Numerical and experimental analysis of nano second laser induced surface textures for light trapping in a-Si thin film for solar cells

Laser texturing with a nanosecond pulsed Nd3+: YAG laser in air and water is used to create surface textures in a-Si thin films based on the laser beam overlap technique that enhances light-trapping along with simultaneous crystallization and defects passivation. The light-trapping characteristics of textures are analyzed by optical reflectance measurements and the influence of crystallinity and light trapping textures on electronic properties are studied using I-V characterization and the results are compared with theoretical analysis. The theoretical analysis is performed based on the actual surface geometry of the textured surface, characterized by an atomic force microscope. Finite element analysis approach is used to solve the Maxwell's equations in two dimensions to analyze wave propagation within thin-film. The influence of texture base and height of the texture profile is studied to obtain the texture dimensions for enhanced efficiency. Theoretical simulation studies clearly show that light trapping efficiency is significantly enhanced with the textured surface and the highest efficiency is obtained with the texture height of approximately 300 nmor more irrespective of the base diameter. More than 95% of light is absorbed at incident angles up to 60 degrees, which is higher than flat thin films (similar to 49%). Experimentally measured reflectance values shows reduction in reflectance from 43% to 14% when optimal height is achieved by treating the samples with 30% and 50% spot overlap.