Grain boundary defect passivation by in situ formed wide-bandgap lead sulfate for efficient and stable perovskite solar cells

The trap-assisted nonradiative recombination at grain surface and grain boundary (GB) of perovskite films impede the further improvement of power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). In addition, the poor moisture stability of perovskite films hinders the commercial application of PSCs. Herein, we report a multifunctional GB modification strategy where the wide-bandgap hydrophobic PbSO4 modification layer is in situ formed at the GBs of perovskite films through the reaction between methylamine sulfate and PbI2. It is revealed that multiple functions are achieved after the formation of PbSO4 modification layer, including crystallization improvement, defect passivation, and hydrophobicity improvement. As a result, the PbSO4 modified device exhibits a PCE enhancement from 19.53% to 21.90% as compared to the control device. Moreover, up to 71% of its initial PCE is maintained for the unencapsulated PbSO4 modified device after aging under a relative humidity of 80 ± 5% for 250 h. This work proposes an effective multifunctional approach to modify the GBs of perovskite films for the purpose of simultaneous increasement of PCE and stability.