Photonic crystal based back reflectors for light management and enhanced absorption in amorphous silicon solar cells

Photonic crystal back-reflectors offer enhanced optical absorption in thin-film solar cells, without undesirable losses. We fabricated metallic photonic crystal back-reflectors using photolithography and reactive-ion etching and deposited a-Si:H solar cells. The photonic crystal has triangular lattice symmetry, a pitch of 760 nm, and was designed with rigorous simulations. Scanning electron microscopy demonstrates excellent long range periodicity and conformal a-Si:H growth. The average light absorption increases by 7%, relative to a flat reference device, with an enhancement factor approaching 6 at near-infrared wavelengths. The photonic crystal back reflector strongly diffracts light and increases optical path lengths of solar photons.