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 (Voc) of 744 mV which is amongst the highest values reported for Kesterite materials.