = 2008 }