We studied solar cells with periodic interface texture. For periods of 550 and 833 nm, we found that the measured photocurrent increases under oblique incidence and assumes a maximum between 20 and 30°. For the geometries used in our experiments, the initial increase occurred for conditions close to those of photonic band gaps. In addition to a forbidden band of energies where waveguide modes cannot propagate, we found that the coupling to the high-energy branches was suppressed under conditions of high symmetry such as sinusoidal interface geometry and perpendicular incidence.