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Judicious Design of Indoline Chromophores for High-Efficiency Iodine-Free Dye-Sensitized Solar Cells

Wang, Zhihui, Wang, He, Liang, Mao, Tan, Yulin, Cheng, Fangyi, Sun, Zhe, Xue, Song
ACS Applied Materials & Interfaces 2014 v.6 no.8 pp. 5768-5778
absorption, cobalt, dyes, electrolytes, electrons, ions, irradiation, lighting, nanocrystals, photosensitizing agents, photostability, photovoltaic cells, titanium dioxide
Indoline photosensitizers exhibit impressive short-circuit photocurrent but generally low molar extinction coefficient and rapid charge recombination, which limits their application in thin-film dye-sensitizerd solar cells (DSCs). Here, we incorporate a new dithieno[3,2-b:2′,3′-d]pyrrole (DTP) segment (i.e., dihexyloxy-triphenylamine (DHO-TPA) substituted DTP) as the conjugated π-linker to construct a series of high molar absorption coefficient indoline dyes (XW69, XW70, and XW71) for DSCs employing a cobalt(II/III) redox electrolyte. Interestingly, this DTP linker is demonstrated as an efficient building block, not only slowing down the kinetics of charge recombination of titania electrons with tris(1,10-phenanthroline)cobalt(III) ions but also making a great contribution to the light absorption properties in comparison with the dihexylaniline substituted DTP. With respect to the dihexyloxy-triphenylamine dye (XW68), these new indoline dyes exhibit stronger light-harvesting and thus better power conversion efficiency of DSCs made from thin titania films. Benefitting from the bulky rigidity of the donor and π-conjugation unit, the XW70 dye displays a promising conversion efficiency as high as 8.78%, with a short-circuit current density (JSC) of 13.3 mA cm–², open-circuit voltage (VOC) of 943 mV, and fill factor (FF) of 0.70 under AM 1.5 illumination (100 mW cm–²). Furthermore, the effect of light irradiation on these dyes adsorbed on nanocrystalline TiO₂ films was investigated, proving the photostability of these indoline chromophores. Our work has valued the feasibility of judicious design of indoline chromophores to obtain organic photosensitizers for high-efficiency iodine-free DSCs made from thin titania films.