Interfacial Modification of Multifunctional Organic Ammonium Salt for PEDOT:PSS‐Based Inverted Perovskite Solar Cells

The performance of inverted perovskite solar cells (PSCs) is highly dependent on the surface properties of the hole‐transport layers (HTLs). Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most widely used HTLs due to its excellent properties. However, some drawbacks severely limit its application in PSCs. Herein, multifunctional bulk organic ammonium salts (BOASs) are deposited onto PEDOT:PSS films and used for interfacial modifications. The BOASs‐modified PEDOT:PSS has better energy‐level alignment with perovskite (PVK) than PEDOT:PSS, resulting in the suppressed voltage loss of PSCs. Depositing BOASs on top of the PSS isolates moisture to inhibit the ionization of sulfonic acid groups, which is beneficial to reduce the acidity and corrosiveness of PEDOT:PSS. In addition, the interfacial modification of BOASs can effectively enlarge the surface energy of PEDOT:PSS films and improve the morphology of the PVK layer. Therefore, the open‐circuit voltage and fill factor of the PSCs based on BOASs‐modified PEDOT:PSS are simultaneously increased to a maximum of 1.03 V and 73%, respectively, resulting in a champion device efficiency of 18.37%. The unencapsulated PSCs based on BOASs‐modified PEDOT:PSS remain more than 80% power conversion efficiency loss after 700 h of exposure to air.