Spray pyrolysis deposited CuSbS2 absorber layers for thin-film solar cells

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.