Investigation of textured back reflectors for microcrystalline silicon based solar cells

Microcrystalline silicon (mu c-Si:H) solar cells require an effective light trapping in the near infrared (NIR) to enhance the long wavelength spectral response. For this purpose we investigated back reflectors based on texture-etched ZnO/Ag stacks prepared on glass substrates by magnetron sputtering. With decreasing sputter pressure the resulting surface texture of the glass/Ag/ZnO substrates after etching exhibits a larger feature size and root mean square roughness. The increase in feature size corresponds to an increase of diffuse reflectivity. Applied in microcrystalline solar cells prepared by VHF plasma enhanced chemical vapour deposition (PECVD), the reflectors showing the largest feature size (prepared at the lowest possible sputter pressure) yielded the highest long wavelength spectral response. The pc-Si n-i-p cells prepared on the latter back reflector exhibited efficiencies of 6.9 % (short circuit current density j(sc) = 18.8 mA/cm(2)) and 7.5 % (j(sc) = 25 mA/cm(2)) for an i-layer thickness of 1 mu m and 3.5 mu m, respectively.