Dual Interface Modification for Reduced Nonradiative Recombination in n-i-p Methylammonium-Free Perovskite Solar Cells

High defect concentrations at the interfaces are the basis of charge extraction losses and instability in perovskite solar cells. Surface engineering with organic cations is a common practice to solve this issue. However, the full implications of the counteranions of these cations for device functioning are often neglected. In this work, we used 4-fluorophenethylammonium cation with varying halide counteranions for the modification of both interfaces in methylammonium-free Pb-based n-i-p devices, observing significant differences among iodide, bromide, and chloride. The cation treatment of the buried and top interfaces resulted in improved surface quality of the perovskite films and largely improved carrier dynamics with reduced nonradiative recombination. Consequently, the optimal interface-modified methylammonium-free perovskite solar cells surpassed 20% efficiency and demonstrated remarkable operational stability. Our findings underscore the potential of comprehensive surface engineering strategies in advancing the perovskite film and device quality, thereby facilitating their broader and more successful applications.