Regioisomeric Effects on Enhancing <i>p</i> ‐Type Characteristics of Self‐Assembled Molecules in Inverted Perovskite Solar Cells

Although self-assembled molecules (SAMs) have significantly advanced the development of inverted perovskite solar cells (PSCs), challenges remain in achieving uniform surface potential and reducing interfacial energy losses. Here, we introduced regioisomers with different bromine substitution sites, 3,7-dibromodibenzothiophene-5,5-dioxide (3,7-Br) and 2,8-dibromodibenzothiophene-5,5-dioxide (2.8-Br), as functional modulators for the widely used [4-(3,6dimethyl-9H-carbazole-9-yl)butyl]phosphonic acid (Me-4PACz). Compared with the meta-substituted 3,7-Br, the para-substituted 2,8-Br provides stronger π-π interactions with Me-4PACz, enhanced p-type characteristics, and a more favorable energy level alignment, thereby facilitating hole extraction. Moreover, the electron-withdrawing yet electron-rich sulfonyl moiety and bromo substituents in 2,8-Br interact with perovskite, leading to more effective interfacial defect passivation and suppression of non-radiative recombination. As a result, the power conversion efficiency (PCE) was enhanced from 23.40% to 25.40% after treatment of Me-4PACz with the 2,8-Br. In addition, the 2,8-Br-treated PSCs demonstrated improved light-soaking stability under one sun illumination and thermal stability at 85°C, compared to the control device.