Electrochemical Deposition of Highly Efficient Cztsse Thin Film Solar Cells

Kesterite Cu₂ZnSn(S,Se)₄ (CZTSSe) thin films are attracting a lot of interest as an alternative system to Cu(In,Ga)Se₂ (CIGS) thin films, owing to their majority carrier type (p-type), proper band gap energy (1.0-1.5 eV), and high optical absorption coefficient (> 10⁴ cm^-1). More promisingly, the CZTSSe is composed of earth-abundant (cf. In in CIGS), environmentally-friendly (cf. Cd in CdTe), and relatively cheap elements. We have recently reported that a highly efficient CZTSSe thin film solar cell can be fabricated via an electrochemical method involving the electrochemical deposition of metallic Cu-Zn-Sn (CZT) precursor thin films and the subsequent sulfurization/selenization process. In this study, we investigated the effect of the electrochemical deposition conditions on the physical and chemical properties of the metallic precursor films and the final CZTSSe thin films. In particular, the oxygen content in the precursor and CZTSSe thin films was found to influence the film morphology and the device performance. By carefully controlling the deposition condition, such as the bath temperature, solution composition, and the cell configuration, the oxygen content in the thin films could be successfully reduced. After some additional optimization processes including the annealing condition, an efficiency exceeding 8% was obtained, which is one of the highest efficiencies reported on the electrochemically deposited CZTSSe thin film solar cells.