Organic Layer Bridged 3D/2D Perovskite Heterojunction for Efficient and Stable All‐Perovskite Tandem Solar Cells

Abstract Wide‐bandgap perovskite solar cells (PSCs) continue to encounter challenges in long‐term stability and open‐circuit voltage (V OC ) deficits, thereby constraining the performance and stability of all‐perovskite tandem solar cells (TSCs). Constructing 3D/2D perovskite heterojunctions represents a promising avenue for performance enhancement; nonetheless, notable shortcomings still persist in carrier transport efficiency and thermal‐stability at the 3D/2D heterojunction interface. Herein, a newly designed cross‐linked polymer is meticulously deposited onto the surface of 3D perovskite, of which freely distributed carbonyl group (C═O) and N/O atoms effectively saturate surface defects and alleviate tensile strains. The improvement of surface properties induces the generation of gradient energy levels, effectively minimizes the recombination loss caused by the accumulation of minority carriers at the 3D/2D interface. More interestingly, the cross‐linked polymer skeleton employs a strong physical barrier to effectively halt the migration of volatile A‐site cations across the 3D/2D interface under thermal stress, maximizing the heterostructure's stability. The resultant wide‐bandgap PSCs and all‐perovskite TSCs achieve a champion power conversion efficiency (PCE) of 20.23% and 28.26% (certified 27.29%), accompanied by exceptional thermal‐stability. This work underscores the vast potential of 3D/2D heterojunction design, offering valuable insights for the advancement of wide‐bandgap PSCs and all‐perovskite TSCs.