Redox-Improved Self-Assembled Monolayers for Inverted Perovskite Solar Cells

Inverted perovskite solar cells (pero-SCs) utilizing nickel oxide (NiO_x)/self-assembled monolayer (SAM) as a hole transport layer (HTL) have demonstrated high power conversion efficiency (PCE). However, variations in the valence states of NiO_x on the surface create complexity in the growth of a high-quality SAM HTL. To address these challenges, a new SAM molecule MeOF-4SHCz is synthesized and utilized to target the Ni³⁺-rich regions on the NiO_x substrate. A redox reaction occurs at the interface and the oxidation product of MeOF-4SHCz forms a new S-O-Ni bonding at the Ni³⁺-rich regions. The application of the combined SAMs of MeOF-4SHCz and the regular SAM MeOF-4PACz can improve the overall coverage and uniformity of the SAM layer on NiO_x. As a result, the optimized inverted pero-SCs based on this redox-improved (ROI)-SAM HTL of MeOF-4SHCz/MeOF-4PACz = 4:1 (w/w) achieve a high PCE of 26.5% (certified as 26.28%) and improved stability with T₉₀ > 1000 hours.