The external quantum efficiencies (EQEs) of state-of-the-art colloidal quantum dotlight-emitting diodes (QLEDs) are now approaching the limit set by the out-couplingefficiency. However, the brightness of these devices is curtailed by the use ofpoorly conducting emitting layers, a consequence of present-day reliance onlong-chain organic capping ligands. Here, we report how conductive andpassivating halides can be implemented in Zn chalcogenide-shelled colloidalquantum dots (CQDs) to enable high-brightness green QLEDs. We use a surfacemanagement reagent, thionylchloride (SOCl2), to chlorinate the carboxylic group of oleic acidand graft the CQD surface with passivating chloride anions. This results indevices with an improved mobility which retain high EQE in the high injectioncurrent region and also feature a reduced turn-on voltage of 2.5V. The treatedQLEDs operate with a brightness of 460,000 cd m-2, significantlyexceeding that of all previously-reported solution-processed LEDs.
近年來，量子點LED的外發光效率已經接近其理論值，而其發光亮度仍不盡人意。其可能原因是用於作為發光層的量子點大多為溶液相合成，其表面包裹的有機長鏈配體由於較差的電導性，大大降低了電子和空穴的傳輸性能，從而也限制了量子點LED的發光亮度。該工作中，我們用原位固態交換法將CdSeZnS量子點薄膜表面的有機長鏈配體用滷素配體來取代，由於其良好的電子空穴傳輸性能，從而實現綠光最高亮度460,000cd m-2。通過理論模擬計算我們得出，由於滷素配體的引入，電子空穴在器件中注入更加平衡，高電流密度下的俄歇複合效率降低，從而使器件外發光效率即使在高電流密度下衰減仍不明顯，從而實現了高亮度LED。