Managing the Spatial Interactions of Ligands on Perovskite Quantum Dot Films for Efficient Photovoltaic Devices

Although perovskite quantum dot (PQD) photovoltaics have evolved swiftly, the stability of their devices still lags far behind that of their polycrystalline counterparts, which limits our understanding of how to modulate the spatial interactions of novel, highly stable ligands in PQD thin films to maximize their photophysical performance. Herein, using the fluorine-rich moiety pentafluorobenzyl as a template, O-(2,3,4,5,6-pentafluorobenzyl)hydroxylammonium (5FBHA) as a post-synthetic ligand was discovered to interact spatially uniformly with PQD films, owing to its visualized high-density stable binding fashion on the PQD surface. Compared to its analogue 2,3,4,5,6-pentafluorobenzylphosphonic acid, 5FBHA resulted in an improved packing mode for its treated PQD film, which further benefited charge-carrier dynamics and enhanced moisture stability. Notably, the best-performing rigid and flexible CsPbI₃ PQD solar cells treated with 5FBHA achieved power conversion efficiencies (PCEs) of 16.21% and 14.37%, respectively, and demonstrated enhanced stability under long-term operation (degradation rate: 0.13% h^-1 vs 0.25% h^-1 for the control one) and N₂-storage conditions (remained 96.8% of the initial value vs 88.6% for the control one). This work poses a logical chemistry design principle that correlates the ligand interaction mode to PQD properties, and facilitates the advancement of promising PQD optoelectronics.