Increased electrical power generated from a thin-film silicon (TF-Si) photovoltaic device can lead to a reduced cost of electricity production that will support the mass adoption of this technology as a renewable energy source. Extracting the highest conversion efficiency from 'champion' large area TF-Si modules has been the focus of development at TEL Solar AG, Trtibbach. The layer deposition process adjustments and further module technology improvements that led to a significant increase in the absolute stabilized module conversion efficiency of large area (1.43 m(2)) tandem MICROMORPH (TM) modules centered first on obtaining high quality amorphous TF-Si deposited materials for the top cell. This was integrated with microcrystalline TF-Si material for the bottom cell that was deposited under conditions close to the transition point between the amorphous and microcrystalline growth regimes. In an optimized solar cell design the TF-Si materials were then combined with effective light management technologies and an improved module layout. The end result of a world record large area (1.43 m(2)) stabilized module conversion efficiency of 12.34% was certified by the European Solar Test Installation (ESTI). The main technology contributions in the device design for this breakthrough result that generated more than 13.2% stabilized efficiency from each equivalent 1 cm(2) of the active area of the full module are described. (C) 2015 Elsevier B.V. All rights reserved.