An Orientation-Enhanced\nInterlayer Enables Efficient\nSn–Pb Binary Perovskite Solar Cells and All-Perovskite Tandem\nSolar Cells with High Fill Factors

The performance of narrow-bandgap (NBG) perovskite solar\ncells\n(PSCs) is limited by the severe nonradiative recombination and carrier\ntransport barrier at the electron selective interface. Here, we reveal\nthe importance of the molecular orientation for effective defect passivation\nand protection for Sn<sup>2+</sup> at the perovskite/C<sub>60</sub> interface. We constructed an internally self-anchored dual-passivation\n(ISADP) layer, where the orientation of PCBM can be significantly\nenhanced by the interaction between ammonium and carbonyl groups.\nIt can facilitate the contact with C<sub>60</sub> and minimize the\nnonradiative energy loss at the electron transport interface. This\nstrategy remarkably enhances the FF of NBG PSCs, from 77.45% to 82.88%,\nand the power conversion efficiency (PCE) from 20.67% to 24.02%. Moreover,\nmonolithic all-perovskite TSCs exhibit a high certified PCE (under\nreverse scan) of 28.12% and a record FF of 84.25%. This work opens\nup a new pathway for enhancing the performance of monolithic all-perovskite\nTSCs.