Influence of hole transport units on the efficiency of polymer light emitting diodes

Charge transport and electroluminescence efficiency in spirobifluorene polymers containing triarylamine as hole transport unit have been studied. The hole mobility as measured by the time-of-flight technique was found to be on the order of 10−4cm2V−1s−1. The field and temperature dependences of the mobility are in accord with the Gaussian disorder model. Best device efficiencies of the blue emitting materials are in the range of 2.9cd∕A. The influence of the hole transport unit on charge transport and device efficiency is analyzed. The efficiency depends critically on the amount of the hole transport unit and decreases with increasing hole mobility.