Impedance spectroscopy was used to investigate the charge transportation and accumulation mechanisms in a mixed-host emissive layer (EML) of phosphorescent organic light-emitting diodes (OLEDs). 1, 3, 5-tris(1-phenyl-1H-benzimidazole-2-yl)benzene (TPBi) and 4, 4′, 4″-tris(N-carbazolyl)-triphenylamine (TCTA) materials were used as the electron transport and hole transport layers, respectively, to fabricate the mixed-host EML device. The results showed enhanced current and power efficiency owing to the use of the same material as the mixed-host EML, eliminating energy barriers within the device, coupled with the negative interfacial charges in the polarized TPBi material. The hole- and electron-split devices of the mixed-host EML OLED were analyzed to comprehensively understand the enhanced electrical properties within the device. Subsequently, the capacitance-frequency (C–F) characteristics of the devices were simulated with an equivalent circuit to quantitatively determine the capacitance and resistance in each organic layer at specific voltages (0–4 V) representing each characteristic step on the capacitance-voltage (C–V) curve.