Improvement of Cu2ZnSnS4 films properties using sulfurized precursor films with Cu-poor/Zn-rich ratio

The precursor films with Cu-poor/Zn-rich composition ratio prepared by spin coating were sulfurized at different temperatures. Effect of sulfur powder amount, annealing temperature and time on the properties of films were comprehensively investigated. The results show that 0.5 g sulfur powder atmosphere can effectively avoid the loss of S in CZTS precursor and secondary phase formation during sulfurization process. Films sulfurized with 0.3 g sulfur powder easily form Cu2-xS secondary phase. The stable kesterite Cu2ZnSnS4 phases with the optimal Cu-poor/Zn-rich composition ratio are easily obtained under 0.5 g sulfur powder atmosphere. Increase of sulfurization temperature induces the formation of films with dense surface morphology and large grain size. Meanwhile films achieve excellent optical absorption in the range of 400–600 nm and exhibit P-type conduction as well as possess around 1.50 eV band gap, which is close to optimal ideal band gap of solar cells. For the samples sulfurized at 550 °C for 50 min, their carrier concentration, mobility, and resistivity reach 1.34 × 1017cm−3, 1.36 cm2/Vs, 3.85 × 10−3 Ω cm, respectively.