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)PbI4 2D perovskite films to suppress the exciton-phonon interaction. The distorted [PbI6](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%. Funding Agencies|Major Research Plan of the National Natural Science Foundation of China [91733302]; European Union [2016YFE0112000]; National Basic Research Program of China-Fundamental Studies of Perovskite Solar Cells [2015CB932200]; National Natural Science Foundation of China [61634001, 51703094]; Natural Science Foundation of Jiangsu Province, China [BK20170991, BK20150043, BK20150064]; National Science Fund for Distinguished Young Scholars [61725502]; Natural Science Fund for Colleges and Universities in Jiangsu Province of China [17KJB150023]; Synergetic Innovation Center for Organic Electronics and Information Displays