Dipolar Carbazole Ammonium for Broadened Electric Field Distribution in High-Performance Perovskite Solar Cells

Abstract

Perovskite solar cells (PSCs) with ammonium passivation exhibit superior device performance and stability. Beyond typical chemical passivation, ammonium salts control the electronic structure of perovskite surfaces, yet the molecular structure–property relationship requires further understanding, especially the dipole effect. Here, we employed carbazole and its halogenated counterpart as the functional group of ammonium salts. 2-Chloro-carbazol-9-ethylammonium iodide (CzCl-EAI) with a rigid, conjugated molecular structure further provides chemical passivation and enhances the ambient stability of perovskites. In addition, we found that halogenation enhances the intramolecular charge transfer for a larger molecular dipole moment, leading to the depletion region of perovskite films threefold wider than that of the PDAI₂ condition. The power conversion efficiency (PCE) of inverted PSCs based on mixed passivation reached 25.16% and certified 24.35% under the quasi-steady-state (QSS) measurement. Unencapsulated devices retained over 91% of initial PCE under ISOS-D-2 conditions over 1100 h and maintained 80% of their initial performance after 500 h of continuous light illumination in ambient air with a 50–60% relative humidity (RH).