Role of air exposure in the improvement of injection efficiency of transition metal oxide/organic contact

Oxygen or air exposure to transition metal oxides (TMOs) was demonstrated to be essential in improving the hole injection (HI) efficiency at the contact formed by TMOs and small organic hole transporter. Current–voltage (J–V) and dark-injection space-charge-limited current (DI-SCLC) techniques were used to cross-examine the TMO/organic contacts. The hole transporter under investigation was N,N′-diphenyl-N,N′-bis(1-naphthyl)(1,1′biphenyl)-4,4′diamine (NPB). The improvement was attributed to the reduction in the energy barrier at TMO/NPB interface, which was a consequence of the work function enhancement of TMO by the oxidation of oxygen in air.