Sulfur-rich sulfurization and solution stability of Cu2ZnSnS4 solar cells fabricated by 2-Methoxyethanol-based process

Abstract

Cu2ZnSnS4 (CZTS) solar cells were fabricated by 2-Methoxyethanol (EGME) solution process. The sulfurization of the CZTS precursors were carried out in a sulfur-rich ambient by refilling the sulfur powders every 30 min during the heat treatment process. A reference sample was prepared by puting the sulfur powders nearby the sample just at the beginning of the sulfurization. It was found that the CZTS sulfurized in a sulfur-rich ambient (re-fill the sulfur powders every 30 min) was critical to obtain the large grain, voids-free Mo/CZTS interface, and a CZTS film without second phases. The cell parameters were improved and the sulfurization time was shortened using the sulfur-rich heat treatment. Based on our proposed sulfurization process, the conversion efficiency of the CZTS solar cell was 5.8%, which is the best result among CZTS solar cells fabricated through EGME solution processes. The efficiency of the CZTS solar cell fabricated by the solution that was stored for 60 days was still larger than 5%. Deterioration of the solution and the CZTS film was found when the solution was stored for 120 days. The sulfur-rich sulfurization condition and the highly stable EGME solution were proposed for high-efficiency CZTS solar cell application.