Multifunctional glasses and their application to photovoltaic technology
Authors:   , Pinto Fuste Cristina Leyre 
Published: March 2024

The sun provides more than 5000 times the power consumed on the planet, with over 4.4×1016 W. It is the original source of almost all the energy sources we know today, both renewable and fossil fuels. The production of electricity directly from solar energy, known as solar photovoltaic energy, is a renewable energy generation technology with great potential, as it directly converts the solar radiation reaching the Earth into electricity. Photovoltaic technology is based on the photovoltaic effect produced in semiconductor materials, whereupon absorbing a photon of specific energy, these materials are able to generate an electron-hole pair and create an electric current. In this work, hierarchical micro- and nano-scale structures have been developed to address these issues present in PV glass: reflectance, soiling, resistance to abrasion, and temperature increase. The nanostructures, categorized as conical subwavelength structures (SWS), act as an effective layer on the glass surface, minimizing Fresnel reflectance. In this way, glass reflectance has been reduced from 7.1% (taking into account both surfaces) to an average of 1.0% averaged across the range of 300 to 1100 nm. Moreover, as these cone-like nanostructures are random in size and distribution, the anti-reflective property is extrapolated to larger angles of incidence, showing an improved incidence angle modifier (IAM) factor, increasing it from 0.80 to 0.88 at 80o of the light angle of incidence. These enhancements are translated into an increase in PV module efficiency of 3.5% measured indoor, and an increase in more than 5.1% at the most unfavorable outdoor conditions (December sunny day, at 66º light angle of incidence). Additionally, the nanocones increase the average distance between the glass surface and any dust or sand particles, drastically reducing the adhesive forces. Consequently, the rate of soiling on the PV modules has been reduced by over 50%. Moreover, due to the monolithic nature of the structures, their resistance to abrasion has increased considerably with respect to comercial solutions, standing more than 500 brush abrasion cycles without noticeable damage. Lastly, the microstructures serve basically the same purpose as the nanocones, acting as anti-reflective structures in the mid infrared spectral region. While the nanostructures affect the UV, visible and near-infrared regions, the microstructures operate in the mid-infrared spectral range, between 8 and 13 μm, where the glass exhibits a resonance, which causes a reflectance peak at 9 μm. These microstructures effectively reduce this reflectance, thereby increasing the glass’s emissivity from 0.83 to 0.95 (the glass is opaque in this spectral range). By increasing the emissivity, the heat produced by the cells is dissipated to the exterior, and thanks to the atmospheric window presented between 8 and 13 μm, this heat escapes through the atmosphere to outer space. This decrease the operating temperature of PV modules on sunny days by more than 0.8ºC with 2.5ºC temperature reduction peaks. This temperature reduction can increase the energy efficiency of the passivate emitter and rear contact (PERC) PV module by 0.28%.