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.