Thermal Crosslinking Dual-Anchor Self-Assembled Monolayers for Improved Interfacial Hole Transport and Perovskite...

Nickel oxide (NiO_x) based hole-transport material (HTM) has been extensively used in inverted structured perovskite solar cells (PSCs) but suffers from interfacial energy mismatch and defect-driven recombination, thus lower power conversion efficiency (PCE). Herein, we have designed low-cost cross-linkable self-assembled monolayers (SAMs) including single-anchoring 4'-(bis(4-vinylphenyl)amino)-[1,1'-biphenyl]-4-carboxylic acid (p-TPA) and dual-anchoring 4'-(bis(4-vinylphenyl)amino)-[1,1'-biphenyl]-3,5-dicarboxylic acid (m-TPA) to address these intrinsic issues. Results of theoretical calculations and experimental characterizations have shown that m-TPA modulation enhanced bidentate binding onto NiO_x, leading to a favorable highest occupied molecular orbital (HOMO) and an optimized molecular geometry. The thermal cross-linked m-TPA demonstrated higher surface coverage, superior interfacial passivation on NiO_x and an optimal Ni²⁺ fraction. The dual-anchor modified NiO_x HTLs exhibited largely reduced perovskite permeation and higher surface electrical conductivity. Consequently, m-TPA-modified PSCs achieved a champion power conversion efficiency (PCE) of 24.16%, which is much higher than pristine NiO_x-based (18.98%) and mono-anchor crosslinked modified ones (22.13%). The PSCs with cross-linked m-TPA modification also exhibited substantially reduced hysteresis and significantly improved device operational stability under environmental/irradiation stress. This work demonstrates the potential of thermal crosslinking SAMs with dual-anchor molecular engineering as an effective strategy to concurrently optimize charge extraction and interfacial resilience in PSCs.