Charge separation and ultraviolet photovoltaic conversion of ZnO quantum dots conjugated with graphene nanoshells

Dong Ick Son, Byoung Wook Kwon, Jeong Do Yang, Dong Hee Park, Won Seon Seo, Hyunbok Lee, Yeonjin Yi, Chang Lyoul Lee, Won Kook Choi

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

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 (η) were 196. 4 μA/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. Graphical abstract: [Figure not available: see fulltext.]

Original languageEnglish
Pages (from-to)747-761
Number of pages15
JournalNano Research
Volume5
Issue number11
DOIs
Publication statusPublished - 2012 Nov 1

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Nanoshells
Graphite
Graphene
Semiconductor quantum dots
Conversion efficiency
Quenching
Chemical bonds
Molecular orbitals
Open circuit voltage
High resolution transmission electron microscopy
Conduction bands
Functional groups
Density functional theory

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Electrical and Electronic Engineering

Cite this

Son, D. I., Kwon, B. W., Yang, J. D., Park, D. H., Seo, W. S., Lee, H., ... Choi, W. K. (2012). Charge separation and ultraviolet photovoltaic conversion of ZnO quantum dots conjugated with graphene nanoshells. Nano Research, 5(11), 747-761. https://doi.org/10.1007/s12274-012-0258-6
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. / Charge separation and ultraviolet photovoltaic conversion of ZnO quantum dots conjugated with graphene nanoshells. In: Nano Research. 2012 ; Vol. 5, No. 11. pp. 747-761.
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abstract = "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 (η) were 196. 4 μA/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. Graphical abstract: [Figure not available: see fulltext.]",
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Son, DI, Kwon, BW, Yang, JD, Park, DH, Seo, WS, Lee, H, Yi, Y, Lee, CL & Choi, WK 2012, 'Charge separation and ultraviolet photovoltaic conversion of ZnO quantum dots conjugated with graphene nanoshells', Nano Research, vol. 5, no. 11, pp. 747-761. https://doi.org/10.1007/s12274-012-0258-6

Charge separation and ultraviolet photovoltaic conversion of ZnO quantum dots conjugated with graphene nanoshells. / 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.

In: Nano Research, Vol. 5, No. 11, 01.11.2012, p. 747-761.

Research output: Contribution to journalArticle

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T1 - Charge separation and ultraviolet photovoltaic conversion of ZnO quantum dots conjugated with graphene nanoshells

AU - Son, Dong Ick

AU - Kwon, Byoung Wook

AU - Yang, Jeong Do

AU - Park, Dong Hee

AU - Seo, Won Seon

AU - Lee, Hyunbok

AU - Yi, Yeonjin

AU - Lee, Chang Lyoul

AU - Choi, Won Kook

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N2 - 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 (η) were 196. 4 μA/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. Graphical abstract: [Figure not available: see fulltext.]

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