We report systematic efficiency variations of green-emitting CdSe@ZnS quantum-dot (QD) LEDs (QLEDs) in response to in situ treatments with 1,2-ethanedithiol (EDT) solutions at various concentrations. The main effect of in situ EDT treatment on a QD layer spin-coated onto a ZnO layer was vacuum-level shift due to dipole moments on the surface of the QD layer and at the interface between QD and ZnO layers. Competing contributions of these dipole moments were responsible for changes in energy level configurations and, accordingly, electron and hole barriers that resulted in discrepancies in electron- and hole-current variations. QLED efficiency was best when treated with an EDT solution of 4 mM, attributable to the largest increase in the hole- to electron current ratio. The maximum luminous yield of the 4 mM EDT-treated QLED was 5.43 cd A-1, which is 10 times higher than that of an untreated device. Furthermore, the luminous yield of this treated device remained as high as 2.56 cd A-1 at a luminance of 500 cd m-2
This work was partly supported by the \u201cHuman Resources Program in Energy Technology\u201d from the Korea Institute of Energy Technology Evaluation and Planning (KETEP), grant from the Ministry of Trade, Industry & Energy (MOTIE), Republic of Korea (No. 20164030201380), and partly by the GRRC program of Gyeonggi province [GRRC-AJOU2016B03, Photonics-Medical Convergence Technology Research Center].
