Cu2+-Doped CsPbI3 Nanocrystals with Enhanced Stability for Light-Emitting Diodes.

Black phase CsPbI3 perovskites have emerged as one of the most promising materials for use in optoelectronic devices due to their remarkable properties. However, black phase CsPbI3 usually possesses poor stability and involves a phase change process, resulting in an undesired orthorhombic (δ) yellow phase. Here, the enhanced stability of CsPbI3 nanocrystals is achieved by incorporating the Cu2+ ion into the CsPbI3 lattice under mild conditions. In particular, the Cu2+-doped CsPbI3 film can maintain red luminescence for 35 days in air while the undoped ones transformed into the nonluminescent yellow phase in several days. Furthermore, first-principles calculations verified that the enhanced stability is ascribed to the increased formation energy due to the successful doping of Cu2+ in CsPbI3. Benefiting from such an effective doping strategy, the as-prepared Cu2+-doped CsPbI3 as an emitting layer shows much better performance compared with that of the undoped counterpart. The turn-on voltage of the Cu2+-doped quantum-dot light-emitting diode (QLED) (1.6 V) is significantly reduced compared with that of the pristine QLED (3.8 V). In addition, the luminance of the Cu2+-doped QLED can reach 1270 cd/m2, which is more than twice that of the pristine CsPbI3 QLED (542 cd/m2). The device performance is believed to be further improved by optimizing the purification process and device structure, shedding light on future applications.