Low-cost nanoporous Cu₂ZnSnS₄ thin-film counter electrode for dye-sensitized solar cells

The Cu₂ZnSnS₄ thin film is a well-known and promising electrode material to substitute for the expensive Pt counter electrode used in dye-sensitized solar cells. In this work, we have proposed a novel nanoporous Cu₂ZnSnS₄ thin film prepared by a simple and non-toxic process for use as the counter-electrode material. The Cu₂ZnSnS₄ thin film was easily prepared by a simple spin coating process using a sol-gel precursor that consists of metal chlorides and thiourea, followed by thermal annealing. By manipulating the thermal annealing conditions, a Cu₂ZnSnS₄ thin film with unique nanoporous morphology could be realized, and this film was very effective as the counter electrode owing to its large surface area. Because the size of Cu₂ZnSnS₄ nanograins was affected by the thermal annealing temperature, the scale of the nanoporous structures of the Cu₂ZnSnS₄ counter electrode, which significantly affects the photovoltaic characteristics of dye-sensitized solar cells, could be controlled by manipulating the annealing temperature. The structure and morphology of nanoporous Cu₂ZnSnS₄ thin films were characterized via X-ray diffraction and scanning electron microscopy analysis, and the photovoltaic performance of dye-sensitized solar cells based on the nanoporous Cu₂ZnSnS₄ counter electrode was also investigated. The nanoporous Cu₂ZnSnS₄ counter electrode exhibited a power conversion efficiency of 4.494% under 100 mW/cm² AM 1.5 simulated light, V_oc of 0.610 V, J_sc of 10.46 mA/cm², and FF of 70.44%, and this power conversion efficiency was comparable to that of a conventional Pt counter electrode (5.719%) for the same device configuration.