Sun, J.; Márquez, J.; Stange, H.; Mainz, R.; Mitzi, D.: Phase and film formation pathway for vacuum-deposited Cu2BaSn(S,Se)4 absorber layers. Physical Review Materials 3 (2019), p. 055402/1-7

Earth-abundant copper barium thioselenostannate, Cu2BaSn(S,Se)4, absorbers have recently demonstrated promising optoelectronic and defect resistance properties for solar harvesting applications. The highest photovoltaic device efficiencies have been achieved in vacuum-based co-sputter deposited films, yet there is a tendency for multi-layer formation consisting of large, platelet-like surface grains and a smaller grain-size underlayer (often accompanied by voids). In this work we use a combination of in-situ and ex-situ X-ray diffraction and scanning electron microscopy to unravel the coupling of phase evolution to film morphology. We find that Cu surface migration and associated Cu-rich phases play a defining role in determining the overall film structure.