Encapsulation of CsPbBr<sub>3</sub> Nanocrystals by a Tripodal Amine Markedly Improves Photoluminescence and Stability Concomitantly via Anion Defect Elimination
Jayita Pradhan, Parikshit Moitra, Umesh, Bidisa Das, Pramita Mondal, Gundam Sandeep Kumar, Uttam Kumar Ghorai, Somobrata Acharya, Santanu Bhattacharya
Abstract
Photoluminescence of halide perovskite nanocrystals (NCs) quenches rapidly due to ambient instability, inherent trap states, and imperfect ligand–NC passivation. We report a novel synthetic strategy to enhance the stability and eliminate trap states of CsPbBr3 NCs simultaneously by in situ introduction of a tripodal tertiary ammonium bromide ion pair ligand [tris(2-aminoethyl)ammonium bromide (TREN·4HBr)]. Tetrabromide ions saturate the PbBr6 octahedra of CsPbBr3 NCs to eliminate the anion vacancies, while TREN with three NH3+ branches enhances efficient encapsulation. TREN·4HBr binds strongly to prevent proton transfer that leads to a facile ligand loss from the NCs surfaces. Ultrafast femtosecond transient absorption kinetics reveals the removal of shallow trap states in the CsPbBr3 NCs leading to a faster carrier recombination to enhance the photoluminescence quantum yield (PLQY). We validate the enhancement in the PLQY by designing light-emitting diodes with an external quantum efficiency of 3.4%. Our work unveils a mechanism for rational improvements of stability and PLQY of CsPbBr3 NCs simultaneously.