Non-Phosphonic Self-Assembled Molecules with Weak Acidity for Inverted Perovskite Solar Cells

Self-assembled monolayers (SAMs) greatly promote the recent rapid development of inverted perovskite solar cells (PSCs). However, SAMs' strong acidity induced by their phosphonic acid group will always accelerate perovskite degradation. By replacing the commonly used phosphonic group with carboxylic, here we develop a new SAM molecule of 9AACz (9-carbazoleacetic acid) with much reduced acidity to fabricate inverted PSCs. 9AACz can self-assemble on an OH-rich ITO substrate owing to the interaction between carboxylic and -OH groups, regulating the work function of ITO and promoting hole extraction. Importantly, the weak acid nature of 9AACz can effectively inhibit acid-induced perovskite degradation, benefiting device stability. Resulting PSCs show high efficiency of 26.1% with good stability, retaining ∼90% of initial efficiency after maximum power point (MPP) tracking at 85°C for 700 h under ISOS-L-2 protocol.