Anti-glare (or antireflection) coatings on transparent substrates (e.g., glass) are important components for a large number of optical and optoelectronic devices, such as displays, lenses, and photovoltaic (PV) panels [1-10]. For instance, the unwanted optical reflection from the encapsulation glass layer of a PV panel could reduce the overall conversion efficiency of the solar device [11-13]. Anti-glare coatings are therefore widely applied on optical glass surfaces to reduce the reflection loss and increase the light transmission of the optical components [1,14]. Traditional quarter-wavelength antireflection coatings can effectively suppress optical reflection by satisfying the destructive interference conditions for the reflected light from the air/coating and the coating/substrate interfaces, thus decreasing the reflection and increasing the transmission of the substrate [14]. To satisfy the destructive interference conditions, the coating thickness needs to be close to one-fourth of the operating wavelength, while the refractive index of the coating (nc) needs to meet nc=√{square root over (nair×ns)}, when nair is the refractive index of air (1.0) and ns is the refractive index of the substrate [6,14]. For a typical glass substrate with a refractive index of 1.5, the anti-glare coating material needs to have a refractive index of ˜1.225. Low-refractive-index materials, such as MgF2 (with a refractive index of ˜1.37), are usually deposited on glass substrates by vacuum-based physical vapor deposition (PVD) technologies (e.g., sputtering) to achieve a precise control over the coating thickness [14-15]. Unfortunately, conventional PVD techniques suffer from high operating and equipment costs, limited material selection, low throughput, and small coating areas. These drawbacks particularly affect the applications where inexpensive anti-glare coatings on large-area glass substrates are needed, such as in solar industry.
To address the high costs and the low throughput issues of the vacuum-deposited anti-glare coatings, various simple solution processing technologies have been developed [1, 6, 16-25]. In many of these methods, nanoporous coatings with a large fraction of entrapped air and thus a low effective refractive index, which could satisfy the aforementioned ideal quarter-wavelength refractive index requirement, were extensively explored [1, 6, 16, 21, 26]. For example, nanoporous polymer coatings created by phase separation of spin-coated polymer blends, followed by selective removal of one component, have been demonstrated to show good anti-glare performance on glass substrates [1]. Multilayer silica nanoparticle coatings on glass substrates applied through common spin, dip, or roller coating techniques have already been commercialized for improving the efficiencies of PV panels (e.g., Honeywell's SOLARC RPV products) [27-29]. Electrostatics-assisted layer-by-layer (LBL) deposition of nanoparticles and polyelectrolyte multilayers is another popular approach in assembling anti-glare coatings on a variety of substrates [21, 30-31]. Monolayers of colloidal nanoparticles created by convective self-assembly [32-33], spin-coating [18, 29, 34-36], or Langmuir-Blodgett deposition [20, 37-38] have also been widely utilized as antireflection coatings on silicon and glass substrates. However, many of these existing wet-processing technologies involve multiple steps (e.g., LBL assembly) [19], are limited to single-sided coatings on planar substrates (approaches involving spin coating) [18], are not very reproducible over large areas [20], and/or are not inherently parallel for industry-scale manufacturing [32]. Thus, there is a need to overcome these deficiencies.