Amidinium‐Based 2D Spacer Cations Enhance Efficiency and High‐Temperature Photostability of Perovskite Solar Cells

Abstract 2D/3D perovskite heterojunctions represent a promising approach to enhance the efficiency and stability of perovskite solar cells (PSCs). However, the photostability at elevated temperatures of conventional 2D/3D heterostructures, employing ammonium‐based spacer cations, is severely limited by deprotonation reactions, hindering their practical application. In this study, amidinium‐based 2D spacer cations as an alternative, leveraging their higher acid dissociation constants, to mitigate deprotonation‐induced instability while providing excellent defect passivation effect is introduced. Amidinium passivation not only facilitates formation of thermally stable 2D/3D heterostructures but also suppresses non‐radiative recombination and enhances carrier transport dynamics. PSCs with amidinium‐based bulk and surface passivation achieve a state‐of‐the‐art power conversion efficiency of 26.52% for 2D/3D PSCs and exhibit outstanding high‐temperature photostability, retaining 90.6% of initial efficiency after 1000 h of continuous illumination at maximum power point at 85 °C. This work offers valuable insights into designing high‐performance, durable PSCs under challenging conditions.