Antireflective gradient-refractive-index material-distributed microstructures with high haze and superhydrophilicity for silicon-based optoelectronic applications

Abstract

We fabricate gradient-index (n) material-based microstructures, i.e., magnesium fluoride (MgF 2 , n $ 1.37) film-coated SU8 ultraviolet curable polymer (n $ 1.59) microcones (MCs) with tapered architectures, on silicon (Si, n $ 3.9) substrates using a soft imprint lithography method for high-performance Si-based optoelectronic applications. The effects of various geometry parameters (i.e., height, filling ratio, and period) of conical MCs on the SU8 film/Si structure including different thicknesses of MgF 2 films on the reflectance properties are investigated by a theoretical analysis using a rigorous coupled-wave analysis simulation. For the fabricated samples, their optical characteristics and surface wetting behaviors are also explored. The MgF 2 film-coated SU8 MCs on Si substrates (i.e., MgF 2 /SU8 MCs/Si) exhibit a superhydrophilic surface with very low water contact angles of <10 and reduce the surface reflection of the bare Si over a wide wavelength of 350-1100 nm, showing the lower average reflectance (R avg ) and solar weighted reflectance (R sw ) values of $14% and $12.1%, respectively, (i.e., R avg $ 15.1% and R sw $ 13% for the SU8 MCs/Si and R avg $ 38.5% and R sw $ 38% for the bare Si). Furthermore, the MgF 2 /SU8 MCs on glasses also show strong light scattering in transmissions at wavelengths of 350-1100 nm, which indicates an average haze ratio of $89.8%, while maintaining high total transmissions. Both the measured and calculated reflectance spectra showed similar results.

Solar power generation enhancement of dye-sensitized solar cells using hydrophobic and antireflective polymers with nanoholes

“…In particular, comparing the dye-sensitized solar cell (DSSC) with other solar cells, it has some advantages such as low manufacturing cost, lightweight, exibility, transparency, and so on. [8][9][10][11] The fabricated molds and stamps can be also repeatedly used for pattern transfer, and thus would facilitate the mass production (i.e., roll-to-roll or roll-to-plate) in industry applications. 2,3 Hence, possibilities exist for further enhancements in PCEs of DSSCs.…”

“…[1][2][3] However, the power conversion efficiencies (PCEs) of DSSCs fall below 13%, mainly due to limitations including the light absorption of the dyes and the interface charge separation between dyes and titanium dioxide (TiO 2 ) electrodes. [10][11][12][13][14] Besides, it can increase the optical transmission of transparent substrates including glasses, polymers, etc. In order to boost the light absorption in the dyed TiO 2 layer of the devices, among various approaches for improving the PCE, one simple method is the employment of efficient antireection coatings (ARCs) on the front surface of the substrates.…”

“…In this respect, so lithography, which has been widely utilized to form the various nanostructures onto the surface of polymers, can be one of them. [8][9][10][11] The fabricated molds and stamps can be also repeatedly used for pattern transfer, and thus would facilitate the mass production (i.e., roll-to-roll or roll-to-plate) in industry applications. In the so lithography, meanwhile, the dimethylsiloxane (PDMS) is generally used as a protective encapsulation layer against mechanical damage to the underlying devices due to its low free surface energy, exibility, transparency, and hardness.…”

“…In the so lithography, meanwhile, the dimethylsiloxane (PDMS) is generally used as a protective encapsulation layer against mechanical damage to the underlying devices due to its low free surface energy, exibility, transparency, and hardness. [10][11][12][13][14] Besides, it can increase the optical transmission of transparent substrates including glasses, polymers, etc. because of its lower refractive index of $1.4-1.43.…”

Hierarchically Designed Light Trapping Films for All‐Day Operating Semitransparent Photovoltaics

“…The bifacial OPV provided advantages in all‐day operation, as it can convert outdoor and indoor light to electricity without modifications such as flipping toward a designated light source (e.g., daytime to sunlight or nighttime to indoor light). For bidirectional light harvesting, we fabricated ST‐OPVs with a 15 nm semitransparent Ag reflective electrode, [ 37 ] and the hierarchical films were bonded to the top and bottom sides of the device, assuming indoor illumination from the bottom and outdoor illumination from the top. Notably, we adopted hierarchical films with different diameters of 10 µm ( d Top ) and 1 µm ( d Bottom ) for the top‐ and bottom‐side films, respectively, as the light travels differently according to the illumination environment.…”