Pyrolysis preparation of Cu2ZnSnS4 thin film and its application to counter electrode in quantum dot-sensitized solar cells

The Cu2ZnSnS4 (CZTS) thin films with uniform and porous surface feature with the pore size of 100-200 nm were successfully prepared by pyrolysis procedure using the methanol solution containing copper chloride dihydrate (0.06 mol dm−3), zinc chloride (0.03 mol dm−3), stannous chloride dihydrate (0.03 mol dm−3), thiourea (0.48 mol dm−3) and deionized water (1.92 mol dm−3) as precursor solution at 380°C in air atmosphere. Electrochemical impedance spectroscopy was applied to evaluate the electrochemical catalytic activity of the pyrolysis CZTS thin films for redox couple of Sn2-/S2− and the charge transfer resistance was 64.08 Ω using the pyrolysis CZTS thin film obtained by repeating the procedure of dipping the FTO substrate into the precursor solution and heating at 380°C for 7 cycles. The assembled quantum dot-sensitized solar cells gave an open-circuit photovoltage of 0.52 V, a short-circuit photocurrent density of 12.96 mA cm−2, and a fill factor of 0.38, corresponding to the photoelectric conversion efficiency of 2.56%. Because the pyrolysis procedure was a facile, low cost and vacuum-free process, and had the advantage of obtaining various porous microstructure thin films and allowing deposition over large areas, the pyrolysis CZTS thin films can serve as an effective counter electrode for QDSCs.