Cu(InGa)Se2 photovoltaics on insulated Stainless Steel Web substrate

This paper presents data on the use of Stainless Steel (SS) foils, coated with 3 to 5μm silicone based resin (SBR) developed by Dow Corning Corporation (DCC) for Cu(InGa)Se₂ based PV devices. The substrate validation was performed by the device performances on R2R deposited Cu(InGa)Se₂ via elemental evaporation and, to a limited extent, on Cu(InGa)Se₂ films from metal precursor selenization. Initially, it is shown that a 430SS base is preferred to others due to a better thermal expansion match to Cu(InGa)Se₂. The SBR-coated SS was found to be an excellent substrate in terms of (i) the adhesion of Mo and Cu(InGa)Se₂ films, (ii) its surface smoothness, and (iii) its operational stability up to 600 °C. Na was introduced into the R2R deposition process by co-evaporating NaF during deposition. Presence of Na in the films was determined by SIMS depth profiling. The highest small area device performance from R2R deposition was 15.2%. In addition, 9ft and 29ft long 8" wide Cu(InGa)Se₂ webs fabricated in the reactor showed machine direction center line, and efficiencies that averaged more than 10%. Precursor selenization process gave the highest efficiency of 12.3% with 10nm NaF deposited on the SBR or on the precursors. Work on developing monolithically integrated 3"×3" mini-modules has been initiated. Encouraging results were obtained in laser scribing the Mo back contact.