Study on photonic-crystal effects on photovoltaic materials towards efficient photovoltaic devices

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We demonstrate an enhancement of the optical absorption and photoelectric-conversion efficiency of an ultrathin (50 nm) silicon active-layer photodetecting device using a two-dimensional photonic crystal. We show both experimentally and with simulations that the incident-light absorption within the active layer is enhanced by optical-resonance effects at the photonic band edge. We also find that a photonic crystal with deeper holes can lead to an even larger absorption enhancement due to better Q-factor matching between the photonic band-edge modes and the intrinsic material absorption. The experimentally observed photocurrent of the fabricated photonic crystal sample is increased by a factor of around 20 at the photonic band-edge wavelength relative to that of a control sample without the photonic crystal which is attributed to the improved Q matching. We also investigate broadband optical absorption enhancement in thin silicon photovoltaic devices by photonic crystal.