Light Trapping Due to TCO Roughness in a-Si :H Solar Cells Measured by Spatially-Resolved Photothermal Deflection

Abstract

Because of the roughness of the front transparent conducting electrode in a-Si :H p-i-n solar cells, light scattering occurs in the different layers. Refractive index differences produce light trapping in the structure. Photothermal Deflection (PD) is used to analyze the contribution of trapped and absorbed light due to total internal reflection at the glass/air interface. Each irradiated spot gives birth to a diffuse ring, with a radius of approximatively twice the glass substrate thickness. The radial distribution of absorbed light is derived by spatially resolved PD from a spot irradiated by a Kr laser beam at 647 nm. Moreover the overall “glass/air” trapping efficiency is measured by a spatially averaged PD method from 350 to 800 nm. This trapping efficiency ranges typically from 2% at 350 nm to 12% at 800 nm.