FULLSPECTRUM project aims to make use of the FULL solar SPECTRUM to produce electricity. Present commercial solar cells used for terrestrial applications are based on single gap semi-conductor solar cells. These cells can by no means make use of the energy of below band gap energy photons since these simply cannot be absorbed by the material.

Approach
FULLSPECTRUM’s innovation is the creation of a multijunction solar cell that makes better use of the entire solar spectrum. The technology uses solar cells made of different materials (including gallium, phosphorus, indium and germanium) with different band gaps stacked on top of each other. Tests have shown that these cells can convert as much as 37.6 % of the sun’s energy into electricity. However, these cells are very expensive, although their cost may be significantly reduced by arranging them in special panels which include lenses that cast a large
amount of solar energy on the cells. Because the cells are much more efficient, fewer photovoltaic panels are required to achieve the same power output, thereby offering a major advantage over conventional silicon cells. Since these cells are very expensive they must
be used in concentrators at very high concentration (between 500 and 1 500 times the natural solar power flux). The adequate concentrators have also been the object of the FULLSPECTRUM research. Concentrator modules and trackers have also been the object of the FULLSPECTRUM research.

Results to date
Triple junction solar cells with 39.7 % efficiency at 293x (x is times the natural solar flux) have been demonstrated. An efficiency of 37.6 % at 1 700x has also been obtained, which is a world efficiency record at this high concentration.
A world record efficiency for dual junction solar cells of 32.6 % has been achieved. These cells are also able to operate at very high concentration and also constitute a step for obtaining good higher efficiency triple junction solar cells in the future. This technology is now being tested on industrial scale at the recently opened Institute of Concentration Photovoltaic Systems (ISFOC).
In another FULLSPECTRUM achievement, the project partners provided the first-ever evidence of the intermediate band effect. This refers to the absorption of photons at three different energy levels, corresponding to three different band gaps. In practical terms, this enables the system to capture low energy photons that would otherwise pass through a conventional solar cell and be lost. In the long term, intermediate band cells might substitute the complex high efficiency multi-junction cells used today.
The consortium reached at the same time a new world record of 7.1 % efficiency of electricity conversion in so-called luminescent solar concentrators (LSC). These concentrators are able to trap and convert the sun rays wherever they come from without additional collectors. The advantage for LSC are their low production cost and that they can be employed nearly everywhere as for example also in transparent windows.

More information:

39.7% – New European Record Efficiency for Solar Cells achieved by Fraunhofer ISE
At 39.7% efficiency for a multi-junction solar cell, researchers at the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg have exceeded their own European record of 37.6% which they achieved just a short time ago. III-V semiconductor multi-junction solar cells are used in photovoltaic concentrator technology for solar power stations.

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