Achieving one-step solution deposition of high quality CsPbBr3 films for efficient solar cells through halide ion exchange

CsPbBr3 perovskite solar cell (PSC) has triggered an increasing interest owing to its high tolerance to thermal and humidity in the open air. The one-step method is preferable for preparing high-quality CsPbBr3 films and thereby highly efficient PSCs. However, the poor solubility of CsBr in common solvents makes it a big challenge to prepare desired CsPbBr3 films using the traditional one-step method. Therefore, researchers have to employ a two-step method to prepare CsPbBr3 films for PSCs. Actually, the one-step solution processed perovskite films is more attractive owing to its compatible advantages to existing large-scale technology. Therefore, it is crucial to develop a one-step method to prepare high-quality CsPbBr3 films. Here, we propose a one-step solution approach to prepare CsPbBr3 films through halide exchange. In this approach, a PbBr2-CsI-DMSO intermediate film is firstly prepared by spin-coating CsPbIBr2/DMSO solution (1.0 M), followed by dropping hydrogen bromide/acetic acid (HBr/HAc) solution while spinning, and subsequently realize the halide ion exchange between Br- and I-, which separately comes from HBr and PbBr2-CsI-DMSO. After completing the halide ions exchange, it forms a new complex of PbBr2-CsBr-DMSO, and eventually converts to CsPbBr3 films through annealing treatment. As a result, high-quality CsPbBr3 films with a thickness of ~260 nm are obtained due to the appropriate concentration of CsPbIBr2/DMSO solution in the initial step. After integrating into an HTL-free carbon-based PSC, it delivers much higher efficiency than that prepared by the traditional one-step method. This work provides a new one-step preparation method for CsPbBr3 films, making it has attractive applications in CsPbBr3-based devices.