HIGH-EFFICIENCY THIN AND COMPACT CONCENTRATOR PHOTOVOLTAICS WITH MICRO-SOLAR CELLS DIRECTLY ATTACHED TO LENS ARRAY WITHOUT SECONDARY OPTICS

摘要

We propose an extremely thin and compact CPV module whose thickness is only several centimeters, about one-tenth the thickness of conventional CPV modules. Our strategy for downsizing the CPV module is to decrease the focal length of the concentrator lens by downsizing the solar cells to the sub-millimeter level and to attach the solar cells directly to the back side of a thin lens array without secondary optics. In addition to the thickness reduction, the use of micro-solar cells provides another advantage in that it suppresses the negative impact of chromatic aberration of refractive lenses on photovoltaic (PV) performance. The latter advantage allows the design of a high-performance compact CPV module without the secondary optics generally needed in conventional CPV modules to eliminate chromatic aberration. To demonstrate our concept, a CPV module with a 400x concentration ratio was assembled by placing triple-junction GaAs solar cells with 0.31 mm~2 aperture area on the back side of a lens array using the fluidic-assembly method, followed by the attachment of a 1 mm-thick circuit board on the lens array. The lens array was 18 mm thick and had total area of 25 cm~2. The solar cells were electrically connected to the circuit board using solder paste. Using this type of module, we demonstrated an uncorrected peak efficiency of 34.7% and fill factor (FF) of 0.79 under on-sun measurement. The relative decrease in FF caused by chromatic aberration was up to 8%. Conventional CPV modules using several-millimeter size solar cells with no homogenizing secondary optics typically have twice as much FF reduction due to chromatic aberration compared to our approach. This result indicates that our proposed thin and compact CPV module can achieve high PV performance without secondary optics.