Room temperature deposition of highly crystalline Cu-Zn-S thin films for solar cell applications using SILAR method

Cu-Zn-S having inexpensive, non-toxic, and earth-abundant constituent elements, combined with suitable optical and electrical properties is a promising candidate as an absorber material for thin film solar cell fabrication. We report the deposition of Cu-Zn-S thin films using Successive Ionic Layer Adsorption and Reaction (SILAR) method under room temperature and atmospheric conditions. Cu-Zn-S thin films are deposited over glass substrates with different Cu/(Cu+Zn) ratio in the precursor solution to investigate the band gap tunability. The as-deposited Cu-Zn-S films are characterized for determining their structural, compositional, morphological, optical and electrical properties. Also studied the stability of electrical properties for a period of six months after the deposition. All the films exhibited p-type conductivity and a relatively high absorption coefficient value between 104 to 105 cm−1 in the visible and near-IR spectral range. We observed that, under the Zn-rich growth conditions, the films formed are having a double band gap structure with lower band gap values in the range 1.6-1.7 eV, making them a suitable absorber material for solar cell fabrication. Under the Cu-rich growth conditions, band gap values reached 2.4-2.6 eV making them a suitable buffer/window layer in solar cell application. Notably, films with Cu/(Cu+Zn) ratio 0.8 showed an optical transparency of 40-70% in the visible spectrum along with an electrical conductivity of 2900 S cm−1, which is much higher than the other reported p-type transparent conducting materials.