Less-Lead Control toward Highly Efficient Formamidinium-Based Perovskite Light-Emitting Diodes

A formamidinium (FA)-based perovskite is an ideal option for the potential efficient light-emitting diode (LED) in view of its high tolerance factor closer to 1. In this work, FA cation-based perovskite nanocrystals FA_0.8Cs_0.2Pb _xBr₃ ( x = 1.0, 0.8, 0.7, and 0.6) are fabricated with stoichiometric modification. The adoption of less-lead precursor is confirmed to be a feasible and effective approach in inhibiting nonradiative recombination by diminishing the presence of uncoordinated metallic Pb atoms. Note that the subsequent devices require the optimized lead ratio for an optimum behavior, a clear influence of Pb ratio on a perovskite LED has been established. No surprisingly, the less-lead perovskites exert positive roles on the perovskite LED performance, not only in terms of efficiency but also in stability. With an optimized composition FA_0.8Cs_0.2Pb_0.7Br₃, the perovskite LED displays the prominent performance with a current efficiency of 28.61 cd A^-1, about 11-fold improvement than the previous best record of pure FA-based perovskite. Additionally, the perovskite device degradation can be mitigated under operating conditions by properly altering precursor stoichiometry, which can be attributed to the hydrogen reaction under moisture-induced ambient. The stoichiometric optimization of the metal Pb in the perovskite is an important strategy on the road to the further development of perovskite LEDs.