Thomson-like electron-hole recombination in organic light-emitting diodes

The quantum electroluminescence (EL) yield (?EL) of a single-layer light-emitting diode (LED) based on a mixture of an oligothiophene (T5Ohex), an aromatic diamine (TPD) and bisphenol A polycarbonate (PC), and of a double-layer LED with a (TPD:PC) hole-transporting layer and an 8-hydroxyquinoline (Alq3) electron-transporting layer, was measured as a function of electric field (F). The devices exhibit maximum ?EL(F) at Fmax around 106 V·cm-1. This behavior can be explained by the carrier motion-controlled Langevin recombination in the low-field region, and the Thomson-like recombination, controlled by the carrier capture, dominating the high-field regime.