Silver‐Doped Cu2(Sn,Ge)S3 Solar Cells

Herein, the usefulness of silver (Ag)‐doping into Cu 2 (Sn,Ge)S 3 (CTGS) solar cells is demonstrated. From an observation via a field emission scanning electron microscope, grain growth promotion of the CTGS thin films by Ag‐doping is revealed. It is found that undesirable defects are suppressed by an adequate Ag‐dopant amount, resulting in reduced nonradiative recombination in photoluminescence spectra for the Ag‐doped CTGS films. For the CTGS solar cell devices, Ag‐doping into the CTGS absorbers mainly improves the short‐circuit current density and open‐circuit voltage. Finally, 3.2%‐efficient Ag‐doped CTGS solar cell is obtained at [Ag]/([Ag] + [Cu]) ratio of 0.05. It is believed that these findings will help to realize the highest efficiency for the CTGS solar cells.