High-performance CH₃NH₃PbI₃ inverted planar perovskite solar cells via ammonium halide additives

Organic-inorganic hybrid perovskites have recently attracted substantial attention as a top candidate for use as light-absorbing materials in high-efficiency, low-cost and solution-processable photovoltaic devices owing to their excellent optoelectronic properties. Here, we fabricated inverted planar perovskite solar cells by incorporating small amounts of ammonium halide NH₄X (X = F, Cl, Br, I) additives into a CH₃NH₃PbI₃ (MAPbI₃) perovskite solution. A compact and uniform perovskite absorber layer with large perovskite crystalline grains is realized by simply incorporating small amounts of additives and by using an anti-solvent engineering technique to control the nucleation and crystal growth of perovskite. The enlarged perovskite grain size with a reduced density of the grain boundaries and improved crystallinity results in fewer charge carrier recombinations and a reduced defect density, leading to enhanced device efficiency (NH₄F: 14.88 ± 0.33%, NH₄Cl: 16.63 ± 0.21%, NH₄Br: 16.64 ± 0.35%, and NH₄I: 17.28 ± 0.15%) compared to that of a reference MAPbI₃ device (Ref.: 12.95 ± 0.48%) and greater device stability. This simple technique involving the introduction of small amounts of ammonium halide additives to regulate the nucleation and crystal growth of perovskite films translates into highly reproducible enhanced device performance.