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 Cs 2 AgBiBr 6 NCs with uniform morphology (8 ± 1 nm) and excellent crystallinity using a thermal injection method. Compared to the photoluminescence quantum yield (PLQY) of Cs 2 AgBiBr 6 NCs (∼0.4%), the highest PLQY of Cs 2 Ag 0.64 K 0.36 BiBr 6 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 ( E b ) and longitudinal optical phonon energy (ℏω op ) of Cs 2 AgBiBr 6 NCs were measured to be 197.9 and 31.7 meV, respectively. For Cs 2 Ag 0.64 K 0.36 BiBr 6 NCs, the values of E b and ℏω op were determined to be 317.6 and 53.1 meV, respectively. These results indicate that the nonradiative exciton recombination in Cs 2 Ag 0.64 K 0.36 BiBr 6 NCs is weaker compared to that in Cs 2 AgBiBr 6 NCs, resulting in the improved PLQY. The K + -alloyed Cs 2 AgBiBr 6 NCs exhibit promising potential for application in light-emitting diodes.