Quasi-Type II Core–Shell Perovskite Nanocrystals for Improved Structural Stability and Optical Gain

In recent years, core–shell lead halide perovskite nanocrystals (PeNCs) and their devices have attracted intensive attention owing to nearly perfect optoelectronic properties. However, the complex photophysical mechanism among them is still unclear. Herein, monodispersed core–shell PeNCs coated with an all-inorganic cesium lead bromide (CsPbBr3) shell epitaxially grown on the surface of formamidinium lead bromide (FAPbBr3) PeNCs were synthesized. Through power- and temperature-dependent photoluminescence (PL) measurements, it is found that the electronic structure of the core–shell FAPbBr3/CsPbBr3 PeNCs has a quasi-type II band alignment. The presence of Cs+ in the shell limits ion migration and helps to stabilize structural and optical properties. On this basis, after being exposed to pulsed nanosecond laser for a period, an amplified spontaneous emission (ASE) can be observed, which is attributed to the effective passivation induced by laser irradiation on defects at the interface. The ASE threshold of the core–shell PeNCs showing high structural and optical stability is 447 nJ/cm2 under pulsed nanosecond optical pumping. The results that are demonstrated here provide a new idea and perspective for improving the stability of perovskite and can be of practical interest for the utilization of the core–shell PeNCs in optoelectronic devices.