High luminance of CuInS2-based yellow quantum dot light emitting diodes fabricated by all-solution processing†
In this work, all-solution processed, multi-layer yellow quantum dot light emitting diodes (QLEDs), consisting of a hole transport layer of poly(9-vinylcarbazole), emissive layer of CuInS2/ZnS (ZCIS) QDs, and electron transport layer of ZnO nanoparticles, are fabricated. To improve the carrier-balance in QLEDs, a ligand-exchange strategy is employed to replace n-dodecanethiol that caps the surface of CuInS2/ZnS quantum dots with 2-ethylhexanethiol. After this processing, improvement of current efficiency and external quantum efficiency of QLEDs is achieved. The optimized diodes exhibit a maximum luminance of 2354 cd m−2 and an external quantum efficiency of 0.63%, together with a lower turn-on voltage (decreases from 3.1 V to 2.7 V) using these ligand-exchanged QDs as emitting materials. Furthermore, CuInS2-based QLEDs in our study exhibit color retainability with increasing voltage and prolonged use, and show great promise for practical application.