Influence of stacking order and intermediate phase at low temperature on Cu2ZnSnS4 thin film formation for solar cell

Abstract

A stacking order of a precursor is one of the important factors that affects the quality of Cu2ZnSnS4 (CZTS) thin film. Understanding of the intermediate phase formation and its reaction mechanism can contribute to the design of a precursor to enhance the performance of CZTS solar cell. In this work, three precursors such as Zn/SnS/Cu, SnS/Cu/Zn, and SnS/Zn/Cu were designed based on previous studies. These precursors were treated for sulfurization process at 560 °C, and annealed at 300 °C for 30 min to investigate the reaction of intermediate phases. The annealed thin film from Zn/SnS/Cu precursor exhibited crystallized and uniform intermediate ternary phase of Cu2SnS3. This easy and uniform transformation to Cu2SnS3 phase as a whole at low temperature using Zn/SnS/Cu precursor resulted in relatively smooth surface of CZTS thin film after sulfurization at high temperature. In contrast, CZTS thin film from SnS/Cu/Zn or SnS/Zn/Cu precursor showed a rough surface morphology with loss of Zn content. A rough surface will degrade the contact between CZTS absorber and CdS buffer layers, resulting in decreased a device performance. Accordingly, CZTS solar cell device fabricated from Zn/SnS/Cu precursor achieved improved efficiency of 4.20%.