Zonal efficiency limit calculation for nanostructured solar cells

We extend the well-known Shockley-Queisser detailed balance calculation for determining the efficiency limit of a solar cell to the case of strong local deviations of the optical power absorption as present in nano-structured photovoltaic devices. In addition, the simple assumption of perfect absorption of all incident light exceeding the bandgap is refined. We present a modified Shockley-Queisser efficiency limit calculation for nano-structured photovoltaic devices, it incorporates a rigorous wave optics calculation and spatially resolved generation of electron-hole pairs. We apply this method to core-shell single-junction InP nanowire array for the use in concentrator solar cells. We investigate the efficiency limits regarding the arrangement of the active regions within the wire. Our results indicate that in a nanowire array solar cell with low volume fill factor the efficiency limit can approach the values of planar thin-film devices. This observation indicates the occurrence of micro-concentration and underlines the necessity of a wave optics approach. The spatially and spectrally resolved analysis shows that generation on the surface of the nanowires is considerable, particularly with regard to high energy photons. Therefore, it is necessary to efficiently extract those carriers.