Silicon based photovoltaic cells are the dominant technology for terrestrial solar energy conversion with the best devices today measuring 25 % in the laboratory. Significantly higher conversion efficiencies up to 38.8 % are so far only reached with multi-junction cells based on III-V semiconductors. However, these materials are too expensive for the use in flat-plat modules on the earth, while for satellite applications they are of high value. NWs allow to significantly reduce material needs without compromising absorption or performance. Combining III-V nanowires (NWs) with today’s silicon photovoltaic technology offers the potential to reach at the same time very high performance devices, efficient use of materials and low cost.
During the Nano-Tandem project, three manufacturing concepts are evaluated against each other. After the second year of the project, the three different approaches for NW based tandem junction solar cells were assessed and a choice was made on which of these to push further in the remaining time of the project. Consequently, one of the approaches was stopped.
The most important impact of the Nano-Tandem project is to present a path for significant performance improvements of photovoltaic modules. Starting from today’s silicon PV technology, the Nano-Tandem technology allows increasing the efficiency through integration of a single NW pn-junction, and at a later stage possibly even a dual NW pn-junction. Efficiency is the most important factor in reducing the cost of solar electricity, as all area related costs are reduced by the overall power output of a PV module. Therefore, efficiency improvements of solar cells are a key to reach competitiveness with conventional energy sources based on fossil fuels or nuclear power. Furthermore, PV modules with higher efficiency allow harvesting of more energy from a constrained area, like a roof, and therefore having a higher value for the customer. Different approaches towards the implementation of “Building-integrated photovoltaics – BIPV” will constitute important steps towards our future “electricity-based society”, and will be an enabler for communication, lighting as well as electrical vehicles. High-tech products like the Nano-Tandem cell will help the European industry to have a unique differentiator compared to silicon PV modules, which have become a commodity product.
