Microlens arrays can improve light transmittance in optical devices or enhance the photoelectrical conversion efficiency of photovoltaic devices. Their surface morphology (aspect ratio and packed density) is vital to photon management in solar cells. Here, we report a 100% packed density paraboloidal microlens array (PMLA), with a large aspect ratio, fabricated by direct-write UV laser photolithography coupled with soft imprint lithography. Optical characterization shows that the PMLA structure can remarkably decrease the front-side reflectance of solar cell device. The measured electrical parameters of the solar cell device clearly and consistently demonstrate that the PMLA film can considerably improve the photoelectrical conversion efficiency. In addition, the PMLA film has superhydrophobic properties, verified by measurement of a large water contact angle, and can enhance the self-cleaning capability of solar cell devices.
A rapid method is developed for fabricating low-cost and high-numerical-aperture photosensitive-gel microlens arrays (MLAs) with well-controlled curvatures. An UV-curable photosensitive-gel film beneath the microholes of a silicon mold can be flexibly deformed by thermally manipulating the surface tension of the photosensitive gel and the pressure difference across the air-photosensitive-gel interface. The concave interface is then solidified through UV curing, forming a MLA with a concave curvature. MLAs with a focal length ranging from 51.4 to 71.9 μm and a numerical aperture (NA) of 0.49 were fabricated. The photocured MLA has high mechanical and thermal strength and is suitable as a master mold for the further production of convex MLAs. The fabricated microlenses have uniform shapes and smooth surfaces. In a demonstration of imaging and focusing performance, clear and uniform images and focused light spots were observed using concave and convex MLAs.
A compact, tunable guided-mode resonant filter (GMRF) is experimentally demonstrated whose spectral reflectance wavelength varies as a function of the illumination position on the device. The GMRF consists of a grating of gradient-varying period ranging from 402.5 to 466.6 nm, which is obtained by casting a stretched polydimethylsiloxane (PDMS) grating wedge. By spatially changing the illumination position on the GMRF over 11 mm, a spectral reflectance peak with low sidelobes varies from 596.8 to 684.1 nm. The influence on the resonance efficiency and the limitation of the wavelength tuning range are discussed in depth. The GMRF is a good candidate as a functional filtering component in wavelength selection and sensing applications.
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