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.

许多宽禁带有机半导体表现出不平衡的电子和空穴传输，因此高效的有机发光二极管需要电子和空穴传输材料的多层结构，以将电荷复合限制在发射层。在这里，我们表明，即使对于电荷传输不平衡的发射器，也可以获得高效的单层有机发光二极管（OLED），而不需要额外的电荷传输和阻挡层。对于空穴为主的发射器，具有欧姆底部电子和顶部孔接触的倒置单层器件架构将发射区移离金属顶部电极，从而使光学输出耦合效率提高了一倍以上。最终，实现了基于热激活延迟荧光的蓝光发射倒置单层OLED，表现出19%的高外量子效率，在高亮度下几乎没有滚降，这表明平衡电荷传输并不是高效率的先决条件单层OLED。