Performance of GaAs Nanowire Array Solar Cells for Varying Incidence Angles

Nanowire array solar cells show intrinsic light trapping and absorption enhancement properties due to the diffraction and optical resonances. Here, we report the effect of varying incidence angle on the performance of GaAs nanowire array solar cells. We provide experimental evidence that nanowire array solar cells are highly efficient at gathering diffuse or tilted incident light, even at very high incidence angles; hence, the performance of the nanowire solar cell is retained up to these high incident light angles. Specifically, the measured efficiency at an incidence angle of 60° is 95% of the efficiency at normal incidence. Moreover, our measurements show that a nonzero incidence angle is beneficial for wavelengths above 600 nm, which results in an efficiency improvement by 0.5% absolute points. This increase is so large that we even measure a small increase in absolute output power at 15° tilt, thus, more than fully compensating for the reduced incoming power over the cell with increasing tilt. We show how this gain arises from an enhanced absorption in the part of the nanowire with a high probability of charge extraction. Thus, nanowires show great promise for the delivery of high efficiency in practical nontracking positioning conditions, as well as under diffuse light illumination.