Absorption enhancement of ultrathin crystalline silicon solar cells with frequency upconversion nanosphere arrays

A design of ultrathin crystalline silicon solar cells patterned with α-NaEr_0.2Y_0.8F₄ upconversion nanosphere (NSs) arrays on the surface was proposed. The light trapping performance of α-NaEr_0.2Y_0.8F₄ NSs with different ratios of sphere diameter to sphere pitch was systematically studied by COMSOL Multiphysics. The influence of different NS diameters and ratio to the average optical absorption of ultrathin crystalline silicon solar cell was calculated, as well as the short circuit current densities. The results show that the average optical absorption of solar cells with 2.33 μm silicon covered by α-NaEr_0.2Y_0.8F₄ NSs of 100 nm in diameter and 5.2 in ratio has improved by 8.5% compared to planar silicon solar cells with the same thickness of silicon. The light trapping performance of different thicknesses of silicon solar cells with the optimized configuration of NSs was also discussed. The results indicate that our structure enhances the light absorption. The presented model will be the basis for further simulations concerning frequency upconversion of α-NaEr_0.2Y_0.8F₄ materials.