Scalable and extremely flexible production technologies are necessary for an affordable realization of customer specific solar cells. Similar requirements are known for example from interference layer systems in the optical industry.
The concept efficient design is based on this knowledge and employs the Semiconductor-Insulator-Semiconductor (SIS) solar cell concept. For the implementation of the SIS concept, a thin dielectric layer is applied on a standard silicon wafer which must be a tunnel barrier. This step is followed by the overcoating with a transparent conductive oxide (TCO). If the material and process parameters are selected wisely, a hetero solar cell will result. The already known indium tin oxide (ITO) as well as the more cost efficient with aluminum doped zinc oxide (AZO) are suitable for TCO. The maximum level of efficiency for such systems is in the area surrounding 20 %. Due to the use of sputtering procedures with process temperatures less than 400°C, a cost efficient production process with extremely low energy recovery time is ensured, which favors the important Euro per Watt peak ratio (€/Wp) and especially for BIPV important ratio Euro per square meter (€/m²).
For this reason, the SIS solar cell concept allows to achieve sustainable customer-specific solutions at appropriate production costs. Integration of optical production technologies, such as laser aided soldering processes and inkjet printing, gives the opportunity for further differentiation and way more degrees of freedom in the design of PV-elements.
The central aim is to optimize the products (tailor made solar cells and modules) in both their design and their function as power generating elements.
The slogan “functional photonic design” indicates the ambition of this approach to optimize all components of a solar cell with regard to performance and design. This is fundamentally for the SIS hetero contact. The color of the cell is adjusted by variation of the layer thickness. In addition, multi-colors can be realized at one cell. The TCO is not just influencing the coloring but also it is advancing the cell in terms of electrical operation.
Due to the high conductivity of the TCO, it is possible to implement a variety of grid designs that can be accommodated to customers’ demands without additional effort. At the moment, Fraunhofer IOF is developing laser-based optical soldering methods in order to interconnect cells and to promote an innovative and cost-efficient production process.
Both the multi-colored design of solar cells and the integration of design elements on cells and modules are already patented. Currently, procedural protection or manufacturing patents are prepared.