Spray pyrolysis deposited CuSbS2 absorber layers for thin-film solar cells
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CuSbS2 thin films were fabricated by spray pyrolysis from metal chloride aqueous solutions, followed by a post-deposition sulfurization step. The structural, chemical, optical and electrical properties of CuSbS2 and the effect of various sulfurization temperatures on CuSbS2 thin film have been systematically studied. We used a two-step sulfurization method. Step 1 at lower temperature was to encourage complete saturation of the as-deposited film with sulfur vapor. And step 2 at higher temperature was to promote the formation and crystallization of CuSbS2. The sulfurization temperature of step 2 is very important for the formation of device-grade CuSbS2 films. With the increase in sulfurization temperature, impurities such as Sb2S3 decreased and the crystallinity of CuSbS2 improved. Until 400 °C, impurities disappeared and phase-pure well-crystallinity CuSbS2 thin films were obtained. When the sulfurization temperature is higher than 400 °C, CuSbS2 gradually changes to Cu3SbS4. The CuSbS2 films sulfurized at 400 °C with optimum band gap of 1.53 eV are p type, and absorption coefficient is larger than 105 cm−1 in the visible light wavelength range. The temperature dependence of electrical conductivity of CuSbS2 has been studied for the first time. At measurement temperatures higher than 140 K the electrical conductivity of the CuSbS2 film is dominated by band conduction and nearest neighbor hopping (NNH). However, at temperatures below 140 K the conduction is predominantly affected by variable range hopping (VRH). Finally, thin-film solar cells based on the sprayed CuSbS2 absorber layers with a maximum photoelectric conversion efficiency of 0.34% have been fabricated.
This work was financially supported by the Fundamental Research Funds for the Central Universities (No. JZ2017HGTB0192), the National Natural Science Foundation of China (Nos. 51302057, 51602088), the Natural Science Foundation of Anhui Province (Nos. 1608085QE92, 1708085MA11) and the Hefei University of Technology 2018 Training Program of Innovation for Undergraduates (Nos. 2018CXCY092, 2018CXCY114).
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