Fabrication of Solar Cells By Tuning the Composition Ratio of AgGaTe₂ to Ga-Rich

Silver gallium telluride (AgGaTe₂), an environmentally friendly material with a high optical absorption coefficient, was fabricated by the close-spaced sublimation (CSS) method. It was found that stoichiometric AgGaTe₂ thin films can be produced by using GaTe as the source material for CSS and controlling the Ga molar concentration. Solar cells based on Cu(In, Ga)Se₂ (CIGS), which has a similar structure to that of AgGaTe₂, have been reported to exhibit conversion efficiencies greater than 20% when the CIGS film is Ga-rich and Cu-poor. By increasing the diffusion/sublimation time during the formation of AgGaTe₂ layers and using source materials with a Ga-rich composition, Ga-enriched AgGaTe₂ thin films were formed. Optimal Ga-rich AgGaTe₂ thin films were produced with extended diffusion/sublimation time, with a Ga mole fraction of 32%. However, Ga-rich Ag-Ga-Te compounds, AgGa₅Te₈ or Ga₂Te₃ were developed. Solar cells containing Ga-rich AgGaTe₂ films displayed improved current density–voltage characteristics and spectral sensitivity compared with those of cells containing stoichiometric AgGaTe₂ films. Under AM 1.5 irradiation, the conversion efficiency of the solar cells was recorded at 1.21%.