Thermal-evaporation-deposited CsCu2I3 films with self-trapped excitons for electrically driven yellow light-emitting diodes

Ternary copper halide CsCu2I3 has shown tremendous potentials in addressing the lead toxicity and instability issues of lead-based perovskites light-emitting diodes (LEDs) toward practical applications. However, the development of CsCu2I3-based LEDs still faces great challenges due to the difficulties in fabricating high-quality CsCu2I3 films and designing well-matched device configurations caused by the inherent wide bandgap. Herein, a thermal evaporation technique conjunction with post-annealing treatment was employed to fabricate high-quality CsCu2I3 films, which show a dense and smooth morphology, an excellent heat/ultraviolet light/moisture/oxygen stability, and a bright broadband yellow emission centered at 550 nm. Temperature-dependent photoluminescence and femtosecond transient absorption spectroscopy measurements indicate that the broadband emission with large Stokes shifts of CsCu2I3 films originates from self-trapped excitons-related recombination. Furthermore, a stepwise “energy ladder” hole transport layer of PEDOT:PSS/Poly-TPD/PVK was applied in CsCu2I3-based LEDs to improve the hole injection and charge carrier recombination, leading to an increased device performances. By collaborative optimization, a yellow LED emitting at 550 nm with a peak luminance of 219.6 cd/m2, an external quantum efficiency of 0.49 %, and a half-lifetime of 48.5 min is realized, providing a new idea for the development of environmental-friendly LEDs based on copper halide systems.