Effects of Aqueous Electrolyte, Active Layer Thickness and Bias Irradiation on Charge Transfer Rates in Solar Cells Sensitized with Top Efficient Carbazole Dyes

Abstract

The photovoltaic performance and electron-transfer dynamics from femtoseconds to milliseconds are explored for very efficient carbazole sensitizers applied in solar cells, including the champion dye ADEKA-1. The photocurrent in the novel, environmentally friendly aqueous electrolyte is about 40% of that in the standard acetonitrile one, both based on cobalt complexes as a redox pair. The drop in the photocurrent is found to be correlated with increased electron recombination between sensitized titania particles and dyes, taking place with a time constant of several hundreds of picoseconds. Electron injection and recombination between titania and dye are slowed down under the presence of water (about 10 times) and with additional 1 sun bias irradiation (about 2 times). These effects are interpreted as due to reduced electronic coupling between the electron donors (dyes) and acceptor framework (titania). Moreover, a decrease in the relative photocurrent, photovoltage, and fill factor of the cells with incre...