Abstract
Solution-processed metal-halide perovskites are emerging as one of the most promising materials for displays, lighting and energy generation. Currently, the best-performing perovskite optoelectronic devices are based on lead halides and the lead toxicity severely restricts their practical applications. Moreover, efficient white electroluminescence from broadband-emission metal halides remains a challenge. Here we demonstrate efficient and bright lead-free LEDs based on cesium copper halides enabled by introducing an organic additive (Tween, polyethylene glycol sorbitan monooleate) into the precursor solutions. We find the additive can reduce the trap states, enhancing the photoluminescence quantum efficiency of the metal halide films, and increase the surface potential, facilitating the hole injection and transport in the LEDs. Consequently, we achieve warm-white LEDs reaching an external quantum efficiency of 3.1% and a luminance of 1570 cd m−2 at a low voltage of 5.4 V, showing great promise of lead-free metal halides for solution-processed white LED applications.
Highlights
Solution-processed metal-halide perovskites are emerging as one of the most promising materials for displays, lighting and energy generation
The emitting layers were prepared by spin-coating a precursor solution of cesium iodide (CsI), copper(I) iodide (CuI), and polyethylene glycol sorbitan monooleate (Tween) with a molar ratio of 1:1:0.006 dissolved in dimethyl sulfoxide (DMSO) (14 wt.%)
The PL excitation (PLE) spectra measured at different emission wavelengths show that the PL emissions of Cs3Cu2I5 and CsCu2I3 crystals stem from their absorption peaks at 287 and 314 nm (Fig. 1d and Supplementary Fig. 2a) respectively, consistent with the absorption spectra[15,16]
Summary
Solution-processed metal-halide perovskites are emerging as one of the most promising materials for displays, lighting and energy generation. Various metal halides possessing broadband white-light emission, such as two-dimensional lead halide perovskite[10,11,12], lead-free halide double perovskite[13], and cesium copper halides[14], have been developed to be emitters in white LEDs. there is no report of electroluminescence (EL) efficiency from those materials yet and the maximum luminance of the device is only around 70 cd m−210, which mainly due to their unfavorable electronic properties[13,14], or low photoluminescence quantum efficiencies (PLQEs)[10]. We find that the optoelectronic properties of the cesium copper iodides can be significantly enhanced by chemisorbing ether groups onto the metal-halide surfaces acting as electron donors Based on this strategy, we first demonstrate efficient and bright warm-white EL based on lead-free halides
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