Device characterization of (AgCu)(InGa)Se2 solar cells

Ag-alloying of Cu(InGa)Se₂ thin films presents the possibility to increase the bandgap with improved structural properties as a result of a lower melting temperature. (AgCu)(InGa)Se₂ films were deposited by elemental co-evaporation and the resulting solar cell behavior was characterized. While the bandgap in the highest efficiency Cu(InGa)Se₂ cells is ~1.15 eV, Ag alloying allows the bandgap to be increased to 1.3 eV with an increase in V_OC, no loss in device efficiency, and fill factors up to 80%. With high Ga content to increase bandgap > 1.5 eV, Ag alloying improves solar cell efficiency. Analysis of the device behavior shows that the basic mechanisms controlling (AgCu)(InGa)Se₂ solar cells and limiting performance with wide bandgap are comparable to those with Cu(InGa)Se₂. Finally the effect of Na in (AgCu)(InGa)Se₂ devices is shown to be comparable to that with Cu(InGa)Se₂ including a decrease in V_OC attributed to interface recombination with insufficient Na.