Post-fabrication electric field and thermal treatment of polymer light emitting diodes and their photovoltaic properties

This work presents post-fabrication electric field and heat treatment methods developed for polymer light emitting diodes (PLEDs), which have degraded due to exposure to oxygen and water vapors during low-cost fabrication performed in standard room conditions. Investigated PLEDs have structures composed of indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene), poly(styrenesulfonate), (PEDOT:PSS), poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV), and aluminum (Al). Heat treatment restores the light emitting function of dysfunctional PLEDs but also causes a high turn-on voltage of 10 V. Electric field treatment utilizing −1 V reduces this high turn-on voltage to 3 V. This procedure also improves open circuit voltages from 5 mV to 55 mV, and short circuit currents from 0.5 nA to 5 nA when PLEDs are operated as photovoltaic cells under a light intensity of 500 mW/m2. Repeated I–V sweep measurements additionally show improved stability and uniformity. The reasons for these improvements, the usage of an optimal treatment temperature of 130 °C, and the usage of treatment voltages of 0 and −1 V are discussed.