Device performance and polymer morphology in polymer light emitting diodes: The control of device electrical properties and metal/polymer contact

We recently demonstrated that the morphology of a spin-cast polymer film can be controlled by the proper choice of solvent, polymer solution concentration, and spin speed [Y. Shi, J. Liu, and Y. Yang, J. Appl. Phys. 87, 4254 (2000)]. In this article, we report the correlation between the morphology and the electrical properties of poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene based light emitting diodes. The performance of these devices, such as device turn-on voltage, current injection efficiency, and quantum efficiency, shows a strong dependence on thin film processing conditions. It is found that aromatic solvents and nonaromatic solvents have very different effects on device performance, which suggests that the solvation induced morphology effect is one of the controlling factors for polymer-based optoelectronic devices. (C) 2000 American Institute of Physics. [S0021-8979(00)07214-5].