Designing photonic materials for effective bandgap modification and optical concentration in photovoltaics

The limiting efficiency for photovoltaic energy conversion based on a semiconductor pn-junction is typically determined using the method of detailed balance put forth by Shockley and Queisser. Here we describe how this theory is altered in the presence of a photonic structure that is capable of modifying the absorption and emission of photons. By incorporating specifically designed photonic structures, higher maximum efficiencies can be achieved for low bandgap materials by restricting the absorption and emission of above bandgap photons. Similarly, restriction of the emission angle leads to increased optical concentration. We consider how both of these effects are modified in the presence of a non-ideal photonic structure.