This paper addresses three independent approaches to improving the performance of Micromorph® tandem solar cells: 1. Thinner cells for higher throughput in mass-production, 2. Optimum cell design and processes yielding stable efficiencies of 11.5% on as-grown ZnO front contact, and finally 3. The introduction of novel textured glass substrates prepared by Corning Incorporated to improve light-management. As a result of the joint research between Oerlikon Solar- Lab and Corning Incorporated, a Micromorph® tandem cell with no anti-reflection coating demonstrated a stable efficiency of 11.9% as independently measured by NREL. This third result represents a new milestone for thin film silicon solar cell technology which is 8% higher than one year ago. Combinations of these improvements are expected to enable cell efficiencies of 12.5% and beyond