Solarex, a business unit of Amoco/Enron Solar, is scaling up its a‐Si:H/a‐SiGe:H tandem device technology for the production of 8 ft2 modules. The current R&D effort is focused on improving the performance, reliability and cost‐effectiveness of the tandem junction technology by systematically optimizing the materials and interfaces in small‐area single‐ and tandem junction cells. Average initial conversion efficiencies of 8.8% at 85% yield have been obtained in pilot production runs with 4 ft2 tandem modules.