- Email: [email protected]
Structural and photovoltaic properties of FeSe2 films prepared by radio frequency magnetron sputtering
Author’s Accepted Manuscript Structural and photovoltaic properties of FeSe2 films prepared by radio frequency magnetron sputtering Rong Jin, Ke Zhao, Xiaoyan Pu, Min Zhang, Fanggong Cai, Xinsheng Yang, Hern Kim, Yong Zhao www.elsevier.com
PII: DOI: Reference:
S0167-577X(16)30817-5 http://dx.doi.org/10.1016/j.matlet.2016.05.087 MLBLUE20898
To appear in: Materials Letters Received date: 16 February 2016 Revised date: 10 May 2016 Accepted date: 16 May 2016 Cite this article as: Rong Jin, Ke Zhao, Xiaoyan Pu, Min Zhang, Fanggong Cai, Xinsheng Yang, Hern Kim and Yong Zhao, Structural and photovoltaic properties of FeSe2 films prepared by radio frequency magnetron sputtering, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2016.05.087 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 galley proof before it is published in its final citable 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.
Structural and photovoltaic properties of FeSe2 films prepared by radio frequency magnetron sputtering Rong Jina, Ke Zhaob, Xiaoyan Pua, Min Zhangc, Fanggong Caia, Xinsheng Yanga,*, Hern Kimd, and Yong Zhaoa a
Key Laboratory of Advanced Technology of Materials (Ministry of Education), Superconductor and New Energy R&D Center, Southwest Jiaotong University, Chengdu, 610031, China
b
School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, 610031, China
c
Physics and Space science school, China West Normal University Nanchong, Sichuan 637002 China
d
Department of Energy Science and Technology, Energy and Environment Fusion Technology Center, Myongji University, Yongin, Gyeonggi-do 17058, Republic of Korea
Abstract Thin films of iron diselenide (FeSe2) on single crystal silicon substrates Si (100) have been obtained by radio frequency magnetron sputtering coupled with thermal post-annealing treatment. The suitable annealing temperature was 500 oC. Surface photovoltaic spectroscopy showed that the photo voltage response of the film was very active in the wavelength range of visible light at different bias voltages. The as-prepared FeSe2 could serve as a potential photovoltaic absorber in solar cells. Keywords: Sputtering; Microstructure; FeSe2; Photovoltage response
1. Introduction Semiconducting nanomaterials made of selenides have a strong quantum confinement effect due to their large exciton Bohr radius, which is essential to a number of exotic phenomena [1-6]. Due to different stoichiometric ratios of Fe/Se, there are several crystalline structures of iron selenides (hexagonal and tetragonal FeSe, cubic and orthorhombic FeSe2, monoclinic Fe3Se4, and trigonal Fe7Se8) with different optical, electrical, and magnetic properties [7-11]. Among them, iron *
Corresponding author, E-mail: [email protected] 1
diselenide has not only high electron conductivity and high optical absorption coefficient, but also a relatively narrow direct band gap of about 1.03 eV [12], which has great significance in solar cell application as the photovoltaic absorber [8,13]. In recent years, researchers have synthesized FeSe2 films using techniques such as molecular beam epitaxy [14], hot-injection [12, 13], thermal evaporation [15,16], selenisation of amorphous iron oxide thin films [17, 18], hydrothermal co-reduction route [19], and photochemical deposition [20]. However, the magnetron sputtering technique has never been reported in growing FeSe2 thin films despite its many advantages such as simple processing, repeatability, high deposition rate, strong adhesion between the film and the substrate, and uniformity. In this work, we used radio frequency magnetron sputtering technique to grow FeSe2 thin films on Si (100) substrates at different annealing temperatures. Si substrate is cheap and very good choice as substrate for growing thin films. Also, Si and FeS2 both have cubic lattice structures. In addition, Si itself has excellent photoelectrical properties [21-22]. Structural and optical properties of FeSe2 thin films with different annealing temperatures were analyzed.
2. Experimental methods FeSe2 thin films were homogeneously deposited on silicon (100) substrates by radio frequency magnetron sputtering with a Fe-Se target (99.99%) as the sputtering source. Before deposition, the substrates were ultrasonically cleaned with acetone, ethanol, and de-ionized water. Sputtering was performed in a 0.5 Pa high-purity Ar atmosphere. The sputtering power was fixed at 60 W and the substrate was heated to 500 oC during the 2 h sputtering process. After deposition, as-grown films were sealed in evacuated quartz glass tubes (<10−5 torr) which have Se-rich environment. Additional Se could suppress the out-diffusion of Se and thus reduce the loss of Se in the deposited material during the annealing. The tubes were heated in a muffle furnace up to 400-600 oC for 6 h, and then slowly cooled down to room temperature. Structural information of the thin films was obtained by X-ray diffraction (XRD, PANalytical X'Pert). Surface morphology and composition of the films were 2
determined by field-emission scanning electron microscope (FESEM, JSM-7001) and energy dispersive X-ray spectroscopy (EDX, INCA spectrometer). A surface photovoltage spectroscopy (SPS) was applied to characterize the photovoltage response and the behavior of photo generated charge carriers of the samples. 3. Results and discussion
Fig. 1. XRD patterns of FeSe2 films annealed at different temperatures.
Fig. 1 shows the effect of annealing temperatures (Ta) on the crystal phases of the films. For the film annealed at 450 oC, besides the Si signal from the substrate, nothing but a Fe peak is observed. For the sample with Ta =550 oC, only Se peaks, which is very close to the Si peak, can be found. However, FeSe2 peaks appear in samples annealed at 400 oC and 500 oC. Moreover, the film annealed at 500 oC has higher relative peak intensity and sharper peak shape (FWHM less than 0.05°), which indicates a better crystallinity. Also, fewer peaks exist in the film with Ta=500 oC, suggesting a less diversity of crystalline orientations. In the Ta=400 oC data, 4 peaks (1 0 1), (1 1 1), (1 2 0), and (2 1 1) have small but similar intensities. These 4 crystallography planes have no common rotation axis among any 3 of them, so in the one-axis-rotating XRD setup, they represent different crystallography orientations. When the post-annealing temperature increases to 500 oC, the relatively large (1 2 0) peak is observed, which is likely the result of a preferred orientation predominating in the thin film. The annealing temperature of 450 oC might have fallen in the middle of the transition that no FeSe2 peak exists; and also, keeping the film at this non steady-state for 6 hours might lead to a segregation of Se from the film. Only 3
Fe showing up in the spectra indicates that Se is in amorphous state. Additionally, 550 o
C seems to be too high for post annealing treatment. The XRD results prove that
FeSe2 is very sensitive to the post-annealing temperature. The competition between the escaping of Se and the crystallization of FeSe2 governs the outcome of the post-annealing [23]. The best post-annealing temperature should be 500 oC. FeSe2 film synthesized by other method has been reported to be improved through 500 oC post-annealing in Se-rich environment [24].
Fig. 2. FESEM images of FeSe2 films annealed at (a) 400 oC, (b) 450 oC, (c) 500oC, (d) 550 oC.
Table 1. The surface elements composition (atom ratio) of films annealed at different temperatures by energy dispersive X-ray spectroscopy (EDX).
Annealing temperature Element
400 oC
450 oC
500 oC
550 oC
Fe
32.41%
13.32%
31.71%
0.76%
Se
67.59%
86.68%
68.29%
99.24%
From the FESEM images (Fig. 2), significant morphological difference can be 4
found between samples annealed at different temperatures. Clusters of grains exist in the sample annealed at 400 oC, suggesting the uniformity of this thin film is not very good. The surface of the film annealed at 500 oC is relatively uniform, in agreement with the one predominant crystalline orientation suggest by the XRD result. Both have Fe/Se ratios close to 1:2 in the EDX results, see Table 1. For the sample annealed at 450 oC, the boundaries between the grains are fuzzy, typical for amorphous state. The EDX result in Table 1 shows a high Se concentration for this sample, so this amorphous material is likely the segregated selenium covering the surface. For the sample annealed at 550 oC, there are “nanoflowers” on the surface, almost entirely Se from EDX analysis. It is probably due to the annealing temperature being too high and the environment is Se-rich.
Fig. 3. The surface photovoltage spectroscopy of FeSe2 films annealed at 500oC with different bias voltage.
The surface photovoltage measurement of the sample annealed at 500 oC, as can be seen in Fig. 3, shows that both positive and negative bias voltages have great impact on the surface photovoltage responses of the FeSe2 film. The higher the positive bias voltage, or external electric field, the stronger the photovoltage response can happen. On the other hand, when a negative external electric field is applied, the response becomes even more intense, indicating that FeSe2 is a p-type semiconductor [25, 26]. When the bias voltage is 2 V, the photovoltage response is about 3 times larger than that with no bias voltage. And when the bias voltage is 0.5 V, the response intensity decreases to about three-fifth with no bias voltage. Thus, the density and the 5
characteristics of photon-generated carriers could be tuned by applied bias voltages. Also, the photovoltage response is very active when the wavelength is between 380 nm to 650 nm for all bias voltages. This wavelength range of solar radiation carries the majority of the solar power onto the earth surface, so the FeSe2 thin film prepared by magnetron sputtering has the potential to be applied as a photovoltaic absorber in solar cell. The photovoltage response could be attributed to its band gap characteristics. However, the physical phenomenon might not be intrinsic and may be caused by synthesis procedure [27]. The detailed mechanism will be reported elsewhere. 4. Conclusions In summary, we have prepared FeSe2 thin films by radio frequency magnetron sputtering. The post-annealing temperature has great influence on the phase structures and morphology of the films. Only films annealed at Ta =500 oC have cubic and orthorhombic crystal structures of FeSe2. The surface photovoltage spectroscopy indicates that the FeSe2 thin film has a large photovoltage response in the wavelength range of visible light, which makes it a great candidate as a photovoltaic absorber material. Acknowledgment The research was supported by Program of International S&T Cooperation (2013DFA51050), the National Natural Science Foundation of China (No. 51271155, No. 51377138), and the 863 Program (2014AA032701). References [1] Zhao LD, Tan G, Hao S, et al. Science. 2016, 351(6269): 141-144. [2] Jiang Q, Hu G. Mater Lett. 2015; 153: 114-117. [3] Han YM, Zhao J, Zhou M, et al. J Mater Chem A. 2015; 3: 4555-4559. [4] Astam A, Akaltun Y, Yıldırım M. Mater Lett. 2016; 166: 9-11. [5] Guo J, Liang S, Shi Y, et al. Phys Chem Chem Phys. 2015; 17: 28985-28992. [6] Tretiakov OA, Abanov A, Sinova J. Appl Phys Lett. 2011; 99:113110. [7] Ge JF, Liu ZL, Liu C, et al. Nat Mater. 2015; 14: 285-289. [8] Wang W, Pan X, Liu W, et al. Chem Commun. 2014; 50: 2618-2620. 6
[9] Li D, Jiang JJ, Liu W, et al. J Appl Phys. 2011; 109: 07C705. [10] Okazaki A. J Phys Soc Jpn. 1961; 16: 1162-1170. [11] Svendsen SR. Acta Chem Scand. 1972; 26: 3757-3774. [12] Qin Z, Yang BC, Zhang SR, et al. Vacuum. 2015; 111: 157-159. [13] Huang S, He Q, Chen W, et al. Nano Energy. 2015; 15: 205-215. [14] Takemura Y, Suto H, Honda N, et al. J Appl Phys. 1997; 81: 5177-5179. [15] Hamdadou N, Khelil A, Morsli M, et al. Vacuum. 2005; 77: 151-156. [16] Mars A, Essaidi H, Ouerfelli J, et al. Mat Sci in Semicon Proc. 2015; 40: 319-324. [17] Ouertani B, Ouerfelli J, Saadoun M, et al. Sol Energ Mat Sol C. 2005; 87: 501-511. [18] Ouertani B, Ouerfelli J, Saadoun M, et al. 2006; 511: 457-462. [19] Liu A, Chen X, Zhang Z, et al. Solid State Commun. 2006; 138: 538-541. [20] Kumaresan R, Ichimura M, Arai E. Thin solid films 2002; 414: 25-30. [21] Ahadi K, Mahdavi S M, Nemati A, et al. Mater Lett. 2012; 72: 107-109. [22] Ahadi K, Cadien K. RSC Adv. 2016; 6: 16301-16307. [23]Takemura Y, Suto H, Honda N, et al. Journal of applied physics, 1997, 81(8): 5177-5179. [24]Hamdadou N, Bernede J C, Khelil A. Preparation of iron selenide films by selenization technique. J Cryst growth. 2002; 241(3): 313-319. [25] Jing L, Sun X, Jing S, et al. Sol Energ Mat and Sol C. 2003; 79: 133-151. [26] Harada T. J Phys Soc Jpn. 1998; 67(4): 1352-1358. [27] Ahadi K, Mahdavi S M, Nemati A, et al. J Mater Sci. Materials in Electronics. 2011; 22: 815-820.
Highlights Uniform FeSe2 thin films were prepared by radio frequency magnetron sputtering. The best post-annealing treatment condition was 500oC. 7
The FeSe2 thin film has a large voltage response in the range of visible light.
8
PII: DOI: Reference:
S0167-577X(16)30817-5 http://dx.doi.org/10.1016/j.matlet.2016.05.087 MLBLUE20898
To appear in: Materials Letters Received date: 16 February 2016 Revised date: 10 May 2016 Accepted date: 16 May 2016 Cite this article as: Rong Jin, Ke Zhao, Xiaoyan Pu, Min Zhang, Fanggong Cai, Xinsheng Yang, Hern Kim and Yong Zhao, Structural and photovoltaic properties of FeSe2 films prepared by radio frequency magnetron sputtering, Materials Letters, http://dx.doi.org/10.1016/j.matlet.2016.05.087 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 galley proof before it is published in its final citable 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.
Structural and photovoltaic properties of FeSe2 films prepared by radio frequency magnetron sputtering Rong Jina, Ke Zhaob, Xiaoyan Pua, Min Zhangc, Fanggong Caia, Xinsheng Yanga,*, Hern Kimd, and Yong Zhaoa a
Key Laboratory of Advanced Technology of Materials (Ministry of Education), Superconductor and New Energy R&D Center, Southwest Jiaotong University, Chengdu, 610031, China
b
School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, 610031, China
c
Physics and Space science school, China West Normal University Nanchong, Sichuan 637002 China
d
Department of Energy Science and Technology, Energy and Environment Fusion Technology Center, Myongji University, Yongin, Gyeonggi-do 17058, Republic of Korea
Abstract Thin films of iron diselenide (FeSe2) on single crystal silicon substrates Si (100) have been obtained by radio frequency magnetron sputtering coupled with thermal post-annealing treatment. The suitable annealing temperature was 500 oC. Surface photovoltaic spectroscopy showed that the photo voltage response of the film was very active in the wavelength range of visible light at different bias voltages. The as-prepared FeSe2 could serve as a potential photovoltaic absorber in solar cells. Keywords: Sputtering; Microstructure; FeSe2; Photovoltage response
1. Introduction Semiconducting nanomaterials made of selenides have a strong quantum confinement effect due to their large exciton Bohr radius, which is essential to a number of exotic phenomena [1-6]. Due to different stoichiometric ratios of Fe/Se, there are several crystalline structures of iron selenides (hexagonal and tetragonal FeSe, cubic and orthorhombic FeSe2, monoclinic Fe3Se4, and trigonal Fe7Se8) with different optical, electrical, and magnetic properties [7-11]. Among them, iron *
Corresponding author, E-mail: [email protected] 1
diselenide has not only high electron conductivity and high optical absorption coefficient, but also a relatively narrow direct band gap of about 1.03 eV [12], which has great significance in solar cell application as the photovoltaic absorber [8,13]. In recent years, researchers have synthesized FeSe2 films using techniques such as molecular beam epitaxy [14], hot-injection [12, 13], thermal evaporation [15,16], selenisation of amorphous iron oxide thin films [17, 18], hydrothermal co-reduction route [19], and photochemical deposition [20]. However, the magnetron sputtering technique has never been reported in growing FeSe2 thin films despite its many advantages such as simple processing, repeatability, high deposition rate, strong adhesion between the film and the substrate, and uniformity. In this work, we used radio frequency magnetron sputtering technique to grow FeSe2 thin films on Si (100) substrates at different annealing temperatures. Si substrate is cheap and very good choice as substrate for growing thin films. Also, Si and FeS2 both have cubic lattice structures. In addition, Si itself has excellent photoelectrical properties [21-22]. Structural and optical properties of FeSe2 thin films with different annealing temperatures were analyzed.
2. Experimental methods FeSe2 thin films were homogeneously deposited on silicon (100) substrates by radio frequency magnetron sputtering with a Fe-Se target (99.99%) as the sputtering source. Before deposition, the substrates were ultrasonically cleaned with acetone, ethanol, and de-ionized water. Sputtering was performed in a 0.5 Pa high-purity Ar atmosphere. The sputtering power was fixed at 60 W and the substrate was heated to 500 oC during the 2 h sputtering process. After deposition, as-grown films were sealed in evacuated quartz glass tubes (<10−5 torr) which have Se-rich environment. Additional Se could suppress the out-diffusion of Se and thus reduce the loss of Se in the deposited material during the annealing. The tubes were heated in a muffle furnace up to 400-600 oC for 6 h, and then slowly cooled down to room temperature. Structural information of the thin films was obtained by X-ray diffraction (XRD, PANalytical X'Pert). Surface morphology and composition of the films were 2
determined by field-emission scanning electron microscope (FESEM, JSM-7001) and energy dispersive X-ray spectroscopy (EDX, INCA spectrometer). A surface photovoltage spectroscopy (SPS) was applied to characterize the photovoltage response and the behavior of photo generated charge carriers of the samples. 3. Results and discussion
Fig. 1. XRD patterns of FeSe2 films annealed at different temperatures.
Fig. 1 shows the effect of annealing temperatures (Ta) on the crystal phases of the films. For the film annealed at 450 oC, besides the Si signal from the substrate, nothing but a Fe peak is observed. For the sample with Ta =550 oC, only Se peaks, which is very close to the Si peak, can be found. However, FeSe2 peaks appear in samples annealed at 400 oC and 500 oC. Moreover, the film annealed at 500 oC has higher relative peak intensity and sharper peak shape (FWHM less than 0.05°), which indicates a better crystallinity. Also, fewer peaks exist in the film with Ta=500 oC, suggesting a less diversity of crystalline orientations. In the Ta=400 oC data, 4 peaks (1 0 1), (1 1 1), (1 2 0), and (2 1 1) have small but similar intensities. These 4 crystallography planes have no common rotation axis among any 3 of them, so in the one-axis-rotating XRD setup, they represent different crystallography orientations. When the post-annealing temperature increases to 500 oC, the relatively large (1 2 0) peak is observed, which is likely the result of a preferred orientation predominating in the thin film. The annealing temperature of 450 oC might have fallen in the middle of the transition that no FeSe2 peak exists; and also, keeping the film at this non steady-state for 6 hours might lead to a segregation of Se from the film. Only 3
Fe showing up in the spectra indicates that Se is in amorphous state. Additionally, 550 o
C seems to be too high for post annealing treatment. The XRD results prove that
FeSe2 is very sensitive to the post-annealing temperature. The competition between the escaping of Se and the crystallization of FeSe2 governs the outcome of the post-annealing [23]. The best post-annealing temperature should be 500 oC. FeSe2 film synthesized by other method has been reported to be improved through 500 oC post-annealing in Se-rich environment [24].
Fig. 2. FESEM images of FeSe2 films annealed at (a) 400 oC, (b) 450 oC, (c) 500oC, (d) 550 oC.
Table 1. The surface elements composition (atom ratio) of films annealed at different temperatures by energy dispersive X-ray spectroscopy (EDX).
Annealing temperature Element
400 oC
450 oC
500 oC
550 oC
Fe
32.41%
13.32%
31.71%
0.76%
Se
67.59%
86.68%
68.29%
99.24%
From the FESEM images (Fig. 2), significant morphological difference can be 4
found between samples annealed at different temperatures. Clusters of grains exist in the sample annealed at 400 oC, suggesting the uniformity of this thin film is not very good. The surface of the film annealed at 500 oC is relatively uniform, in agreement with the one predominant crystalline orientation suggest by the XRD result. Both have Fe/Se ratios close to 1:2 in the EDX results, see Table 1. For the sample annealed at 450 oC, the boundaries between the grains are fuzzy, typical for amorphous state. The EDX result in Table 1 shows a high Se concentration for this sample, so this amorphous material is likely the segregated selenium covering the surface. For the sample annealed at 550 oC, there are “nanoflowers” on the surface, almost entirely Se from EDX analysis. It is probably due to the annealing temperature being too high and the environment is Se-rich.
Fig. 3. The surface photovoltage spectroscopy of FeSe2 films annealed at 500oC with different bias voltage.
The surface photovoltage measurement of the sample annealed at 500 oC, as can be seen in Fig. 3, shows that both positive and negative bias voltages have great impact on the surface photovoltage responses of the FeSe2 film. The higher the positive bias voltage, or external electric field, the stronger the photovoltage response can happen. On the other hand, when a negative external electric field is applied, the response becomes even more intense, indicating that FeSe2 is a p-type semiconductor [25, 26]. When the bias voltage is 2 V, the photovoltage response is about 3 times larger than that with no bias voltage. And when the bias voltage is 0.5 V, the response intensity decreases to about three-fifth with no bias voltage. Thus, the density and the 5
characteristics of photon-generated carriers could be tuned by applied bias voltages. Also, the photovoltage response is very active when the wavelength is between 380 nm to 650 nm for all bias voltages. This wavelength range of solar radiation carries the majority of the solar power onto the earth surface, so the FeSe2 thin film prepared by magnetron sputtering has the potential to be applied as a photovoltaic absorber in solar cell. The photovoltage response could be attributed to its band gap characteristics. However, the physical phenomenon might not be intrinsic and may be caused by synthesis procedure [27]. The detailed mechanism will be reported elsewhere. 4. Conclusions In summary, we have prepared FeSe2 thin films by radio frequency magnetron sputtering. The post-annealing temperature has great influence on the phase structures and morphology of the films. Only films annealed at Ta =500 oC have cubic and orthorhombic crystal structures of FeSe2. The surface photovoltage spectroscopy indicates that the FeSe2 thin film has a large photovoltage response in the wavelength range of visible light, which makes it a great candidate as a photovoltaic absorber material. Acknowledgment The research was supported by Program of International S&T Cooperation (2013DFA51050), the National Natural Science Foundation of China (No. 51271155, No. 51377138), and the 863 Program (2014AA032701). References [1] Zhao LD, Tan G, Hao S, et al. Science. 2016, 351(6269): 141-144. [2] Jiang Q, Hu G. Mater Lett. 2015; 153: 114-117. [3] Han YM, Zhao J, Zhou M, et al. J Mater Chem A. 2015; 3: 4555-4559. [4] Astam A, Akaltun Y, Yıldırım M. Mater Lett. 2016; 166: 9-11. [5] Guo J, Liang S, Shi Y, et al. Phys Chem Chem Phys. 2015; 17: 28985-28992. [6] Tretiakov OA, Abanov A, Sinova J. Appl Phys Lett. 2011; 99:113110. [7] Ge JF, Liu ZL, Liu C, et al. Nat Mater. 2015; 14: 285-289. [8] Wang W, Pan X, Liu W, et al. Chem Commun. 2014; 50: 2618-2620. 6
[9] Li D, Jiang JJ, Liu W, et al. J Appl Phys. 2011; 109: 07C705. [10] Okazaki A. J Phys Soc Jpn. 1961; 16: 1162-1170. [11] Svendsen SR. Acta Chem Scand. 1972; 26: 3757-3774. [12] Qin Z, Yang BC, Zhang SR, et al. Vacuum. 2015; 111: 157-159. [13] Huang S, He Q, Chen W, et al. Nano Energy. 2015; 15: 205-215. [14] Takemura Y, Suto H, Honda N, et al. J Appl Phys. 1997; 81: 5177-5179. [15] Hamdadou N, Khelil A, Morsli M, et al. Vacuum. 2005; 77: 151-156. [16] Mars A, Essaidi H, Ouerfelli J, et al. Mat Sci in Semicon Proc. 2015; 40: 319-324. [17] Ouertani B, Ouerfelli J, Saadoun M, et al. Sol Energ Mat Sol C. 2005; 87: 501-511. [18] Ouertani B, Ouerfelli J, Saadoun M, et al. 2006; 511: 457-462. [19] Liu A, Chen X, Zhang Z, et al. Solid State Commun. 2006; 138: 538-541. [20] Kumaresan R, Ichimura M, Arai E. Thin solid films 2002; 414: 25-30. [21] Ahadi K, Mahdavi S M, Nemati A, et al. Mater Lett. 2012; 72: 107-109. [22] Ahadi K, Cadien K. RSC Adv. 2016; 6: 16301-16307. [23]Takemura Y, Suto H, Honda N, et al. Journal of applied physics, 1997, 81(8): 5177-5179. [24]Hamdadou N, Bernede J C, Khelil A. Preparation of iron selenide films by selenization technique. J Cryst growth. 2002; 241(3): 313-319. [25] Jing L, Sun X, Jing S, et al. Sol Energ Mat and Sol C. 2003; 79: 133-151. [26] Harada T. J Phys Soc Jpn. 1998; 67(4): 1352-1358. [27] Ahadi K, Mahdavi S M, Nemati A, et al. J Mater Sci. Materials in Electronics. 2011; 22: 815-820.
Highlights Uniform FeSe2 thin films were prepared by radio frequency magnetron sputtering. The best post-annealing treatment condition was 500oC. 7
The FeSe2 thin film has a large voltage response in the range of visible light.
8