Thermodynamic limits of nanophotonic light trapping in thin film silicon solar cells

We have extended an earlier thermodynamic treatment of light-trapping in lattice-textured solar cells to higher absorptances. This treatment is used to calculate the quantum efficiency spectra and short-circuit current densities J(SC) for thin-film silicon solar cells with ideal lattice textures. An optimal triangular lattice period of 900 nm yields a calculated J(SC) that is 2 mA/cm(2) larger than for ideal random textures in a 1000 nm thick cell. We compare the calculations to recent experiments with periodically textured cells. While the experimental cells give J(SC) values that are comparable to the best cells with conventional textures, they do not show the features associated with the prediction of higher J(SC). We discuss the role of imperfections in the periodic texturing, and suggest that cells used with solar tracking may realize the predicted J(SC) improvement.