Simulation and fabrication of surface-modified glass coverslips to enhance energy harvesting on indoor MOS solar cells

In this work, analytical and numerical simulations of the reflectance of glass coverslips with different rough-layer thickness carried out to establish the conditions of use as low reflectance intensifier plates for energy harvesting on indoor solar cells. Reflectance simulations as a function of the wavelength were obtained for surface-modified glass coverslips over silicon (air/surface rough layer/glass/silicon) based on the refractive in-dices of the three regions over silicon with negligible extinction coefficients and, for silicon, with a very low value (k = 0.019). The rough layer was modeled with different thicknesses in the range of 50 to 300 nm and with an intermediate refractive index between air and glass (n = 1.25). The thickness of the glass coverslips was varied in the range of 45 μm to 160 μm with a typical bulk refractive index of 1.50. As a result, glass coverslips have been found to enhance the conversion efficiency (η) of light energy into electrical energy for solar cells with surface reflectance higher than that of glass coverslips for indoor energy harvesting applications. The best results of glass coverslips as intensifier plates were obtained for the lowest surface average reflectance in the wavelength range of 300 to 1100 nm. The one-dimensional numerical simulation using COMSOL was very close to the analytical modeling of the air/surface rough layer/glass/silicon structure. An experimental improvement of the conversion yield was observed for any glass coverslips placed on indoor MOS solar cells. Current density x voltage curves (JxV), using indoor light illumination of 11.7 mW/cm2 at 25oC on the sample surface, were extracted for different thicknesses of the processed glass coverslips and the main electrical parameters were obtained for the MOS photovoltaic cells such as the short circuit current (Jsc), the open circuit voltage (Voc) and energy conversion efficiency (η). As a result, a significant increase of the indoor energy conversion efficiency was obtained for the thickness of the glass coverslip of 81.7 μm compared to those without chemical thinning (~130 μm thick), this is to say, η ≈ 5.15% against η ≈ 3.36%, respectively, which was explained by a decrease of surface reflectance of the glass coverslips in accordance with the simulation results of the rough layers.