4.8 Article

Unraveling the Origin of Operational Instability of Quantum Dot Based Light-Emitting Diodes

Journal

ACS NANO
Volume 12, Issue 10, Pages 10231-10239

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acsnano.8b03386

Keywords

quantum dot based light-emitting diodes; operational stability; charge injection balance; Auger recombination; degradation of organic hole transport layer

Funding

  1. Basic Science Research Program through the National Research Foundation of Korea (NRF) - Ministry of Education [2018R1D1A1B07047824]
  2. Nanomaterials Technology Development Program through the National Research Foundation of Korea (NRF) - Ministry of Education [2016M3A7B4910620]
  3. Ministry of Trade, Industry Energy (MOTIE) [10076340]
  4. Sao Paulo Research Foundation - FAPESP [2013/16911-2]

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We investigate the operational instability of quantum dot (QD)-based light-emitting diodes (QLEDs). Spectroscopic analysis on the QD emissive layer within devices in chorus with the optoelectronic and electrical characteristics of devices discloses that the device efficiency of QLEDs under operation is indeed deteriorated by two main mechanisms. The first is the luminance efficiency drop of the QD emissive layer in the running devices owing to the accumulation of excess electrons in the QDs, which escalates the possibility of nonradiative Auger recombination processes in the QDs. The other is the electron leakage toward hole transport layers (HTLs) that accompanies irreversible physical damage to the HTL by creating nonradiative recombination centers. These processes are distinguishable in terms of the time scale 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 propose mechanistic models for the operation of QLEDs in individual quantum dot levels and their degradation during operation and offer rational guidelines that promise the realization of high-performance QLEDs with proven operational stability.

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