Restrain Phase Segregation by In Situ Buried Prenucleation for Efficient and Stable Wide-Band Gap Perovskite Cells

The phase segregation of wide-band gap perovskite solar cells (PSCs) typically originates from defect centers and strain induced by nonstoichiometric compounds. In this study, we have discovered an excess of PbI₂ at the buried interface in inverted wide-band gap PSCs. To address this issue, RbI is introduced to interact with the excessive PbI₂, thereby in situ forming a layer of inorganic perovskite RbPbI₃. The presence of RbPbI₃ as prenucleation centers facilitates intimate contact and enhances crystallinity of the wide-band gap perovskite, thereby alleviating lattice strain and reducing nonradiative recombination centers. Consequently, ion migration is suppressed, and phase segregation at the buried interface is inhibited. After the addition of RbI, the power conversion efficiency (PCE) of the wide-band gap semitransparent device is increased from 17.96 to 19.5%, and the bifacial factor is 83.4%. Furthermore, after continuous illumination at an intensity equivalent to AM 1.5 G for 1000 h, the device based on RbI retains approximately 81.71% of its initial PCE.