Fabrication and characterization of Cu2ZnSnS4 thin films for photovoltaic application by low-cost single target sputtering process

• Fabrication of Cu2ZnSnS4 (CZTS) thin films by single-target sputtering process.
• Low-cost sulfurization treatment of the as-deposited CZTS films.
• Systematic investigation of structural, electrical and optical properties.
• The CZTS-based solar cell had a photovoltaic conversion efficiency of 4.4%.

Highly crystallized single-phase Cu2ZnSnS4 thin films were fabricated using a simple single-target sputtering technique followed by low-cost sulfurization treatment with sulfur powder. The effects of sulfurization temperature (ranging from 400 to 550 °C) on the structure, morphology, composition, optical and electrical properties of the synthesized CZTS thin film were investigated systematically. The increased sulfurization temperature was found to affect the elemental composition slightly but significantly improve crystallinity, carrier mobility and optical band gap of CZTS films. In particular, the CZTS film sulfurized at 500 °C had excellent optical and electrical properties (an optical band gap of 1.53 eV, a hole concentration of 3.2 × 1015 cm−3, and a carrier mobility of 57.6 cm2(V.s)−1). Furthermore, CZTS-based solar cells were successfully fabricated. Current-voltage (J-V) characteristics indicated that the current density had a tendency of increase with the increase of sulfurization temperature, which was attributed to the relatively large grains and high mobility achieved at a high sulfurization temperature. Importantly, the solar cell based on the CZTS thin film sulfurized at 500 °C had the best performance with a photovoltaic conversion efficiency of 4.4%, open-circuit voltage of 650 mV, short-circuit current density of 19.2 mA/cm2, and fill factor of 37%.