Organic chromophore-sensitized ZnO solar cells: Electrolyte-dependent dye desorption and band-edge shifts

An organic chromophore D5 (3-(5-(4-(diphenylamino)styryl)thiophene-2-yl)-2-cyanoacrylic acid) was tested as a sensitizer in photoelectrochemical mesoporous ZnO solar cells. Using thin (∼3 μm) mesoporous ZnO electrodes, high incident photon-to-current conversion efficiencies of up to 70% were obtained, while power conversion efficiencies up to 2.4% were found in simulated sunlight (100 mW cm−2). Long dye adsorption times (16 h) could be used without aggregation or precipitation of the dye. The composition of the iodide/triiodide-based electrolyte was found to be crucial in optimization of the ZnO-based dye-sensitized solar cell. A high concentration of Li+ ions was found to be shift the ZnO conduction band edge to more negative potential, whereas opposite behavior is found for mesoporous TiO2 cells. It was also found to be detrimental for solar cell performance and stability. Electrolyte-dependent and photoinduced dye desorption from the ZnO electrode was identified as a major stability problem in D5-sensitized ZnO solar cells.