In‐Situ Constructed Cations for 2D/3D Perovskite Heterostructure for Stable and Efficient Photovoltaics

ABSTRACT Constructing two‐dimensional (2D) perovskite capping layer on three‐dimensional (3D) perovskite is an effective strategy to passivate defects, tune energetic structure and improve stability in perovskite solar cells (PSCs). However, the disordered migration of A‐site ions poses great threat to the photovoltaic performance and stability. Moreover, the introduced spacer cations can undergo deprotonation process upon light and thermal excitation, further inducing the degradation of perovskite film. To address these issues, n ‐hexyl phosphonic acid (HPA) is adopted to in‐situ construct spacer cations through multiple hydrogen bonds with FA ⁺ , and thereby forming 2D perovskite. In the determined 2D/3D perovskite, the formation energy of A‐site defects is significantly enhanced. Consequently, the power conversion efficiency (PCE) of 26.32%, and 24.91% are achieved at 0.072 and 1.012 cm ² , along with an excellent stability, retaining 95.5%, 92.5%, 90% of its initial efficiency after 3000 h at 30°C in N ₂ atmosphere, 45% ± 5 RT air and 800 h at 85°C in N ₂ atmosphere, respectively. In addition, a PCE of 19.24% is also implemented on a 5 × 5 cm ² rigid module.