For practical application of LEDs, a key indicator of device quality is its efficiency at high current densities (or brightness). For most LEDs, their efficiencies reduce at high current densities. This behavior is termed as efficiency roll-off, which can be caused by either luminescence quenching (a reduction in luminescence efficiency due to non-radiative processes) or an excessive population of charge carriers passing through the device without forming electron-hole pairs. Here, we show that typical PeLEDs based on MQWs also suffer from serious efficiency rolloff, with the EQE peaking at 30 mA cm−2 and rolling-off by 55% (relative to the peak value) at 400 mA cm−2. We investigate the origin of the efficiency roll-off, by simultaneously measuring EL and photoluminescence (PL) on a working LED device. We find that the efficiency roll-off in PeLEDs is mainly due to luminescence quenching most likely caused by nonradiative Auger recombination, and the luminescence quenching effect can be suppressed by increasing the width of perovskite QWs. Based on our improved understanding of device operation, we are able to raise the efficiency of PeLEDs to 12.7% with significantly reduced roll-off.
15 th, Mar. 2018