Annealing behavior of reactively sputtered precursor films for Cu2ZnSnS4 solar cells

Reactively sputtered Cu–Zn–Sn–S precursor films are prepared and recrystallized by rapid thermal processing to generate Cu2ZnSnS4 solar cell absorber layers. We study how the film properties are affected by substrate heating and composition. The stress, density and texture in the films were measured. Compressive stress was observed for the precursors but did not correlate to the deposition temperature, and had no influence on the properties of the annealed films or solar cells. However, the substrate temperature during precursor deposition had a large effect on the behavior during annealing and on the solar cell performance. The films deposited at room temperature had, after annealing, smaller grains and cracks, and gave shunted devices. Cracking is suggested to be due to a slightly higher sulfur content, lower density or to minor differences in material quality. The grain size in the annealed films seems to increase with higher copper content and higher precursor deposition temperature. The best device in the current series gave an efficiency of 4.5%.

► We sputter Cu–Zn–Sn–S-films at different temperatures and Cu/Sn ratios.
► There is no correlation between deposition temperature and stress in the films.
► A rapid anneal transforms the films to large grained Cu2ZnSnS4.
► Precursor deposition temperature affects morphology of annealed films.
► The highest solar cell efficiency from this series was 4.5%.