The outcome of replacing Sn completely by Ge in Kesterite Cu2ZnSnSe4 solar cells

In this work, the fabrication and properties of a Ge-based Kesterite Cu
₂
ZnGeSe
₄
solar cell have been discussed. The substitution and the existence of the quaternary compound has been verified by physical methods. The device has a power conversion efficiency of 5.5% under AM1.5G illumination which is among the highest reported for pure Ge substitution. In depth electrical and optical analysis show that the Cu
₂
ZnGeSe
₄
absorber has less bulk defects, less or no band tailing and no sub band gap emissions, which are all characteristic of Cu
₂
ZnSnSe
₄
devices. These beneficial opto-electronic properties also result in a high open circuit voltage (V
_oc
) of 744 mV which is amongst the highest reported for Kesterite materials.