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

Abstract

CuInS 2 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 hydroxylterminated CuInS 2 based quantum dots capped with 6mercaptohexanol. 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 ∼70%. Using these hydroxyl-terminated CuInS 2 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.

Quantum Dot Light-Emitting Diode with Ligand-Exchanged ZnCuInS₂ Quantum Dot

“…The current efficiency was improved with decreasing carbon chain length of the alkyl thiol ligands, and the highest current efficiency of 0.083 cd/A was obtained. This value is quite low compared with reported QLEDs with Cd-free QDs such as InP and CuInS 2 [10], [15]. However, this is the first demonstration of QLEDs with ligand-exchanged ZnCuInS 2 QDs, and the thick and multiple shell coating layers are useful techniques for realizing highly efficient QLEDs with ZnCuInS 2 QDs.…”

“…Previous papers demonstrated that PL-QYs of more than 80% were achieved, and this value is high enough for practical display and biological applications [13], [14]. Furthermore, the luminance performance of QLEDs with Cd-free QDs has been improved by controlling the organic ligand [15]; however, further investigation is required due to insufficient understanding of carrier dynamics in QLEDs.…”

Pontos quânticos ambientalmente amigáveis: destaque para o óxido de zinco

“…15,108,109 Como mencionado acima, NPs de ZnO têm sido consideradas boas candidatas para o desenvolvimento de dispositivos optoeletrôni-cos devido seu band gap direto de 3,37 eV à temperatura ambiente e pela alta energia de ligação do éxciton de 60 meV. As NPs de ZnO são uma alternativa ideal à camada transportadora de elétrons devido à sua estabilidade térmica e menor sensibilidade ao oxigênio e à umidade.…”

Rational Design and Synthesis of Highly Luminescent Multinary Cu‐In‐Zn‐S Semiconductor Nanocrystals with Tailored Nanostructures

“…As one of the most popular alternative candidates, I–III–VI 2 semiconductor NCs, such as CuInS 2 and AgInS 2 , have become rising stars due to their lower toxicity, high extinction coefficients, and pronounced defect tolerance as well as their attractive potentials in optoelectronic and biomedical applications . In particular, CuInS 2 is one of the most intensively studied NC, and a lot of literatures have been reported on synthetic recipes and potential applications . Nevertheless, the intrinsic surface traps or internal defects facilitate nonradiative recombination, resulting in a lower photoluminescence quantum yield (PLQY) .…”