The conversion efficiency of solar cells recently produced using III-V semiconductors have reached highly impressive rates. German scientists have now also developed group III-V silicon tandem solar cells with a conversion efficiency of 35.9%. At this rate, it is clear that this kind of solar technology has the greatest potential to break the 50% conversion threshold.
The impressive performance of III-V solar cells stem from their band gap; the band gap of group III (aluminum, gallium, indium) and group V (nitrogen, phosphorus, arsenic) and other elements are within 1 to 3 electron volts (eV). These band gap levels provide direct band gap semiconductors with excellent photoelectric conversion and electronic transmission characteristics. Furthermore, they supply LED, optoelectronics, and communications technologies with essential semiconductor materials. Following the development of 5G and WiFi 6, III-V semiconductors will continue to thrive.
In April of 2020, the National Renewable Energy Laboratory (NREL) in the United States developed “six-junction” III-V solar cells that achieved a conversion efficiency of 47.1%. It was determined that III-V semiconductors could be used in traditional heterogeneous integration of silicon crystals. This example of solar energy technology is precisely what German institute Fraunhofer ISE produced.
The NREL used tandem photovoltaics to superimpose III-V semiconductors on existing silicon wafers at the atomic level to create “triple junction” solar cells.
The high conversion efficiency of multi-junction solar cells is caused by how the thin-film solar cells are composed of multiple different semiconductors, which absorb a spectrum of varying band gaps to generate more energy. According to Fraunhofer ISE, the world record results of the AM1.5g simulation reinforce the potential of tandem silicon solar cells.
Patrick Schygulla, a Ph.D candidate studying III-V solar photoelectricity and concentrator photovoltaics at Fraunhofer ISE, stated that while in terms of structure, NREL’s III-V semiconductor-silicon solar cell is actually quite similar to a typical two-terminal multi-junction solar cell, the new design actually allows us to further improve the longevity of charge carriers and increase the voltage of solar cells.
With its great conversion efficiency and lightweight structure, the usage of III-V semiconductor solar cells has not been uncommon in the past. In fact, NASA applied this technology for their Mars exploration from as early as the 1950s. However, due to the complex epitaxy and semiconductor processes, the cost of production and usage were high, and the range of application was limited in comparison to that of III-V silicon solar cells. These downfalls aside, this technology would be very helpful in the development of drones and electric vehicles.