Materials chemistry of CZTS and CIGS absorbers
The many chemical reactions taking place during formation of CZTS or CIGS “absorber layers” combine to impart some of the key properties that determine solar cell performance. We investigate reactions occurring in the films and at their surfaces and interfaces during high temperature formation, from both experimental and theoretical standpoints. The purpose is to find out how different compounds react with each other and how the reactions depend on the conditions, such as temperature and pressure. CZTS and CIGS are both applied in solar cells, but they have very different chemical behaviour due to their different elements and crystal structures. Understanding the observations demands detailed knowledge about the chemical and electrical properties of the compounds.
Examples of the chemical reactions occurring are the exchange of material between the solid film and the hot atmosphere during the formation, which causes the film composition to change; as well as rearrangement of the crystal structure resulting from heating, which causes large changes in material properties. By understanding the relationship between the reactions in the material and the process variables, we can develop improved materials and better synthetic strategies, leading to ever better performance in solar cells.
The picture above shows evolution of photoluminescence from a CZTS film due to heating, resulting from the smooth transition from an ordered (low temperature) to a disordered crystal structure (high temperature). Disorder in the crystal structure must be controlled to achieve the desired electronic properties.
Contact: Jonathan Scragg
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