Enhancing light harvesting in organic solar cells with pyramidal rear reflectors

We report enhanced light absorption in semi-transparent organic solar cells by using pyramidal rear reflectors to induce light trapping in the photoactive layer. Pyramidal rear reflectors with a base angle of 30° were molded from a transparent polymer on planar substrates. Compared with a planar rear reflector, the pyramidal structure leads to a more than 2.5 times longer path length in the active layer for the incident light. Experimental demonstration showed an 11%–75% enhancement in the photocurrent and overall efficiency of the solar cells, depending on the device size and active layer thickness.