Optimal design of the light absorbing layer in thin film silicon solar cells

In order to obtain high sunlight transmittance for silicon thin film solar cells, the textured surface such as pyramid shapes is commonly considered along the boundary between the silicon layer and the transparent conductive oxide (TCO) layer. Layered structure design having the improved transmittance into the light absorbing layer for specific frequencies is derived using the so called topology optimization design method combined with the time dependent finite element analysis. A triangle patterned textured surface is considered as the initial shape for two-dimensional wave analysis and the periodic boundary condition is applied to both sides of the unit-structure model. The design objective is set to maximize the energy flux at the specified wave absorbing area during some time period so that the objective function is evaluated as the time integration of a Poynting vector formulation. A multiple layered pattern representing a silicon layer and a TCO layer in turn is obtained for the optimal shape of the light absorbing boundary. As thicknesses of each layer are associated with the incident beam wavelength, various wavelengths of incident light condition are considered and each of the optimal design cases according to the wavelength are compared.