Vanadium-doped indium tin oxide as hole-injection layer in organic light-emitting devices

Organic light-emitting devices were fabricated by using vanadium-doped indium tin oxide (ITO) as the hole-injection layers between the hole transport layer, N,N′-dia(1-napthl)-N,N′-diphenyl benzidine and the ITO anode. The vanadium-doped ITO layer was 15-nm thick with three different vanadium concentrations (6, 10.5, and 12.5mol%). Three different resistivities (10, 500, and 10000Ωcm) and work functions (5, 5.2, and 5.4eV) were obtained. The device with 6mol% V-doped ITO layer possessing the least resistivity (10Ωcm) and work function (5eV) has the lowest turn-on voltage (below 3V), the lowest operating voltage (below 7V), the highest luminance (1000cd∕m2 below 7V), and the highest power efficiency (>5lm∕W at 10mA∕cm2) among all. Such performance was attributed to the balance between the carrier concentration and the energy barrier for the hole injection.