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 MoOhole injection layer(HIL) and a MoOdoped hole transport layer(HTL),and present a systematical and comparative investigation on these devices.Compared with OLEDs with only MoOHIL or MoOdoped HTL,OLEDs with both MoOHIL and MoOdoped HTL show superior performance in driving voltage,power efficiency,and stability.Based on the typical NPB/Alqheterojunction structure,OLEDs with both MoOHIL and MoOdoped HTL show a driving voltage of 5.4 V and a power efficiency of 1.41 lm/W for 1000 cd/m~2,and a lifetime of around 0.88 h with an initial luminance of 5268 cd/m~2 under a constant current of 190 mA/cm2 operation in air without encapsulation.While OLEDs with only MoOHIL or MoOdoped HTL show higher driving voltages of 6.4 V or 5.8 V and lower power efficiencies of 1.201m/W or 1.341m/W for 1000cd/m~2,and a shorter lifetime of 0.33 or 0.60 h with an initial luminance of around 5122 or 5300cd/m~2 under a constant current of 200 or 216mA/cm~2 operation.Our results demonstrate clearly that using both MoOHIL and MoOdoped 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 MoOdoped HTL.