Role of ZnS Particles in the Performance of Cu<sub>2</sub>ZnSnS<sub>4</sub> Thin Film Solar Cells: A Comparative Study by Active Control of Zinc Deposition in Coevaporated Precursors
Lan Huang, Shijin Wang, Lan Zhong, Ling Chen, Xudong Xiao
Abstract
Formation of ZnS particles in the Cu 2 ZnSnS 4 (CZTS) light absorber layer of CZTS solar cells may impede the photocarrier collection as well as the open circuit voltage. Coevaporation of Cu, Zn, Sn, and S elements can provide a uniform and well‐mixed Cu–Zn–Sn–S precursor at atomic level, yet the annealing/sulfurization process does not preserve such elemental distribution. The Zn element in the formed CZTS absorber thin films from such a uniform precursor distributes unevenly, especially aggregating near the rear interface, and thus deteriorates the film quality. Herein, the movement pathway of the Zn element in the coevaporated precursor during annealing is investigated through energy dispersive X‐ray spectroscopy (EDX) mapping and secondary ion mass spectroscopy (SIMS) profiling. With the understanding of the segregation behavior of the Zn element, an active manipulation of the initial distribution of Zn in the precursor is accordingly designed to effectively alleviate the accumulation of Zn near the rear Mo/CZTS interface and therefore improve the crystalline quality of the absorber. The results suggest that properly controlling the precursor.