Solution-processed p-type CuxS hole injection layers for quantum dot light-emitting diodes†

Abstract

Quantum dot light-emitting diodes (QLEDs) have been extensively investigated due to their unique optoelectronic properties, and their efficiencies have gradually approached the theoretical upper limit. However, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), the most commonly used hole injection layer (HIL) in conventional QLEDs, seriously reduces the stability of QLEDs because of its hygroscopicity and acidity. Herein, we report a molecular-based precursor solution method for fabricating Cu_xS thin films to replace the conventional PEDOT:PSS HILs in QLEDs. It was found that the optical and electrical properties of the as-prepared Cu_xS HILs are strongly dependent on the annealing temperature. Under the optimal annealing conditions, the Cu_xS thin films exhibit a high hole concentration (1.90 × 10¹⁶ cm⁻³), a high conductivity (3.25 × 10⁻³ S cm⁻¹), a high transmittance of 92% in the range of 400–800 nm and a work function of 5.50 eV, making them highly suitable for application as HILs of QLEDs. QLEDs with the Cu_xS HILs exhibit a maximum brightness of 23 798 cd m⁻², a maximum external quantum efficiency (EQE) of 16.63%, and a current efficiency of 23.88 cd A⁻¹. These results demonstrate that the solution-deposited p-type Cu_xS thin films have potential for application as HIL materials in QLEDs.