Effect of back reflectors on light trapping in μc-Si:H cells has been investigated with self-ordered Al substrates obtained by anodic oxidation. With increasing the period of the patterned substrates from 0 to 1.1 μm, 1-μm-thick μc-Si:H cells on the patterned substrates have shown a significant enhancement of spectral response in the near infrared region, giving an increment of the short circuit current density from 18 to 24 mA/cm2. This enhanced light trapping effect are attributed to the improved reflectivity of the rear side and effective light scattering at the front side, as well as light scattering at the rear side.

The microcavity effect of two-dimensional W surface-relief gratings has been investigated by means of the finite-difference time-domain simulation. The peak structure of the spectral emissivity of W gratings with a number of microcavities is in good agreement with the spectral features of a single microcavity. This result shows that the emissivity enhancement by W gratings with microcavities is mainly attributable to the microcavity effect that arises from each microcavity. It is that the spectral emissivity can be controlled by a combination of several microcavities with different parameters, and that not only a rectangular but a cylindrical microcavity also shows the microcavity effect according to its cavity modes.