Minimizing heating generation in quantum dot LEDs by increasing quasi-Fermi level splitting

Abstract Minimizing heat accumulation is essential to prolong quantum dot LEDs' operational lifetime. Reducing heat generation at the source is the ideal solution because quantum dot LEDs are composed of low thermal conductivity materials which limits heat dissipation. Achieving high brightness and high quantum efficiency at low driving voltage are the keys to realizing this goal. In this work, we propose to enhance the brightness of quantum dot LEDs at low driving voltages by using a monolayer of large quantum dots to reduce the packing number in the emitting layer. This strategy allows us to achieve a higher charge population per quantum dot for a given number of total charges without charge leakage, enabling enhanced quasi-Fermi level splitting and brightness at low driving voltage. Thanks to the minimized heat generation, these LEDs show a record high power conversion efficiency of 23% and an unprecedented T 95 operation lifetime (the time for the luminance to decrease to 95% of the initial value) of more than 48,000 h at 1,000 cd m -2 . The underline mechanism – enhanced quasi-Fermi level splitting enables high brightness at low driving voltage - was confirmed by our latest electrically excited transient absorption spectroscopy.