A-Site Cation Incorporation Into the Hole Transport Layer for Efficient Quasi-2D Perovskite Solar Cells

The buried interface of perovskite plays a crucial role in attaining superior performance, partly due to its influence on the structure of the overlying perovskite. Here, a novel buried-interface strategy is proposed that incorporates A-site cations (FA⁺ or Rb⁺) into the hole transport layer (HTL) to optimize perovskite crystallization. The introduction of A-site cations results in the formation of perovskite as seed at the interface, which effectively promotes the growth of the overlying perovskite with improved orientation, crystallinity, and rearranged phase distribution. Furthermore, an in-depth understanding of the influence of the crystallization process is tracked by in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) techniques. Meanwhile, it is found that that FA⁺, due to the black phase α-FAPbI₃, is more suitable for optimizing the upper perovskite compared with Rb⁺ (δ-RbPbI₃), and their incorporation can alter the structure of the PEDOT chains, thereby enhancing the carrier transport efficiency. With this approach, the 2D perovskite devices (n = 4) based on FACl-PEDOT:PSS achieve a remarkable power conversion efficiency (PCE) of 18.37%. The optimized device without encapsulation retains 87% of its initial efficiency after 1440 h of exposure in ambient.