Facile synthesis of composition-tuned ZnO/Zn x Cd1-x Se nanowires for photovoltaic applications
© Luo et al.; licensee Springer. 2015
Received: 2 February 2015
Accepted: 28 March 2015
Published: 15 April 2015
ZnO/Zn x Cd1-x Se coaxial nanowires (NWs) have been successfully synthesized by combining chemical vapor deposition with a facile alternant physical deposition method. The shell composition x can be precisely tuned in the whole region (0 ≤ x ≤ 1) by adjusting growth time ratio of ZnSe to CdSe. As a result, the effective bandgaps of coaxial nanowires were conveniently modified from 1.85 eV to 2.58 eV, almost covering the entire visible spectrum. It was also found that annealing treatment was in favor of forming the mixed crystal and improving crystal quality. An optimal temperature of 350°C was obtained according to our experimental results. Additionally, time resolved photo-luminescence spectra revealed the longest carrier lifetime in ZnO/CdSe coaxial nanowires. As a result, the ZnO/CdSe nanowire cell acquired the maximal conversion efficiency of 2.01%. This work shall pave a way towards facile synthesis of ternary alloys for photovoltaic applications.
KeywordsZnO/ZnCdSe coaxial nanowires Composition tuning Alternant physical deposition Solar cell
One-dimensional nanostructures have attracted considerable attention due to their unique advantages and potential applications in photovoltaic devices [1-3]. In particular, nanostructured oxide semiconductors, such as ZnO nanowires (NWs) and TiO2 nanocrystals, have been widely applied to photo-electrochemical (PEC) cells or solar cells owing to the low cost and high stability against photocorrosion, and mature fabrication techniques [4-13]. However, these oxide semiconductors have a relatively wide bandgap and can not efficiently absorb sunlight in visible region, yielding a low efficiency. A series of semiconductor nanocrystals, such as ZnSe , CdSe , CdS , CdSeTe , ZnCdSe , and ZnCdTe , have been coated onto the surface of ZnO or TiO2 to expand photoresponse. As compared with binary alloys, ternary materials are the more efficient sensitizers due to their tunable bandgaps and band structures [17-26]. Many efforts have been devoted to tune their compositions by different fabrication methods. For instance, Xu et al. fabricated type II ZnO/Zn x Cd1-x Se nanocables via an ion-exchange approach ; Ruchi et al. prepared TiO2/Zn x Cd1-x Se nanotubes through a successive ionic layer adsorption and reaction technique ; Li et al. synthesized Zn x Cd1-x Se shell layer on ZnO NWs by chemical vapor deposition (CVD) method . In spite of these efforts, the composition of ternary alloys can not be conveniently controlled because of the different ion concentrations in solution method or the different saturated vapor pressures of elements in vapor method. Hence, up to date, it is still a challenge to develop a simple and facile route to fabricate composition-tuned ternary alloys.
In this work, we successfully synthesized Zn x Cd1-x Se shell layers on ZnO NWs with tunable compositions (0 ≤ x ≤ 1) by an alternant physical deposition method. The scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), transmission analysis and time resolved photo-luminescence (TRPL) were performed to investigate their morphologies, crystal structures, compositions, and optical properties, respectively. It has been found that the composition of ZnCdSe shell could be conveniently and precisely controlled by adjusting growth time ratio of ZnSe to CdSe. Meanwhile, solar cells based on different ZnO/ZnCdSe coaxial NWs were assembled and their performances were evaluated as well. This work opens a novel avenue for facile synthesis of sophisticated ternary alloys.
Synthesis of ZnO NWs and Zn x Cd1-x Se shells
For photovoltaic applications, the as-prepared ZnO/Zn x Cd1-x Se coaxial NWs were used as the working electrodes. Nanostructured counter electrode was prepared by sputtering a thin layer of Cu2S on aluminum zinc oxide (AZO) glass. The two electrodes were sealed together with a 60-μm-thick polypropylene spacer (Surlyn, DuPont, Wilmington, USA), and the internal space of the cell was filled with a polysulfide electrolyte (1.0 M S, 1.0 M Na2S, and 0.1 M NaOH in deionized water). The active area of the solar cell was about 0.5 cm2.
The morphologies of the as-prepared ZnO and ZnO/Zn x Cd1-x Se NWs were measured with a field emission SEM (LEO 1530, Zeiss, Thornwood, USA). The structures and compositions were characterized by XRD (X’Pert PRO, PANalytical, Chapel Hill, USA) and TEM (Tecnai F30, Fei, Hillsboro, USA). The transmission spectra were measured using a Varian Cary 5000 UV-vis NIR spectrophotometer (Agilent, Santa Clara, USA). TRPL measurements were carried out in an Edinburgh FLS920 spectrofluorometer (Edinburgh Instruments Ltd, Livingston, UK) at room temperature. The detected energies for different samples were in accordance with their estimated bandgaps (1.85, 1.98, 2.05, 2.18, 2.34, and 2.58 eV). Current density-voltage (J-V) characteristics of solar cells were recorded under AM1.5 solar illumination (100 mW · cm−2). The incident photon-to-current conversion efficiency (IPCE) was measured on a broadband spectroscopy system consisting of a grating monochromator (Spectra Pro-750i, Acton Research Corporation, Trenton, USA), a 100 W bromine-tungsten lamp, and a lock-in amplifier (SR830 DSP, Stanford Research Systems, Sunnyvale, USA), by comparing with a reference Si and Ge cells.
Results and discussion
Performances of solar cells measured under AM1.5 (100 mW · cm −2 )
J sc (mA · cm −2 )
V oc (V)
In summary, we demonstrated that the ZnO/Zn x Cd1-x Se coaxial NWs with tunable shell compositions could be facilely synthesized by combining CVD with an alternant physical deposition method. Morphological studies by SEM show that the entire ZnO nanowire can be coated with a relatively uniform shell. XRD and TEM results disclosed that the composition x can be precisely controlled by adjusting growth time ratio of ZnSe to CdSe; meanwhile, annealing treatment under a suitable temperature is beneficial for forming ternary alloys and improving crystal quality. Transmission analysis indicated that the effective bandgap of ternary alloys could be modified in a wide range from 1.85 eV to 2.58 eV by composition tuning. Time resolved photo-luminescence spectra revealed that carrier lifetime of ZnO/Zn x Cd1-x Se coaxial NWs exponentially decreases with the increase of Zn content. A maximal conversion efficiency of 2.01% was achieved in ZnO/CdSe nanowire cell. This work provides a facile method to synthesis ternary alloys with tunable composition.
The work was supported by ‘973’ Program (No. 2012CB619301 and 2011CB925600), the National Natural Science Foundations of China (No. 61106008 and 61227009), the Natural Science Foundations of Fujian Province, and the fundamental research funds for the central universities.
- Xu S, Qin Y, Xu C, Wei YG, Yang RS, Wang ZL. Self-powered nanowire devices. Nat Nanotechnol. 2010;5:366–73.View ArticleGoogle Scholar
- Wang GM, Wang HY, Ling YC, Tang YC, Yang XY, Fitzmorris RC, et al. Hydrogen-treated TiO2 nanowire arrays for photoele-ctrochemical water splitting. Nano Lett. 2011;11:3026–33.View ArticleGoogle Scholar
- Cao YY, Wu ZM, Ni JC, Waseem AB, Li J, Li SP, et al. Type-II core/shell nanowire heterostructures and their photovoltaic applications. Nano-Micro Lett. 2012;4:135–41.View ArticleGoogle Scholar
- Hong Y, Tian CG, Jiang BJ, Wu AP, Zhang Q, Tian GH, et al. Facile synthesis of sheet-like ZnO assembly composed of small ZnO particles for highly efficient photocatalysis. J Mater Chem A. 2013;1:5700–8.View ArticleGoogle Scholar
- Chong E, Kim S, Choi JH, Choi DG, Jung JY, Jeong JH, et al. Interior-architectured ZnO nanostructure for enhanced electrical conductivity via stepwise fabrication process. Nanoscale Res Lett. 2014;9:428.View ArticleGoogle Scholar
- Nezu S, Larramona G, Choné C, Jacob A, Delatouche B, Pe’re’ D, et al. Light soaking and gas effect on nanocrystalline TiO2/Sb2S3/CuSCN photovoltaic cells following extremely thin absorber concept. J Phys Chem C. 2010;114:6854–9.View ArticleGoogle Scholar
- Zaera RT, Ryan MA, Katty A, Hodes G, Bastide S, Clément CL. Fabrication and characterization of ZnO nanowires/CdSe/CuSCN eta-solar cell. C R Chimie. 2006;9:717–29.View ArticleGoogle Scholar
- Consonni V, Renet S, Garnier J, Gergaud P, Artús L, Michallon J, et al. Improvement of the physical properties of ZnO/CdTe core-shell nanowire arrays by CdCl2 heat treatment for solar cells. Nanoscale Res Lett. 2014;9:222.View ArticleGoogle Scholar
- Foo KL, Hashim U, Muhammad K, Voon CH. Sol– gel synthesized zinc oxide nanorods and their structural and optical investigation for optoelectronic application. Nanoscale Res Lett. 2014;9:429.View ArticleGoogle Scholar
- Park J, Ryu H, Son T, Yeon S. Epitaxial growth of ZnO/InN core/shell nanostructures for solar cell applications. Appl Phys Express. 2012;5:101201.View ArticleGoogle Scholar
- Zak AK, Hashim AM, Darroudi M. Optical properties of ZnO/BaCO3 nanocomposites in UV and visible regions. Nanoscale Res Lett. 2014;9:399.View ArticleGoogle Scholar
- Yan JF, Zhou F. TiO2 nanotubes: structure optimization for solar cells. J Mater Chem. 2011;21:9406–18.View ArticleGoogle Scholar
- Wang YJ, Wang QS, Zhan XY, Wang FM, Safdar M, He J. Visible light driven type II heterostructures and their enhanced photocatalysis properties: a review. Nanoscale. 2013;5:8326–39.View ArticleGoogle Scholar
- Wu ZM, Zhang Y, Zheng JJ, Lin XG, Chen XH, Huang BW, et al. An all-inorganic type-II heterojunction array with nearly full solar spectral response based on ZnO/ZnSe core/shell nanowires. J Mater Chem. 2011;21:6020–6.View ArticleGoogle Scholar
- Wang H, Wang T, Wang XN, Liu R, Wang BY, Wang HB, et al. Double-shelled ZnO/CdSe/CdTe nanocable arrays for photovoltaic applications: microstructure evolution and interfacial energy alignment. J Mater Chem. 2012;22:12532.View ArticleGoogle Scholar
- Lee YL, Chang CH. Efficient polysulfide electrolyte for CdS quantum dot-sensitized solar cells. J Power Sources. 2008;185:584–8.View ArticleGoogle Scholar
- Pan ZX, Zhao K, Wang J, Zhang H, Feng YY, Zhong XH. Near infrared absorption of CdSe x Te1–x alloyed quantum dot sensitized solar cells with more than 6% efficiency and high stability. ACS Nano. 2013;7:5215–22.View ArticleGoogle Scholar
- Myung Y, Kang JH, Choi JW, Jang DM, Park J. Polytypic ZnCdSe shell layer on a ZnO nanowire array for enhanced solar cell efficiency. J Mater Chem. 2012;22:2157–65.View ArticleGoogle Scholar
- Zhan XY, Wang QS, Wang FM, Wang YJ, Wang ZX, Cao JL, et al. Composition-tuned ZnO/Zn x Cd1−x Te core/shell nanowires array with broad spectral absorption from UV to NIR for hydrogen generation. ACS Appl Mater Interfaces. 2014;6:2878–83.View ArticleGoogle Scholar
- Myung Y, Myung DJ, Sung TK, Sohn YJ, Jung GB, Cho YJ, et al. Composition-tuned ZnO-CdSSe core-shell nanowire arrays. ACS Nano. 2010;4:3789–800.View ArticleGoogle Scholar
- Panda SK, Hickey SG, Waurisch C, Eychmuller A. Gradated alloyed CdZnSe nanocrystals with high luminescence quantums yields and stability for optoelectronic and biological application. J Mater Chem. 2011;21:11550–5.View ArticleGoogle Scholar
- Sung TK, Kang JH, Jang DM, Myung Y, Jung GB, Kim HS, et al. CdSSe layer-sensitized TiO2 nanowire arrays as efficient photoelectrode. J Mater Chem. 2011;21:4553–61.View ArticleGoogle Scholar
- Chen ZH, Yeung SY, Li H, Qian JC, Zhang WJ, Li YY, et al. Controlled growth of ZnO/Zn1-x Pb x Se core-shell nanowires and their interfacial electronic energy alignment. Nanoscale. 2012;4:3154–61.View ArticleGoogle Scholar
- Shu T, Zhou ZM, Wang H, Liu GH, Xiang P, Rong YG, et al. Efficient quantum dot-sensitized solar cell with tunable energy band CdSe x S1-x quantum dots. J Mater Chem. 2012;22:10525–9.View ArticleGoogle Scholar
- Li HX, Cheng CW, Li XL, Liu JP, Guan C, Tay YY, et al. Composition-graded Zn x Cd1−x Se@ZnO core − shell nanowire array electrodes for photoelectrochemical hydrogen generation. J Phys Chem C. 2012;116:3802–7.View ArticleGoogle Scholar
- Groeneveld E, Berkum SV, Schooneveld MMV, Gloter A, Meeldijk JD, Heuvel DJVD, et al. Highly luminescent (Zn, Cd)Te/CdSe colloidal heteronanowires with tunable electron–hole overlap. Nano Lett. 2012;12:749–57.View ArticleGoogle Scholar
- Xu J, Yang X, Wang HK, Chen X, Luan CY, Xu ZX, et al. Arrays of ZnO/Zn x Cd1-x Se nanocables: band gap engineering and photovoltaic applications. Nano Lett. 2011;11:4138–43.View ArticleGoogle Scholar
- Gakhar R, Merwin A, Summers K, Pilli SK, Chidambaram D. Application of Zn x Cd1-x Se-sensitized TiO2 nanotube arrays as photoanodes for solar cells. J Mater Chem A. 2014;2:10116.View ArticleGoogle Scholar
- Fernandes JA, Migowski P, Fabrim Z, Feil AF, Rosa G, Khan S, et al. TiO2 nanotubes sensitized with CdSe via RF magnetron sputtering for photoelectrochemical applications under visible light irradiation. Phys Chem Chem Phys. 2014;16:9148.View ArticleGoogle Scholar
- Yoon YJ, Park KS, Heo JH, Park JG, Nahm S, Choi KJ. Synthesis of Zn x Cd1-x Se (0 ≤ x ≤1) alloyed nanowires for variable-wavelength photodetectors. J Mater Chem. 2010;20:2386–90.View ArticleGoogle Scholar
- Venugopal R, Lin PI, Chen YT. Photoluminescence and Raman scattering from catalytically grown Zn x Cd1-x Se alloy nanowires. J Phys Chem B. 2006;110:11691–6.View ArticleGoogle Scholar
- Denton AR, Ashcroft NW. Vegard’s law. Phys Rev A. 1991;43:3161–4.View ArticleGoogle Scholar
- Xu J, Tang YB, Chen X, Luan CY, Zhang WF, Zapien JA, et al. Synthesis of homogeneously alloyed Cu2-x (S y Se1-y ) nanowire bundles with tunable compositions and bandgaps. Adv Funct Mater. 2010;20:4190–5.View ArticleGoogle Scholar
- Wang K, Chen JJ, Zhou WL, Zhang Y, Yan YF, Pern J, et al. Direct growth of highly mismatched type II ZnO/ZnSe core/shell nanowire arrays on transparent conducting oxide substrates for solar cell applications. Adv Mater. 2008;20:3248–53.View ArticleGoogle Scholar
- Lunz U, Kuhn J, Goschenhofer F, Schüssler U, Einfeldt S, Becker CR, et al. Temperature dependence of the energy gap of zincblende CdSe and Cd1-x Zn x Se epitaxial layers. J Appl Phys. 1996;80:6861.View ArticleGoogle Scholar
- Hill R, Richardson D. The variatian of energy gap with composition in ZnS-Te alloys. J Phys C Solid State Phys. 1973;6:L115.View ArticleGoogle Scholar
- Richardson D, Hill R. The origins of energy gap bowings in substitutional semiconductor alloys. J Phys C Solid State Phys. 1972;5:821.View ArticleGoogle Scholar
- Yan KY, Zhang LX, Qiu JH, Qiu YC, Zhu ZL, Wang JN, et al. A quasi-quantum well sensitized solar cell with accelerated charge separation and collection. J Am Chem Soc. 2013;135:9531–9.View ArticleGoogle Scholar
- Lin Y, Zhou R, Lan J, Zhang QF, Cao GZ, Zhu JG. Efficient band alignment for Zn x Cd1-x Se QD-sensitized TiO2 solar cells. J Mater Chem. 2014;2(10):3669–76.View ArticleGoogle Scholar
- Wu ZM, Wang WP, Cao YY, He JL, Luo Q, Wassem AB, et al. A beyond near-infrared response in a wide-bandgap ZnO/ZnSe coaxial nanowire solar cell by pseudomorphic layers. J Mater Chem A. 2014;2:1457–14576.Google Scholar
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