K-Alloyed Lead-free Double-Perovskite Cs2AgBiBr6 Nanocrystals for Use in Light-Emitting Diodes

Lead-free double-perovskite nanocrystals (NCs) have emerged as a promising material to address the issues of instability and toxicity associated with lead-based materials. Metal ion doping or alloying strategies have been widely used to tailor and optimize the optical and electrical properties of semiconductor materials. In this study, we prepared monodisperse Cs2AgBiBr6 NCs with uniform morphology (8 ± 1 nm) and excellent crystallinity using a thermal injection method. Compared to the photoluminescence quantum yield (PLQY) of Cs2AgBiBr6 NCs (∼0.4%), the highest PLQY of Cs2Ag0.64K0.36BiBr6 NCs reached 6.82%, with an extended exciton lifetime from 2.08 to 10.64 ns, which is approximately 5.1 times longer. The exciton binding energy (Eb) and longitudinal optical phonon energy (ℏωop) of Cs2AgBiBr6 NCs were measured to be 197.9 and 31.7 meV, respectively. For Cs2Ag0.64K0.36BiBr6 NCs, the values of Eb and ℏωop were determined to be 317.6 and 53.1 meV, respectively. These results indicate that the nonradiative exciton recombination in Cs2Ag0.64K0.36BiBr6 NCs is weaker compared to that in Cs2AgBiBr6 NCs, resulting in the improved PLQY. The K+-alloyed Cs2AgBiBr6 NCs exhibit promising potential for application in light-emitting diodes.