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

Organic bulk heterojunction comprising a pentacene and C-60 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 C-60 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 C-60 in the CGL result in different probabilities of charge transfer from pentacene to C-60 and imbalanced charge transport, thereby leading to completely different device performance. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3644970]