Optical Modeling of Capped Multi-Layer Porous Silicon as a Back Reflector in Thin-Film Solar Cells

A model for the optical properties of closed-porosity silicon is developed as a tool for design and optimization of porous silicon stacks made of layers of alternate (high/low) porosity which are possible candidates for use as back reflectors in thin-film silicon solar cells on cheap substrates. The model takes into account the change in pore morphology during the epitaxial growth process of the silicon film on the stack, with the pores taking the form of relatively large closed cavities where retardation and interference effects play an important role. The calculated front-surface reflectance of structures consisting of a silicon epitaxial layer with a plasma-textured front surface grown over a reflecting porous silicon stack are compared with the corresponding experimental measurements, showing a good agreement between theory and experiment