Prismatic covers for boosting the efficiency of high-concentration PV systems

Prismatic cover experiments were performed on GaInP/Ga(In)As/Ge triple-junction concentrator solar cells having grid designs with up to 39% metal coverage. The devices were characterized both before and after the application of optically-clear silicone covers patterned with cylindrical-lens microstructures. In solar-simulator LIV measurements at 1 sun and at 500 suns, we observed a boost in the efficiency of prism-covered cells, relative to before covering, of up to 34%, depending on the grid coverage fraction. The spectral response of the cells before and after covering was also characterized, and the observed boost in external quantum efficiency was found to be consistent with the LIV performance gains. Also studied were the lateral tolerances allowed by the prismatic covers, for alignment to the underlying cell grid structure, as a function of the maximum angle of incidence of the light impinging onto the cell. Ray-tracing simulations were performed, and found to be consistent with preliminary angular-dependence spectral response measurements done under monochromatic illumination.