Cost reduction is one of the primary research aims of the solar photovoltaic (PV) industry as current costs limit the application of this technology. This project, which has achieved significant cost reductions in the production of 30 cm by 30 cm amorphous silicon modules, has opened up new fields of application for this renewable energy technology. The main objective of the CLIMAX (i.e. cost-effective large area integrated multi-junction amorphous silicon solar cell structures) project was the development and optimisation of new types of large area photovoltaic amorphous silicon thin-film modules. The project aimed to deliver 30 cm by 30 cm amorphous silicon modules, with an enhanced stabilised conversion efficiency of 8% using an integrated two-terminal tandem device structure and showing variable costs (direct manpower and materials) of only 1 ECU per peak of Watt. The achievement of these objectives would result in an energy-efficient and cost-effective PV system, which would open up new fields of application. The application of the modules would be in stand-alone systems, such as in the roofs of isolated houses, but also in grid-connected systems to meet expensive peak load demand. Due to ongoing research it was also intended that this project would result in advanced deposited silicon materials, new band-gap engineering and profiling concepts as well as numerical computer simulations for the analysis of such structures.