Broadband omnidirectional antireflection (AR) coating based on inverse transfer design towards high efficiency photovoltaic cells

Abstract

The solar spectrum reaching Earth spans from ultraviolet to infrared wavelengths with a cutoff at around 2.5 μm. About 30% of the irradiance is absorbed by the atmosphere, and the rest is absorbed by the Earth's surface. The radiance available for generating renewable energy ranges from 400 nm to 2.0 μm. Silicon and III-V materials are used for photovoltaic (PV) cells. The PV cells reflect 30% of incoming radiation and to reduce this reflection, antireflection coating (ARC) is being used. Conventional techniques such as single or stacked multi-layer ARC or micro-nanostructures ARC are used. However, they lack in providing broadband and omnidirectional transmission, which limits its conversion efficiency in today’s PV cells. We present broadband ARC achieved with an inverse transfer design, a prospect towards significantly high conversion efficiency PV cells. The ARC exhibit significantly increased transmission more than 96% over the solar spectrum ranges up to 2.5 μm, even with wide angles of incidence from ~ 0° to >70°. This transmission over the same angles of incidence, is significantly higher than that of ARC based on quarter-wavelength optical thickness (QWOT), a state-of-art ARC. The results also rival the transmission performance of state-of-the-art nanostructure-based ARC even at large angles of incidence, but are significantly easier to fabricate using standard e-beam evaporation and/or sputtering. The results show over broadband spectrum ranges, radiation back due to reflection makes to zero, leading to significantly increased conversion efficiency of the PV cells.