Inverted device architecture for high efficiency single-layer organic light-emitting diodes with imbalanced charge transport
Xiao Tan, Dehai Dou, Lay‐Lay Chua, Rui‐Qi Png, Daniel G. Congrave, Hugo Bronstein, Martin Baumgarten, Yungui Li, Paul W. M. Blom, Gert‐Jan A. H. Wetzelaer
Abstract
Many wide-gap organic semiconductors exhibit imbalanced electron and hole transport, therefore efficient organic light-emitting diodes require a multilayer architecture of electron- and hole-transport materials to confine charge recombination to the emissive layer. Here, we show that even for emitters with imbalanced charge transport, it is possible to obtain highly efficient single-layer organic light emitting diodes (OLEDs), without the need for additional charge-transport and blocking layers. For hole-dominated emitters, an inverted single-layer device architecture with ohmic bottom-electron and top-hole contacts moves the emission zone away from the metal top electrode, thereby more than doubling the optical outcoupling efficiency. Finally, a blue-emitting inverted single-layer OLED based on thermally activated delayed fluorescence is achieved, exhibiting a high external quantum efficiency of 19% with little roll-off at high brightness, demonstrating that balanced charge transport is not a prerequisite for highly efficient single-layer OLEDs.