Characterization of Cu2ZnSnS4 thin films deposited by one-step thermal evaporation for a third generation solar cell

Highlights: • TiO₂ nanorods have been successfully synthesized on the FTO-coated glass substrates. • Mono-phase CZTS thin films were successfully obtained by one-step thermal evaporation. • The stoichiometry of the CZTS thin films was revealed to be Cu-poor and Zn-rich. • The band gap was determined to be 1.47 eV for CZTS thin film annealed 450 °C. • The constructed superstrate-type CZTS solar cell exhibited a 0.61% efficiency. -- Abstract: In this study, one-step thermal evaporation was employed for the fabrication of phase-pure CZTS thin films on glass substrates from single crystalline Cu-poor ingot grown by Bridgman technique. Structural analyses revealed the formation of a mono-phase CZTS kesterite structure for the thin films annealed at 450 ^°C under N₂ atmosphere. The AFM measurements demonstrated significant morphological changes in films with increasing the annealing temperature from 200 ^°C to 450 ^°C, supporting the results obtained via XRD and Raman studies. From the optical measurements, the band gap was estimated to be 1.47 eV for the CZTS film annealed at 450 °C, which is close to the optimum value required for photovoltaic applications. As a device application of the optimized CZTS thin films, an attempt was made to construct a TiO₂ NRs based and CdS-free FTO/TiO₂ NRs/CZTS/Ag superstrate CZTS solar cells. TiO₂ NRs were grown by hydrothermal technique, which offers a simple and a cost-effective route for large-scale production of one-dimensional nanostructures. The solar cell exhibited an open-circuit voltage of 0.35 V, a short-circuit current density of 7.28 mA/cm², a fill factor of 23.9% and a power conversion efficiency of 0.61%, the highest efficiency recorded so far for a single-dimensional TiO₂ nanostructures based superstrate CZTS solar cell.