Direct Synthesis of Short‐Chain Alkylammonium Capped FAPbI 3 Perovskite Nanocubes for High‐Efficiency Solar Cells

ABSTRACT Formamidinium lead iodide (FAPbI 3 ) perovskite quantum dots (PQDs) hold promise for photovoltaic applications; however, achieving simultaneous cubic morphology, α‐phase stability, and efficient charge transport remains a significant challenge. While post‐synthetic treatments or direct synthesis using short‐chain ligands can enhance charge transport, they require additional processing steps and often destabilize the α phase and promote anisotropic growth with poor colloidal stability. Here, we report the direct synthesis of short‐chain alkylammonium‐capped FAPbI 3 nanocubes through hot injection of decylammonium iodide, which induces isotropic growth and yields uniform, cubic PQDs. Comprehensive characterization reveals preserved α‐phase stability and enhanced optical properties in decylammonium‐capped PQDs compared with longer‐chain counterparts. The resulting PQDs form thin films with denser and more oriented packing. Solar cells based on these PQDs exhibit higher carrier mobility and lower trap density, achieving a power conversion efficiency (PCE) of 16.4% and retaining approximately 80% of their initial efficiency after 50 days under ambient conditions. Short‐chain ligands enabled simplified processing, yielding a PCE of 12.3% without methyl acetate treatment, compared with 5.6% for the long‐chain one. These findings demonstrate that the synthesis‐stage introduction of short alkylammonium ligands offers an effective and simplified strategy for improving PQD solar cell performance.