Densely Packed D-p-A Photosensitizers on TiO2 Enable Efficient Dye-Sensitized Solar Cells

Rigid and coplanar molecular structures are important for photosensitizers, but their packing status on the surface of nanocrystalline mesoporous titanium dioxide (TiO2) films requires more attention. Here, we designed three indolo[3,2-b]carbazole-based organic dyes ZL002, ZL004, and ZL006 with a coplanar structure by introducing flexible Z-type double and triple bonds having a smaller stereo-effect, and a rigid backbone from a benzene ring connected by a single bone. We studied the properties of photoelectricity, electron injection, and charge transport based on the ZL dyes adsorbed on the surface of TiO2, and their dye-sensitized solar cell performance. We found that rigid single bonds and triple bonds widen absorption and preserve the vertical coplanar status of the dyes on TiO2. The coplanar and rigid dye ZL004 densely packed on the surface of TiO2 gives smaller relaxation loss, higher electron-injection efficiency, and longer charge-recombination lifetime. As a result, the best efficiency of 11.6% based on dye ZL004 is achieved from their densely packed structure on the surface of TiO2.