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摘要: 在Si衬底上制备的Cu2ZnSnS4(CZTS)太阳能电池具有CZTS与Si衬底的晶格失配低的优点, 但目前其转换效率仍较低. 本文采用异质结太阳能电池仿真软件Afors-het对Si衬底CZTS太阳能电池进行数值计算. 对现有的p-CZTS/n-Si太阳能电池的计算结果表明, 在该电池结构中p-CZTS和n-Si分别起窗口层和吸收层的作用, 但p-CZTS具有高光吸收系数, 使大部分入射光无法透过p-CZTS层进而被n-Si吸收, 限制了电池的转换效率. 本文提出以p-Si作为衬底的n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si太阳能电池结构. 计算得到的p-CZTS/p-Si结构的暗态电流密度-电压(J–V)特性曲线均为线性曲线, 表明p-CZTS与p-Si为欧姆接触以及p-Si作为p-CZTS的背电极的可行性. 进一步计算了p-Si的厚度与掺杂浓度、p-CZTS的厚度与掺杂浓度对n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si太阳能电池光伏特性的影响, 在不考虑寄生串并联电阻效应和缺陷态的理想情况下, 电池的最高转换效率为28.41%. 本文计算结果表明, n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si太阳能电池可解决现有p-CZTS/n-Si结构存在的问题, 是一种合适的Si衬底CZTS太阳能电池结构.Abstract: The Cu2ZnSnS4 (CZTS) solar cell prepared on Si substrate has an advantage of low lattice mismatch between CZTS and Si substrate, but the conversion efficiency of reported p-CZTS/n-Si solar cells is still low at present. In this work, the CZTS solar cells on Si substrate are calculated numerically by heterojunction solar cell simulation software Afors-het. The calculated results show that the p-CZTS and n-Si act as window layer and absorber respectively in the p-CZTS/n-Si solar cell because the band gap of p-CZTS is larger than that of n-Si. The conversion efficiency of p-CZTS/n-Si solar cell increases as the thickness of p-CZTS window layer decreases. The highest calculated conversion efficiency of p-CZTS/n-Si solar cell is 18.57%. In the best p-CZTS/n-Si solar cell, most of the incident light cannot pass through the p-CZTS window layer due to the high absorption coefficient of p-CZTS, which limits the conversion efficiency of solar cell. In order to solve the problems existing in the p-CZTS/n-Si structure, a novel n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si solar cell structure is proposed, where n-ZnO:Al and i-ZnO are window layers, n-CdS is buffer layer, p-CZTS is absorber, and p-Si is substrate and back electrode. The dark current density-voltage (J-V) characteristic curves of p-CZTS/p-Si structure varying with the thickness and doping concentration of p-Si and the doping concentration of p-CZTS are calculated to investigate the feasibility of p-Si as a back electrode of p-CZTS. All the calculated J-V characteristic curves of p-CZTS/p-Si structure are linear, indicating the formation of ohmic contact between p-CZTS and p-Si. The photovoltaic properties of n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si solar cell are further calculated. The built-in electric field distributed in n-ZnO:Al, i-ZnO, n-CdS, and p-CZTS contribute to the collection of photo-generated carriers. The conversion efficiency of n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si solar cell is enhanced with the decrease of the thickness of p-Si and the increase of doping concentrations of p-Si and p-CZTS and the thickness of p-CZTS. Without considering the effect of parasitic series resistance and parallel resistance and defect states, the highest conversion efficiency of ideal n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si solar cell is 28.41%. The calculated results in this work show that the n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si solar cell has an appropriate structure for CZTS solar cell on Si substrate.
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Key words:
- Cu2ZnSnS4 /
- Si /
- back electrode /
- photovoltaic property
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图 1 仿真结构示意图 (a) p-CZTS/n-Si; (b) p-CZTS/p-Si; (c) n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si
Figure 1. Diagrams of different structures: (a) p-CZTS/n-Si; (b) p-CZTS/p-Si; (c) n-ZnO:Al/i-ZnO/CdS/CZTS/p-Si.
图 2 p-CZTS/n-Si太阳能电池性能随 (a) n-Si的厚度dn-Si, (b) n-Si的掺杂浓度Nn-Si, (c) p-CZTS的厚度dp-CZTS, (d) p-CZTS的掺杂浓度Np-CZTS的变化关系
Figure 2. The performances of p-CZTS/n-Si solar cell with the changes of (a) the thickness of n-Si (dn-Si), (b) the doping concentration of n-Si (Nn-Si), (c) the thickness of p-CZTS (dp-CZTS), (d) the doping concentration of p-CZTS (Np-CZTS).
图 3 最优p-CZTS/n-Si太阳能电池的 (a) J–V特性曲线, (b)光谱响应, (c)载流子产生率分布图
Figure 3. The (a) J–V characteristic curve, (b) spectral response, (c) generation rate distribution of the optimal p-CZTS/n-Si solar cell
图 4 p-CZTS/p-Si的J-V特性曲线随p-Si厚度dp-Si的变化
Figure 4. J-V characteristic curves of p-CZTS/p-Si with the change of the thickness of p-Si (dp-Si).
图 5 p-CZTS/p-Si的J-V特性曲线随p-Si掺杂浓度Np-Si的变化
Figure 5. J-V characteristic curves of p-CZTS/p-Si with the change of the doping concentration of p-Si (Np-Si).
图 6 p-Si掺杂浓度为 (a) 1 × 1015 cm–3, (b) 1 × 1017 cm–3, (c) 1 × 1019 cm–3时, p-CZTS/p-Si的能带图
Figure 6. Band diagrams of p-CZTS/p-Si when the doping concentrations of p-Si are (a) 1 × 1015 cm–3, (b) 1 × 1017 cm–3, (c) 1 × 1019 cm–3
图 7 p-CZTS/p-Si的J-V特性曲线随p-CZTS掺杂浓度Np-CZTS的变化
Figure 7. J-V characteristic curves of p-CZTS/p-Si with the change of the doping concentration of p-CZTS (Np-CZTS).
图 8 p-CZTS掺杂浓度为 (a) 1 × 1015 cm–3, (b) 1 × 1017 cm–3, (c) 1 × 1019 cm–3时, p-CZTS/p-Si的能带图
Figure 8. Band diagrams of p-CZTS/p-Si when the doping concentrations of p-CZTS are (a) 1 × 1015 cm–3, (b) 1 × 1017 cm–3, (c) 1 × 1019 cm–3.
图 9 n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si太阳能电池的性能随 (a) p-Si厚度dp-Si, (b) p-Si掺杂浓度Np-Si, (c) p-CZTS厚度dp-CZTS, (d) p-CZTS掺杂浓度Np-CZTS的变化关系
Figure 9. The performances of n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si solar cell with the changes of (a) the thickness of p-Si (dp-Si), (b) the doping concentration of p-Si (Np-Si), (c) the thickness of p-CZTS (dp-CZTS), (d) the doping concentration of p-CZTS (Np-CZTS).
图 10 优化的n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si太阳能电池的 (a) J–V特性曲线, (b)光谱响应, (c)内建电场, (d)能带图
Figure 10. The (a) J–V characteristic curve, (b) spectral response, (c) built-in electric field, (d) band diagram of the optimal n-ZnO:Al/i-ZnO/n-CdS/p-CZTS/p-Si solar cell.
表 1 仿真参数取值
Table 1. Simulated parameters.
参数 p-CZTS n-CdS i-ZnO n-ZnO p-Si n-Si 介电常数 10 10 9 9 11.9 11.9 电子亲和能/eV 3.8 4.2 4.6 4.6 4.05 4.05 禁带宽度/eV 1.53 2.4 3.3 3.3 1.12 1.12 导带有效密度/cm–3 2.2 × 1018 1.8 × 1019 2.2 × 1018 2.2 × 1018 3.32 × 1018 3.32 × 1018 价带有效密度/cm–3 1.8 × 1019 2.4 × 1018 1.8 × 1019 1.8 × 1019 1.44 × 1019 1.44 × 1019 电子迁移率/(cm2·V–1·s–1) 100 100 100 100 1450 1450 空穴迁移率/(cm2·V–1·s–1) 57.6 25 25 25 500 500 受主掺杂浓度/cm–3 变量 0 0 0 变量 0 施主掺杂浓度/cm–3 0 1 × 1017 1 × 105 1 × 1018 0 变量 缺陷浓度/cm–3 1 × 1012 6 × 1016 1 × 1017 1 × 1017 — — 电子俘获截面/cm2 4.13 × 10–14 1 × 10–17 1 × 10–12 1 × 10–12 — — 空穴俘获截面/cm2 4.13 × 10–11 1 × 10–13 1 × 10–15 1 × 10–15 — — 厚度/μm 变量 0.05 0.2 0.2 变量 变量 
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