Nano-crystalline silicon solar cell architecture with absorption at the classical 4n(2) limit.

We develop a periodically patterned conformal photonic-plasmonic crystal based solar architecture for a nano-crystalline silicon solar cell, through rigorous scattering matrix simulations. The solar cell architecture has a periodic array of tapered silver nano-pillars as the back-reflector coupled with a conformal periodic structure at the top of the cell. The absorption and maximal current, averaged over the entire range of wavelengths, for this solar cell architecture is at the semi-classical 4n(2) limit over a range of common thicknesses (500-1500 nm) and slightly above the 4n(2) limit for a 500 nm nc-Si cell. The absorption exceeds the 4n(2) limit, corrected for reflection loss at the top surface. The photonic crystal cell current is enhanced over the flat Ag back-reflector by 60%, for a thick 1000 nm nc-Si layer, where predicted currents exceed 31 mA/cm(2). The conformal structure at the top surface focuses light within the absorber layer. There is plasmonic concentration of light, with intensity enhancements exceeding 7, near the back reflector that substantially enhances absorption.