title: Controlling surface defects of non-stoichiometric copper-indium-sulfide quantum dots.
abstract: Quantum dots (QDs) can be used for a wide range of practical applications including solar energy conversion, light-emitting display, bio-imaging, and sensing. However, toxic heavy metal elements of Pb- and Cd-based QDs cause potential environmental problems and limit their wide applicability. To overcome this limitation, CuInS2 (CIS) QDs, which have a bulk bandgap energy of 1.5eV and relatively high absorptivity, can be a good alternative. However the photoluminescence quantum yield (PLQY) of CIS QDs is too low for practical applications. Here we investigate the effects of experimental factors in the solution synthesis of CIS/ZnS QDs on intrinsic defects and surface defects from photoluminescence (PL) analysis. A heating-up method is used with dodecanethiol as a sulfur source, a ligand, and a medium. The Cu-to-In feeding ratio is changed to control the PL spectrum in the range of visible to near infrared (NIR) frequencies. The PLQY is increased above 40% in all of the ranges through ZnS shell passivation and additional process optimization (e.g., controlled cooling rate and additional feeding of In(3+) ion precursor). This work demonstrates the role of intrinsic defects in PL and the importance of suppressing the formation of the surface defects to increase the PLQY.
authors: Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea.
authors: Jae Chul
authors: JC
authors: Park
authors: Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea; KAIST Institute for NanoCentury (KINC CNiT), Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea. Electronic address: yoonsung@kaist.ac.kr.
authors: Yoon Sung
authors: YS
authors: Nam
mesh_terms: D003300:Copper / Q000737:chemistry*; D004058:Diffusion; D006358:Hot Temperature; D007204:Indium / Q000737:chemistry*; D008024:Ligands; D046529:Microscopy, Electron, Transmission; D036103:Nanotechnology / Q000379:methods; D010777:Photochemistry / Q000379:methods; D045663:Quantum Dots; D019265:Spectroscopy, Near-Infrared; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013440:Sulfides / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature; D017967:Zinc Compounds / Q000737:chemistry
chemical_list: D008024:Ligands; D013438:Sulfhydryl Compounds; D013440:Sulfides; D017967:Zinc Compounds; D007204:Indium; D003300:Copper; C031238:zinc sulfide
keywords: CuInS(2); Photoluminescence quantum yield; Quantum dots; Toxic elements-free