Parasitic loss suppression in photonic and plasmonic photovoltaic light trapping structures.

In this paper, we examine the optical loss mechanisms and mitigation strategies in classical photovoltaic light trapping structures consisting of diffractive gratings integrated with a backside reflector, which couple normal incident solar radiation into guided modes in solar cells to enhance optical absorption. Parasitic absorption from metal or dielectric backside reflectors is identified to be a major loss contributor in such light trapping structures. We elucidate the optical loss mechanism based on the classical coupled mode theory. Further, a spacer design is proposed and validated through numerical simulations to significantly suppress the parasitic loss and improve solar cell performance.