Nanocrystalline copper iodide enabling high-efficiency organic LEDs

Abstract

High-efficiency organic light-emitting diodes (LEDs) can be achieved by employing efficiency-effective materials coupling with suitable device architectures. Among them, there have been numerous hole-injection and -transport materials reported, but having issues of high-cost, solution-process feasibility, and toxic solvent involvement. Here, we demonstrated a low-cost solution-processable nanocrystalline copper iodide (CuI) as a hole-injection and -transport material for the fabrication of high-efficiency organic LEDs. The CuI dispersion can be prepared by using a non-toxic ammonia-water solution with processing being carried out at a relatively low temperature of 110 o C. The annealed CuI film exhibited more superior optical properties, a better hole injection capability, and a better crystalline nature as comparing with the unannealed one or the typical hole-injection counterpart. The annealing resulted nanocrystalline CuI had enabled a green device with a maximum external quantum efficiency (EQE max ) of 17%, a maximum power efficacy (PE max ) of 64 lm W −1 and a maximum current efficacy (CE max ) of 62 cd A −1 , an increment of 54, 33 and 15%, respectively, as comparing with the unannealed counterpart. The respective increments are 35, 41 and 38% as comparing with the typical hole-injection material. Additionally, a blue hazard-free candlelight organic LED has also been fabricated with an EQE max of 15%, PE max of 43 lm W −1 and CE max of 41 cd A −1 . Electrical simulation was also performed to get recombination rate and electric field distribution in active layer. CuI based OLED exhibited higher recombination rate and lower electric filed distribution as comparing with PEDOT:PSS based OLED. The superior performance may be attributed to the enhanced recombination due to efficient injection, transport of holes, and a potential inner light scattering medium aiding light extraction due to its nanocrystalline nature. Our results show that the nanocrystalline CuI can be an inexpensive substitute for the conventionally used hole-injection materials to achieve high-efficiency lighting sources. • Nanocrystalline CuI as an effective Hole-injection/transport layer for organic LEDs. • CuI dispersion is prepared in a non-toxic ammonia-water solution. • Electro-simulation study comparison of CuI and PEDOT:PSS. • Superior device performance in comparison with PEDOT: PSS and amorphous counterpart.