Temperature-dependent electroluminescence in poly [2-methoxy-5(2′-ethylhexyloxy)-p-phenylenevinylene] light-emitting diode

Temperature-dependent quantum efficiency in the device structure indium-tinoxide/[(2-methoxy-5(2'-ethylhexyloxy-)-p-phenylenevinylene)]/Ca/Al has been investigated over the temperature range from 20 to 296 K. A blueshift is observed in the electroluminescence spectra with an increasing temperature or voltage. From Fourier transform infrared spectra and UV-visible analyses have been observed that the conjugated length of the polymer chain decreases due to photo oxidation under UV component of sun light. The change in band gap resulting from the change in the conjugated length causes the observed blueshift. Quantum efficiency increases with decreasing temperature partly because of the enhancement of photoluminescence efficiency and partly because of the improved balance of holes and electrons. At a fixed temperature, an optimum voltage is required to obtain the maximum efficiency, and with increasing temperature, this voltage increases. (C) 2001 American Institute of Physics.