Two-Dimensional Cs₂ AgIn_x Bi_{1- x} Cl₆ Alloyed Double Perovskite Nanoplatelets for Solution-Processed Light-Emitting...

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 AgIn_x Bi_{1- 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 AgIn_0.9 Bi_0.1 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.