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.