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

Abstract

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 (<i>J</i>). However, at high <i>J</i>, 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 <i>J</i> 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 (<i>e</i>.<i>g</i>., 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 <i>J</i> 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.