Optoelectronic characteristics of MEH-PPV + BT blend thin films in polymer light emitting diodes

Abstract

Due to the unique optical and electronic properties of conjugated polymers, much research has been conducted to study the effect of the incorporation of electron-transporting materials on the polymer blends’ compatibility and their capability for use in optoelectronic devices. In this work, to characterize the optoelectronic properties of blend thin films of poly [2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) with benzothiadiazole (BT), polymer light- emitting diodes (PLEDs) with single-emission layers of MEH-PPV + BT blends have been fabricated. The influence of MEH-PPV + BT blend weight ratios over ITO/PEDOT:PSS/MEH-PPV + BT/Al PLEDs performances, e.g., lifetime, turn-on voltage, and current density-voltage (J-V) characteristics, has been studied. According to the obtained results, the turn-on voltage of the devices successfully decreased with the addition of the BT as an electronic transportation material. At an optimum condition, we obtained a turn-on voltage as low as 5 V and a lifetime of about 190 h for a device incorporating 65% BT. The logarithmic plots of the J-V characteristics of the fabricated devices showed a power law behavior (J ∝ Vk+1) with three distinct regions. The J-V characteristics have been explained by the Fowler–Nordheim (FN) tunneling model. It was found that the hole-injection barrier height decreases with increasing BT content in the range of 0–65%. According to the obtained results, in all of our investigations, the electroluminescence (EL) originated exclusively from the MEH-PPV material, even for the high BT contents.