Fig. 2: Characterizations of cesium–copper–iodide LEDs with Tween.

a Schematic diagram of the device structure. b EL spectra of the device under different voltages. Inset, the photograph of LED with the logo of IAM. The substrate area is 12 mm × 12 mm. c Dependence of current density and luminance on the driving voltage. Before turning on, the device shows low current density, indicating suppressed leakage current by the thin organic layer between crystallines⁴. After that, the luminance increases quickly and reaches a luminance of 1570 cd m⁻² at a low voltage of 5.4 V. d EQE versus current density. The LED reaches a peak EQE of 3.1%. e Histogram of peak EQEs. Statistics of 91 devices show an average peak EQE of 1.8% with a relative standard deviation of 23.5%.