Design and Simulation of Single-Junction and Multi-junction Thin-Film Solar Cells Based on Copper Tin Sulfide
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https://doi.org/10.1007/s11664-020-08382-6 Ó 2020 The Minerals, Metals & Materials Society
Design and Simulation of Single-Junction and Multi-junction Thin-Film Solar Cells Based on Copper Tin Sulfide SAMANEH AMIRI1 and SAJJAD DEHGHANI 1.—Faculty of Advanced [email protected]
Technologies,
Shiraz
1,2
University,
Shiraz,
Iran.
2.—e-mail:
In this paper, single- and multi-junction thin-film solar cells based on copper tin sulfide (CTS) are proposed. The proposed single-junction cell consists of copper zinc tin sulfide (CZTS) and CTS, as a bilayer absorber. The doublejunction structure is made of CZTS and CTS absorber layers for the top and bottom cells, respectively. Furthermore, a CZTS/(CZTSe)/CTS triple-junction cell, which is based on earth-abundant and non-toxic elements, is investigated. The performance of the proposed cells in the presence of tin sulfide layers as the back surface field to reduce recombination is also examined. In order to reach the maximum efficiency, the thickness of layers is varied and optimized. The simulated efficiency of the triple-junction structure, including CZTS, CZTSe, and CTS with the optimal thickness of 0.4 lm, 0.7 lm, and 0.7 lm, respectively, was as high as 34.1%. Key words: Thin-film solar cells, CZTS, CTS, multi-junction, kesterite, tandem cell
INTRODUCTION Solar cells are promising technologies for solving the energy problem by providing clean and safe energy.1,2 Thin-film solar cells are very attractive in reducing the manufacturing cost of photovoltaic devices.3 Recently, a conversion efficiency of 21.7% has been reported for copper indium gallium sulfide (CIGS) solar cells. But indium and gallium are rare elements, which are expected to increase the cost drastically.4 In contrast to CIGS, kesterite materials such as Cu2ZnSnS4 (CZTS), Cu2ZnSnSe4 (CZTSe) and Cu2SnS3 (CTS) are made from cheap and abundant elements.4,5 They are p-type semiconductors with high optical absorption coefficients (> 104 cm1).4,5 Recently, CTS has been used as the absorbing layer of thin-film solar cells. As reported earlier, CTS may have various bandgap energies in the range of 0.87–1.77 eV.6,7 Kuku et al. fabricated the first CTS solar cell with a conversion efficiency of
(Received December 30, 2019; accepted July 31, 2020)
0.11% by direct evaporation.6,7 In 2015, Kanai et al. fabricated a CTS cell with a conversion efficiency of 4.29% using co-evaporation followed by short annealing.8 In 2017, the performance of the CTS singlejunction solar cell was numerically investigated for the first time.9 The higher bandgap of CTS is in the orthorhombic phase, and hence there is a greater open circuit voltage, so a maximum efficiency of 12% was obtained in this case.9 To absorb the largest percentage of the solar spectrum and increase the overall cell efficiency, multi-junction solar cells with moderate and narrow bandgap materials are utilized. In these structures, the top cell absorbs high-energy photons, the next cell absorbs lower-energy photons, and so on.10,11 In this paper, three so
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