000150259 001__ 150259
000150259 005__ 20180501105939.0
000150259 0247_ $$2doi$$a10.5075/epfl-thesis-4805
000150259 02470 $$2urn$$aurn:nbn:ch:bel-epfl-thesis4805-4
000150259 02471 $$2nebis$$a6121837
000150259 037__ $$aTHESIS_LIB 000150259 041__$$aeng
000150259 088__ $$a4805 000150259 245__$$aStrategies to Optimizing Dye-Sensitized Solar Cells$$bOrganic Sensitizers, Tandem Device Structures, and Numerical Device Modeling 000150259 269__$$a2010
000150259 260__ $$aLausanne$$bEPFL$$c2010 000150259 300__$$a176
000150259 336__ $$aTheses 000150259 520__$$aDye-sensitized solar cells (DSCs) constitute a novel class       of hybrid organic-inorganic solar cells. At the heart of the       device is a mesoporous film of titanium dioxide       (TiO2) nanoparticles, which are coated with a       monolayer of dye sensitive to the visible region of the solar       spectrum. The role of the dye is similar to the role of       chlorophyll in plants; it harvests solar light and transfers       the energy via electron transfer to a suitable material (here       TiO2) to produce electricity — as opposed to       chemical energy in plants. DSCs are fabricated of abundant       and cheap materials using inexpensive processes (e.g.       screen-printing) and are likely to be a significant       contributor to the future commercial photovoltaic technology       portfolio. The work conducted during this thesis aimed at optimizing       the DSC using three different strategies: The use of       versatile organic sensitizers for stable and efficient DSCs,       the study of tandem device architectures in combination with       other solar cells to harvest a larger fraction of the solar       spectrum, and the development of a validated optoelectric       model of the DSC. Organic donor-π-acceptor dyes are an interesting       alternative to the standard metal-organic complexes used in       DSCs. Efficient photovoltaic conversion and stable       performance could be demonstrated with three classes of donor       systems, namely diphenylamine, difluorenylaminophenyl, and       π-extended tetrathiafulvalene. The highest conversion       efficiencies were obtained with a difluorenylaminophenyl       donor system (η = 8.3 % with a volatile       electrolyte and η = 7.6 % with a solvent-free       ionic liquid, which was a new record for organic dyes at the       time of publication). Surprisingly, efficient regeneration of       the oxidized dye by the       I-/I3- redox mediator was       found with the π-extended tetrathiafulvalene system, even       though the thermodynamic driving force was as low as 150 mV.       So far driving forces of 300-500 mV had been regarded as       necessary for efficient regeneration of the dye cation. Also,       important structure-property relationships pertaining to the       recombination of electrons with the electrolyte and to the       stability of the device could be identified (i.e. effect of       linear vs. branched structure, linker length, and moieties       used). The power conversion efficiency of solar cells can be       extended beyond the limit for a single cell (∼ 30 %) by       using multiple cells with different optical gaps in a tandem       device. DSCs and chalcopyrite Cu(In,Ga)Se2 (CIGS)       solar cells have complementary optical gaps and are thus       suitable systems for integration in a tandem device. It was       shown that a monolithic DSC/CIGS tandem device has the       potential for increased efficiency over a mechanically       stacked device due to increased light transmission to the       bottom cell, and a monolithic DSC/CIGS device with an initial       efficiency of η = 12.2 % was demonstrated. The       degradation of the devices — induced by the corrosion       of the CIGS cell in contact with the       I-/I3- redox mediator       — could be retarded with a protective thin conformal       ZnO/TiO2 oxide layer coated on the CIGS cell by       atomic layer deposition. Finally, an experimentally validated optical and       electrical model of the DSC has been developed to assist the       optimization process, which is predominantly conducted by       empirical means in the DSC research community. The optical       model allows to accurately calculate the internal       quantum efficiency of devices, i.e. the ratio of extracted       electrons to absorbed photons by the dye, a crucial and so       far difficult to determine characteristic. Intrinsic       parameters — like injection efficiency, electron       diffusion length, or distribution of trap states in the       TiO2 — can be extracted from experimental       steady-state and time-dependent data with the electric model.       The model allows to make a comprehensive and quantitative       loss analysis of the different optical and electric loss       channels in the DSC. The model has been implemented with a       graphical user interface for straightforward usage. All three optimization strategies — organic dyes,       tandem architecture, and device modeling — developed       during this thesis make a valuable contribution to the       development and commercialization of inexpensive and high       efficiency DSCs. They enable a comprehensive view of the       system and pave the way for a systematic analysis and       reduction of losses, which has been the ultimate route to       success for several established photovoltaic       technologies.
000150259 6531_ $$aphotovoltaics 000150259 6531_$$adye-sensitized solar cell
000150259 6531_ $$aorganic sensitizer 000150259 6531_$$adonor-acceptor system
000150259 6531_ $$atandem solar cell 000150259 6531_$$amultijunction
000150259 6531_ $$aCu(In,Ga)Se2 000150259 6531_$$aCIGS
000150259 6531_ $$aoptical and electric model 000150259 6531_$$aloss analysis
000150259 6531_ $$aelectron transport and recombination 000150259 6531_$$ananostructure
000150259 700__ $$0244013$$aWenger, Sophie$$g178830 000150259 720_2$$0240191$$aGrätzel, Michael$$edir.$$g105292 000150259 8564_$$s10584790$$uhttps://infoscience.epfl.ch/record/150259/files/EPFL_TH4805.pdf$$yTexte intégral / Full text$$zTexte intégral / Full text 000150259 909C0$$0252060$$pLPI$$xU10101
000150259 909CO $$ooai:infoscience.tind.io:150259$$pSB$$pthesis-bn2018$$pDOI2$$pDOI$$pthesis
000150259 918__ $$aSB$$cISIC$$dEDCH 000150259 919__$$aLPI
000150259 920__ $$b2010 000150259 970__$$a4805/THESES
000150259 973__ $$aEPFL$$sPUBLISHED
000150259 980__ aTHESIS