220 V/50 Hz Compatible Bipolar Quantum‐Dot Light‐Emitting Diodes

Abstract Alternating current (AC)‐driven quantum‐dot light‐emitting diodes (QLEDs) are superior to direct current‐driven QLEDs because they can be directly integrated into household AC electricity and have high stability. However, achieving high‐performance AC‐driven QLEDs remains challenging. In this work, a bipolar QLED with coplanar electrodes is realized by horizontally connecting a regular QLED and an inverted QLED in series using an Al bridging layer. The bipolar QLED can be turned on with either a positive or a negative bias voltage, with a high external quantum efficiency (EQE) of 22.9%. By replacing the Al with Ag, the resistances of the electron transport layers are effectively reduced, and thus the bipolar QLED shows an enhanced brightness of 16370 cd m −2 at 15 V. By connecting multiple bipolar QLEDs in series, the resulting light source can be directly driven by a 220 V/50 Hz household power supply without the need for back‐end electronics. The bipolar QLED can also be realized by vertically stacking a regular QLED and an inverted QLED with a metallic intermediate connection layer. It is demonstrated that the coplanar or vertical bipolar QLEDs could find potential applications in household AC electricity play‐and‐plug solid‐state lighting and single‐ or double‐sided displays.