A universal ionic liquid solvent for non-halide lead sources in perovskite solar cells

Replacing lead iodide (PbI2) with suitable non-halides lead source has been found to be an effective method to control crystallization and fabricate high-performance perovskite solar cells (PSCs). However, the solubility of non-halide lead sources is highly limited by traditional solvents due to the chemical interaction limitation. Here, we report a series of non-halide lead sources (e.g., lead acetate (PbAc2), lead sulfate (PbSO4), lead carbonate (PbCO3), lead nitrate (Pb(NO3)2), lead formate (Pb(HCOO)2) and lead oxalate (PbC2O4)) can be well dissolved in an ionic liquid solvent methylammonium acetate (MAAc). We found that the universal strong coordination of CO with lead ion (Pb2+) and the formation of hydrogen bonds were observed in perovskite precursor solution. This allows the dissolution of non-halide lead salts and is able to produce perovskite film with smooth, compact, and full coverage crystal grain. The power conversion efficiency (PCE) of 14.48%, 19.21%, and 20.13% in PSCs based on PbSO4, PbAc2, and PbCO3 was achieved, respectively, in the absence of any additives and passivation agents. This study demonstrates the universality of ionic liquid for the preparation of PSCs based on non-halides lead sources.