Effect of organic bulk heterojunction as charge generation layer on the performance of tandem organic light-emitting diodes

Abstract

Organic bulk heterojunction comprising a pentacene and C60 blend can be used as the charge generation layer (CGL) in tandem organic light-emitting diodes (OLEDs) for significantly improved power efficiency. Herein, we systematically study the effects of the ratio and thickness of the CGL on the performance of tandem OLEDs. We have found that the efficiency of tandem OLEDs not only is related to the thickness of the CGL but also strongly depends on the ratio of pentacene to C60 in the CGL. Investigations regarding the capacitance-voltage and atomic force microscopy measurements clearly indicate that different thicknesses of the CGL lead to different behaviors of the charge distributions, and different ratios of pentacene to C60 in the CGL result in different probabilities of charge transfer from pentacene to C60 and imbalanced charge transport, thereby leading to completely different device performance.