Porous silica coatings for radiative cooling and anti-reflection for enhancing solar photovoltaics performance

The cover glass of solar photovoltaic (PV) modules is known to suffer from reflectance losses, while elevated operating temperatures further reduce PV efficiency. This study investigates the application of porous silica coatings to reduce solar reflectance in the spectral range of 300–1200 nm and enhance thermal emissivity in the mid-infrared range of 8–13 μm. A sol-gel method employing a base/acid double-catalysis technique was used to synthesize a silicon dioxide (SiO$_2$) sol, which was subsequently spin-coated onto glass substrates to form porous silica layers. The materials and optical properties of the coatings were characterised using scanning electron microscopy, Fourier transform infrared spectroscopy, and spectrophotometry. A two-layer design demonstrates a 1.2% absolute increase in solar transmittance (300–1200 nm) with a porous silica layer, along with an enhancement in mid-infrared emissivity (8–13 μm) from 87% to 90%, compared to bare glass. A three-layer configuration increases the emissivity to 96%, but with a 1.1% absolute reduction in transmittance within the 300–1200 nm range.