Inverted Perovskite Solar Cells With Acid-Base Neutralized Self-Assembled Molecules.

Self-assembled monolayers (SAMs) have greatly contributed to the recent rapid development of inverted perovskite solar cells (PSCs). However, the acid nature of -PO(OH)2 in SAM commonly induces severe device degradation. Here we propose a universal method to develop neutralized SAM-N molecule through typical acid-base reaction between commonly used SAM molecules and methylamine (MA). In comparison with acid SAM (pH of 3), SAM-N shows neutral nature with pH value of 7, avoiding acid-induced device degradation. Importantly, SAM-N molecules can still assemble on neighboring ITO to regulate the work function and promote holes extraction. Resulting Cs0.05FA0.9MA0.05PbI3 PSCs show high PCE of 26.53%. Besides, long-term stability is also obtained in MA-free device (Cs0.05FA0.95PbI3), with 97.3% of initial efficiency after MPP tracking for 1000 h at 85°C with ISOS-L-2 protocol.