Nanocrystalline silicon solar cells were enhanced with a photonic crystal back-reflector. Rigorous scattering matrix simulations were used to optimize a photonic crystal back-reflector consisting of a triangular lattice of nano-holes, with a pitch near 800 nm. The photonic crystal back-reflector with a pitch of 800 nm was fabricated on the crystalline silicon substrate by photolithography and reactive-ion etching, and coated with silver and zinc oxide. Nanocrystalline silicon solar cells were grown on the patterned substrates. We observed similar to 7% enhancement of the absorption and photo-generated current relative to a Ag/ZnO substrate, with an enhancement ratio of 1.5 near the band edge. Significant enhancement occurred in photon absorption at near infrared wavelengths greater than 700 nm, due to diffraction resonances of the incoming light. (C) 2010 Elsevier B.V. All rights reserved.