Efficient organic light‐emitting diodes (OLEDs) commonly comprise a multilayer stack including charge‐transport and charge‐ and exciton‐blocking layers, to confine charge recombination to the emissive layer. Here, a highly simplified single‐layer blue‐emitting OLED is demonstrated based on thermally activated delayed fluorescence with the emitting layer simply sandwiched between ohmic contacts consisting of a polymeric conducting anode and a metal cathode. The single‐layer OLED exhibits an external quantum efficiency of 27.7% with minor roll‐off at high brightness. The internal quantum efficiency approaches unity, demonstrating that highly simplified single‐layer OLEDs without confinement layers can achieve state‐of‐the‐art performance, while greatly reducing the complexity of the design, fabrication, and device analysis. Efficient blue single‐layer organic light‐emitting diodes are demonstrated, achieving 27.7% external quantum efficiency, low roll‐off, and low operating voltages. The internal quantum efficiency approaches unity, demonstrating that highly simplified single‐layer OLEDs without confinement layers can achieve state‐of‐the‐art performance, while greatly reducing the complexity of the design, fabrication, and device analysis.