Solution processes for ultrabroadband and omnidirectional graded-index glass lenses with near-zero reflectivity in high concentration photovoltaics

Wide-angle broadband antireflection coatings with nano-taper hydrated alumina film

Wide-angle and broadband antireflection (AR) coating is of the essence in modern optical systems in many fields, which has a great influence on the stray light and imaging quality. A simple and convenient manufacturing method is proposed to address this issue based on a composite coating combining the nano-tapered Al₂O₃•xH₂O (AH) structure and high-low index thin film stack. The optical properties of nano-tapered AH structure at various thickness are first studied and modeled in optics by several homogeneous sub-layers with the graded equivalent index. The designed composite AR coatings are manufactured by vacuum deposition and wet etching subsequently in the hot deionized water. Compared to the common dielectric multilayer antireflection stack, the composite coating presents excellent AR performance. The measured average reflectance values of the double-side coated BK7 glass are as low as 0.40%, 0.41%, 0.56% and 3.13% in 400-1100nm band at angles of incidence (AOI) of 6°, 20°, 40°, and 60°, respectively, while the measured average transmittance at normal incidence increases up to 99.3%. Finally, the process reproductivity, environmental reliability test including long term storage, high temperature annealing and 85°C-85% relative humidity storage of the composite coatings are evaluated. The proposed AR scheme provides a low-cost, efficient, wide-angle and broadband AR coating for kinds of large-curvature components and complex surfaces in fields of consumer electronics, automotive, security, etc.

Bidirectional planar-displacement waveguide tracker for high-concentration photovoltaics

A bidirectional planar-displacement waveguide tracker was devised to replace the traditional two-axis tracking system for high-concentration photovoltaics, with improved module thickness, optical field uniformity, and current matching. The concentrating magnification reaches 725 times, and the sun tracking angle is more than 170°, which is equivalent to 11.3 tracking hours per day. The module thickness is only 6.16 cm. This design enabled us to place the module flat on the ground, in which swing was not required. This will greatly improve the mechanical strength and the lifetime of the module and solve the development dilemma faced by III-V multijunction solar cells.

Self-Assembly of Carbon Black/AAO Templates on Nanoporous Si for Broadband Infrared Absorption

Broadband absorption in the mid-infrared region is of significance for wide applications, such as photo/thermal detection, infrared stealth, and thermal imaging. Recently, metal-based plasmonic absorbers have been developed in the mid-infrared region. However, the fabrication cost, thickness, and bandwidth of these absorbers applied in aerospace still need to be improved. In this study, we propose and experimentally demonstrate a large-area, rather thin, metal-free absorber with broadband mid-infrared absorption based on a low-cost self-assembly process. The metal-free absorber is fabricated by spraying carbon black nanoparticles onto 5 μm-thick transferrable anodic aluminum oxide (AAO) templates on nanoporous Si graded-index films, which are fabricated by ion irradiation. Experimental results show that the average absorbance can reach 97.5% in the range of 2.5-15.3 μm. Full-wave numerical simulations show that the electromagnetic fields are greatly enhanced into pores, as these random carbon black particles serve as scatter centers and couple light into 5 μm-thick AAO templates, enhancing the interaction of light with carbon black significantly, and reveal that the high-performance broadband absorption is attributed to the light-trapping effect. The significant light absorption combined with a low-cost, high-production self-assembly technique suggests that the absorber can be used in the fields of optoelectronics and integrated photonics.