Heterointeraction-Induced Nucleation Promoting Vertical Growth and Suppressing Phase Separation for Efficient Wide-Bandgap Perovskite Solar Cells and Tandem Devices

As a key component of perovskite-based tandem photovoltaic devices, wide-bandgap (WBG) perovskite solar cells (PSCs) have been extensively explored recently. For WBG perovskite with mixed Cs/formamidinium (FA) cations and I/Br anions, it is challenging to control ordered crystal growth due to component complexity, and defect-mediated halogen migration causes severe phase separation, leading to poor film quality and inferior device performance. In this work, CsPb₂Br₅ has been developed to serve as a heteronucleation agent to regulate the crystal growth of Cs_0.2FA_0.8Pb(I_0.6Br_0.4)₃ perovskite for producing high-quality film. Theoretical and experimental results show that CsPb₂Br₅ reduces the energy barrier of nucleation and increases the defect formation energy, which not only promotes the homogeneous nucleation and guides the vertical growth of perovskite, which is beneficial for charge transport, but also reduces the defect density and releases the residual strains that suppress phase separation in the film. Therefore, optimized 1.80-eV PSCs yield a champion power conversion efficiency of 20.14% and a record-high fill factor of 85.39% with enhanced device stability. Notably, the constructed 4-terminal tandem devices yield promising power conversion efficiencies of 31.13% (perovskite/silicon) and 28.39% (all-perovskite). This work adds critical building blocks for efficient and stable WBG PSCs by rational crystallization control.