Identifying the limitations of today's colloidal quantum dots (CQDs) organic surface chemistries, the researchers developed an efficient chlorination process that efficiently replaces poorly conducting organic ligands with highly conductive inorganic single-atomic-layer surface ligands. Doing so, they obtained CQD films with simultaneously high conductivity and high quantum efficiency.
The high conductivity facilitates charge carrier injection and mitigates the accumulation of electrons and holes near the ETL and HTL, suppressing Auger recombination even at high injection current densities, the researchers explained. QLEDs obtained with the chlorinated CQDs yielded a maximum brightness of 460,000 cd/m 2, twice as much that of any reported LEDs using solution-processed emitting layers, they claim. Turn-on voltage was also reduced from 3.5V to 2.5V while increasing the roll-off current threshold.
Peak external quantum efficiencies (EQEs) measured for chlorinated blue, green and red QLEDs were at 12%, 16.5% and 20%, respectively. The researchers conclude their paper noting that this chlorination strategy can be extended to QLEDs with different emission wavelengths to mitigate efficiency roll-off at high injection current densities. They also see it as a possible step towards electrically pumped CQD lasers.
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