The fabrication of microstructure on solar glass surface with laser microprocessing

Abstract

Photovoltaic (PV) technology, as a renewable energy technology, is considered to be the most reliable and effective way to solve the nowadays energy crisis. Many works have been done with the aim to enhance the photoelectric conversion efficiency. An indirect way to fulfill the enhancement is to reduce the surface reflection loss and thus improve the solar cells’ absorption of sunlight. Based on this method, three kinds of textured anti-reflection structures were designed and fabricated on solar glass by means of laser induced backside dry etching (LIBDE) technique. Due to the fact that there is a high transmittance of solar glass in the band of visible and infrared light, ultraviolet (UV) lasers such as excimer and high harmonic lasers were mostly applied in the etching of transparent solar glass. The fabrication efficiency by UV lasers, however, was limited by the laser machining system. In this work, a laser texturization system to machine on solar glass was established and investigated, in which, a 1064 nm central wavelength ytterbium-doped short-pulsed fiber laser was applied as the irradiation source and solar glasses were successfully etched by the infrared fiber laser with an assistant absorbing layer. Different from other studies, the mostly used metallic thin films were substituted by a non-metallic layer, i. e. 1mm thickness alumina wafer (95% Al2O3) with a surface roughness below 350 nm and alumina powder with a mean particle size of 2.071 um. Surface morphologies of etched sample by LIBDE were measured and examined by means of scanning electronic microscope (SEM) and 3D profiler. Moreover, the surface elements after etching were analyzed by Raman spectrometer and Energy Dispersive Spectrometer (EDS). The etching mechanism was explored and investigated based on the above analysis and relationships between laser parameters and etching process were discussed. According to the theory of physical optics, the reflectance of two micro structures (convex pyramid and cosine pits array) were deducted by formulas of Fresnel reflection coefficient and the curves were plotted and analyzed by Matlab numerical analytical software. Based on the calculations, ZEMAX, an optical design software, was applied into the simulation of the different surface structures, the results shows that all the microstructures have the potential to reduce the reflectance and increase the incident irradiance of sunlight, while the cosine pits array texturization performs much better than others. From the point of view, anti-reflection samples in three kinds of patterns catalogs were obtained by setting different texturing paths. The mean reflectance of solar glass was reduced to nearly 5% according to the measurement of UV-VIS-NIR spectrometer. It shows the great potential application of this technology.