Long-Lived Charge Separation Enabled by Molecular Engineering of Phenazine-Based Hole Transport Materials

Abstract

Achieving long-lived charge-separated states is paramount for advancing perovskite solar cells technology, enhancing efficiency, and enabling kinetically slow processes like photocatalysis. While hole transport materials (HTMs) are essential for efficient charge extraction, conventional materials suffer from high defect densities at the perovskite/HTM interface, leading to severe nonradiative recombination losses. Previous strategies for surface passivation often rely on external treatments, which pose scalability challenges. This work overcomes these limitations by integrating passivation functionality directly into HTMs through targeted molecular engineering of phenazine derivatives. By leveraging the anchoring capability of the 1,10-phenanthroline (Phen) skeleton and strategically incorporating electron-donating (─NH2, ─OCH3) and electron-withdrawing (─NO2, ─Br) groups, electron density is systematically modulated to control charge transfer dynamics. Electron-donating groups (EDGs) increase charge density on the phenazine core, suppressing trap-assisted recombination and stabilizing charge-separated states. In contrast, electron-withdrawing groups (EWGs) promote dipole formation at perovskite defect sites, leading to prolonged charge separation, as confirmed by observed sustained bleaching in transient absorption spectroscopy. This study reveals the profound impact of substituent electronic effects on interfacial interactions, offering a molecular design strategy for optimizing charge transport and defect mitigation in perovskite optoelectronics. These findings provide a scalable approach to enhancing perovskite-based photovoltaics and photocatalytic applications.