Lead-free, air-stable ultrathin Cs3Bi2I9 perovskite nanosheets for solar cells

Organometallic halide perovskite materials have attracted great attention in the past few years owing to their excellent optical properties and solution-processable fabrication. However, the further development of these lead-based materials is restricted by the toxic heavy-metal element Pb. Herein, we present a dissolution-recrystallization method to fabricate high-quality lead-free Cs3Bi2I9 perovskite nanosheets film and further explore its potential application in solar cells with three different kinds of hole transport materials. The solar cells based on ultrathin Cs3Bi2I9 nanosheets show remarkable improvement in the photovoltaic performance and a high power conversion efficiency of 3.20% has been achieved in the solar cell with CuI as the hole transport material, which is the highest efficiency value of Bi-based perovskite solar cells that has been reported so far. The Cs3Bi2I9 nanosheets based solar cell with CuI also showed a long-term stability in ambient air. These encouraging results of our work demonstrate the possibility of further improvement of the performance of lead-free perovskite solar cells.