Topotactically Grown Bismuth Sulfide Network Film on Substrate as Low-Cost Counter Electrodes for Quantum Dot-Sensitized Solar Cells

Bi2S3 films consisting of two-dimensional interconnected Bi2S3 single-crystalline nanorod networks have been fabricated on a F:SnO2 (FTO) glass substrate through the formation of intermediate BiOI nanosheets from layer-structured BiI3 by chemical vapor deposition and subsequent hydrothermal transformation into Bi2S3 networks. A continuous lattice and structure-directed topotactic transformation mechanism is supposed for the formation of Bi2S3 network film. The prepared Bi2S3/FTO films were employed as counter electrode (CE) for CdSe quantum dot-sensitized solar cells for the first time and showed better photovoltaic performance than that from the convenient Pt CE. The influence of the preparation conditions for Bi2S3/FTO films on the resulting solar cell performance was systematically investigated and optimized with use of J-V curves, scanning electron microscopy (SEM), UV-vis absorption, and electrochemical impedance spectroscopy. To further improve the cell device efficiency, the modification of the Bi2S3 network CE with metal particles was also studied.