Broadband photon management of subwavelength structures surface for full-spectrum utilization of solar energy. (15th November 2017) - Xu, Yuanpei
Highlights: A novel photon management is experimentally proposed. Near perfect absorption is achieved with the top hexagonal nanohole arrays. Enhanced transmission is obtained through anti-reflection TiO2 /SiO2 films. The photon management has omnidirectional and polarization-insensitive properties. Abstract: In this work, advanced photon-management composite subwavelength structures are fabricated to manage solar energy in the full-spectrum (300–2500 nm) wavelength range for the application of the photovoltaic-thermoelectric hybrid systems to fully utilize the solar energy. This proposed photon-management method will simultaneously realize efficient light trapping for the photons with above-bandgap energy in solar cells and the utilization of the below-bandgap photons and the waste heat resulting from the thermalization effect in solar cells with bottom thermoelectric devices. The typical structure is designed: Top ordered hexagonal nanohole arrays can trap above-bandgap photons to enhance the absorption in the silicon wafer, and TiO2 /SiO2 bilayer films are deposited on the bottom side of the wafer to improve the transmission of the below-bandgap photons. ∼97% total absorptance for wavelengths of 300–1100 nm is achieved with optimized diameters of central nanoholes. The total transmittance, on the other hand, is improved to ∼60% from 1200 nm to 2500 nm. The results indicate that the structures realize the appropriate allocation of photons within different wavelength ranges to different devices for sufficient utilization of full-spectrum solar energy. This novel full-spectrum photon management benefits from the strong scattering effect among the nanoholes and the gradient refractive index of bilayer films. Moreover, the photon-management performance shows angle-independent and polarization-insensitive characteristics. This method can be applied to various kinds of solar cells for photovoltaic-thermoelectric hybrid systems and may provide thoughts for other solar harvesting applications.