Quantifying Efficiency Roll‐Off Factors in Quantum‐Dot Light‐Emitting Diodes

The application of quantum‐dot light‐emitting diodes (QLEDs) is hindered by efficiency roll‐off at high current densities. Factors contributing to this roll‐off include Auger recombination, electric field‐induced quenching, Joule heating, and electron leakage into the hole transport layer. However, a method to quantitatively attribute the contribution of each factor to roll‐off has not yet been available, leaving the primary cause of roll‐off unidentified. This work addresses this gap using electrically pumped transient absorption spectroscopy, which measures the accumulated electrons and electric field in quantum dots (QDs). This study also introduces a method to quantify electron leakage in QLEDs using this spectroscopic technique. Based on the spectroscopic experimental results, the contribution of each factor to roll‐off is quantified. A green QLED with a peak external quantum efficiency (EQE) of 26.8% is studied as an example. The EQE declines to 20.5% at a current density of 354 mA cm−2, where field‐induced quenching accounts for 5% of the efficiency roll‐off, and electron leakage contributes 95%. Contributions from Auger recombination and heat‐induced quenching are negligible. This work demonstrates strong correlations between roll‐off and electron leakage amplitude using statistical data obtained in multiple QLEDs, confirming that electron leakage is the primary factor in EQE roll‐off. The contributions of Auger recombination, electric field‐induced quenching, and electron leakage to the efficiency roll‐off of QLEDs are quantified using electrically pumped transient absorption spectroscopy. The bleach signal, Stark effect signal, and leakage signal are used to calculate each of these factors, respectively. Electron leakage is proved to be the primary factor of EQE roll‐off.