An Orientation-Enhanced Interlayer Enables Efficient Sn–Pb Binary Perovskite Solar Cells and All-Perovskite Tandem Solar Cells with High Fill Factors

The performance of narrow-bandgap (NBG) perovskite solar cells (PSCs) is limited by the severe nonradiative recombination and carrier transport barrier at the electron selective interface. Here, we reveal the importance of the molecular orientation for effective defect passivation and protection for Sn²⁺ at the perovskite/C₆₀ interface. We constructed an internally self-anchored dual-passivation (ISADP) layer, where the orientation of PCBM can be significantly enhanced by the interaction between ammonium and carbonyl groups. It can facilitate the contact with C₆₀ and minimize the nonradiative energy loss at the electron transport interface. This strategy remarkably enhances the FF of NBG PSCs, from 77.45% to 82.88%, and the power conversion efficiency (PCE) from 20.67% to 24.02%. Moreover, monolithic all-perovskite TSCs exhibit a high certified PCE (under reverse scan) of 28.12% and a record FF of 84.25%. This work opens up a new pathway for enhancing the performance of monolithic all-perovskite TSCs.