Mn 2+ ‐Doped CsPbI 3 Nanocrystals for Perovskite Light‐Emitting Diodes with High Luminance and Improved Device Stability

Cubic α‐CsPbI 3 has promising applications in the optoelectronic field for its excellent properties. However, α‐CsPbI 3 black phase is instable at room temperature and easily converts into nonluminescent yellow orthorhombic phase (δ‐CsPbI 3 ). Herein, the stability of α‐CsPbI 3 is significantly improved by incorporating Mn 2+ dopants into the perovskite lattice. Mn 2+ : CsPbI 3 has essentially the same crystal structure as the parent α‐CsPbI 3 , and Mn 2+ doping can promote photoluminescence quantum yield (PLQY) from 55% to 93%. Importantly, Mn 2+ : CsPbI 3 can maintain 60% PLQY after exposing in air for 45 days, whereas the undoped CsPbI 3 completely loses its luminescence in 10 days. First‐principles calculations testify that improved stability and optical properties of Mn 2+ : CsPbI 3 are primarily attributed to the increased formation energy and tolerance factor. Accordingly, the luminance, external quantum efficiency (EQE), and T 50 lifetime of Mn 2+ : CsPbI 3 perovskite light‐emitting diode (PeLED) reach 1066 cd m −2 , 1.8%, and 2500 s, whereas the values for the undoped counterpart are only 415 cd m −2 , 0.6%, and 140 s, respectively. In addition, it is evidenced that introducing a LiF buffer layer between hole transport layer and perovskite emissive layer can further boost the device performance, particularly, the luminance and T 50 lifetime achieve 1394 cd m −2 and 225 min at 140 cd m −2 .