Non-vacuum prepared 9.1% efficient Cu2Zn(Sn,Ge)(S,Se)4 solar cells using a novel selenization process

A novel selenization process is used to prepare Cu2Zn(Sn,Ge)(S,Se)4 (CZTGSSe) thin films. During this selenization process, Ge is introduced into the solution deposited precursors from a GeSe2 source and assists the formation and crystallization of CZTGSSe. The composition, morphology and phases for the selenized films are investigated and solar cells are prepared. The results suggest Ge is incorporated into the material and no obvious secondary phases except ZnSe are detected in CZTGSSe. The obtained CZTGSSe layers are constituted of large crystal grains and show uniform morphology. Based on the CZTGSSe absorber, solar cells with efficiencies up to 9.1% can be fabricated.