Solution-processed inorganic copper(I) thiocyanate as a hole injection layer for high-performance quantum dot-based light-emitting diodes

We report the advantageous properties of inorganic copper(I) thiocyanate (CuSCN) as a solution-processable hole injection material in quantum dot-based light-emitting diodes (QLEDs). CuSCN, with its high work function, it decreases the turn-on voltage (Vth) by 0.8 volt to 3.4 V as compared with devices based on the most-widely used poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) (Vth = 4.2 V). As a transparent, highly stable and low cost commercial material, CuSCN acting as the hole injection layer (HIL) gives the QLED better Vth, and comparable performance to PEDOT: PSS- based QLED for other parameters including maximum luminance and external quantum efficiency. The decreased Vth can improve the power efficiency and is a necessary step in meeting market demand. The successful demonstration of the solution-processed inorganic HIL using simple and low temperature processing routes provide guidelines and prospects for the development of reliable all-inorganic and tandem QLEDs and possible commercial applications at a large scale.