Investigation on Thermally Induced Efficiency Roll-Off: Toward Efficient and Ultrabright Quantum-Dot Light-Emitting Diodes

Quantum-dot light-emitting diodes (QLEDs) with high brightness have potential application in lighting and display. The high brightness is realized at high current density (J). However, at high J, the efficiency drops significantly, thereby limiting the achievable brightness. This notorious phenomenon has been known as efficiency roll-off, which is likely caused by the Auger- and/or thermal-induced emission quenching. In this work, we show that the Joule heat generated during device operation significantly affects the roll-off characteristics of QLEDs. To realize ultrabright and efficient QLEDs, the thermal stability of QDs is improved by replacing the conventional oleic acid ligands with 1-dodecanethiol. By further using a substrate with high thermal conductivity, the Joule heat generated at high J is effectively dissipated. Because of the effective thermal management, thermal-induced emission quenching is significantly suppressed, and consequently, the QLEDs exhibit a high external quantum efficiency (EQE) of 16.6%, which is virtually droop-free over a wide range of brightness (e.g., EQE = 16.1% @ 10⁵ cd/m² and 140 mA/cm²). Moreover, due to the reduced efficiency roll-off and enhanced heat dissipation, the demonstrated QLEDs can be operated at a very high J up to 3885 mA/cm², thus enabling the devices to exhibit a record-high brightness of 1.6 × 10⁶ cd/m² and a lumen density of 500 lm/cm². Our work demonstrates the significance of thermal management for the development of droop-free and ultrabright QLED devices for a wide variety of applications including lighting, transparent display, projection display, outdoor digital signage, and phototherapy.