All Green Solvents for Fabrication of CsPbBr₃ Films for Efficient Solar Cells Guided by the Hansen Solubility Theory

Toxic solvents used in the fabrication of perovskite solar cells are an obstacle for their commercialization. Replacing those toxic solvents with green solvents is very important for both ecological environment safety and the health of operators working in manufactory and labs. CsPbBr₃-based solar cells have attracted increasing attention due to its high stability. Herein, high-quality CsPbBr₃ films are prepared using all green solvents based on a two-step spin-coating method. In the first step, a green solvent system of polyethylene glycol (PEG) with the addition of γ-butyrolactone is used for preparing PbBr₂ solutions by matching the Hansen solubility parameters (HSPs) between PbBr₂ and the mixed solvent system. By optimizing the HSPs and viscosity, a new complex of PbBr₂·(PEG) is formed by spin-coating from the PbBr₂ solution, followed by acetic acid dropping while spinning. In the second step, green water is used to dissolve CsBr to prepare a high concentration CsBr/H₂O solution. High-quality CsPbBr₃ films with full coverage are obtained by spin-coating CsBr/H₂O solution onto the PbBr₂·(PEG) films after annealing. As a result, a solar cell with configuration of fluorine-doped tin oxide/TiO₂/CsPbBr₃/carbon exhibits a power conversion efficiency of 8.11% due to its high-quality harvest layer.