Structure-property correlations of tetraphenylbenzidine-based self-assembled monolayers for perovskite and organic solar cells

Abstract

Self-assembled monolayers (SAMs) play a critical role in improving the performance of p-i-n type perovskite solar cells (PSCs) and organic solar cells (OSCs) by modulating interfacial energetics and morphology. However, designing SAMs that are effective across both technologies remains challenging due to the lack of clear, unified structure-property relationships. Here, we develop three new SAMs based on the triphenylamine (TPD) core, 6PA-TPD, 6PA-TPDO, and 6PA-TPDF, leveraging TPD’s tunable energy levels, high hole mobility, and thermal stability. We investigate the impacts of methoxy and fluorine substitutions on key molecular properties, including dihedral angle, dipole moment, HOMO level, work function, surface morphology, and surface energy. Device studies show that 6PA-TPDO achieves the highest power conversion efficiency of 23.18% in p-i-n type PSCs, while 6PA-TPDF delivers a peak efficiency of 18.27% in OSCs. Correlation analysis reveals two complementary design strategies: in p-i-n type PSCs, optimizing dipole moment, work function, and surface morphology is crucial; in OSCs, tuning the HOMO level is the dominant factor. These findings provide actionable molecular design guidelines for TPD-based SAMs, enabling targeted interfacial engineering across distinct photovoltaic technologies.