Solar cells are devices for producing electricity which use incident illumination to supplying electrons to an external circuit. The use of these has even been described as the “art of converting sunlight directly into electricity” (Wenham et al. 1994). There are a range of technologies and materials used to produce solar cells, each with their own benefits and drawbacks. By far, the most common and familiar example of a solar cell is that of crystalline silicon. Crystalline silicon solar cells currently dominate the world market and held over 93.5 % market share in 2005 (Singh and Jennings 2007), decreasing to 83 % in 2010 (Tyagi et al. 2013) and 86 % in 2011 (Fraunhofer 2012). Crystalline silicon solar cells have a long history and have undergone major improvements in efficiency over the years. The first crystalline silicon solar cell had a limited efficiency of 6 % (Chapin et al. 1954); however, new solar cells have been developed with efficiencies greater than 25 % in the laboratory and 22 % in full modules (Green et al. 2012; Beardall et al. 2009). Although solar cells are generally optimized to absorb strongly across the whole solar spectrum, each individual technology will have variations in performance. These variations are due to a number of factors including the properties of the semiconductor, such as the bandgap.