High Current\nEfficiency Red Perovskite Light-Emitting\nDiodes Meeting Rec. 2020 Standard

Cesium lead iodide light-emitting diodes (LEDs) are attractive\nfor displays due to their Rec. 2020 red standard compliance. However,\nachieving high current efficiencies (CEs), which is important for\ndisplays, is challenging because their emission spectrum is near the\ntail of the photopic luminosity function. Substituting some iodine\nwith bromine can improve CEs by enlarging the bandgap, but defects\neasily form in iodine–bromine mixed perovskites. Here, we successfully\nreduced defect formation by adding organic ammonium salts and zwitterions.\nThe organic ammonium salts do not form low-dimensional perovskites\nunder the hydrogen bonding interaction of zwitterions. Instead, they\npassivate the cesium vacancy by forming new hydrogen bonds after perovskite\ncrystallization. This approach leads to a red perovskite LED with\na high CE of 12.8 cd A<sup>–1</sup> and a peak external quantum\nefficiency of 20.3%, meeting the Rec. 2020 standard. It can be extended\nto large-area devices (2500 mm<sup>2</sup>) without a significant\nefficiency loss.