Optical Performance of Ag-based Back Reflectors with different Spacers in Thin Film Si Solar Cells

We have compared different Ag-based back reflectors (BRs) applied to superstrate-type microcrystalline Si devices grown on Asahi U glass. In particular, substitution of the conventional ZnO:Al layer by MgF2, with lower refractive index and no free-carrier absorption, has been investigated. As electrical issues can mask the optical performance of the BR when evaluated by EQE measurements, a purely optical method that compares the intensity of Raman spectra generated with long wavelength excitation light has been applied. Based on this investigation, MgF2/Ag is potentially superior to ZnO:Al/Ag, even when MgF2 is used in the form of ultrathin layer (few nm, likely island-like). Nevertheless, the novel dual-function n-SiOx/Ag BR outperforms all the other BRs.