Son, Dong Ick Kwon, Byoung Wook Yang, Jeong Do Park, Dong Hee Seo, Won Seon Lee, Hyunbok Yi, Yeonjin Lee, Chang Lyoul Choi, Won Kook 2024-01-20T13:34:25Z 2024-01-20T13:34:25Z 2021-09-04 2012-11 1998-0124 https://pubs.kist.re.kr/handle/201004/128736 ZnO-graphene quasi core-shell quantum dot (QD) structures in which the inner ZnO QDs are covered with graphene nanoshells have been synthesized via a simple solution process method. The outer graphene nanoshells were identified as a single graphene layer using high resolution transmission electron microscopy (HR-TEM). Zn-O-C (graphene) chemical bonds between the inner ZnO QDs and the oxygen-containing functional groups introduced into the graphene layer are believed to be important in the formation of the consolidated quasi core-shell QD structure. A multilayer structure organic ultraviolet (UV) photovoltaic (PV) device was fabricated using ZnO-graphene core-shell QDs as the absorption layer. A quenching behavior as large as 71% near the UV emission peak for the ZnO-graphene core-shell QDs was observed in the photoluminescence. Density of state (DOS) calculations for the graphene using density functional theory (DFT) revealed that the static quenching can be attributed to a faster charge separation via the direct electron transfer from the conduction band (CB) of the ZnO QDs to the induced lowest unoccupied molecular orbitals (LUMO) of the graphene nanoshell resulting from the Zn-O-C bonding. This charge separation mechanism was confirmed experimentally using time-correlated single photon counting (TCSPC) measurements. The calculated average lifetime of 0.13 ns and 0.165 ns of the 375 and 383 nm UV emissions, respectively, for the ZnO-graphene core-shell QDs were approximately 10 times faster than those of 1.86 ns and 1.83 nm for the reference ZnO QDs; this is indicative of the existence of an additional high efficiency relaxation channel. The observed saturation current density (J (sc)), open circuit voltage (V (oc)), fill factor (FF), and power conversion efficiency (eta) were 196.4 mu A/cm(2), 0.99 V, 0.24, and 2.33%, respectively. In this study, it was found that the UV power conversion efficiency of ZnO QDs could be significantly improved by invoking a fast photoinduced charge separation and the subsequent transport of carriers to the collecting electrodes through conjugation with highly conductive graphene nanoshell acceptors to the ZnO QDs donor. English TSINGHUA UNIV PRESS PHOTOINDUCED ELECTRON-TRANSFER OXIDE PHOTOLUMINESCENCE POLYMER NANOPARTICLES CELLS Charge separation and ultraviolet photovoltaic conversion of ZnO quantum dots conjugated with graphene nanoshells Article 10.1007/s12274-012-0258-6 1 NANO RESEARCH, v.5, no.11, pp.747 - 761 NANO RESEARCH 5 11 747 761 scie scopus 000311397700001 2-s2.0-84869863847 Chemistry, Physical Nanoscience & Nanotechnology Materials Science, Multidisciplinary Physics, Applied Chemistry Science & Technology - Other Topics Materials Science Physics Article PHOTOINDUCED ELECTRON-TRANSFER OXIDE PHOTOLUMINESCENCE POLYMER NANOPARTICLES CELLS Graphene nanoshell ZnO-graphene quasi core-shell quantum dot (QD) ultraviolet (UV) photovoltaic cell photoinduced charge separation quenching