The compositions of quaternary compound semiconductor Cu₂ ZnSnS₄ (CZTS) not only are non-toxic, but also have high abundances in the earth crust, thus its raw materials cost is relative cheap. As a direct band-gap semiconductor, the absorption curve of CZTS is very well matching with solar radiation spectra, and has a large optical absorption coefficient. Besides, its crystal structure, composition, and properties can be easily adjusted and controlled. So, CZTS presents excellent optoelectric performance, and is considered as the ideal key materials for the development of green, low-cost, high-efficient, and stable thin film solar cells. Recently, the crystal structures, physical and chemical properties, preparation technology, and various applications of CZTS have been extensive investigated. Especially, the researches about adjust and control the structure or composition to improve the photoelectric conversion efficiency of CZTS-based thin film solar cells have been received extensive concerning. In this review, the progress of CZTS research (including crystal structure evolution, preparation technology, optoelectric properties, and applications) has been summarized, in which the relationship between intrinsic factors (such as crystal structures, defects, surface, interface, and alloy effects) and photovoltaic performance of CZTS has been emphasized. Meanwhile, as the novel energy conversion materials, the applications of CZTS in the fields of photocatalysis and thermoelectrics have been also discussed. Finally, current challenge and future hotspots of CZTS are point out, and the possible breakthrough direction is forecasted.

Contents
1 Introduction
2 Crystal structure evolution
3 Preparation technologies
3.1 Vapor phase methods
3.2 Liquid phase methods
3.3 Solid phase methods
4 Theoretical calculations
4.1 Crystal structure and basic physical properties
4.2 Aolly semiconductors
4.3 Defects
5 Applications
5.1 Photovoltaics
5.2 Photocatalysis
5.3 Thermoelectrics
6 Challenge and outlook