Nickel Oxide Hole Injection/Transport Layers for Efficient Solution-Processed Organic Light-Emitting Diodes

摘要

Solution-processed nickel oxides (s-NiO_x) are used as hole injection and transport layers in solution-processed organic light-emitting diodes (OLEDs). By increasing the annealing temperature, the nickel acetate precursor fully decomposes and the s-NiO_x film shows larger crystalline grain sizes, which lead to better hole injection and transport properties. UV—ozone treatment on the s- NiO_x surface is carried out to further modify its surface chemistry, improving the hole injection efficiency. The introduction of more dipolar species of nickel oxy- hydroxide (NiO(OH)) is evidenced after the treatment. Dark injection-space charge limited (DI—SCL) transient measurement was carried out to compare the hole injection efficiency of s-NiO_x and poly(3,4-ethylenedioxythiophene):poly- (styrenesulfonate) (PEDOT:PSS) hole injection layers (HIL). The UV—ozone treated s-NiO_x shows significantly better hole injection, with a high injection efficiency of 0.8. With a p-type thin film transistor (TFT) configuration, the high-temperature annealed s-NiO_x film shows a hole mobility of 0.141 cm~2 V~(-1) s~(-1), which is significantly higher compared to conventional organic hole transport layers (HTLs).