Surface morphology improvement of three-dimensional solar cell with Cu2ZnSnS4 absorber

• Three-dimensional structure solar cells were fabricated with a Cu2ZnSnS4 absorber.
• The efficiency was improved by annealing CZTS absorber layer with a CZTS cover.
• The efficiency was improved with lower sulfur concentration solution.

Solar cells with a three-dimensional (3D) structure were fabricated with a Cu2ZnSnS4 (CZTS) absorber (CZTS 3D-cell). CZTS absorbers were deposited by spray pyrolysis deposition (SPD) onto CdS buffer layers and then annealed in a nitrogen atmosphere without a cover, with a SLG plate cover, and with a CZTS covering layer deposited on a 3D substrate. The short circuit current density (Jsc) was improved by annealing with a CZTS covering layer, due to a reduction of cracks on the surface of the CZTS absorber. A CZTS 3D cell was then fabricated using a solution with lower sulfur concentration to suppress the evaporation of S, which resulted in a reduction of holes on the surface of the CZTS absorber and an increase in Jsc and the conversion efficiency (η). The η value was 1.13%, which is the highest efficiency for a CZTS 3D-solar cell to our knowledge.