Minimizing Interfacial Defects at 3D/2D Perovskite Heterojunction for Efficient and Stable Solar Cells

3D/2D perovskite heterojunction solar cells have attracted intensive interest, due to great advantages of both high power conversion efficiency (PCE) and superior stability. For constructing the heterojunction, transferring pure-phase 2D single crystals onto 3D perovskite effectively avoids the generation of cascaded energy barrier and promotes the carrier transport. However, the interfacial defects during the formation of 3D/2D perovskite heterojunction are scarcely noticed. To address this issue, a thin interfacial layer of octyl ammonium iodide (OAI) is introduced between 3D and 2D perovskites herein. The results show that OAI not only mitigates the erosion of 3D perovskite and passivates the residual PbI₂, but also suppresses the surface vacancies defects of both 3D and 2D perovskite layers. The formation of 3D/OAI/2D heterojunction with highly interfacial lattice match induces the generation of compression strain, suppression of carrier recombination and promotion of carrier transport. The 3D/OAI/2D heterojunction devices processed in air ambient have achieved remarkable PCE of 25.07%, retaining over 90% of the initial PCEs after storing in air for 2500 h or continuous one-sun illumination for 1034 h. This work demonstrates an effective strategy of eliminating interfacial defects and lattice mismatch at transferred or epitaxial 3D/2D perovskite heterojunction for advanced optoelectronic applications.