Unlocking the Role of the Bifacial Dipole of the Interlayer\nfor High-Performance Perovskite Photovoltaics

An\ninterlayer with a suitable dipole moment can effectively tune\nthe energy structure of the high-performance perovskite solar cells\n(PVSCs). Beyond the electrode–interlayer interface, an additional\ndipole with the perovskite layer also forms and influences the interfacial\nband bending, which has been neglected at the bottom interface. In\nthis study, we access this issue by employing amine- and ammonium-containing\npolyelectrolytes to modify CsPbI<sub>2</sub>Br-based PVSC interfaces.\nThe amine and ammonium groups induce different dipole orientations\ndue to their different chemical bonds with the perovskite or substrate.\nWe find that device performance is actually determined by the net\ndipole across the bifacial sides of the interlayer rather than any\nindividual one. This validates the significance of the dipole moment\nformed between the perovskite and the interlayer at the bottom interface.\nBy precisely controlling these dipoles, we achieved a 17.6% efficiency,\nwhich represents one of the best among CsPbI<sub>2</sub>Br-based PVSCs.\nThis work highlights the importance of bifacial dipoles and offers\ninsights into the working mechanism of the interlayers for high-performance\nPVSCs.