Influence of Ge doping on defect distributions of Cu2Zn(Snx Ge1−x) (Sy Se1−y) fabricated by nanocrystal ink deposition with selenization

Copper zinc tin sulfide (CZTS) solar cells have recently attracted attention as a potential low cost, earth abundant replacement for CIGS cells. This new thin film material boasts theoretical efficiencies on par with CIGS, but instead uses the relatively common elements zinc and tin rather than the rarer and more expensive indium and gallium. Band gap tuning by adding Ga has been previously used to improve performance for CIGS devices. A mechanism for band gap tuning in CZTS could prove advantageous as well. Recently, the incorporation of germanium in CZTSSe has been shown to provide a potential method for band gap adjustment and may serve as a way to improve the performance of CZTSSe in a manner that is similar to the role of Ga in CIGS. Several experiments are currently being performed to examine this effect on the efficiency of ink based CZTSSe devices. The material parameters of Ge doped CZTSSe have not yet been thoroughly investigated. This paper reports measurements of defect distributions in CZTSSe samples with varying amounts of Ge. The defect energies are compared to those of CZTS and the relation of defects to cell performance is explored.