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Colloidal synthesis of Cu2FeSnSe4 nanocrystals for solar energy conversion
Materials Letters 136 (2014) 306–309
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Colloidal synthesis of Cu2FeSnSe4 nanocrystals for solar energy conversion Yike Liu a, Mengmeng Hao a, Jia Yang a, Liangxing Jiang a,n, Chang Yan b, Chun Huang a, Ding Tang a, Fangyang Liu a,b,nn, Yexiang Liu a a b
School of Metallurgy and Environment, Central South University, Changsha 410083, China Australian Centre for Advanced Photovoltaics, School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney, Australia
art ic l e i nf o
a b s t r a c t
Article history: Received 22 July 2014 Accepted 14 August 2014 Available online 21 August 2014
Cu2FeSnSe4 (CFTSe) nanocrystals have been synthesized by a hot-injection method. The structure of prepared CFTSe nanocrystals is determined by XRD, high resolution TEM image, and SAED pattern. The composition of the CFTSe nanocrystals is confirmed from the results of EDS and XPS. Results clearly prove the formation of CFTSe nanocrystals using the hot-injection method in this study. A band gap of 1.60 70.02 eV for CFTSe nanocrystals is obtained from the UV–vis–NIR data. Moreover, the corresponding CFTSe nanocrystals-film shows a clear photoresponse in photoelectrochemical measurement. Our work illustrates that CFTSe nanocrystals have potential application in the field of solar energy conversion. & 2014 Elsevier B.V. All rights reserved.
Keywords: Nanocrystalline materials Thin films Solar energy materials
1. Introduction Among numerous thin film solar cells, Cu(In,Ga)Se2 (CIGS) thin film solar cell has attracted tremendous attention owing to its high power conversion efficiency and good stability [1]. However, the scarcity of indium and gallium and increasing price of them become the bottlenecks for the large-scale, cost-effective production of the material. Theoretical calculations have demonstrated that the presence of tetrahedrally coordinated copper atoms is a critical feature for the exhibition of good photovoltaic properties of chalcogenide absorbers [2]. Hence, a class of chalcogenide semiconductors Cu2FeSn(S, Se)4 (CFTSSe) [3–5] has been regarded as a promising alternative due to their analogous crystal structures to CIGS facilitating the formation of favorable intermediate phase [6] and earth-abundant composition. Yan et al. used a simple hotinjection method to synthesize Cu2FeSnS4 (CFTS) nanocrystals which show a notable and stable photo-electrochemical response [4]. Huang et al. reported that Cu2(FexZn1 x)SnS4 nanocrystals were synthesized by the hot injection method [7]. Tunable band gap and structure of Cu2(Zn, Fe)SnS4 thin films for photovoltaic application have been fabricated using a chemical spray pyrolysis method [8].
n
Corresponding author. Tel. þ86 731 88830474. Corresponding author at: School of Metallurgy and Environment, Central South University, Changsha 410083, China. Tel.: þ86 731 88830474. E-mail addresses: [email protected] (L. Jiang), [email protected] (F. Liu). nn
http://dx.doi.org/10.1016/j.matlet.2014.08.072 0167-577X/& 2014 Elsevier B.V. All rights reserved.
The investigation of pure selenide CFTSe is scarcely reported until now. For instance, bulk CFTSe were prepared and investigated by the melt and anneal technique [9,10]. The CFTSe sheets, which display P-type conductivity and valuable optical and electrical properties, have been synthesized using a solvothermal method by Cao et al. [11]. However, the synthesis of CFTSe nanomaterials, to the best of our knowledge, is still in progress and has not been reported in the literatures. Colloidal semiconductor nanocrystals have been proven to show great potential in future photonic and optoelectronic devices due to their novel size and shape-dependent properties [12,13]. On the other hand, the hot injection-based method has been employed widely for the preparation of numerous colloidal semiconductor nanocrystals because of its advantages such as high quality product, simplicity and short reaction time [14]. Here we first report the synthesis of CFTSe nanocrystals with a narrow size distribution by the hot injection method, which plays a key role in the fabrication of both nanocrystals-inks and nanocrystal arrays that can be used in the field of photovoltaics. The structure, morphology, composition and absorption spectra of the products are characterized using different methods. Moreover, the photo-responsiveness of CFTSe nanocrystals is studied using photoelectrochemical measurement and its potential application in the realm of solar energy conversion is discussed in detail. 2. Experimental section In a typical synthesis, the Se precursor was prepared by dissolving 5 mmol selenium powder into the mixture of 5 ml
Y. Liu et al. / Materials Letters 136 (2014) 306–309
oleylamine (OLA) and 7 mmol dimethylaminoborane (DMAB) at 110 1C, obtaining a colorless and transparent solution. 1.5 mmol copper (II) acetylacetonate (Cu(acac)2), 0.75 mmol iron (II) acetylacetonate (Fe(acac)2), 0.75 mmol tin(II) chloride (SnCl2), and 12 ml oleylamine were added into a three-neck flask (100 ml) connected to a Schlenk line. Then the temperature was raised up to around 130 1C under vacuum, stirring for degassing about an hour and purging thrice with Ar. The flask was then heated to 270 1C, where 3.5 ml of 1 M solution of Se/DMAB in oleylamine was injected. After injection, the solution turns dark, and the temperature was held at 270 1C for 15 min. After the reaction, the products were purified by precipitation–dispersion cycles utilizing toluene and ethanol (1:3 v/v). The synthesized CFTSe nanocrystals were characterized by transmission electron microscopy (TEM) and selected area electron diffraction (SAED) via a JEM 2100 F microscope at 200 kV accelerating voltage. The crystal structure and composition were characterized by X-ray diffraction (Riguaku 3014) and energydesperive X-ray spectroscopy (EDAX-GENSIS60S), respectively, using a dried thin film sample prepared by drop-casting the nanocrystal-ink. UV–vis–NIR spectra were carried out to evaluate the optical properties of CFTSe nanocrystals using an UV–vis–NIR HITACHI U-4100 spectrophotometer. The spectral bandwidth is 0.1 nm and sampling interval is 1.0 nm.
307
3. Results and discussions The structure of prepared CFTSe nanocrystals is determined by TEM, as shown in Fig. 1. It can be seen from Fig. 1(a) and (b) that irregular and faceted shape nanocrystals are obtained with an average diameter of 15.5 71.9 nm. In Fig. 1(c), high resolution transmission electron microscopy (HRTEM) image illustrates that the CFTSe nanocrystals have good crystallinity and lattice fringes with an interplanar spacing of 3.27 Å, which is in good coincidence with the (111) plane of cubic phase CFTSe (d111 ¼3.28 Å), demonstrating the nano-scale evidence for the structure of synthesized CFTSe nanocrystals. In addition, the lattice data calculated from SAED pattern of randomly chosen region of CFTSe nanocrystals agrees well with the lattice parameters of CFTSe (Fig. 1(d)). To further reveal the crystal structure of CFTSe nanocrystals, X-ray diffraction (XRD) is used for prepared samples. Fig. 2(a) shows the XRD pattern of the synthesized sample. It can be seen that the obtained sample is composed of cubic phase Cu2FeSnSe4 (JCPDS 270167). Five major peaks for thin film, at about 2θ ¼ 7.051, 44.961, 53.341, 65.631 and 72.361 corresponding to (111), (220), (311), (400) and (331), were identified [11]. No evidence of other impurities such as CuSe, SnSe, etc. can be found from the XRD pattern. The elemental composition of synthesized CFTSe nanocrystals was investigated using EDS analysis. The ratio of the compositional elements is
Fig. 1. (a, b) TEM images, (c) HRTEM image and (d) SEAD pattern of CFTSe nanocrystals.
308
Y. Liu et al. / Materials Letters 136 (2014) 306–309
estimated to be Cu/Fe/Sn/Se: 2.09/0.84/0.92/4, which suggests that composition of CFTSe nanocrystals is close to the stoichiometry of CFTSe. In order to clarify valence states of element Cu, Fe, Sn, and Se of the CFTSe nanocrystals, XPS characterization of the specific four elements was conducted. As shown in Fig. 3, the binding energies of Cu 2p, Fe 2p, Sn 3d, and Se 3d of the nanocrystals in the XPS are consistent with those reported in literatures [15,16]. The valence states of Cu, Fe, Sn and Se ions are þ1, þ2, þ4, and 2, respectively. Considering the large difference among Cu, Fe, and Sn precursor reactivity, in this research a novel Se precursor (a soluble
Fig. 2. XRD pattern of CFTSe nanocrystals.
alkylammonium selenide) with high activity, which has been employed at the previous work in our research [17,18], was used. It was found that the content of Se precursor played a critical role in controlling the phase pure of CFTSe nanocrystals. The results of experiments showed that the use of excess Se was necessary in order to obtain pure CFTSe nanocrystals. In addition, the size and size dispersion of the synthesized CFTSe were determined by the reaction temperature. Injection temperature higher than 285 1C resulted in uncontrolled growth of the nascent crystallites and synthesized non-uniform nanocrystals with wide size dispersion, while temperatures lower than 250 1C were insufficient to induce rapid nucleation. UV–vis–NIR absorption spectroscopy is used to evaluate the optical properties of the CFTSe nanocrystals and results are shown in Fig. 4(a). The optical band gap of the nanocrystals is estimated to be 1.60 70.02 eV by extrapolating the linear region of the plot of the absorbance squared versus energy. The value is higher than the previous literature for CFTSe sheets, which may result from the quantum confinement effect often observed for metal selenide nanocrystals [19]. This value is close to the band gap value of Cu2ZnSnS4 nanocrystals (1.50 eV) [20] and the optimal value for solar cell application [21]. In order to further evaluate the potential of this material for photo-electrical conversion applications, the photo-responsiveness of CFTSe nanocrystals was tested. The CFTSe nanocrystal thin films were prepared by directly drop-casting nanocrystal ink onto the ITO conductive glasses. The film was mounted to a custom built threeelectrode photoelectrochemical cell containing 0.5 M H2SO4 as the electrolyte solution. The graphite electrode and saturated calomel reference electrode (SCE) were used as counter electrode and reference electrode, respectively. The incident light intensity used
Fig. 3. The X-ray photoelectron spectroscopy (XPS) spectra of as-synthesized CFTSe nanocrystals: (a) Cu 2p; (b) Fe 2p; (c) Sn 3d; and (d) Se 2p.
Y. Liu et al. / Materials Letters 136 (2014) 306–309
309
Fig. 4. (a) UV–vis–NIR absorption spectrum of CFTSe nanocrystals. Inset is the plot of (ahv)2 versus hv (eV) for the nanocrystals. (b) The transient photocurrent spectrum for the obtained CFTSe films at 0.4 V versus SCE.
was 100 mW/cm2, and a bias voltage of 0.4 V versus SCE was applied. The photo-response from the CFTSe nanocrystals is shown in Fig. 4(b). The measured photocurrent density is as high as 0.07 mA cm 2, which is approximately five times than that for CFTS nanocrystals film in our previous report [4]. It remains constant over many cycles (8 cycles demonstrated here), showing good photoresponse and photostability of CFTSe nanocrystals film. This phenomenon demonstrates the potential application of CFTSe nanocrystals and /or the corresponding thin film in the field of solar energy conversion. 4. Conclusions A colloidal synthesis of CFTSe nanocrystals via the hot-injection method is presented. CFTSe nanocrystals possess an irregular, faceted shaped and a fairly narrow size distribution with an average particle size of 15.5 7 1.9 nm. The structure of the synthesized CFTSe nanocrystals is confirmed by HRTEM image, SAED pattern and XRD. The results of EDS and XPS confirmed the composition of the CFTSe nanocrystals. The use of excess of Se was found to be necessary to balancing relativity of cationic precursors to obtain pure CFTSe. In addition, the reaction temperature plays a critical role on the size and size dispersion of the nanocrystals. An optical band gap of 1.60 70.02 eV for CFTSe nanocrystals is estimated by UV–vis–NIR data. The CFTSe nanocrystals film yields a good photoresponse in photoelectrochemical tests. Our work demonstrates that the synthesized CFTSe nanocrystals have potential application in the field of solar energy conversion.
Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant nos. 51222403 and 51272292) and China Postdoctoral Science Foundation (Grant nos. 2012M511403, 2013T60777 and 2014T70788).
References [1] Green MA, Emery K, Hishikawa Y, Warta W, Dunlop ED. Prog Photovolt: Res Appl 2014;22:1–9. [2] Domain C, Laribi S, Taunier S, Guillemoles JF. J Phys Chem Solids 2003;64:1657–63. [3] Zhang X, Bao N, Ramasamy K, Wang YHA, Wang Y, Lin B, et al. Chem Commun 2012;48:4956–8. [4] Yan C, Huang C, Yang J, Liu F, Liu J, Lai Y, et al. Chem Commun 2012;48:2603–5. [5] Jiang X, Xu W, Tan R, Song W, Chen J. Mater Lett 2013;102:39–42. [6] Romanyuk YE, Marushko LP, Piskach LV, IV Kityk, Fedorchuk AO, Pekhnyo VI, et al. CrystEngComm 2013;15:4838. [7] Huang C, Chan Y, Liu F, Tang D, Yang J, Lai Y, et al. J Mater Chem A 2013;1:5402–7. [8] Khadka DB, Kim J. J Phys Chem C 2014. [9] Quintero E, Quintero M, Moreno E, Lara L, Morocoima M, Pineda F, et al. J Phys Chem Solids 2010;71:993–8. [10] Infante ER, Delgado JM, Rivera SAL. Mater Lett 1997;33:67–70. [11] Zhang B, Cao M, Li L, Sun Y, Shen Y, Wang L. Mater Lett 2013;93:111–4. [12] Hillhouse HW, Beard MC. Curr Opin Colloid Interface Sci 2009;14:245–59. [13] El-Sayed MA. Acc Chem Res 2004;37:326–33. [14] Donega CD, Liljeroth P, Vanmaekelbergh D. Small 2005;1:1152–62. [15] Norako ME, Brutchey RL. Chem Mate 2010;22:1613–5. [16] Liang X, Wei X, Pan D. J Nanomater 2012. [17] Liu Y, Liu F, Huang C, Lv X, Lai Y, Li J, et al. Mater Lett 2013;108:110–3. [18] Liu Y, Yang J, Gu E, Cao T, Su Z, Jiang L, et al. J Mater Chem A 2014;2:6363–7. [19] Tang J, Sargent EH. Adv Mater 2011;23:12–29. [20] Guo Q, Hillhouse HW, Agrawal R. J Am Chem Soc 2009;131:11672–3. [21] Goetzberger A, Hebling C, Schock HW. Mater Sci Eng R 2003;40:1–46.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Colloidal synthesis of Cu2FeSnSe4 nanocrystals for solar energy conversion Yike Liu a, Mengmeng Hao a, Jia Yang a, Liangxing Jiang a,n, Chang Yan b, Chun Huang a, Ding Tang a, Fangyang Liu a,b,nn, Yexiang Liu a a b
School of Metallurgy and Environment, Central South University, Changsha 410083, China Australian Centre for Advanced Photovoltaics, School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney, Australia
art ic l e i nf o
a b s t r a c t
Article history: Received 22 July 2014 Accepted 14 August 2014 Available online 21 August 2014
Cu2FeSnSe4 (CFTSe) nanocrystals have been synthesized by a hot-injection method. The structure of prepared CFTSe nanocrystals is determined by XRD, high resolution TEM image, and SAED pattern. The composition of the CFTSe nanocrystals is confirmed from the results of EDS and XPS. Results clearly prove the formation of CFTSe nanocrystals using the hot-injection method in this study. A band gap of 1.60 70.02 eV for CFTSe nanocrystals is obtained from the UV–vis–NIR data. Moreover, the corresponding CFTSe nanocrystals-film shows a clear photoresponse in photoelectrochemical measurement. Our work illustrates that CFTSe nanocrystals have potential application in the field of solar energy conversion. & 2014 Elsevier B.V. All rights reserved.
Keywords: Nanocrystalline materials Thin films Solar energy materials
1. Introduction Among numerous thin film solar cells, Cu(In,Ga)Se2 (CIGS) thin film solar cell has attracted tremendous attention owing to its high power conversion efficiency and good stability [1]. However, the scarcity of indium and gallium and increasing price of them become the bottlenecks for the large-scale, cost-effective production of the material. Theoretical calculations have demonstrated that the presence of tetrahedrally coordinated copper atoms is a critical feature for the exhibition of good photovoltaic properties of chalcogenide absorbers [2]. Hence, a class of chalcogenide semiconductors Cu2FeSn(S, Se)4 (CFTSSe) [3–5] has been regarded as a promising alternative due to their analogous crystal structures to CIGS facilitating the formation of favorable intermediate phase [6] and earth-abundant composition. Yan et al. used a simple hotinjection method to synthesize Cu2FeSnS4 (CFTS) nanocrystals which show a notable and stable photo-electrochemical response [4]. Huang et al. reported that Cu2(FexZn1 x)SnS4 nanocrystals were synthesized by the hot injection method [7]. Tunable band gap and structure of Cu2(Zn, Fe)SnS4 thin films for photovoltaic application have been fabricated using a chemical spray pyrolysis method [8].
n
Corresponding author. Tel. þ86 731 88830474. Corresponding author at: School of Metallurgy and Environment, Central South University, Changsha 410083, China. Tel.: þ86 731 88830474. E-mail addresses: [email protected] (L. Jiang), [email protected] (F. Liu). nn
http://dx.doi.org/10.1016/j.matlet.2014.08.072 0167-577X/& 2014 Elsevier B.V. All rights reserved.
The investigation of pure selenide CFTSe is scarcely reported until now. For instance, bulk CFTSe were prepared and investigated by the melt and anneal technique [9,10]. The CFTSe sheets, which display P-type conductivity and valuable optical and electrical properties, have been synthesized using a solvothermal method by Cao et al. [11]. However, the synthesis of CFTSe nanomaterials, to the best of our knowledge, is still in progress and has not been reported in the literatures. Colloidal semiconductor nanocrystals have been proven to show great potential in future photonic and optoelectronic devices due to their novel size and shape-dependent properties [12,13]. On the other hand, the hot injection-based method has been employed widely for the preparation of numerous colloidal semiconductor nanocrystals because of its advantages such as high quality product, simplicity and short reaction time [14]. Here we first report the synthesis of CFTSe nanocrystals with a narrow size distribution by the hot injection method, which plays a key role in the fabrication of both nanocrystals-inks and nanocrystal arrays that can be used in the field of photovoltaics. The structure, morphology, composition and absorption spectra of the products are characterized using different methods. Moreover, the photo-responsiveness of CFTSe nanocrystals is studied using photoelectrochemical measurement and its potential application in the realm of solar energy conversion is discussed in detail. 2. Experimental section In a typical synthesis, the Se precursor was prepared by dissolving 5 mmol selenium powder into the mixture of 5 ml
Y. Liu et al. / Materials Letters 136 (2014) 306–309
oleylamine (OLA) and 7 mmol dimethylaminoborane (DMAB) at 110 1C, obtaining a colorless and transparent solution. 1.5 mmol copper (II) acetylacetonate (Cu(acac)2), 0.75 mmol iron (II) acetylacetonate (Fe(acac)2), 0.75 mmol tin(II) chloride (SnCl2), and 12 ml oleylamine were added into a three-neck flask (100 ml) connected to a Schlenk line. Then the temperature was raised up to around 130 1C under vacuum, stirring for degassing about an hour and purging thrice with Ar. The flask was then heated to 270 1C, where 3.5 ml of 1 M solution of Se/DMAB in oleylamine was injected. After injection, the solution turns dark, and the temperature was held at 270 1C for 15 min. After the reaction, the products were purified by precipitation–dispersion cycles utilizing toluene and ethanol (1:3 v/v). The synthesized CFTSe nanocrystals were characterized by transmission electron microscopy (TEM) and selected area electron diffraction (SAED) via a JEM 2100 F microscope at 200 kV accelerating voltage. The crystal structure and composition were characterized by X-ray diffraction (Riguaku 3014) and energydesperive X-ray spectroscopy (EDAX-GENSIS60S), respectively, using a dried thin film sample prepared by drop-casting the nanocrystal-ink. UV–vis–NIR spectra were carried out to evaluate the optical properties of CFTSe nanocrystals using an UV–vis–NIR HITACHI U-4100 spectrophotometer. The spectral bandwidth is 0.1 nm and sampling interval is 1.0 nm.
307
3. Results and discussions The structure of prepared CFTSe nanocrystals is determined by TEM, as shown in Fig. 1. It can be seen from Fig. 1(a) and (b) that irregular and faceted shape nanocrystals are obtained with an average diameter of 15.5 71.9 nm. In Fig. 1(c), high resolution transmission electron microscopy (HRTEM) image illustrates that the CFTSe nanocrystals have good crystallinity and lattice fringes with an interplanar spacing of 3.27 Å, which is in good coincidence with the (111) plane of cubic phase CFTSe (d111 ¼3.28 Å), demonstrating the nano-scale evidence for the structure of synthesized CFTSe nanocrystals. In addition, the lattice data calculated from SAED pattern of randomly chosen region of CFTSe nanocrystals agrees well with the lattice parameters of CFTSe (Fig. 1(d)). To further reveal the crystal structure of CFTSe nanocrystals, X-ray diffraction (XRD) is used for prepared samples. Fig. 2(a) shows the XRD pattern of the synthesized sample. It can be seen that the obtained sample is composed of cubic phase Cu2FeSnSe4 (JCPDS 270167). Five major peaks for thin film, at about 2θ ¼ 7.051, 44.961, 53.341, 65.631 and 72.361 corresponding to (111), (220), (311), (400) and (331), were identified [11]. No evidence of other impurities such as CuSe, SnSe, etc. can be found from the XRD pattern. The elemental composition of synthesized CFTSe nanocrystals was investigated using EDS analysis. The ratio of the compositional elements is
Fig. 1. (a, b) TEM images, (c) HRTEM image and (d) SEAD pattern of CFTSe nanocrystals.
308
Y. Liu et al. / Materials Letters 136 (2014) 306–309
estimated to be Cu/Fe/Sn/Se: 2.09/0.84/0.92/4, which suggests that composition of CFTSe nanocrystals is close to the stoichiometry of CFTSe. In order to clarify valence states of element Cu, Fe, Sn, and Se of the CFTSe nanocrystals, XPS characterization of the specific four elements was conducted. As shown in Fig. 3, the binding energies of Cu 2p, Fe 2p, Sn 3d, and Se 3d of the nanocrystals in the XPS are consistent with those reported in literatures [15,16]. The valence states of Cu, Fe, Sn and Se ions are þ1, þ2, þ4, and 2, respectively. Considering the large difference among Cu, Fe, and Sn precursor reactivity, in this research a novel Se precursor (a soluble
Fig. 2. XRD pattern of CFTSe nanocrystals.
alkylammonium selenide) with high activity, which has been employed at the previous work in our research [17,18], was used. It was found that the content of Se precursor played a critical role in controlling the phase pure of CFTSe nanocrystals. The results of experiments showed that the use of excess Se was necessary in order to obtain pure CFTSe nanocrystals. In addition, the size and size dispersion of the synthesized CFTSe were determined by the reaction temperature. Injection temperature higher than 285 1C resulted in uncontrolled growth of the nascent crystallites and synthesized non-uniform nanocrystals with wide size dispersion, while temperatures lower than 250 1C were insufficient to induce rapid nucleation. UV–vis–NIR absorption spectroscopy is used to evaluate the optical properties of the CFTSe nanocrystals and results are shown in Fig. 4(a). The optical band gap of the nanocrystals is estimated to be 1.60 70.02 eV by extrapolating the linear region of the plot of the absorbance squared versus energy. The value is higher than the previous literature for CFTSe sheets, which may result from the quantum confinement effect often observed for metal selenide nanocrystals [19]. This value is close to the band gap value of Cu2ZnSnS4 nanocrystals (1.50 eV) [20] and the optimal value for solar cell application [21]. In order to further evaluate the potential of this material for photo-electrical conversion applications, the photo-responsiveness of CFTSe nanocrystals was tested. The CFTSe nanocrystal thin films were prepared by directly drop-casting nanocrystal ink onto the ITO conductive glasses. The film was mounted to a custom built threeelectrode photoelectrochemical cell containing 0.5 M H2SO4 as the electrolyte solution. The graphite electrode and saturated calomel reference electrode (SCE) were used as counter electrode and reference electrode, respectively. The incident light intensity used
Fig. 3. The X-ray photoelectron spectroscopy (XPS) spectra of as-synthesized CFTSe nanocrystals: (a) Cu 2p; (b) Fe 2p; (c) Sn 3d; and (d) Se 2p.
Y. Liu et al. / Materials Letters 136 (2014) 306–309
309
Fig. 4. (a) UV–vis–NIR absorption spectrum of CFTSe nanocrystals. Inset is the plot of (ahv)2 versus hv (eV) for the nanocrystals. (b) The transient photocurrent spectrum for the obtained CFTSe films at 0.4 V versus SCE.
was 100 mW/cm2, and a bias voltage of 0.4 V versus SCE was applied. The photo-response from the CFTSe nanocrystals is shown in Fig. 4(b). The measured photocurrent density is as high as 0.07 mA cm 2, which is approximately five times than that for CFTS nanocrystals film in our previous report [4]. It remains constant over many cycles (8 cycles demonstrated here), showing good photoresponse and photostability of CFTSe nanocrystals film. This phenomenon demonstrates the potential application of CFTSe nanocrystals and /or the corresponding thin film in the field of solar energy conversion. 4. Conclusions A colloidal synthesis of CFTSe nanocrystals via the hot-injection method is presented. CFTSe nanocrystals possess an irregular, faceted shaped and a fairly narrow size distribution with an average particle size of 15.5 7 1.9 nm. The structure of the synthesized CFTSe nanocrystals is confirmed by HRTEM image, SAED pattern and XRD. The results of EDS and XPS confirmed the composition of the CFTSe nanocrystals. The use of excess of Se was found to be necessary to balancing relativity of cationic precursors to obtain pure CFTSe. In addition, the reaction temperature plays a critical role on the size and size dispersion of the nanocrystals. An optical band gap of 1.60 70.02 eV for CFTSe nanocrystals is estimated by UV–vis–NIR data. The CFTSe nanocrystals film yields a good photoresponse in photoelectrochemical tests. Our work demonstrates that the synthesized CFTSe nanocrystals have potential application in the field of solar energy conversion.
Acknowledgments This work was supported by the National Natural Science Foundation of China (Grant nos. 51222403 and 51272292) and China Postdoctoral Science Foundation (Grant nos. 2012M511403, 2013T60777 and 2014T70788).
References [1] Green MA, Emery K, Hishikawa Y, Warta W, Dunlop ED. Prog Photovolt: Res Appl 2014;22:1–9. [2] Domain C, Laribi S, Taunier S, Guillemoles JF. J Phys Chem Solids 2003;64:1657–63. [3] Zhang X, Bao N, Ramasamy K, Wang YHA, Wang Y, Lin B, et al. Chem Commun 2012;48:4956–8. [4] Yan C, Huang C, Yang J, Liu F, Liu J, Lai Y, et al. Chem Commun 2012;48:2603–5. [5] Jiang X, Xu W, Tan R, Song W, Chen J. Mater Lett 2013;102:39–42. [6] Romanyuk YE, Marushko LP, Piskach LV, IV Kityk, Fedorchuk AO, Pekhnyo VI, et al. CrystEngComm 2013;15:4838. [7] Huang C, Chan Y, Liu F, Tang D, Yang J, Lai Y, et al. J Mater Chem A 2013;1:5402–7. [8] Khadka DB, Kim J. J Phys Chem C 2014. [9] Quintero E, Quintero M, Moreno E, Lara L, Morocoima M, Pineda F, et al. J Phys Chem Solids 2010;71:993–8. [10] Infante ER, Delgado JM, Rivera SAL. Mater Lett 1997;33:67–70. [11] Zhang B, Cao M, Li L, Sun Y, Shen Y, Wang L. Mater Lett 2013;93:111–4. [12] Hillhouse HW, Beard MC. Curr Opin Colloid Interface Sci 2009;14:245–59. [13] El-Sayed MA. Acc Chem Res 2004;37:326–33. [14] Donega CD, Liljeroth P, Vanmaekelbergh D. Small 2005;1:1152–62. [15] Norako ME, Brutchey RL. Chem Mate 2010;22:1613–5. [16] Liang X, Wei X, Pan D. J Nanomater 2012. [17] Liu Y, Liu F, Huang C, Lv X, Lai Y, Li J, et al. Mater Lett 2013;108:110–3. [18] Liu Y, Yang J, Gu E, Cao T, Su Z, Jiang L, et al. J Mater Chem A 2014;2:6363–7. [19] Tang J, Sargent EH. Adv Mater 2011;23:12–29. [20] Guo Q, Hillhouse HW, Agrawal R. J Am Chem Soc 2009;131:11672–3. [21] Goetzberger A, Hebling C, Schock HW. Mater Sci Eng R 2003;40:1–46.