Epitaxial Si films carried by thick polycrystalline Si as a drop-in replacement for conventional Si wafers

We demonstrate the fabrication of a new type of wafer equivalent from the gas phase. The demonstrators are 160 mu m thick and 9x9 cm(2) in size. They consists of a 30 mu m-thick p-type monocrystalline epitaxial layer that is carried by a CVD-deposited, 130 mu m-thick, p(+)-type polycrystalline Si layer. A SiO2 layer in between the epitaxial Si and the poly-Si passivates the rear side of the cell and functions as a reflector. Openings in the oxide make the contact to the base and form a PERL-type rear side. The wafer bow is (0.3 +/- 0.2 mm). The wafer surface is (100)-oriented. Optical analysis demonstrates an absorption corresponding to a short circuit current density of (38.5 +/- 0.5) mA/cm(2) from a 22.6 mu m-thick epitaxial layer when textured with random pyramids. Small p-type demonstrator solar cells exhibit a base saturation current density of (111 +/- 20) fA/cm(2) as deduced from a quantum efficiency measurement. The poly-Si-carried (PolCa) wafer equivalent shortcuts the conventional wafer production process, since it avoids crunching and melting of the poly-Si, growing of the ingot and sawing of the wafers.