Localized Lead-Chelating Insulator Bottom Contact for Efficient and Stable p-i-n Perovskite Solar Cells

The defective bottom interfaces of perovskites and hole-transport layers (HTLs) limit the performance of p-i-n structure perovskite solar cells (PSCs). Here, that adding an ultrathin local contact layer of lead chelation polymer poly (methyl methacrylate) (PMMA) on PTAA HTLs is reported to fill its pinholes and strongly coordinate with the bottom uncoordinated Pb²⁺ simultaneously, resulting in a reduced amorphous region in perovskites near HTLs and a passivated perovskite bottom surface. Transient reflection (TR) spectroscopy results show that the ultrathin insulation layer does not affect the charge transport and collection efficiency at the PTAA and perovskite interface. This locally contacted PMMA can trigger a template-induced specific facet orientation growth, regulating the (111) facet as the preferred facet orientation and releasing the residual lattice strain for perovskites. In addition, the deep HOMO energy of PMMA can alleviate the permeation of I₂ into PTAA and suppress the reaction between them. Therefore, a performance of 22.6% and much-enhanced stability (e.g., stability of T₈₀ for photo-oxygen increased over 5 times, light-thermal over 4 times) of FA_0.90Cs_0.10PbI_2.83Br_0.17-based PSCs is demonstrated.