Energy Transfer from Blue-Emitting CsPbBr₃ Perovskite Nanocrystals to Green-Emitting CsPbBr₃ Perovskite Nanocrystals

Cesium lead halide (CsPbBr 3 ) perovskite nanocrystals (NCs) have great potential for optoelectronic applications. However, their photoluminescence quantum yield (PLQY) in the film state is lower than that in the solution state due to concentration quenching; thus, PLQY is an issue in light-emitting device applications. Here, we demonstrate that energy donor–acceptor systems of CsPbBr 3 NCs, composed of the same halogen composition but with different sizes, realize efficient suppression of concentration quenching and high optical stability. The energy band gap of CsPbBr 3 NCs depends on their size due to the quantum confinement effect and behaves as quantum dots (QDs). The PLQY of a green-emitting CsPbBr 3 QD (GPeQD) film mixed with smaller blue-emitting CsPbBr 3 QDs (BPeQDs) was approximately 2 times higher than that of the neat film (20%). PL, photoluminescence excitation (PLE), and transient PL (TRPL) spectroscopies revealed that this improvement of PLQY in the film state has roots in FRET from BPeQD to GPeQD, resulting in efficient suppression of concentration quenching. The emission color in this energy donor–acceptor system was stable in the solution and film states, although this could not be achieved by cesium lead halide NCs with different halogens due to the halogen exchange reaction and resulting emission color change.