Micro-changes, macro-impact: enhancing hole transfer by tailoring peripheral substituents of hole transport materials for efficient perovskite solar cells.

Optimizing hole transfer at the perovskite/hole transport layer (HTL) interface remains critical for enhancing the efficiency and stability of perovskite solar cells (PSCs). Herein, we design a series of small-molecule-based hole transport materials (HTMs) via systematic tuning of peripheral functional group positions, aiming to enhance heterogeneous interfacial charge transfer at the perovskite/HTL interface. Among them, HTM 9,9'-([1,1'-biphenyl]-4,4'-diyl)bis(N 3,N 6-bis(7-methoxy-9,9-dimethyl-9H-fluoren-2-yl)-N 3,N 6-bis(4-(methylthio)phenyl)-9H-carbazole-3,6-diamine) (OPSF) exhibits superior intrinsic properties and adopts a well-aligned planar adsorption configuration on the perovskite surface, thereby facilitating efficient hole extraction and transport. Accordingly, OPSF-based devices achieve power conversion efficiencies (PCEs) of 25.61% (0.055 cm2) and 24.39% (1.0 cm2), highlighting OPSF as a promising HTM candidate for PSC applications. This work not only offers alternative strategies for efficient HTMs but also provides new insights into the interfacial engineering of the hole transfer process in PSCs.