Unravelling the origin of operational instability of quantum dot based light-emitting diodes
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We investigate the operational instability of quantum dot based light-emitting diodes (QLEDs). Spectroscopic analysis on the QD emissive layer within devices in chorus with the optoelectronic and electrical characteristics of devices disclose that the device efficiency of QLED under operation is deteriorated by two main mechanisms. The first is the luminance efficiency drop of the QD emissive layer owing to the accumulation of excess electrons in QDs. The other is the electron leakage toward hole transport layers (HTLs) that accompanies irreversible physical damage to the HTL by creating non-radiative recombination centers. These processes are distinguishable in terms of the timescale and the reversibility, but both stem from a single origin, the discrepancy between electron versus hole injection rates into QDs. Based on experimental and calculation results, we offer rational guidelines that promise the realization of high performance QLEDs with proven operational stability.