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In situ gas-solid reaction for fabrication of copper antimony sulfide thin film as photovoltaic absorber
Accepted Manuscript In-situ gas-solid reaction for fabrication of copper antimony sulfide thin film as photovoltaic absorber Yu Zhang, Jianhua Tian, Kejian Jiang, Jinhua Huang, Huijia Wang, Yanlin Song PII: DOI: Reference:
S0167-577X(17)31150-3 http://dx.doi.org/10.1016/j.matlet.2017.07.106 MLBLUE 22948
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
7 June 2017 7 July 2017 24 July 2017
Please cite this article as: Y. Zhang, J. Tian, K. Jiang, J. Huang, H. Wang, Y. Song, In-situ gas-solid reaction for fabrication of copper antimony sulfide thin film as photovoltaic absorber, Materials Letters (2017), doi: http:// dx.doi.org/10.1016/j.matlet.2017.07.106
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In-situ gas-solid reaction for fabrication of copper antimony sulfide thin film as photovoltaic absorber Yu Zhang1,2 ·Jianhua Tian1 · Kejian Jiang2* ·Jinhua Huang2 ·Huijia Wang1,2 · Yanlin Song2* 1
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P.R. China
2
Key Laboratory of Green Printing, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P.R. China
ABSTRACT In this report, a facile, low-cost, in-situ gas-solid reaction method has been sucessfully employed for the deposition of copper antimony sulfide (CuSbS2) semiconductor film，where copper and antimony metal precursor is first spin-coated on the TiO2 substrate, followed by reaction with H2S gas and further thermal annealing. The CuSbS2 film shows broad absorption ranged from 400 nm to 830 nm with a band gap of 1.57 eV. X-ray photoelectron spectroscopy (XPS) analysis confirms valence states of the synthetic samples for Cu+, Sb3+ and S2-, verifying phase-pure CuSbS2. Besides, the CuSbS2 films made by one-step method show good photoelectric property with a high potential as photovoltaic absorber. Keywords: CuSbS2; In-situ gas-solid reaction; Solar energy materials; Thin films 1. Introduction In recent years, great efforts have been paid on the study of multiple chalcogenide semiconductor materials due to their potential applications in various optoelectronic devices [1-4]. Among them, copper antimony sulfide (CuSbS2 ) as a promising ternary semiconductor materials, is comprised of relatively earth abundant and less toxic elements, and possesses an ideal direct band gap (Eg) of 1.4-1.6 eV with a strong light absorption coefficient (α＞104 cm-1), which 1
provide a potential application in the field of thin film photovoltaic [5]. So far, various fabrication methods, such as spray pyrolysis [6], thermal evaporation [7], hot-injection [8], and chemical bath deposition (CBD) [3] have been reported to synthesize CuSbS2. Besides, CuSbS2 devices are also fabricated [4, 5, 7] and show a maximum efficiency of 3.13 % [9]. Recently, we developed a simple, low-cost, in-situ gas-solid reaction method for the deposition of binary metal sulfide Sb2S3 and CdS. In this approach, an antimony (or cadmium) salt was first introduced from solution into a nanoporous TiO2 film and subsequently transformed into Sb2S3 (or CdS) through reaction with H2 S [10, 11]. Herein, we tried to further extend this method for the fabrication of ternary copper antimony sulfide (CuSbS2) semiconductor film, and investigated the structural, morphological, optical and electrical properties. 2. Experimental section TiO2 films were prepared on cleaned soda-lime glass substrates by blade coating of 20 nm-sized TiO2 paste (DSL 18NM-T, Dyesol) and calcination at 500℃ for 30 minutes. On the TiO2 films, copper antimony sulfur (CuSbS2) were fabricated through different deposition approches using in-situ gas-solid reaction method. For one-step deposition approach, a mixed ethanol solution of CuCl2 and SbCl3 was spin-coated on the 1.1 µm-thick TiO2 substrate, and then immersed in prefabricated H2S atmosphere. Finally the film was calcinated at 350 °C for 10 min in glove box. The resulting film was marked as CuSbS2-1. For the sake of contrast, two-step approach was employed for the deposition of CuSbS2 films, where one separate solution (CuCl2 or SbCl3) was coated on the TiO2 film, and treated by the H2S gas. Then another solution was deposited on the as-prepared film using the same procedures, followed by the calcination. Here, two differen sequences were used for the deposition of CuSbS2 using the two-step method. From 2
the sequence of CuCl2 to SbCl3, the corresponding film is named as CuSbS2 -2. With an inverse sequence, the resulting film is named as CuSbS2-3. Specific experimental operation steps are shown in Supporting Information. 3. Results and Discussion The crystallinity and phase purity of the CuSbS2 were characterized by X-ray diffraction (XRD). The sample CuSbS2-1(Fig. 1a), prepared using the one-step deposition approach, exhibits the diffraction peaks at 12.20°, 28.45°, 28.73°, 29.66°, 29.91°, 39.05°, 42.61°, 50.28°and 52.03°, corresponding to (200), (111), (410), (020), (301), (501), (321), (800) and (212) faces of orthorhombic structured chalcostibite CuSbS2 patterns (JCPDS 44-1417) [7, 12]. The patterns show pure CuSbS2 phase without any impurities, implying the formation of on the TiO2 films. In Fig.S1, both CuSbS2-2 and CuSbS2-3 samples present the similiar diffraction peaks as those for CuSbS2-1. The results imply following mechanism for the formation of CuSbS2 as different procedures of in-situ gas-solid method: CuCl2 + H2 S → CuS + 2HCl ↑, 2SbCl3 + 3H2S → Sb2S3 + 6HCl ↑, 2CuS + Sb2S3 → 2CuSbS2 + S ↑.Considering facile fabrication of CuSbS2 and accurate control of the compositions, the sample (CuSbS2-1) prepared by one-step deposition method was employed for further investigation. Fig. 1b shows the morphology of CuSbS2-1 prepared by in-situ gas-solid reaction. It is clear that a large number of tiny CuSbS2 particles homogeneously distributed throughout the entire TiO2 matrices. The X-Ray Energy Dispersive Spectrometer (EDS) spectroscopy (Fig.1b) provides an average Cu/Sb/S elemental ratio of 1.04:1:2.03, which is very close to the stoichiometric value of 1:1:2 of CuSbS2. This result confirms the formation of chalcostibite (CuSbS2) and free of other structures, such as Cu3SbS4, Cu12Sb4S13 [13]. The EDS mapping images (Fig. S2) show that Cu, Sb and S elements are uniformly distributed on the entire 3
porous TiO2 film. The cross sectional SEM image (Fig. 1c) presents a 1.1 µm-thick CuSbS2-1 film. In TEM images (Fig.1d), CuSbS2 can be distinguished as small particles with crystal grain size of about 2 nm, and well-decorated on the surface of 20 nm TiO2 balls. Besides, chalcostibite sample shows a broad absorption over a wide wavelength range from 400 nm to 830 nm (Fig. 1e). The band gap value is estimated to be about 1.57 eV using Tauc plots, which is among optimal band gaps for light absorbers used in high-efficiency solar cells. The Raman spectra (Fig. 1f) exhibit a strong peak at 335 cm-1 and small peaks at 69 and 100 cm-1, which is assigned to orthorhombic CuSbS2 [7, 14]. Here, the peak at 144 cm-1 can be assigned to anatase TiO2 substrate. The Raman spectra prove that only CuSbS2 phase is present on the TiO2 film.
Fig. 1 XRD patterns (a), top-view SEM image and EDS spectra (b), cross sectional SEM image (c), TEM and HRTEM images (d), UV-vis absorption spectra and Tauc plots (e), and Raman spectra (f) of CuSbS2-1 film. X-ray photoelectron spectroscopy (XPS) was employed to further verify the valence states of Cu, Sb and S for CuSbS2-1. Fig. 2a shows the survey XPS scan of the CuSbS2-1 surface in binding energy range of 0~1100 eV, where the peaks corresponding to Ti 2p, O 1s, Cu 2p, Sb 3d and S 2p are clearly observed. The high resolution XPS spectra of Cu 2p, Sb 3d and S 2p are 4
shown in Fig. 2b-d. Cu 2p spectrum show doublet at the binding energy of 952.6 eV (2p1/2) and 932.9 eV (2p3/2 ) with a separation of 19.7 eV, which are in good agreement with Cu+, and no peaks at 936, 942, 955 and 965 eV are observed for Cu2+ [5]. The binding energies for Sb 3d3/2 and 3d5/2 are 538.7 and 529.2 eV, respectively, corresponding to the value of Sb3+. The peaks at 163.0 and 161.9 eV represent the S 2p1/2 and 2p3/2, respectively, which are consistent with the chemical state of sulfur (S2-) in the CuSbS2 [3, 7]. Hence, XPS analysis further confirm phase-pure CuSbS2 is obtained and valence states for the CuSbS2 samples are Cu+, Sb3+ and S2-.
Fig. 2 X-ray photoelectron spectra (XPS) survey scan (a), Cu (2p) (b), Sb (3d) (c), and S (2p) (d) core levels of CuSbS2-1 film. To evaluate the potential application as light absorber in photovoltaic device, photoresponse performance was investigated for the CuSbS2-decorated TiO2 film coated on FTO-glass substrates. Figure 3a shows the dark and light current-potential (I-V) curves for the samples (CuSbS2-1, CuSbS2-2 and CuSbS2-3), where for the light I-V curves, the samples were performed at 100 mA cm-2 illumination AM 1.5G at room temperature. Clearly, all the samples show higher photocurrent compared with the corresponding dark current under the entire bias ranged from -600 mV to 600 mV, implying that photo-excited carriers (hole and electron) were generated in the CuSbS2 films, and transferred to external circuit with the aid of the external electric field. Among 5
the samples, CuSbS2 -1 shows the highest light current under light. We speculate that higher photoelectric property for CuSbS2-1 may relate to fabrication method employed for CuSbS2, where CuCl2 and SbCl3 were homogeneously mixed according to a certain proportion, ensuring fabrication of high quality CuSbS2. For further exploring the photoresponse performance, curve of current versus time for sample CuSbS2-1 was recorded in the darkness and light under a bias of 10 mV. As shown in Fig. 3b, the sample CuSbS2-1 shows high and stable light photocurrent with photosensitivity (I-I0)/I0 of 0.4, where I0 and I denote dark and light current, respectively. The value of 0.4 is larger than those for CuSbS2 prepared by chemical bath deposition [15]. The results indicate that the one-step in-situ gas-solid reaction can provide a facile and low-cost method for the deposition of ternary copper antimony sulfide with high photoresponse performance as photovoltaic absorber.
Fig. 3 (a) Current-potential (I-V) curves for CuSbS2-1, CuSbS2-2 and CuSbS2-3-based devices of darkness and light; (b) Photocurrent response curve for CuSbS2-1-based device. 4. Conclusion Herein, in-situ gas-solid reaction was successfully utilized to fabricate copper antimony sulfide (CuSbS2) on nanoporous TiO2 films through two different synthetic routes. The CuSbS2 was characterized by XRD, UV-vis, XPS and Raman spectra, indicating pure orthorhombic 6
structured CuSbS2. The SEM and TEM show that the CuSbS2 was homgeneously distriuted on TiO2 film with size of about 2 nm. The CuSbS2 shows high photoresponse performance with (I-I0)/I0 of 0.4. The results indicate that high quality ternary copper antimony sulfide could be fabricated by the facile and low-cost one-step in-situ gas-solid reaction method. Acknowledgements This work was supported by the National Nature Science Foundation of China (Grant Nos. 61405207, 21174149, 21572235 and 51473173). References [1] L. Yu, R.S. Kokenyesi, D.A. Keszler, A. Zunger, Adv. Energy Mater. 3 (2013) 43-48. [2] D.B. Mitzi, O. Gunawan, T.K. Todorov, K. Wang, S. Guha, Sol. Energy Mat. Sol. C. 95 (2011) 1421-1436. [3] C. Macías, S. Lugo, Á. Benítez, I. López, B. Kharissov, A. Vázquez, Y. Peña, Mater. Res. Bull. 87 (2017) 161-166. [4] Z. Liu, J. Huang, J. Han, T. Hong, J. Zhang, Z. Liu, Phys. Chem. Chem. Phys. 18 (2016) 16615-16620. [5] B. Yang, L. Wang, J. Han, Y. Zhou, H. Song, S. Chen, J. Zhong, L. Lv, D. Niu, J. Tang, Chem. Mater. 26 (2014) 3135-3143. [6] S. Manolache, A. Duta, L. Isac, M. Nanu, A. Goossens, J. Schoonman, Thin Solid Films 515 (2007) 5957-5960. [7] L. Wan, C. Ma, K. Hu, R. Zhou, X. Mao, S. Pan, L.H. Wong, J. Xu. J. Alloy. Compd. 680(2016) 182-190. [8] Y.C. Choi, E.J. Yeom, T.K. Ahn, S.Il Seok, Angew. Chem. Int. Edit. 54 (2015) 4005-4009. 7
[9] C. Yan, Z. Su, E. Gu, T. Cao, J. Yang, J. Liu, F. Liu, Y. Lai, J. Li, Y. Liu, RSC Adv. 28 (2012) 10481-10484. [10] L. Zheng, K. Jiang, J. Huang, Y. Zhang, B. Bao, X. Zhou, H. Wang, B. Guan, L. Yang, Y. Song, J. Mater. Chem. A 10 (2017) 4791-4796. [11] Y. Zhang, J. Tian, K. Jiang, J. Huang, L. Zhang, H. Wang, B. Bao,Y. Song, J. Mater. Sci.-Mater. El. DOI: 10.1007/s10854-017-7263-1. [12] K. Ramasamy, B. Tien, P.S. Archana, A. Gupta, Chem. Mater. 124 (2014) 227-230. [13] T. Rath, A.J. MacLachlan, M.D. Brown, S.A. Haque, J. Mater. Chem. A 47 (2015) 24155-24162. [14] K. Ramasamy, H. Sims, W.H. Butler, A. Gupta. Chem. Mater. 26 (2014) 2891-2899. [15] R.E. Ornelas-Acosta, S. Shaji, D. Avellaneda, G.A. Castillo, T.K.D. Roy, B. Krishnan, Mater. Res. Bull. 61 (2015) 215-225. Figure captions Fig. 1 XRD patterns (a), top-view SEM image and EDS spectra (b), cross sectional SEM image (c), TEM and HRTEM images (d), UV-vis absorption spectra and Tauc plots (e), and Raman spectra (f) of CuSbS2-1 film. Fig. 2 X-ray photoelectron spectra (XPS) survey scan (a), Cu (2p) (b), Sb (3d) (c), and S (2p) (d) core levels of CuSbS2-1 film. Fig. 3 (a) Current-potential (I-V) curves for CuSbS2-1, CuSbS2-2 and CuSbS2-3-based devices of darkness and light; (b) Photocurrent response curve for CuSbS2-1-based device.
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HIGHLIGHTS: In-situ gas-solid reaction technique is developed for the fabrication of CuSbS2 thin film. Phase-pure CuSbS2 is obtained by different synthetic routes. CuSbS2 films made by one-step in-situ gas-solid method show good photoelectric property.
9
S0167-577X(17)31150-3 http://dx.doi.org/10.1016/j.matlet.2017.07.106 MLBLUE 22948
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
7 June 2017 7 July 2017 24 July 2017
Please cite this article as: Y. Zhang, J. Tian, K. Jiang, J. Huang, H. Wang, Y. Song, In-situ gas-solid reaction for fabrication of copper antimony sulfide thin film as photovoltaic absorber, Materials Letters (2017), doi: http:// dx.doi.org/10.1016/j.matlet.2017.07.106
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In-situ gas-solid reaction for fabrication of copper antimony sulfide thin film as photovoltaic absorber Yu Zhang1,2 ·Jianhua Tian1 · Kejian Jiang2* ·Jinhua Huang2 ·Huijia Wang1,2 · Yanlin Song2* 1
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P.R. China
2
Key Laboratory of Green Printing, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P.R. China
ABSTRACT In this report, a facile, low-cost, in-situ gas-solid reaction method has been sucessfully employed for the deposition of copper antimony sulfide (CuSbS2) semiconductor film，where copper and antimony metal precursor is first spin-coated on the TiO2 substrate, followed by reaction with H2S gas and further thermal annealing. The CuSbS2 film shows broad absorption ranged from 400 nm to 830 nm with a band gap of 1.57 eV. X-ray photoelectron spectroscopy (XPS) analysis confirms valence states of the synthetic samples for Cu+, Sb3+ and S2-, verifying phase-pure CuSbS2. Besides, the CuSbS2 films made by one-step method show good photoelectric property with a high potential as photovoltaic absorber. Keywords: CuSbS2; In-situ gas-solid reaction; Solar energy materials; Thin films 1. Introduction In recent years, great efforts have been paid on the study of multiple chalcogenide semiconductor materials due to their potential applications in various optoelectronic devices [1-4]. Among them, copper antimony sulfide (CuSbS2 ) as a promising ternary semiconductor materials, is comprised of relatively earth abundant and less toxic elements, and possesses an ideal direct band gap (Eg) of 1.4-1.6 eV with a strong light absorption coefficient (α＞104 cm-1), which 1
provide a potential application in the field of thin film photovoltaic [5]. So far, various fabrication methods, such as spray pyrolysis [6], thermal evaporation [7], hot-injection [8], and chemical bath deposition (CBD) [3] have been reported to synthesize CuSbS2. Besides, CuSbS2 devices are also fabricated [4, 5, 7] and show a maximum efficiency of 3.13 % [9]. Recently, we developed a simple, low-cost, in-situ gas-solid reaction method for the deposition of binary metal sulfide Sb2S3 and CdS. In this approach, an antimony (or cadmium) salt was first introduced from solution into a nanoporous TiO2 film and subsequently transformed into Sb2S3 (or CdS) through reaction with H2 S [10, 11]. Herein, we tried to further extend this method for the fabrication of ternary copper antimony sulfide (CuSbS2) semiconductor film, and investigated the structural, morphological, optical and electrical properties. 2. Experimental section TiO2 films were prepared on cleaned soda-lime glass substrates by blade coating of 20 nm-sized TiO2 paste (DSL 18NM-T, Dyesol) and calcination at 500℃ for 30 minutes. On the TiO2 films, copper antimony sulfur (CuSbS2) were fabricated through different deposition approches using in-situ gas-solid reaction method. For one-step deposition approach, a mixed ethanol solution of CuCl2 and SbCl3 was spin-coated on the 1.1 µm-thick TiO2 substrate, and then immersed in prefabricated H2S atmosphere. Finally the film was calcinated at 350 °C for 10 min in glove box. The resulting film was marked as CuSbS2-1. For the sake of contrast, two-step approach was employed for the deposition of CuSbS2 films, where one separate solution (CuCl2 or SbCl3) was coated on the TiO2 film, and treated by the H2S gas. Then another solution was deposited on the as-prepared film using the same procedures, followed by the calcination. Here, two differen sequences were used for the deposition of CuSbS2 using the two-step method. From 2
the sequence of CuCl2 to SbCl3, the corresponding film is named as CuSbS2 -2. With an inverse sequence, the resulting film is named as CuSbS2-3. Specific experimental operation steps are shown in Supporting Information. 3. Results and Discussion The crystallinity and phase purity of the CuSbS2 were characterized by X-ray diffraction (XRD). The sample CuSbS2-1(Fig. 1a), prepared using the one-step deposition approach, exhibits the diffraction peaks at 12.20°, 28.45°, 28.73°, 29.66°, 29.91°, 39.05°, 42.61°, 50.28°and 52.03°, corresponding to (200), (111), (410), (020), (301), (501), (321), (800) and (212) faces of orthorhombic structured chalcostibite CuSbS2 patterns (JCPDS 44-1417) [7, 12]. The patterns show pure CuSbS2 phase without any impurities, implying the formation of on the TiO2 films. In Fig.S1, both CuSbS2-2 and CuSbS2-3 samples present the similiar diffraction peaks as those for CuSbS2-1. The results imply following mechanism for the formation of CuSbS2 as different procedures of in-situ gas-solid method: CuCl2 + H2 S → CuS + 2HCl ↑, 2SbCl3 + 3H2S → Sb2S3 + 6HCl ↑, 2CuS + Sb2S3 → 2CuSbS2 + S ↑.Considering facile fabrication of CuSbS2 and accurate control of the compositions, the sample (CuSbS2-1) prepared by one-step deposition method was employed for further investigation. Fig. 1b shows the morphology of CuSbS2-1 prepared by in-situ gas-solid reaction. It is clear that a large number of tiny CuSbS2 particles homogeneously distributed throughout the entire TiO2 matrices. The X-Ray Energy Dispersive Spectrometer (EDS) spectroscopy (Fig.1b) provides an average Cu/Sb/S elemental ratio of 1.04:1:2.03, which is very close to the stoichiometric value of 1:1:2 of CuSbS2. This result confirms the formation of chalcostibite (CuSbS2) and free of other structures, such as Cu3SbS4, Cu12Sb4S13 [13]. The EDS mapping images (Fig. S2) show that Cu, Sb and S elements are uniformly distributed on the entire 3
porous TiO2 film. The cross sectional SEM image (Fig. 1c) presents a 1.1 µm-thick CuSbS2-1 film. In TEM images (Fig.1d), CuSbS2 can be distinguished as small particles with crystal grain size of about 2 nm, and well-decorated on the surface of 20 nm TiO2 balls. Besides, chalcostibite sample shows a broad absorption over a wide wavelength range from 400 nm to 830 nm (Fig. 1e). The band gap value is estimated to be about 1.57 eV using Tauc plots, which is among optimal band gaps for light absorbers used in high-efficiency solar cells. The Raman spectra (Fig. 1f) exhibit a strong peak at 335 cm-1 and small peaks at 69 and 100 cm-1, which is assigned to orthorhombic CuSbS2 [7, 14]. Here, the peak at 144 cm-1 can be assigned to anatase TiO2 substrate. The Raman spectra prove that only CuSbS2 phase is present on the TiO2 film.
Fig. 1 XRD patterns (a), top-view SEM image and EDS spectra (b), cross sectional SEM image (c), TEM and HRTEM images (d), UV-vis absorption spectra and Tauc plots (e), and Raman spectra (f) of CuSbS2-1 film. X-ray photoelectron spectroscopy (XPS) was employed to further verify the valence states of Cu, Sb and S for CuSbS2-1. Fig. 2a shows the survey XPS scan of the CuSbS2-1 surface in binding energy range of 0~1100 eV, where the peaks corresponding to Ti 2p, O 1s, Cu 2p, Sb 3d and S 2p are clearly observed. The high resolution XPS spectra of Cu 2p, Sb 3d and S 2p are 4
shown in Fig. 2b-d. Cu 2p spectrum show doublet at the binding energy of 952.6 eV (2p1/2) and 932.9 eV (2p3/2 ) with a separation of 19.7 eV, which are in good agreement with Cu+, and no peaks at 936, 942, 955 and 965 eV are observed for Cu2+ [5]. The binding energies for Sb 3d3/2 and 3d5/2 are 538.7 and 529.2 eV, respectively, corresponding to the value of Sb3+. The peaks at 163.0 and 161.9 eV represent the S 2p1/2 and 2p3/2, respectively, which are consistent with the chemical state of sulfur (S2-) in the CuSbS2 [3, 7]. Hence, XPS analysis further confirm phase-pure CuSbS2 is obtained and valence states for the CuSbS2 samples are Cu+, Sb3+ and S2-.
Fig. 2 X-ray photoelectron spectra (XPS) survey scan (a), Cu (2p) (b), Sb (3d) (c), and S (2p) (d) core levels of CuSbS2-1 film. To evaluate the potential application as light absorber in photovoltaic device, photoresponse performance was investigated for the CuSbS2-decorated TiO2 film coated on FTO-glass substrates. Figure 3a shows the dark and light current-potential (I-V) curves for the samples (CuSbS2-1, CuSbS2-2 and CuSbS2-3), where for the light I-V curves, the samples were performed at 100 mA cm-2 illumination AM 1.5G at room temperature. Clearly, all the samples show higher photocurrent compared with the corresponding dark current under the entire bias ranged from -600 mV to 600 mV, implying that photo-excited carriers (hole and electron) were generated in the CuSbS2 films, and transferred to external circuit with the aid of the external electric field. Among 5
the samples, CuSbS2 -1 shows the highest light current under light. We speculate that higher photoelectric property for CuSbS2-1 may relate to fabrication method employed for CuSbS2, where CuCl2 and SbCl3 were homogeneously mixed according to a certain proportion, ensuring fabrication of high quality CuSbS2. For further exploring the photoresponse performance, curve of current versus time for sample CuSbS2-1 was recorded in the darkness and light under a bias of 10 mV. As shown in Fig. 3b, the sample CuSbS2-1 shows high and stable light photocurrent with photosensitivity (I-I0)/I0 of 0.4, where I0 and I denote dark and light current, respectively. The value of 0.4 is larger than those for CuSbS2 prepared by chemical bath deposition [15]. The results indicate that the one-step in-situ gas-solid reaction can provide a facile and low-cost method for the deposition of ternary copper antimony sulfide with high photoresponse performance as photovoltaic absorber.
Fig. 3 (a) Current-potential (I-V) curves for CuSbS2-1, CuSbS2-2 and CuSbS2-3-based devices of darkness and light; (b) Photocurrent response curve for CuSbS2-1-based device. 4. Conclusion Herein, in-situ gas-solid reaction was successfully utilized to fabricate copper antimony sulfide (CuSbS2) on nanoporous TiO2 films through two different synthetic routes. The CuSbS2 was characterized by XRD, UV-vis, XPS and Raman spectra, indicating pure orthorhombic 6
structured CuSbS2. The SEM and TEM show that the CuSbS2 was homgeneously distriuted on TiO2 film with size of about 2 nm. The CuSbS2 shows high photoresponse performance with (I-I0)/I0 of 0.4. The results indicate that high quality ternary copper antimony sulfide could be fabricated by the facile and low-cost one-step in-situ gas-solid reaction method. Acknowledgements This work was supported by the National Nature Science Foundation of China (Grant Nos. 61405207, 21174149, 21572235 and 51473173). References [1] L. Yu, R.S. Kokenyesi, D.A. Keszler, A. Zunger, Adv. Energy Mater. 3 (2013) 43-48. [2] D.B. Mitzi, O. Gunawan, T.K. Todorov, K. Wang, S. Guha, Sol. Energy Mat. Sol. C. 95 (2011) 1421-1436. [3] C. Macías, S. Lugo, Á. Benítez, I. López, B. Kharissov, A. Vázquez, Y. Peña, Mater. Res. Bull. 87 (2017) 161-166. [4] Z. Liu, J. Huang, J. Han, T. Hong, J. Zhang, Z. Liu, Phys. Chem. Chem. Phys. 18 (2016) 16615-16620. [5] B. Yang, L. Wang, J. Han, Y. Zhou, H. Song, S. Chen, J. Zhong, L. Lv, D. Niu, J. Tang, Chem. Mater. 26 (2014) 3135-3143. [6] S. Manolache, A. Duta, L. Isac, M. Nanu, A. Goossens, J. Schoonman, Thin Solid Films 515 (2007) 5957-5960. [7] L. Wan, C. Ma, K. Hu, R. Zhou, X. Mao, S. Pan, L.H. Wong, J. Xu. J. Alloy. Compd. 680(2016) 182-190. [8] Y.C. Choi, E.J. Yeom, T.K. Ahn, S.Il Seok, Angew. Chem. Int. Edit. 54 (2015) 4005-4009. 7
[9] C. Yan, Z. Su, E. Gu, T. Cao, J. Yang, J. Liu, F. Liu, Y. Lai, J. Li, Y. Liu, RSC Adv. 28 (2012) 10481-10484. [10] L. Zheng, K. Jiang, J. Huang, Y. Zhang, B. Bao, X. Zhou, H. Wang, B. Guan, L. Yang, Y. Song, J. Mater. Chem. A 10 (2017) 4791-4796. [11] Y. Zhang, J. Tian, K. Jiang, J. Huang, L. Zhang, H. Wang, B. Bao,Y. Song, J. Mater. Sci.-Mater. El. DOI: 10.1007/s10854-017-7263-1. [12] K. Ramasamy, B. Tien, P.S. Archana, A. Gupta, Chem. Mater. 124 (2014) 227-230. [13] T. Rath, A.J. MacLachlan, M.D. Brown, S.A. Haque, J. Mater. Chem. A 47 (2015) 24155-24162. [14] K. Ramasamy, H. Sims, W.H. Butler, A. Gupta. Chem. Mater. 26 (2014) 2891-2899. [15] R.E. Ornelas-Acosta, S. Shaji, D. Avellaneda, G.A. Castillo, T.K.D. Roy, B. Krishnan, Mater. Res. Bull. 61 (2015) 215-225. Figure captions Fig. 1 XRD patterns (a), top-view SEM image and EDS spectra (b), cross sectional SEM image (c), TEM and HRTEM images (d), UV-vis absorption spectra and Tauc plots (e), and Raman spectra (f) of CuSbS2-1 film. Fig. 2 X-ray photoelectron spectra (XPS) survey scan (a), Cu (2p) (b), Sb (3d) (c), and S (2p) (d) core levels of CuSbS2-1 film. Fig. 3 (a) Current-potential (I-V) curves for CuSbS2-1, CuSbS2-2 and CuSbS2-3-based devices of darkness and light; (b) Photocurrent response curve for CuSbS2-1-based device.
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HIGHLIGHTS: In-situ gas-solid reaction technique is developed for the fabrication of CuSbS2 thin film. Phase-pure CuSbS2 is obtained by different synthetic routes. CuSbS2 films made by one-step in-situ gas-solid method show good photoelectric property.
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