Sulfonated Dopant-Free Hole-Transport Material Promotes Interfacial Charge Transfer Dynamics for Highly Stable Perovskite Solar Cells

The integration of a functional group into dopant-free hole-transport materials (HTMs) to modify the perovskite|HTM interface has become a promising strategy for high-performance and stable perovskite solar cells (PSCs). In this work, a sulfonated phenothiazine-based HTM is reported, namely TAS, which consists of a butterfly structure with a readily synthesized N,​N-​bis[4-​(methylthio)​phenyl]​aniline side functional group. The interaction between TAS and perovskite via Pb–S bond induces a dipole moment that deepens the valence band of perovskite and thereby leads to enhanced open-circuit voltage in corresponding n-i-p PSCs. More importantly, the functionalization of perovskite surface via Pb–S bond promotes the hole extraction reaction while suppressing the interfacial non-radiative recombination, contributing to a 20–50% performance improvement compared to less- (4-​(methylthio)​-​N-​[4-​(methylthio)​phenyl]​aniline, DAS) or non-interacting (N,N-bis(4-methoxyphenyl)aniline, TAO) counterparts. Consequently, TAS-based PSCs exhibit superior device stability with a high PCE retention (>90% of the initial value) after 125 days of storage in the air.