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

Temperature-dependent quantum efficiency in the device structure indium-tin oxide/[(2-methoxy-5(2'-ethylhexyloxy-)-p-phenylenevinylene)]/Ca/Al has been investigated over the temperature range from 20 to 296 K. A blueshift is o bserved in the electroluminescence spectra with an increasing temperature o r voltage. From Fourier transform infrared spectra and UV-visible analyses have been observed that the conjugated length of the polymer chain decrease s due to photo oxidation under UV component of sun light. The change in ban d gap resulting from the change in the conjugated length causes the observe d blueshift. Quantum efficiency increases with decreasing temperature partl y because of the enhancement of photoluminescence efficiency and partly bec ause 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 Institut e of Physics.