Improvement of Performance of Organic Light-Emitting Diodes with Both a MoO₃ Hole Injection Layer and a MoO₃ Doped Hole Transport Layer

We improve the performance of organic light-emitting diodes (OLEDs) with both a MoO₃ hole injection layer (HIL) and a MoO₃ doped hole transport layer (HTL), and present a systematical and comparative investigation on these devices. Compared with OLEDs with only MoO₃ HIL or MoO₃ doped HTL, OLEDs with both MoO₃ HIL and MoO₃ doped HTL show superior performance in driving voltage, power efficiency, and stability. Based on the typical NPB/Alq₃ heterojunction structure, OLEDs with both MoO₃ HIL and MoO₃ doped HTL show a driving voltage of 5.4 V and a power efficiency of 1.41 lm/W for 1000 cd/m², and a lifetime of around 0.88 h with an initial luminance of 5268 cd/m² under a constant current of 190 mA/cm² operation in air without encapsulation. While OLEDs with only MoO₃ HIL or MoO₃ doped HTL show higher driving voltages of 6.4 V or 5.8 V and lower power efficiencies of 1.20 lm/W or 1.34 lm/W for 1000 cd/m², and a shorter lifetime of 0.33 or 0.60 h with an initial luminance of around 5122 or 5300 cd/m² under a constant current of 200 or 216 mA/cm² operation. Our results demonstrate clearly that using both MoO₃ HIL and MoO₃ doped HTL is a simple and effective approach to simultaneously improve both the hole injection and transport efficiency, resulting from the lowered energy barrier at the anode interface and the increased hole carrier density in MoO₃ doped HTL.