Thermodynamic limits of nanophotonic light trapping in thin film silicon solar cells¹

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/cm² 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.