Optoelectronic properties of thin film Cu2ZnGeSe4 solar cells

The fabrication and properties of a Ge-based Kesterite Cu₂ZnGeSe₄ (CZGSe) solar cell are discussed. The existence of the quaternary compound has been verified by physical methods such as X Ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS). The Cu₂ZnGeSe₄ solar cell has a power conversion efficiency (PCE) of 5.5% under AM1.5G illumination which is among the highest reported for pure Ge substitution. Detailed low temperature current-voltage and time-resolved photoluminescence measurements show that the Cu₂ZnGeSe₄ absorber has less bulk defects and less band tailing in contrast to the typical characteristics of Cu₂ZnSnSe₄ devices. These beneficial opto-electronic properties also resulted in a high open circuit voltage (V_oc) of 744 mV which is amongst the highest values reported for Kesterite materials.