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1. Direct Light‐Writing of Nanoparticle‐Based Metallo‐Dielectric Optical Waveguide Arrays Over Silicon Solar Cells for Wide‐Angle Light Collecting Modules

   https://doi.org/10.1002/adom.201900661  

   Biria, Saeid ; Wilhelm, Thomas S. ; Mohseni, Parsian K. ; Hosein, Ian D. ( August 2019 , Advanced Optical Materials)

   Here presented are the properties and performance of a new metallo‐dielectric waveguide array structure as the encapsulation material for silicon solar cells. The arrays are produced through light‐induced self‐writing combined with in situ photochemical synthesis of silver nanoparticles. Each waveguide comprises a cylindrical core consisting of a high refractive index polymer and silver nanoparticles homogenously dispersed in its medium, all of which are surrounded by a low refractive index common cladding. The waveguide array‐based films are processed directly over a silicon solar cell. Arrays with systematically varied concentration of AgSbF₆as the salt precursor are explored. The structures are tested for their wide‐angle light capture capabilities, specifically toward enhanced conversion efficiency and current production of encapsulated solar cells. Observed are increases in the external quantum efficiency, especially at wide incident angles up to 70°, and nominal increases in the short circuit current density by 1 mA cm⁻²(relative to an array without nanoparticles). Enhanced light collection is explained in terms of the beneficial effect of scattering by the nanoparticles along the waveguide cores. This is a promising approach toward solar cell encapsulants that aid to increase solar cell output over both the course of the day and year.

    

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2. Microfiber Optic Arrays as Top Coatings for Front-Contact Solar Cells toward Mitigation of Shading Loss

   https://doi.org/acsami.9b17803  

   Chen, Fu-Hao ; Biria, Saeid ; Hosein, Ian Dean ( November 2019 , ACS applied materials interfaces)

   Microfiber optic array structures are fabricated and employed as an optical structure overlaying a front-contact silicon solar cell. The arrays are synthesized through light-induced self-writing in a photo-crosslinking acrylate resin, which produces periodically spaced, high-aspect-ratio, and vertically aligned tapered microfibers deposited on a transparent substrate. The structure is then positioned over and sealed onto the solar cell surface. Their fiber optic properties enable collection of non-normal incident light, allowing the structure to mitigate shading loss through the redirection of incident light away from contacts and toward the solar cell. Angle-averaged external quantum efficiency increases nominally by 1.61%, resulting in increases in short-circuit current density up to 1.13 mA/cm2. This work demonstrates a new approach to enhance light collection and conversion using a scalable, straightforward, light-based additive manufacturing process. 

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3. Improving Light Absorption in a Perovskite/Si Tandem Solar Cell via Light Scattering and UV‐Down Shifting by a Mixture of SiO 2 Nanoparticles and Phosphors

   https://doi.org/10.1002/adfm.202204328  

   Lee, Seongha ; Kim, Chan Ul ; Bae, Sumin ; Liu, Yulin ; Noh, Young Im ; Zhou, Ziyu ; Leu, Paul W. ; Choi, Kyoung Jin ; Lee, Jung‐Kun ( June 2022 , Advanced Functional Materials)

   The optical properties of a textured antireflective coating (ARC) polymeric film are engineered by combining the down‐conversion effect of large phosphor particles and the multiple scattering effect of SiO₂nanoparticles. In order to address the parasitic absorption of ultraviolet (UV) light, phosphors are added to convert UV light to visible light. However, the embedded phosphors increase the reflectance of the ARC film, due to the large particle size (>5 µm) and high refractive index (n ≈  1.9) of phosphors. Such a backward scattering problem of phosphors is compensated by adding spherical SiO₂nanoparticles. Experimental and computational results show that SiO₂nanoparticles in the ARC film decrease the reflectance by increasing the diffuse transmittance. This optically engineered ARC film successfully promotes the light absorption of the perovskite/silicon tandem solar cell, leading to the improvement of power conversion efficiency of the tandem cell from 22.48% to 23.50%.

    

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4. Prototyping of Superhydrophobic Surfaces from Structure-Tunable Micropillar Arrays Using Visible Light Photocuring

   https://doi.org/10.1002/adem.201801150  

   Li, Hansheng ; Chen, Fu-Hao ; Biria, Saeid ; Hosein, Ian D. ( January 2019 , Advanced Engineering Materials)

   A new approach is reported to fabricate micropillar arrays on transparent surfaces by employing the light‐induced self‐writing technique. A periodic array of microscale optical beams is transmitted through a thin film of photo‐crosslinking acrylate resin. Each beam undergoes self‐lensing associated to photopolymerization‐induced changes in the refractive index of the medium, which counters the beam's natural tendency to diverge over space. As a result, a microscale pillar grows along each beam's propagation path. Concurrent, parallel self‐writing of micropillars leads to the prototyping of micropillar‐based arrays, with the capability to precisely vary the pillar diameter and inter‐spacing. The arrays are spray coated with a thin layer of polytetrafluoroethylene (PTFE) nanoparticles to create large‐area superhydrophobic surfaces with water contact angles greater than 150° and low contact angle hysteresis. High transparency is achieved over the entire range of micropillar arrays explored. The arrays are also mechanically durable and robust against abrasion. This is a scalable, straightforward approach toward structure‐tunable micropillar arrays for functional surfaces and anti‐wetting applications. 

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5. Silica Nanowire Growth on Coscinodiscus Species Diatom Frustules via Vapor–Liquid–Solid Process

   https://doi.org/10.1002/smll.201801822  

   Li, Aobo ; Zhao, Xiaoguang ; Anderson, Stephan ; Zhang, Xin ( October 2018 , Small)

   Diatom frustules are a type of porous silicon dioxide microparticle that has long been used in applications ranging from biomedical sensors to dye‐sensitized solar cells. The favorable material properties, enormous surface area, and enhanced light scattering capacity support the promise of diatom frustules as candidates for next generation biomedical devices and energy applications. In this study, the vapor–liquid–solid (VLS) method is employed to incorporate silica nanowires on the surface of diatom frustules. Compared to the original frustule structures, the frustule–nanowire composite material's surface area increases over 3‐fold, and the light scattering ability increases by 10%. By varying the gold catalyst thickness during the VLS process, tuning of the resultant nanowire length/density is achieved. Through material characterization, it is determined that both float growth and root growth processes jointly result in the growth of the silica nanowires. From a thermodynamics point of view, the preferential growth of the silica nanowires on frustules is found to have resulted from the enormous partial surface area of gold nanoparticles on the diatom frustules. The frustule–nanowire composite materials have potential applications in the development of novel biomedical sensing devices and may greatly enhance next generation solar cell performance.

    

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