The effects of energetic disorder and polydispersity in conjugation length on the efficiency of polymer-based light-emitting diodes

Energetic disorder plays a critical role in governing the performance of organic light-emitting diodes (OLEDs). This is particularly true for polymer-based OLEDs in which disorder can be controlled but not eliminated. Contrary to the common assumption that energetic disorder has only a negative effect on performance, we provide experimental evidence of improved efficiency when the energetic disorder is increased upon deliberate addition of traps via an increase in polymer chain length distribution. We use numerical calculations to extract the mechanisms responsible for the observed improvements and discuss the general conditions under which traps can be introduced to increase device efficiency.