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/cm2, 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
Similar content being viewed by others
References
Schön, J. H.; Kloc, Ch.; Bucher, E.; Batlogg B. Efficient organic photovoltaic diodes based on doped pentacene. Nature 2000, 403, 408–410.
Peumans, P.; Uchida S.; Forrest, S. R. Efficient bulk heterojunction photovoltaic cells using small-molecular-weight organic thin films. Nature 2003, 425, 158–162.
Huynh, W. U.; Dittmer, J. J.; Alivisatos, A. P. Hybrid nanorod-polymer solar cells. Science 2002, 295, 2425–2427.
Seol, M.; Kim, H.; Tak, Y.; Yong, K. Novel nanowire array based highly efficient quantum dot sensitized solar cell. Chem. Commun. 2010, 46, 5521–5523.
Chang, C. H.; Lee, Y. L. Chemical bath deposition of CdS quantum dots onto mesoscopic TiO2 films for application in quantum-dot-sensitized solar cells. Appl. Phys. Lett. 2007, 91, 053503.
Chen, J.; Song, J. L.; Sun, X. W.; Deng, W. Q.; Jiang, C. Y.; Lei, W.; Huang, J. H.; Liu, R. S. An oleic acid-capped CdSe quantum-dot sensitized solar cell. Appl. Phys. Lett. 2009, 94, 153115.
Gao, X. F.; Li, H. B.; Sun, W. T.; Chen, Q.; Tang, F. Q.; Peng, L. M. CdTe Quantum Dots-Sensitized TiO2 Nanotube Array Photoelectrodes. J. Phys. Chem. C. 2009, 113, 7531–7535.
Lee, Y. L.; Lo, Y. S. Highly efficient quantum-dot-sensitized solar cell based on co-sensitization of CdS/CdSe. Adv. Funct. Mater., 2009, 19, 604–609.
Sun, W. T.; Yu, Y.; Pan, H. Y.; Gao, X. F.; Chen, Q.; Peng, L. M. CdS quantum dots sensitized TiO2 nanotube-array photoelectrodes. J. Am. Chem. Soc., 2008, 130, 1124–1125.
Plass, P.; Pelet, S.; Krueger, J.; Grätzel, M.; Bach, U. Quantum dot sensitization of organic-inorganic hybrid solar cells. J. Phys. Chem. B 2002, 106, 7578–7580.
Zaban, A.; Mićić, O. I.; Gregg, B. A.; Nozik, A. J. Photosensitization of nanoporous TiO2 electrodes with InP quantum dots. Langmuir 1998, 14, 3153–3156.
Li, F.; Son, D. I.; Kim, T. W.; Ryu, E.; Kim, S. W.; Lee, S. K.; Cho, Y. H. Photovoltaic cells fabricated utilizing core-shell CdSe/ZnSe quantum dot/multiwalled carbon nanotube heterostructures. Appl. Phys. Lett. 2009, 95, 061911.
Yang, R. D.; Tripathy, S.; Li, Y.; Sue, H. J. Photoluminescence and micro-Raman scattering in ZnO nanoparticles: The influence of acetate adsorption. Chem. Phys. Lett., 2005, 411, 150–154.
Chen, Y.; Bagnall, D. M.; Koh, H. J.; Park, K. T.; Hiraga, K.; Zhu, Z.; Yao, T. Plasma assisted molecular beam epitaxy of ZnO on c-plane sapphire: Growth and characterization. J. Appl. Phys. 1998, 84, 3912.
Biju, V.; Itoh, T.; Baba, Y.; Ishikawa, M. Quenching of photoluminescence in conjugates of quantum dots and single-walled carbon nanotube. J. Phys. Chem. B. 2006, 110, 26068–26074.
Coe, S.; Woo, W. K.; Bawendi, M.; Bulović, V. Electro-luminescence from single monolayers of nanocrystals in molecular organic devices. Nature 2002, 420, 800–803.
Li, F.; Son, D. I.; Seo, S. M.; Cha, H. M.; Kim, H. J.; Kim, B. J.; Jung, J. H.; Kim, T. W. Organic bistable devices based on core/shell CdSe/ZnS nanoparticles embedded in a conducting poly(N-vinylcarbazole) polymer layer. Appl. Phys. Lett. 2007, 91, 122111.
Sariciftci, N. S.; Smilowitz, L.; Heeger, A. J.; Wudl, F. Photoinduced electron transfer from a conducting polymer to buckminsterfullerene. Science 1992, 258, 1474–1476.
Kraabel, B.; McBranch, D.; Sariciftci, N. S.; Moses, D.; Heeger, A. J. Ultrafast spectroscopic studies of photoinduced electron transfer from semiconducting polymers to C60. Phys. Rev. B 1994, 50, 18543–18552.
Li, F.; Son, D. I.; Cho, S. H.; Kim, W. T.; Kim, T. W. Flexible photovoltaic cells fabricated utilizing ZnO quantum dot/carbon nanotube heterojunctions. Nanotechnology 2009, 20, 155202.
Son, D. I.; Kwon, B. W.; Yang, J. D.; Park, D. H.; Angadi, B.; Choi, W. K. High efficiency ultraviolet photovoltaic cells based on ZnO-C60 core-shell QDs with organic-inorganic multilayer structure. J. Mater. Chem. 2012, 22, 816–819.
Jannik, C. M.; Geim, A. K.; Katsnelson, M. I.; Novoselov, K. S.; Booth, T. J.; Roth, S. The structure of suspended graphene sheets. Nature 2007, 446, 60–63.
Son, D. I.; Kwon, B. W.; Park, D. H.; Seo, W. S.; Yi, Y.; Angadi, B.; Lee, C. L.; Choi, W. K. Emissive ZnO-graphene quantum dots for white-light-emitting diodes. Nat. Nanotech. 2012, 7, 465–471.
Son, D. I.; Kim, T. W.; Shim, J. H.; Jung, J. H.; Lee, D. U.; Lee, J. M.; Park, W. I.; Choi, W. K. Flexible organic bistable devices based on graphene embedded in an insulating poly(methyl methacrylate) polymer layer. Nano Lett. 2010, 10, 2441–2447.
Lahaye, R. J. W. E.; Jeong, H. K.; Park, C. Y.; Lee, Y. H. Density functional theory study of graphite oxide for different oxidation levels. Phys. Rev. B 2009, 79, 125435.
Mohiuddin, T. M. G.; Lombardo, A.; Nair, R. R.; Bonetti, A.; Savini, G.; Jalil, R.; Bonini, N.; Basko, D. M.; Galiotis, C.; Marzari, N.; Novoselov, K. S.; Geim, A. K.; Ferrari, A. C. Uniaxial strain in graphene by Raman spectroscopy: G peak splitting, Grüneisen parameters, and sample orientation. Phys. Rev. B 2009, 79, 205433.
Ni, Z. H.; Yu, T.; Lu, Y. H.; Wang, Y. Y.; Feng, Y. P.; Shen, Z. X. Uniaxial strain on graphene: Raman spectroscopy study and band-gap opening. ACS Nano, 2008, 2, 2301–2305.
Fan, Z. J.; Kai, W.; Yan, J.; Wei, T.; Zhi, L. J.; Feng, J.; Ren, Y. M.; Song, L. P.; Wei, F. Facile synthesis of graphene nanosheets via Fe reduction of exfoliated graphite oxide. ACS Nano, 2011, 5, 191–198.
Pan, B.; Cui, D.; Ozkan, C. S.; Ozkan, M.; Xu, P.; Huang, T.; Liu, F.; Chen, H.; Li, Q.; He, R.; Gao, F. Effects of carbon nanotubes on photoluminescence properties of quantum dots. J. Phys. Chem. C 2008, 112, 939–944.
Beek, W. J. E.; Wienk, M. M.; Janssen, R. A. J. Efficient hybrid solar cells from zinc oxide nanoparticles and conjugated polymers. Adv. Mater. 2004, 16, 1009–1013.
Son, D. I.; Park, D. H.; Choi, W. K.; Cho, S. H.; Kim, W. T.; Kim, T. W. Carrier transport in flexible organic bistable devices of ZnO nanoparticles embedded in an insulating poly(methyl methacrylate) polymer layer. Nanotechnology 2009, 20, 195203.
Wang, G.; Yang, J.; Park, J.; Gou, X.; Wang, B.; Liu, H.; Yao, J. Facile synthesis and characterization of graphene nanosheets. J. Chem. Phys. C 2008, 112, 8192–8195.
Moon, I. K.; Lee, J.; Ruoff, R. S.; Lee, H. Reduced graphene oxide by chemical graphitization. Nat. Commun. 2010, 1, 1–6.
Cote, L. J.; Kim, F.; Huang, J. Langmuir-Blodgett assembly of graphite oxide single layers. J. Am. Chem. Soc. 2009, 131, 1043–1049.
Park, S.; An, J.; Jung, I.; Piner, R. D.; An, S. J.; Li, X.; Velamakanni, A.; Ruoff, R. S. Colloidal suspensions of highly reduced graphene oxide in a wide variety of organic solvents. Nano Lett. 2009, 9, 1593–1597.
Li, D.; Müller, M. B.; Gilje, S.; Kaner, R. B.; Wallace, G. G. Processable aqueous dispersions of graphene nanosheets. Nat. Nanotech. 2008, 3, 101–105.
Higginbotham, A. L.; Kosynkin, D. V.; Sinitskii, A.; Sun, Z.; Tour, J. M. Lower-defect graphene oxide nanoribbons from multiwalled carbon nanotubes. ACS Nano 2010, 4, 2059–2069.
Lomeda, J. R.; Doyle, C. D.; Kosynkin, D. V.; Hwang, W. F.; Tour, J. M. Diazonium functionalization of surfactant-wrapped chemically converted graphene sheets. J. Am. Chem. Soc. 2008, 130, 16201–16206.
Yang, D.; Velamakanni, A.; Bozoklu, G.; Park, S.; Stoller, M.; Piner, R. D.; Stankovich, S.; Jung, I.; Field, D. A.; Ventrice, Jr. C. A.; Ruoff, R. S. Chemical analysis of graphene oxide films after heat and chemical treatments by X-ray photoelectron and micro-Raman spectroscopy. Carbon 2009, 47, 145–152.
Fan, Z. J.; Kai, W.; Yan, J.; Wei, T.; Zhi, L. J.; Feng, J.; Ren, Y. M.; Song, L. P.; Wei, F. Facile synthesis of graphene nanosheets via Fe reduction of exfoliated graphite oxide. ACS Nano 2011, 5, 191–198.
Mattevi, C.; Eda, G.; Agnoli, S.; Miller, S.; Mkhoyan, K. A.; Celik, O.; Mastrogiovanni, D.; Granozzi, G.; Garfunkel, E.; Chhowalla, M. Evolution of electrical, chemical, and structural properties of transparent and conducting chemically derived graphene thin films. Adv. Func. Mater. 2009, 19, 2577–2583.
Tang, L.; Wang, Y.; Li, Y.; Feng, H.; Lu, J.; Li, J. Preparation, structure, and electrochemical properties of reduced graphene sheet films. Adv. Funct. Mater. 2009, 19, 2782–2789.
Nakajima, T.; Mabuchi, A.; Hagiwara, R. A new structure model of graphite oxide. Carbon 1988, 26, 357–361.
Gaussian 03, Revision C.02, Frisch, M. G.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A.; Vreven, Jr. T.; Kudin, K. N.; Burant, J. C., et al. Gaussian Inc., Wallingford CT, 2004.
Park, S.; Ruoff, R. S. Chemical methods for the production of graphenes. Nat. Nanotech. 2009, 7, 217–224.
Choulis, S. A.; Choong, V. E.; Patwardhan, A.; Mathai, M. K.; So, F. Interface Modification to improve hole-injection properties in organic electronic devices. Adv. Funct. Mater. 2006, 16, 1075–1080.
Sun, Q.; Wang, Y. A.; Li, L. S.; Wang, D.; Zhu, T.; Xu, J.; Yang, C.; Li, Y. F. Bright, multicoloured light-emitting diodes based on quantum dots. Nat. photonics, 2007, 1, 717–722.
Yang, H. Y.; Son, D. I.; Kim, T. W.; Lee, J. M.; Park, W. I. Enhancement of the photocurrent in ultraviolet photo-detectors fabricated utilizing hybrid polymer-ZnO quantum dot nanocomposites due to an embedded graphene layer. Org. Electron. 2010, 11, 1313–1317.
Author information
Authors and Affiliations
Corresponding author
Electronic supplementary material
Rights and permissions
About this article
Cite this article
Son, D.I., Kwon, B.W., Yang, J.D. et al. Charge separation and ultraviolet photovoltaic conversion of ZnO quantum dots conjugated with graphene nanoshells. Nano Res. 5, 747–761 (2012). https://doi.org/10.1007/s12274-012-0258-6
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s12274-012-0258-6