Quantum efficiency of thin film silicon solar cells on a highly doped substrate

Abstract

The analysis of internal quantum efficiency of monocrystalline silicon solar cells is extended to thin film cells on a highly doped substrate. Our model evaluates the internal quantum efficiency of cells in the limit of strong and weak absorption, i.e. for light with absorption lengths falling below and exceeding the base width of the cells. These two regimes yield two characteristic lengths, which allow one to distinguish between recombination within the epitaxial layer and into the substrate. The implicit equations for the diffusion lengths of base and substrate are numerically and graphically solved. In all cases, the evaluation gives limiting values. For the special case of thin film silicon solar cells, we are able to determine the substrate diffusion length with high accuracy. For the base diffusion length we deduce a lower bound.