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

An interlayer with a suitable dipole moment can effectively tune the energy structure of the high-performance perovskite solar cells (PVSCs). Beyond the electrode–interlayer interface, an additional dipole with the perovskite layer also forms and influences the interfacial band bending, which has been neglected at the bottom interface. In this study, we access this issue by employing amine- and ammonium-containing polyelectrolytes to modify CsPbI2Br-based PVSC interfaces. The amine and ammonium groups induce different dipole orientations due to their different chemical bonds with the perovskite or substrate. We find that device performance is actually determined by the net dipole across the bifacial sides of the interlayer rather than any individual one. This validates the significance of the dipole moment formed between the perovskite and the interlayer at the bottom interface. By precisely controlling these dipoles, we achieved a 17.6% efficiency, which represents one of the best among CsPbI2Br-based PVSCs. This work highlights the importance of bifacial dipoles and offers insights into the working mechanism of the interlayers for high-performance PVSCs.