CHARACTERIZATION OF LIGHT-EMITTING-DIODES AND SOLAR-CELLS BASED ON POLY-PHENYLENE-VINYLENE

Due to its good processability and thermal stability poly-p-phenylene-vinylene (PPV) is well suited for electronic devices. In this paper we report on electrical properties of PPV-based light-emitting diodes and solar cells. At room temperature I-V-characteristics in the dark reveal a good diode behaviour with a maximum rectification ratio of 10(6). The threshold voltage for visible electroluminescence (EL) is device dependent and under best conditions we measure values as low as 2 V. Impedance measurements show that our diodes can be described within the Schottky barrier model, e.g. as a serial circuit of resistive and capacitive components, for both the bulk and the junction. At low temperatures the I-V-characteristics become almost symmetrical and EL appears in both current directions, indicating that the Schottky junction is not necessary for the observation of EL in conjugated polymers. Under white light illumination an open-circuit voltage of more than 1 V and a power conversion efficiency of about 0.1% can be achieved, suggesting the possible application as solar cells. Ageing experiments point to a significant influence of oxygen on the electrical properties and consequently on the lifetime of the devices.