Stable Yellow Light-Emitting Devices Based on Ternary Copper Halides with Broadband Emissive Self-Trapped Excitons

Abstract

Great successes have been achieved in developing perovskite light-emitting devices (LEDs) with blue, green, red, and near-infrared emissions. However, as key optoelectronic devices, yellow-colored perovskite LEDs remain challenging, mainly due to the inevitable halide separation in mixed halide perovskites under high bias, causing undesired color change of devices. In addition to this color-missing problem, the intrinsic toxicity and poor stability of conventional lead-halide perovskites also restrict their practical applications. We herein report the fabrication of stable yellow LEDs based on a ternary copper halide CsCu2I3, addressing the color instability and toxicity issues facing current perovskite yellow LED’s compromise. Joint experiment–theory characterizations indicate that the yellow electroluminescence originates from the broadband emission of self-trapped excitons centered at 550 nm as well as the comparable and reasonably low carrier effective masses favorable for charge transport. With a maximum luminance of 47.5 cd/m2 and an external quantum efficiency of 0.17%, the fabricated yellow LEDs exhibit a long half-lifetime of 5.2 h at 25 °C and still function properly at 60 °C with a half-lifetime of 2.2 h, which benefits from the superior resistance of CsCu2I3 to heat, moisture, and oxidation in ambient environmental conditions. The results obtained promise the copper halides with broadband light emission as an environment-friendly and stable yellow emitter for the LEDs compatible with practical applications.

Efficient and bright warm-white electroluminescence from lead-free metal halides

“…After that, the current density and luminance increase quickly. These features are very different from the literature 13,15,21 , suggesting the carrier injection and transport properties are significantly enhanced in our lead-free metal-halide LED device. The device shows a brightness up to 1570 cd m −2 at a low voltage of 5.4 V and external quantum efficiency (EQE) of 3.1%, representing the first efficient and bright warm-white LEDs based on lead-free metal halide ( Supplementary Table 1).…”

“…Without Tween, the device performance is very poor, with a brightness of 35 cd m −2 and a peak EQE of 0.04% ( Supplementary Fig. 4), which is similar to the literature 15,21 . Furthermore, as changing the ratio of CsI:CuI to 1:2 to form a CsCu 2 I 3 -rich film ( Supplementary Fig.…”

“…Among them, solution-processable cesium copper iodides seem promising for white LED applications, because they usually have high PLQEs with broad visible emission from self-trapped excitons or reorganized excited states, and relatively good air stability [15][16][17][18][19][20] . However, the electronic properties of the cesium copper iodides are unfavorable for LEDs since the charge transport is poor due to the large effective mass of carriers 14 , and the charge injection is difficult due to the large bandgaps 15,21 . Here we find that the optoelectronic properties of the cesium copper iodides can be significantly enhanced by simply chemisorbing ether groups onto the metal-halide surfaces acting as electron donors.…”

Lead‐Free Halide Perovskites for Light Emission: Recent Advances and Perspectives

“…[ 2a,225 ] The reported emissive layers consist mainly of low‐dimensional perovskites or low‐dimensional Cu‐based halide materials, including 0D Cs 3 Cu 2 I 5 , 1D CsCu 2 I 3 , 2D Cs 3 Sb 2 Br 9 , 2D (OAm) 2 SnBr 4 , 2D PEA 2 SnI 4 , 2D TEA 2 SnI 4 , 2D (PEAI) 3.5 (CsI) 5 (SnI 2 ) 4.5 . [ 66,86,136,195,206,208,228 ] Low‐dimensional perovskites or halide materials generally possess low electronic dimensionalities and result in low carrier mobilities and undesirable performances. Besides, the large organic group in low‐dimensional perovskites also impede the carriers transport.…”

One‐Dimensional Molecular Metal Halide Materials: Structures, Properties, and Applications

“…In electroluminescence (EL) application, Ma et al fabricated highly stable yellow LEDs based on all‐inorganic CsCu 2 I 3 . [ 77 ] The yellow EL originates from the broadband emission of STEs centered at 550 nm with a maximum luminance of 47.5 cd m −2 and an external quantum efficiency of 0.17%. The fabricated LEDs show a long half lifetime of 5.2 h at room temperature and still function properly at 60 °C with a half lifetime of 2.2 h.…”