Stoichiometry Control for the Tuning of Grain Passivation and Domain Distribution in Green Quasi-2D Metal Halide Perovskite Films and Light-Emitting Diodes

Quasi-2D metal halide perovskite films are promising for efficient light-emitting diodes (LEDs), because of their efficient radiative recombination and suppressed trap-assisted quenching compared with pure 3D perovskites. However, because of the multidomain polycrystalline nature of solution-processed quasi-2D perovskite films, the composition engineering always impacts the emitting properties with complicated mechanisms. Here, defect passivation and domain distribution of quasi-2D perovskite films prepared with various precursor compositions are systematically studied. As a result, in perovskite films prepared from stoichiometric quasi-2D precursor compositions, large organic ammonium cations function well as passivators. In comparison, precursor compositions of simply adding large organic halide salt into a 3D perovskite precursor ensure not only the defect passivation but also the effective formation of quasi-2D perovskite domains, avoiding unfavorable appearance of low-order domains. Quasi-2D perovskite films fabricated with a well-designed precursor composition achieve a high photoluminescence quantum yield of 95.3% and an external quantum efficiency of 14.7% in LEDs.