Fabrication and reliability of copper zinc tin sulfide (CZTS) thin film solar cells

Thin film solar cells have advantages over traditional crystalline-based solar cells in the manufacturing process. Thin film solar cells can be flexible, which makes them easier to mass-produce and cheaper to manufacture. One such solar cell is known as copper zinc tin sulfide, Cu2ZnSnS4 (CZTS), which is a compound semiconductor made of copper, zinc, tin, and sulfur. Each component of CZTS is abundant in the earth's crust; furthermore, none of them are harmful to the environment in the amounts typically used. CZTS is a promising absorber for low-cost thin film solar cells because of its adequate band-gap energy and large light absorption coefficient. The primary objective of this research is to improve the fabricating processes and to study the stability of CZTS thin film solar cells. The fabricating process of CZTS thin film solar cell consists of depositing multilayers such as a contact, transparent conductive oxide (TCO), n-type buffer layer, and p-type absorber layer. In this research, radio frequency (RF) and direct current (DC) magnetron sputtering, chemical bath deposition (CBD), and atomic layer deposition (ALD) techniques are used for depositing the precursor, buffer layer, and TCO layer. The cells require a sulfurization and annealing process and in this research a process employing elemental sulfur is used. The CZTS thin film solar cells are fabricated on rigid glass and flexible glass that are compatible with a roll-to-roll process. The degradation of CZTS solar cell conversion efficiency and TCO layers under mechanical and environmental loadings, which includes bending, accelerated thermal cycling (ATC), and damp heat experiments, are also conducted in this research.