Bright Free Exciton Electroluminescence from Mn-Doped Two-Dimensional Layered Perovskites

Two-dimensional (2D) perovskites incorporating hydrophobic organic spacer cations show improved film stability and morphology compared to their three-dimensional (3D) counterparts. However, 2D perovskites usually exhibit low photoluminescence quantum efficiency (PLQE) owing to strong exciton–phonon interaction at room temperature, which limits their efficiency in light-emitting diodes (LEDs). Here, we demonstrate that the device performance of 2D perovskite LEDs can be significantly enhanced by doping Mn 2+ in (benzimidazolium) 2 PbI 4 2D perovskite films to suppress the exciton–phonon interaction. The distorted [PbI 6 ] 4– octahedra by Mn-doping and the rigid benzimidazolium (BIZ) ring without branched chains in the 2D perovskite structure lead to improved crystallinity and rigidity of the perovskites, resulting in suppressed phonon–exciton interaction and enhanced PLQE. On the basis of this strategy, for the first time, we report yellow electroluminescence from free excitons in 2D ( n = 1) perovskites with a maximum brightness of 225 cd m –2 and a peak EQE of 0.045%.