Rapid CIS-process for high efficiency PV-modules: development towards large area processing

The guideline for our CIGS-thin film process development is the scalability to large areas for low cost and high throughput module fabrication. Our technology consequently applies established large area sputter coating processes for the Cu-, In-, Ga, Se-precursors as well as for the back- and front-electrode. The characteristics of our absorber formation are an advanced two-step stacked elemental layer process including Cu(Ga)-In-Se precursor deposition, rapid thermal processing (RTP) to CIGS in a sulfur-containing ambient and a controlled sodium doping technique. Within our laboratory 12-cell mini-module baseline (substrate size: 10 cm x 10 cm) peak and average conversion efficiencies of 14.7% and 13.2% +/- 1.5%, respectively, have been achieved. By varying the sulfur content from run to run in the gas atmosphere of the absorber formation process the total S/(Se + S) ratio in the obtained CIGS films has been changed between 0% and 18%. Although TEM-EDX- and SIMS-analyses on the CIGS-absorbers reveal an increased concentration of sulfur (and also gallium) towards the molybdenum back electrode, open circuit voltage and minority carrier lifetime monotonously increase with the average S/(Se + S) ratio determined by XRF. Our scaling up efforts towards pilot module processing necessitate a transfer of our laboratory RTP-technology to a fast heating system for large area substrates (60 cm x 90 cm) at a high throughput. The essential task of heating the single-side-coated glass panel homogeneously is successfully demonstrated in a prototype heating chamber proving that a temperature deviation of +/- 10 degreesC is not exceeded even at high heating rates. (C) 2001 Elsevier Science B.V. All rights reserved.