Scaps simulation of zno/in2s3/cu2sn3s7/mo solar cell - Phung Dinh Hoat

Journal of Science and Technology 54 (1A) (2016) 183-189 SCAPS SIMULATION OF ZnO/In2S3/Cu2Sn3S7/Mo SOLAR CELL Phung Dinh Hoat 1, * , Do Phuc Hai 2 1 Faculty of Engineering Physics and Chemistry, Le Quy Don Technical University, 236 Hoang Quoc Viet Street, Cau Giay District, Hanoi 2 School of Engineering Physics, Hanoi University of Science and Technology, 1 Dai Co Viet Street, Hai Ba Trung District, Hanoi * Email: hoatma@gmail.com Received: 30 August 2015. Accepted for publication: 26 October 2015 ABSTRACT Operation of ZnO/In2S3/Cu2Sn3S7/Mo solar cell was calculated using the SCAPS software. Main input data were energy band gap Eg, absorption coefficient α, thickness d, mobility μ and carrier concentration n of the ZnO, In2S3 and Cu2Sn3S7 films obtained from experiments. In all calculation processes, parameters of the ZnO (Eg = 3.3 eV, d = 0.2 μm, μn = 100 cm 2 /(Vs)) and In2S3 (Eg = 2.96 eV, d = 0.1 μm, μn = 50 cm 2 /(Vs)) films were kept constant. Effects of thickness d and carrier concentration np of the Cu2Sn3S7 (αmax = 4.2×10 4 cm -1 , Eg = 1.46 eV) film on Voc, Jsc, Vm, Jm, FF and η of the cell were investigated in the ranges of d = 0.3 – 3.5 μm and np = 10 17 – 1020 cm-3. Under the standard AM 1.5G illumination at 300 K, the ZnO/In2S3/Cu2Sn3S7/Mo solar cell having Rs = 10 Ω.cm 2 and Rsh = 1×10 6 Ω.cm2 using Cu2Sn3S7 film having d = 2 µm, αmax = 4.2×10 4 cm -1 , Eg = 1.46 eV, μp = 15 cm 2 /(Vs) and np = 10 20 cm -3 has the highest conversion efficiency ηmax = 18.0 % with Voc = 0.98 V, Jsc = 31.2 mA/cm 2 , Vm = 0.62 V, Jm = 28.8 mA/cm 2 and FF = 58.8 %. Keywords: Cu2Sn3S7, SCAPS, Solar cell. 1. INTRODUCTION Recently, compounds consisting of cheap, earth abundant and environmental green Cu, Sn and S elements of ternary system Cu-Sn-S, such as Cu2SnS3, Cu2Sn3S7, Cu4SnS4, Cu5Sn2S7, Cu4Sn7S16 and Cu4SnS6 etc [1 - 5], have attracted much attention because of their good optical and electrical properties for various potential applications not only in thin film solar cells but also in other optoelectronic devices. Among these compounds, only the Cu2SnS3 has been widely investigated ranging from fabricating techniques and physical property characterization of the film to the operating of thin film solar cell using the Cu2SnS3 film as an absorption layer. Despite the fact that the Cu2Sn3S7 compound has been reported to possess similar properties for solar cell application when compared with the Cu2SnS3 [6], to date there are only a few works [2, Phung Dinh Hoat, Do Phuc Hai 184 7] on preparations and physical properties of the Cu2Sn3S7 film. Especially, there is no report on solar cells using the Cu2Sn3S7 film as the absorption layer. We have successfully fabricated the Cu2Sn3S7 film by directly spraying a mixture of solutions containing 0.42M SC(NH2)2, 0.18M SnCl4.5H2O and 0.12M CuCl2.2H2O on Pyrex glass at 320 o C using the nitrogen gas as carrying gas. Physical properties of the prepared Cu2Sn3S7 film were studied by XRD, SEM, EDAX, AFM, UV-vis. The prepared Cu2Sn3S7 film has suitable physical properties for solar cell application, i.e., p-type semiconducting, energy band gap Eg = 1.46 eV and absorption coefficient α > 104 cm-1 in the range of wave length λ = 300 – 1100 nm [2]. It is worthwhile investigating the operation of solar cell using the Cu2Sn3S7 film as the absorption layer in combining with an n-type semiconducting buffer layer such as In2S3, CdS films etc. In this paper, using our obtained experimental results of the Cu2Sn3S7 film as the input parameters for the absorption layer, we used the one-dimensional solar cell device simulator SCAPS software, which has succeeded in simulating CdTe and CIGS-based thin film solar cells [8, 9], to study the operation of ZnO/In2S3/Cu2Sn3S7/Mo solar cell. The influence of the two main parameters of the Cu2Sn3S7 absorption film i.e. thickness d and carrier concentration np on characteristic parameters Voc, Jsc, FF and η of ZnO/In2S3/Cu2Sn3S7/Mo solar cell was investigated in the range of d = 0.3 – 3.5 μm and np = 10 17 – 1020 cm-3, respectively. Results obtained from this work will give some clues to experimental research of this solar cell to save labour, time and cost. 2. EXPERIMENTAL PROCEDURES In the ZnO/In2S3/Cu2Sn3S7/Mo solar cell, ZnO, In2S3 and Cu2Sn3S7 films are the window, buffer and absorption layers, respectively. Fundamental material properties of the ZnO, In2S3 and Cu2Sn3S7 films defining the basic calculation case are listed in Table 1. Table 1. Fundamental material parameters. Parameters ZnO In2S3 Cu2Sn3S7 Thickness d (μm) 0.2 0.1 0.3 – 3.5 Band gap Eg (eV) 3.3 2.96 1.46 Relative dielectric constant εr (F/cm) 9 8.4 10 Electron affinity χ (eV) 4.45 4.2 4.5 Electron mobility μe (cm 2 /(Vs)) 100 50 50 Hole mobility μh (cm 2 /(Vs)) 25 15 15 Donor density ND (cm -3 ) 1.10 18 1.10 17 1.10 1 Acceptor density NA (cm -3 ) 1.10 1 1.10 1 10 17 – 1020 The energy band gap and absorption coefficient of In2S3 and Cu2Sn3S7 were deduced from our experiments while the other parameters of all three films were obtained from the reported literature [10]. Figure 1 plots the absorption coefficient versus wavelength of ZnO [11], In2S3 and Cu2Sn3S7 films. Scaps simulation of ZnO/Ni2S3/Cu2Sn3S7/Mo Solar Cell 185 Figure 1. Absorption coefficient of ZnO, In2S3 and Cu2Sn3S7 films. Inset is the AM 1.5G solar spectrum. The front and back contacts are characterized by the work function, reflectivity and surface recombination velocity. The work functions of ZnO, In2S3 and Cu2Sn3S7 were 4.45, 4.2 and 4.5 eV, respectively. The reflection was assumed to be 100 % at the back contact and 0 % at the front contact. The surface recombination velocities of electron (Sn) and hole (Sp) were respectively 10 7 , 10 4 cm/s at the front contact and 10 4 , 10 7 cm/s at back contact. The contacts between metal and semiconductor were Ohmic. The shunt and series resistances of the solar cell were chosen as Rsh = 10 6 Ω.cm2 and Rs = 10 Ω.cm 2 , respectively. All calculations were performed under the standard AM1.5G solar spectrum (100 mW/cm 2 ) illumination [12] shown in Fig. 1. The operating temperature was set at 300 K. 3. RESULTS AND DISCUSSION 3.1. Effect of thickness d of Cu2Sn3S7 film on characteristic parameters of ZnO/In2S3/Cu2Sn3S7/Mo solar cell To study effect of thickness d of the Cu2Sn3S7 film on characteristic parameters of ZnO/In2S3/Cu2Sn3S7/Mo solar cell, d was changed from 0.3 to 3.5 μm while the carrier concentration of the Cu2Sn3S7 film was kept constant at np = 10 18 cm -3 . Figure 2a and 2b show the change of J-V and QE (λ) curves of ZnO/In2S3/Cu2Sn3S7/Mo solar cell as varying the Cu2Sn3S7 thickness, respectively. The dependence of the solar cell characteristic parameters Voc, Jsc, Vm, Jm, FF and η on the Cu2Sn3S7 film thickness are plotted in Fig. 3 and summarized in Table 2. It can be seen in Fig. 2b that with the increasing of Cu2Sn3S7 film thickness from 0.3 to 2.0 μm the quantum efficiency of the solar cell increases significantly. This is due to the more photon absorption of a thicker Cu2Sn3S7 film and it leads to a higher value of Jsc. The Jsc enhances considerably from 26.4 to 32.0 mA/cm 2 , while the Voc increases in a small range from 0.78 to 0.80 V (Fig. 3a). The conversion efficiency η of the solar cell increases from 11.3 to 12.9 % (Fig. 3b). Phung Dinh Hoat, Do Phuc Hai 186 In the range of thickness d = 2.0 – 3.5 μm of the Cu2Sn3S7 film, all characteristic parameters of the solar cell are almost unchanged. It demonstrates that the ability to collect and convert light energy into electricity of the solar cell is saturated. The saturated thickness of Cu2Sn3S7 film is determined 2 μm. Using the 2-μm-thick Cu2Sn3S7 film with np = 10 18 cm -3 , the ZnO/In2S3/Cu2Sn3S7/Mo solar cell has the characteristic parameters Voc = 0.80 V, Jsc = 32.0 mA/cm 2 , FF = 50.3 % and η = 12.9 %. Figure 2. J-V (a) and QE (b) curves of ZnO/In2S3/Cu2Sn3S7/Mo solar cell using Cu2Sn3S7 film with different thicknesses. 0 1 2 3 4 24 27 30 33 0 1 2 3 4 0.75 0.78 0.81 V o c ( V ) d ( m) d ( m) J s c ( m A /c m 2 ) 0 1 2 3 4 10 11 12 13 d m 0 1 2 3 4 48 50 52 54 56 F F ( % ) d m) d ( m) ( % ) Figure 3. Dependence of Voc, Jsc, FF and η of ZnO/In2S3/Cu2Sn3S7/Mo solar cell on thickness of Cu2Sn3S7 film. Table 2. Effect of thickness d of Cu2Sn3S7 film on characteristic parameters Voc, Jsc, Vm, Jm, FF and η of ZnO/In2S3/Cu2Sn3S7/Mo solar cell. d (μm) 0.3 0.5 1.0 1.5 2.0 2.5 3.5 Voc (V) 0.78 0.79 0.80 0.80 0.80 0.80 0.80 Jsc (mA/cm 2 ) 26.35 29.51 31.07 31.56 31.97 32.30 32.30 FF (%) 54.95 51.81 50.97 50.65 50.31 50.00 50.00 η (%) 11.35 12.08 12.61 12.78 12.90 13.00 13.00 Vm (V) 0.48 0.46 0.46 0.46 0.46 0.45 0.45 Jm (mA/cm 2 ) 23.61 26.42 27.21 27.83 28.30 28.68 28.68 (a) (b) Scaps simulation of ZnO/Ni2S3/Cu2Sn3S7/Mo Solar Cell 187 3.2. Effect of carrier concentration np of Cu2Sn3S7 film on characteristic parameters of ZnO/In2S3/Cu2Sn3S7/Mo solar cell Figure 4. J-V (a) and QE (b) curves of ZnO/In2S3/Cu2Sn3S7/Mo solar cell using Cu2Sn3S7 film with different carrier concentration. 10 17 10 18 10 19 10 20 0.4 0.6 0.8 1.0 10 17 10 18 10 19 10 20 31 32 33 np (cm -3 ) J sc ( m A /c m 2 ) n p (cm-1) V o c ( V ) 10 17 10 18 10 19 10 20 6 9 12 15 18 10 17 10 18 10 19 10 20 40 50 60 n p (cm -3 ) F F ( % ) n p (cm-1) ( % ) Figure 5. Dependence of Voc, Jsc, FF and η of ZnO/In2S3/Cu2Sn3S7/Mo solar cell on carrier concentration of Cu2Sn3S7 film. To study effect of carrier concentration np of the Cu2Sn3S7 film on characteristic parameters of ZnO/In2S3/Cu2Sn3S7/Mo solar cell, np was changed from 10 17 to 10 20 cm -3 while the thickness of film was kept constant at saturated value d = 2 μm. J-V and QE (λ) curves of solar cell using the Cu2Sn3S7 film having different carrier concentrations are shown in Fig. 4a and 4b, respectively. Calculation results of Voc, Jsc, FF, η, Vm and Jm of ZnO/In2S3/Cu2Sn3S7/Mo solar cell are depicted in Fig. 5 and summarized in Table 3. Generally, resistivity ρ of a p-type film is inversely proportional to the carrier concentration np. Therefore, a higher value of np of the absorption film makes a lower value of ρ leading to a higher value of Voc of the solar cell using that film (Fig. 4a). Figure 5a shows that when np of the Cu2Sn3S7 film increases from 10 17 to 10 20 cm -3 , the Voc of ZnO/In2S3/Cu2Sn3S7/Mo solar cell increases linearly from 0.80 to 0.98 V, while Jsc of the solar cell decreases from 31.97 to 31.18 mA/cm 2 and np hardly affects the quantum efficiency QE (Fig. 4b). Figure 5b reveals that η of the solar cell increases from 12.9 to 18.0 % as increasing the carrier concentration of the Cu2Sn3S7 film. Using the Cu2Sn3S7 film with np = 10 20 cm -3 and d = 2 μm, the ZnO/In2S3/Cu2Sn3S7/Mo solar cell has the highest fill factor FF of 58.8 % and the best conversion efficiency η of 18.0 % with Voc = 0.98 V and Jsc = 31.18 mA/cm 2 . (a) (b) Phung Dinh Hoat, Do Phuc Hai 188 Table 3. Effect of carrier concentration np of Cu2Sn3S7 film on characteristic parameters Voc, Jsc, Vm, Jm, FF and η of ZnO/In2S3/Cu2Sn3S7/Mo solar cell. np (cm -3 ) 1×10 17 5×10 17 1×10 18 5×10 18 1×10 19 5×10 19 1×10 20 Voc (V) 0.80 0.84 0.86 0.90 0.92 0.96 0.98 Jsc (mA/cm 2 ) 31.97 31.64 31.53 31.33 31.28 31.20 31.18 FF (%) 50.31 52.72 53.74 55.66 56.49 58.10 58.80 η (%) 12.90 14.09 14.61 15.77 16.29 17.47 18.00 Vm (V) 0.46 0.49 0.51 0.55 0.57 0.61 0.62 Jm (mA/cm 2 ) 28.30 28.57 28.53 28.68 28.66 28.82 28.81 4. CONCLUSION In this work, the operation of ZnO/In2S3/Cu2Sn3S7/Mo solar cell was simulated using SCAPS software. The effects of thickness and carrier concentration of Cu2Sn3S7 film on characteristic parameters Voc, Jsc, Vm, Jm, FF and η of the solar cell were studied. The saturated value of Cu2Sn3S7 film thickness is 2 μm. The conversion efficiency of the solar cell increases correspondingly with the increase of carrier concentration of the Cu2Sn3S7 film. The highest conversion efficiency η of 18.0 % with Voc = 0.98 V, Jsc = 31.18 mA/cm 2 , Vm = 0.62 V, Jm = 28.8 mA/cm 2 and FF = 58.8 % was achieved in the ZnO/In2S3/Cu2Sn3S7/Mo solar cell using the Cu2Sn3S7 absorption film having physical parameters np = 10 20 cm -3, d = 2 µm, α > 104 cm-1 in the range λ = 300 – 1100 nm, Eg = 1.46 eV, μp = 15 cm 2 /(Vs) under the standard AM 1.5G solar spectrum (100 mW/cm 2 ) illumination at 300 K. Acknowledgements. This work was financially supported by the Vietnam Ministry of Education and Training (2013-2014, Code: B2013-01-56). REFERENCES 1. 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Các thông số chính đầu vào là bề rộng vùng cấm Eg, hệ số hấp thụ α, bề dày d, độ linh động μ và nồng độ hạt tải n của các màng ZnO, In2S3 và Cu2Sn3S7 thu được từ thực nghiệm. Trong quá trình mô phỏng, các thông số của các màng ZnO (Eg = 3,3 eV, d = 0,2 μm, μn = 100 cm 2 /(Vs)) và In2S3 (Eg = 2,96 eV, d = 0,1 μm, μn = 50 cm 2 /(Vs)) đã được giữ không đổi. Ảnh hưởng của bề dày d và nồng độ hạt tải np của màng Cu2Sn3S7 (αmax = 4,2×10 4 cm -1 , Eg = 1,46 eV) lên Voc, Jsc, Vm, Jm, FF và η của pin đã được khảo sát trong các khoảng giá trị d = 0,3 – 3,5 μm và np = 10 17 – 1020 cm-3. Trong điều kiện chiếu sáng tiêu chuẩn AM 1.5G ở nhiệt độ 300 K, pin mặt trời ZnO/In2S3/Cu2Sn3S7/Mo có Rs = 10 Ω.cm 2 và Rsh = 1×10 6 Ω.cm2 sử dụng màng Cu2Sn3S7 có d = 2 µm, αmax = 4,2×10 4 cm -1 , Eg = 1,46 eV, μp = 15 cm 2 /(Vs) và np = 10 20 cm -3 đạt hiệu suất lớn nhất ηmax = 18,0 % với Voc = 0,98 V, Jsc = 31,2 mA/cm 2 , Vm = 0,62 V, Jm = 28,8 mA/cm 2 và FF = 58,8 %. Từ khóa: Cu2Sn3S7, SCAPS, Pin mặt trời.