Fluoridation-assisted Interfacial Dipole for CsPbI3 Perovskite Solar Cells with over 22% Efficiency.

Inorganic CsPbI3 perovskite attracts remarkable interest in photovoltaic applications due to its outstanding thermal stability and optoelectronic properties. However, CsPbI3 perovskite solar cells (PSCs) significantly suffer from severe energy losses due to interface nonradiative recombination and poor charge carrier transport, predominantly affecting their photovoltaic performance and operational stability. Herein, an interfacial dipole engineering is introduced for CsPbI3 PSCs, in which azetidinium chloride (Az) and its fluorinated derivative 3,3-difluoroazetidinium chloride (DFAz) are employed to manipulate the interface properties of PSCs and thus diminish energy losses. Systematically theoretical calculations and experimental studies reveal that the fluoridation-assisted ammonium molecule could form a stronger interaction with perovskites and thereby arrange the dipole alignment on the superficial layer of perovskites, which could simultaneously ameliorate passivation effect and energy level alignment of the perovskite and hole transport layers, thereby suppressing interface recombination. Meanwhile, the coordinated bonding between the ammonium and hole transport layer facilitates charge transport at the heterojunction interface by offering additional carrier transport channels. Consequently, the CsPbI3 PSCs deliver a high efficiency of up to 22.05%. This work provides important design principles of interface engineering for high-performance solar cells to minimize energy losses.