Hydroxyl-Terminated CuInS2 Based Quantum Dots: Toward Efficient and Bright Light Emitting Diodes

CuInS2 based quantum dots are emerging as low toxic materials for new generation white lighting technology due to their broad and color-tunable emissions as well as large Stokes shifts. Here, we developed a simple and in situ ligand exchange strategy for the fabrication of hydroxyl terminated CuInS2 based quantum dots capped with 6-mercaptohexanol. During the ligand exchange, long-chain methyl-terminated oleylamine on the quantum dots' surface can be effectively and efficiently replaced by the short-chain hydroxyl-terminated 6-mercaptohexanol, enabling their solubility in polar organic solvents such as methanol, ethanol, and dimethylformamide. Moreover, the resulting hydroxyl-terminated quantum dots exhibit well-preserved photoluminescence properties with quantum yields of similar to 70%. Using these hydroxyl-terminated CuInS2 based quantum dots as an emitting layer, we fabricated efficient and bright light emitting diodes by adopting an inverted device structure. The optimized devices show a maximum luminance of 8,735 cd/m(2) and an external quantum efficiency of 3.22%. Furthermore, the performance enhancement can be explained by considering the decreased energy barriers between the electron transport layer and the emitting layer. The combination of high efficiency and enhanced brightness as well as the potential all-solution processability using green solvents makes hydroxyl-terminated quantum dots capped with 6-mercaptohexanol a new generation of materials for light emitting applications.