By Doug Malchow, Sensors Unlimited - Goodrich ISR Systems
Researchers and manufacturers of concentrated photovoltaic (CPV) cells have recently achieved record solar cell conversion efficiencies of 41 percent by overlaying three semiconductor layers. Careful selection of both the materials and the chemical structures used within the cell will result in matching the absorbance of each layer to the sun's spectrum. When this occurs, each layer contributes equal amounts of electrical current to the cell's output.
Because the layers are photodiode junctions connected in series, the maximum current output of the cell is limited by the output of the lowest-performing layer. It's important to ensure that all three layers work efficiently; otherwise, the current from the strong layers will dissipate power into a weak layer. The multijunction cells are usually assembled at the focal point of light concentrators, which are designed to focus the equivalent of 500 suns onto an area measuring 1 cm2. This then generates amps of current.