Management of light-trapping effect for a-Si:H/μc-Si:H tandem solar cells using novel substrates, based on MOCVD ZnO and etched white glass

The authors have successfully developed "W-textured" ZnO:B-coated soda-lime glass substrates with higher haze value and lower reflectance and thus, improved light-trapping effect, especially, in the long wavelength region. In order to obtain higher efficiency the authors have applied here this technique to a white glass substrate which has higher transmittance. The authors have investigated the relationship between its refractive index on each side of the glass before RIE etching and the RMS roughness of ZnO:B layer coated by the MOCVD method (on either side of the glass) after etching. For the surface morphology of the ZnO:B layer deposited on the side of the RIE-etched white glass with lower refractive index, it was found, in this study, that it shows mountain-chain-like double texture with higher haze value. Whereas ZnO:B layers deposited on soda-lime glass (SLG) investigated in a previous study, have cauliflower-like morphology and lower haze values. By using the newly developed white glass substrates, a higher short-circuit current density J(sc) could be obtained corresponding to an improved spectral response, especially in the long wavelength regions ( > 500 nm). As a result, the a-Si:H/mu c-Si:H solar cell fabricated on this newly developed substrate has an initial efficiency of 13.2% which is higher than the one for substrates based on soda-lime glass. This shows that this newly developed W-textured substrate is a promising solution for the deposition of high-efficiency thin-film silicon solar cells. (C) 2013 Elsevier B.V. All rights reserved.