High-Efficiency Polycrystalline Perovskite Light-Emitting Diodes Based on Mixed Cations

• Published in: ACS nano 2018-03, Vol.12 (3), p.2883-2892
• Main Authors: Cho, Himchan, Kim, Joo Sung, Wolf, Christoph, Kim, Young-Hoon, Yun, Hyung Joong, Jeong, Su-Hun, Sadhanala, Aditya, Venugopalan, Vijay, Choi, Jin Woo, Lee, Chang-Lyoul, Friend, Richard H, Lee, Tae-Woo
• Format: Article
• Language: English
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.8b00409

We have achieved high-efficiency polycrystalline perovskite light-emitting diodes (PeLEDs) based on formamidinium (FA) and cesium (Cs) mixed cations without quantum dot synthesis. Uniform single-phase FA1–x Cs x PbBr3 polycrystalline films were fabricated by one-step formation with various FA:Cs molar proportions; then the influences of chemical composition on film morphology, crystal structure, photoluminescence (PL), and electroluminescence (EL) were systematically investigated. Incorporation of Cs+ cations in FAPbBr3 significantly reduced the average grain size (to 199 nm for FA:Cs = 90:10) and trap density; these changes consequently increased PL quantum efficiency (PLQE) and PL lifetime of FA1–x Cs x PbBr3 films and current efficiency (CE) of PeLEDs. Further increase in Cs molar proportion from 10 mol % decreased crystallinity and purity, increased trap density, and correspondingly decreased PLQE, PL lifetime, and CE. Incorporation of Cs also increased photostability of FA1–x Cs x PbBr3 films, possibly due to suppressed formation of light-induced metastable states. FA1–x Cs x PbBr3 PeLEDs show the maximum CE = 14.5 cd A–1 at FA:Cs = 90:10 with very narrow EL spectral width (21–24 nm); this is the highest CE among FA-Cs-based PeLEDs reported to date. This work provides an understanding of the influences of Cs incorporation on the chemical, structural, and luminescent properties of FAPbBr3 polycrystalline films and a breakthrough to increase the efficiency of FA1–x Cs x PbBr3 PeLEDs.