Fabrication of a semi-transparent thin-film Sb2Se3 solar cell

Accepted Manuscript Fabrication of a semi-transparent thin-film Sb2Se3 solar cell Zhiwen Chen, Xiaohai Guo, Huafei Guo, Changhao Ma, Jianhua Qiu, Ningyi Yuan, Jianning Ding PII: DOI: Reference:

S0167-577X(18)31753-1 https://doi.org/10.1016/j.matlet.2018.10.173 MLBLUE 25216

To appear in:

Materials Letters

Received Date: Revised Date: Accepted Date:

21 September 2018 18 October 2018 30 October 2018

Please cite this article as: Z. Chen, X. Guo, H. Guo, C. Ma, J. Qiu, N. Yuan, J. Ding, Fabrication of a semi-transparent thin-film Sb2Se3 solar cell, Materials Letters (2018), doi: https://doi.org/10.1016/j.matlet.2018.10.173

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Fabrication of a semi-transparent thin-film Sb2Se3 solar cell Zhiwen Chena, Xiaohai Guoa, Huafei Guoa, Changhao Maa,Jianhua Qiua, Ningyi Yuan*a and Jianning Ding*ab aSchool

of Materials Science and Engineering, Jiangsu Collaborative Innovation

Center for Photovoltaic Science and Engineering, Jiangsu Province Cultivation Base for State Key Laboratory of Photovoltaic Science and Technology, Changzhou University, Changzhou 213164, China. bMicro/Nano

Science and Technology Center, Jiangsu University, Zhenjiang, 212013,

China. Abstract: Semi-transparent solar cells have been well developed in recent years, and can potentially be applied in many areas. Sb2Se3 has also received an increasing amount of attention because of its excellent optoelectronic properties. In order to combine these advantages, we attempted to fabricate a semi-transparent thin-film Sb2Se3 solar cell which meanwhile maintains the high efficiency. The effect of thickness of Sb2Se3 thin film on the optical and electrical properties were investigated. The optical absorption and power conversion efficiency were improved for Sb2Se3 thin film solar cells as the increase of the thickness of Sb2Se3 thin film, however, the obtained 120-nm-thick Sb2Se3 film was completely opaque. The optimized device was achieved with the thickness of 80 nm which exhibits the semi-transparent property and almost the same efficiency as the 120 nm Sb2Se3 thin film solar cell. This work demonstrates that the fabricated device has potential for applications in small wearable devices and may be extended to large-area glass-face applications. Keywords: Semitransparent, Sb2Se3, SnO2, Solar energy materials, Thin films Corresponding authors. Tel./fax: +0519 86450008 E-mails：[email protected]; [email protected];

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1. Introduction With the rapid development of the global economy, energy crises and environmental problems have caused worldwide concerns to photovoltaic technology. Various high-efficiency, low-cost, and low-pollutant solar cells have been proposed as potential solutions, such as CdTe and Cu(In,Ga)Se2 based solar cells[1], However, these types of solar cells cannot be further developed because of the toxicity of Cd and the scarcity of In and Ga. In order to overcome these problems, some based on oxide materials have also been proposed as potential solutions, such as, single cuprous oxide films synthesized by radical oxidation at low temperature for PV application[2]; efficiency enhancement of ZnO/Cu2O solar cells with well oriented and micrometer grain sized Cu2O films[3], and compounds using non-toxic and naturally abundant elements, such as SnS, Sb2Se3, and CZTS(Se), have recently been used to fabricate the absorption layer in thin-film solar cells[4–6]. Among these materials, Sb2Se3 has attracted more attention because of its excellent optoelectronic properties, such as a suitable band gap (1.17 eV direct and 1.03 eV indirect), large absorption coefficient (>105 cm−1), and decent carrier mobility (≈10 cm2 V−1 s−1)

[7].

Furthermore, it is a

binary compound with high vapor pressure that can be easily crystallized, which allows the generation of high-quality poly-crystalline films by simple evaporation [8]. The efficiency of thin-film Sb2Se3 solar cells that employ CdS as the buffer layer has reached 5.6% by rapid thermal evaporation (RTE) [5]. In 2016, Tang et al. used the aqueous SnO2 as the buffer layer deposited by spray method and the efficiency of SnO2/Sb2Se3 solar cell was 3.05%

[9].

Recently, we employed a low-temperature

method to fabricate an SnO2/Sb2Se3 solar cell and the resulting PCE was 2.47% under the condition of a 450-nm Sb2Se3 layer thickness [10]. Although semi-transparency and high efficiency are typically conflicting in conventional semiconductor compound solar cells because of the required thickness, the CdTe solar cell can almost completely filter UV light and well maintain photovoltaic performance, it additionally shows a high average visible transmittance[11]. Due to its semi-transparent characteristic, it can be used as BIPV material that can generate electricity while

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keeping the house bright. In view of this, we have attempted to fabricate a non-toxic and semi-transparent Sb2Se3 solar cell to replace the semi-transparent CdTe solar cell. In this study, a semi-transparent thin film Sb2Se3 solar cell was prepared by RTE. As compared to the thickest Sb2Se3 thin film, the optimized Sb2Se3 layer with a thickness of 80 nm not only maintains its semi-transparent characteristic, but also has the high efficiency. Thus, the proposed Sb2Se3 thin-film is a promising solar cell material that can be implemented in small wearable devices. This work also present new possibilities for semi-transparent Sb2Se3 solar cells which can be used in largearea glass-face applications. 2. Experimental details 2.1 Device fabrication First, SnCl4 and ice-water mixture were mixed together at a volume ratio of 1:45.5 to obtain a transparent solution at 0℃, Next, FTO glass substrates were immersed in the solution and then placed in a drying cabinet at 100℃. After 2.5 h, the coated substrates were rinsed with ethanol and dried in a drying cabinet at 70 ℃, next, we placing SnO2 in a rapid annealing furnace and employing the RTE method under a low vacuum of 2.5 mTorr. To vary the thickness of the Sb2Se3 films, the deposition times were varied as follows: 50, 60, and 70 s. Finally, an ultra-thin layer of gold electrode was deposited using a thermal evaporator. 2.2 Measurement and characterization X-ray diffraction (XRD; SMART APEX, Bruker, Germany) was used to analyze the thin-film SnO2/Sb2Se3 crystallized structure. To measure the absorbance of

the

thin-film

SnO2/Sb2Se3,

we

used

an

ultraviolet-visible

(UV-vis)

spectrophotometer (CARY 100 UV-Vis, Agilent Technologies, USA) operating within the wavelength range of 300 to 900 nm. Additionally, J-V curves were measured by using a solar simulator under 100 mW/cm2 AM 1.5 to obtain Voc, Jsc, the FF, and the PCE. The external quantum efficiency (EQE) of the semi-transparent Sb2Se3 solar cell was obtained by using a commercial EQE system (QEXL, PV Measurements, Inc, USA).

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3. Results and discussion XRD patterns of SnO2/Sb2Se3 thin film at different thickness are illustrated in Fig. 1. Sb2Se3 thin films with the deposition times of 50-, 60-, and 70-s had the thicknesses of 50, 80, and 120 nm, respectively. Additionally, all of the diffraction peaks were observed to be consistent with those of the crystallized structures of SnO2 (JCPDS card No. 15-0861) and Sb2Se3 (JCPDS card No. 46-1088). As expected, variation of the deposition time for the Sb2Se3 thin film did not result in a miscellaneous phase or any structural changes. There has no preferred orientation observed in the films which indicates Sb2Se3 thin films had a polycrystalline structure. Moreover, the crystallinity was improved with increasing the film thickness. We fabricated a solar cell with the following layers: FTO/SnO2/Sb2Se3/Au, as is depicted in Fig. 2a. The Sb2Se3 absorption layer can be clearly identified in the crosssectional SEM image of the device (Fig. 2b). The thickness of Sb2Se3 thin film shown in Fig. 2b is only 80 nm that is extremely thin, however, the grains of Sb2Se3 layer are large, compact, and homogeneous. Because this structure can effectively minimize the grain-boundary energy and trap states, excellent device performance can be achieved. Sb2Se3 thin films with different thickness were found to yield similar absorption spectra, but different absorption intensities. Specially, the 80-nm-thick Sb2Se3 film was semi-transparent (inset of Fig. 2c) and had high average visible light absorption within the wavelength range of 300 to 700 nm (Fig. 2c). Furthermore, the highest absorbance was observed at a wavelength of 400 nm. The corresponding J-V curves, as determined via the solar simulator, are shown in Fig. 3a, and the device performance parameters for each of the thin-film Sb2Se3 solar cells are provided in Table 1. The device performance parameters were improved as increasing the thickness of Sb2Se3 thin film. It was indicated that 120nm-thick cell exhibited a higher open circuit voltage Voc, short-circuit current density Jsc, and fill factor FF than the 50-nm- and 80-nm-thick Sb2Se3 solar cells, which is attributed to the fact that 120-nm-thick Sb2Se3 film has higher photon absorption, better electron mobility and electron extraction, and less charge recombination.

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Therefore, the good PCE was achieved for 120-nm-thick cell. As compared to the 120-nm-thick cell, the PCE of the 80-nm-thick cell was only slightly reduced, but it was able to remain its semi-transparency. Fig. 3b shows the EQE plots for the Sb2Se3 solar cells, the EQE of all solar cells can be observed to plateau between 300 and 700 nm, and reached a maximum at a wavelength of 400 nm. The high energy photons are absorbed near the front surface and the diffusion length near the surface is shorter due to the surface recombination. As a result, the light generated carriers cannot be collected efficiently. With the photon energy decreasing, the absorption region is getting close to the junction and thus the collected efficiency of generated carriers is increasing and reach to a maximum. The lower energy photons can pass through the junction region and be absorbed near the back surface. That may be the reason that the collection efficiency will decrease with the photon wavelength increasing. The semitransparent solar cell with an 80-nm-thick Sb2Se3 film demonstrated an impressive Jsc value of 22.0 mA/cm2, which is in good agreement with the corresponding value extracted from the EQE spectrum. These results showed that an 80-nm-thick Sb2Se3 thin film solar cell can yield an efficiency of 2.03% and also have the semitransparency. 4. Conclusions In summary, we successfully fabricated a semi-transparent thin-film Sb2Se3 solar cell with the Sb2Se3 thickness of approximately 80 nm. As compared to the 120-nmthick Sb2Se3 film cell, the PCE was not significantly reduced, yielding a value of 2.03%. Moreover, the semi-transparent characteristics of the compound were retained, and high absorption was achieved. Therefore, the proposed Sb2Se3 thin-film can be used to fabricate semi-transparent devices, which has potential for applications in small wearable devices and may be extended to large-area glass-face applications. Acknowledgments This work was supported by the National Natural Science Foundation of china (Grant No. 91648109, 51335002, 51572037, 51272033), the Priority Academic Program Development of Jiangsu Higher Education Institutions.

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References [1] M. A. Green, K. Emery, W. Warta, E. D. Dunlop, D. H. Levi, W. Y. Baillie, Prog. Photovoltaics: Res. Appl. 19 (2017) 84-92. [2] Z. G. Zang, A. Nakamura, J. Temmyo, Optics Express. 21 (9) (2013) 1144811456. [3] Z. G. Zang, Appl. Phys. Lett. 112 (4) (2018) 042160. [4] P. Sun, L. Z. Sun, S. W. Lee, H. H. Park, S. B. Kim, C. X. Yang, R. G. Gordon, Adv. Energy Mater. 4 (2014) 1400496. [5] Y. Zhou, L.Wang, S. Y. Chen, S. K. Qin, X. S. Liu, J. Chen, D. J. Xue, M. Luo, Y. Z. Cao, Y. B. Cheng, E. H. Sargent, J. Tang, Nat. Photonics. 9 (2015) 409-415. [6] W. Wang, M. T. Winkler, O. Guna, T. Gokmen, T. K. Todorov, Y. Zhu, D. B. Mitzi, Adv. Energy Mater. 4 (2014) 1301465. [7] C. Chen, D. C. Bobela, Y. Yang, K. Zeng, J. Tang, Front. Optoelectron. 10 (2017) 18-30. [8] X. S. Liu, J. Chen, M. Luo, M. Y. Leng, Z. Xia, Y. Zhou, S. K. Qin, D. J. Xue, L. Lv, H. Huang, D. M. Niu, J. Tang, Acs. Appl. Mater. Interfaces. 6 (2014) 1068710695. [9] S. C. Lu, Y. Zhao, C. Chen, Y. Zhou, D. B. Li, K. H. Li, W. H. Chen, X. X. Wen, C. W, R. Kondrotas, N. Lowe, J. Tang, Adv. Electron Mater. 329 (2017) 1-8. [10] X. H. Guo, H. F. Guo, C. H. Ma, J. N. Ding, N. Y. Yuan, Mater. Lett. 222 (2018) 142-145. [11] H. Zhang, J. M. Kurley, J. C. Russell, J. Jiang,D. V. Talapin, J. Am. Chem. Soc. 138 (2016) 7464-7467.

Figure Caption Fig. 1. XRD patterns of SnO2 /Sb2Se3 thin-film at different thickness. Fig. 2(a) The three-dimensional structure diagram of semitransparent Sb2Se3 thin-film solar cell.(b)Cross-section SEM image with the structure of FTO/SnO2/Sb2Se3/Au when Sb2Se3 at 80 nm.(c) Absorbance of semitransparent thin-film solar cell at different thickness. Inset: Crystal structure of the semitransparent Sb2Se3 thin- film at 80 nm and photograph of the Changzhou University’s badge under light. Fig.3(a) Current density-voltage (J-V) curves.(b) External Quantum Efficiency (EQE) spectra of semitransparent Sb2Se3 solar cell at different thickness.

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Table 1. Device performance parameters of semitransparent Sb2Se3 solar cell at different thickness. Deposited times(s) 50 60 70

Film thickness(nm) 50 80 120

Voc(mV) 187 220 222

Jsc(mA/cm2 ) 21.9 22.0 22.4

FF(%)

PCE(%)

39.2 41.8 42.4

1.60 2.03 2.10

Highlights:



Successfully

fabricated a semi-transparent thin-film Sb2Se3 solar cell.



An 80-nm-thick Sb2Se3 thin film solar cell can yield an efficiency of 2.03% and also have the semi-transparency.

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