Two‐Dimensional Cs2AgInxBi1‐xCl6 Alloyed Double Perovskite Nanoplatelets for Solution‐Processed Light‐Emitting Diodes

Lead-free double perovskites have emerged as a promising class of materials with potential to be integrated into a wide range of optical and optoelectronic applications. Herein, the first synthesis of 2D Cs2 AgInx Bi1- x Cl6 (0 ≤ x ≤ 1) alloyed double perovskite nanoplatelets (NPLs) with well controlled morphology and composition is demonstrated. The obtained NPLs show unique optical properties with the highest photoluminescence quantum yield of 40.1%. Both temperature dependent spectroscopic studies and density functional theory calculation results reveal that the morphological dimension reduction and In-Bi alloying effect together boost the radiative pathway of the self-trapped excitons of the alloyed double perovskite NPLs. Moreover, the NPLs exhibit good stability under ambient conditions and against polar solvents, which is ideal for all solution-processing of the materials in low-cost device manufacturing. The first solution-processed light-emitting diodes is demonstrated using the Cs2 AgIn0.9 Bi0.1 Cl6 alloyed double perovskite NPLs as the sole emitting component, showing luminance maximum of 58 cd m-2 and peak current efficiency of 0.013 cd A-1 . This study sheds light on morphological control and composition-property relationships of double perovskite nanocrystals, paving the way toward ultimate utilizations of lead-free perovskite materials in diverse sets of real-life applications.