Sunlight is the most abundant renewable energy source available on Earth, supplying over 1.5×1022J (15,000 Exajoules) of energy to the Earth's surface daily. This amount of energy is 10,000 times greater than the 1.3EJ of energy consumed daily by the Earth's population. However, the capital costs involved with harvesting solar energy make supplying energy to the electrical grid using photovoltaic (“PV”) generation unfavorable compared to existing standard technology, e.g., coal, nuclear, etc. Thus, substantial improvements are necessary to justify a shift from existing power generation technologies to photovoltaic-generated energy.
The main challenge in the photovoltaic industry is making solar cells more cost effective. Thus, it is desirable to produce less expensive cells with higher efficiencies. To date, the National Renewable Energy Lab (NREL) is believed to have achieved a record efficiency of 40.7% (AM1.5D, low AOD, 240 suns, 25° C.) for metamorphic or lattice mismatched and 40.1% (AM1.5D, low AOD, 135 suns, 25° C.) for lattice matched three-junction photovoltaic cells such as GaInP/GaInAs/Ge cells. However, this is well below the desired efficiency of 60% or higher believed necessary to make PV technology a feasible substitute for existing power generation technologies, so additional improvements are necessary.