Research On Matching Of The Front And Rear Surface Texturing For Silicon-based Solar Cells

A solar cell is an electrical device that converts the energy of light directly into electricity by photovoltaic effect.Improving light trapping capacity is an approach to increase the conversion efficiency of solar cells from optical perspective.Surface texturing is a technique to reduce reflection in addition to applying anti-reflection coatings.Technically,it is not only the reflected loss,but also the escaped loss and transmitted loss that limit the light trapping capacity of a solar cell.Single-side optical design of solar cells has limitations.Incidence light that passing through the cell substrate would interact with the rear side interface,which has impact on escaped loss and transmitted loss,so the overall light trapping capacity of a cell is determined by the front surface texture and rear surface texture jointly.As the wafer used in silicon-based solar cells are getting thinner,which leads to more impact of rear surface texture on the overall light trapping capacity,research on matching of the front and rear surface texturing for silicon-based solar cells could be more important and necessary.Many studies have focused on optical optimization for the front side surface,which only takes reflected loss into consideration,for instance,the rear surface polishing step in manufacturing passivated emitter and rear cell(PERC)solar cells just ignores the influence of rear surface structure on overall light trapping capacity of cells.In this thesis,we studied the optical properties of different combinations of front and rear surface texture.Many types of texture have been developed for silicon-based solar cells,among which the upright pyramid,the inverted pyramid and the V-groove are suitable for practical applications,considering both optical and electrical properties,as well as producing process.Taking into account of these three types of texture,ray tracing simulations were conducted to obtain optical properties of both-side textured silicon-based solar cells that combine different types of texture and different angles of texture,focusing on the analysis of double-sided inverted pyramid textured structure and double-sided V-groove textured structure.To integrate theory with practical application of metal catalysis chemical etching(MCCE)on making inverted pyramid texture,an optimized structure of double-sided inverted pyramid textured structure was introduced and verified by experiments from both optical and electrical perspectives.The double-sided V-groove textured structures have unique optical properties.According to simulation results,the light trapping capacity would improve generally in the case that the extension directions of front and rear surface V-groove texture are perpendicular to each other.The reason is that the front surface V-groove texture deflects the incident light,so that the light passing through the substrate can be reflected multiple times in the extension direction of the rear surface V-groove texture,thereby reducing transmitted loss and escaped loss.However,the light trapping capacity is relatively poor in the case that the V-grooves on the front and back surface is parallel to each other.As for the double-sided inverted pyramid textured structures,the simulations were conduct to evaluate the light trapping performance that can be achieved under different angle combinations.The optical gain and various optical losses are analysed in detail.Further,we dig into the situation that the inverted pyramid angle is 54.74 ° under MCCE method,pointing out the approach of rear surface polishing for PERC solar cells to get a complete planarized rear surface can be detrimental to light trapping.Analysis suggests that when maintaining the front surface morphology as etched,structures with small angle(10 to 20 degrees)inverted pyramids at the rear surface can have an approximately 1.66% improvement in optical gain compared with rear surface totally planarized structures(related to the substrate thickness).Meanwhile,experiments were conducted by applying MCCE method,the pre-treatment steps were optimized and summarized,approaches that could adjust the angle of the inverted pyramid were explored.The experimental results basically verified the simulation results.The importance of matching the front and rear surface texturing for silicon-based solar cells is illustrated theoretically and experimentally in this thesis.The simulation contents and experiments provide a new sight for the design and control of texture on silicon-based solar cells in practical applications.