Carrier conduction mechanism for phosphorescent material doped organic semiconductor

The mobility of charge carriers has been investigated in the pristine and phosphorescent material doped 4,4('),4(')-tris(N-carbazolyl) triphenylamine (TCTA) using time-of-flight photoconductivity technique. Doping phosphorescent material fac-tris(2-phenylpyridine) iridium [Ir(ppy)(3)] increases the electron mobility whereas the hole mobility decreases to the order of 10(-4)-10(-6) cm(2)/V s measured at room temperature with different bias voltages. The analysis of field and temperature dependences of the mobility agrees well with the Gaussian disorder model. The calculated positional disorders (Sigma) for TCTA, Ir(ppy)(3)-doped TCTA, and tris(1-phenylisoquinoline) iridium [Ir(piq)(3)]-doped TCTA are 0.12, 2.05, and 1.62 for hole, respectively; 3.89 for electron in only Ir(ppy)(3)-doped TCTA. The ambipolar transport for holes and electrons is possible by doping TCTA with Ir(ppy)(3) (green dopant) whereas only hole transport with reduced mobility is achieved for Ir(piq)(3) (red dopant).