Novel profiled thin-film polycrystalline silicon solar cells on stainless steel substrates

In order to obtain higher conversion efficiencies while keeping the manufacturing cost low in thin-film PV technologies, a possible low bandgap material is amorphous silicon germanium. Although record efficiencies in excess of 15% have been reported for triple-junction solar cells comprising these alloys, concerns regarding the stability and quality of this material still need to be overcome. Another approach is the introduction of thin-film micro- or polycrystalline silicon with a band gap of 1.1 eV, deposited at a temperature that is low enough to allow cheap, “foreign” carrier materials. Apart from the application of a modified PECVD method utilizing frequencies in the VHP domain, the hot wire CVD (HWCVD) method appears a particularly promising technique for the deposition of high-quality thin-film intrinsic or doped poly-Si. In this contribution, special attention will be paid to the latest developments in the application of hot-wire deposited silicon thin films in solar cells. By implementing a profiled hydrogen-diluted HWCVD growth scheme that produces a thin small-grained seed layer on top of a thin n-layer, we have been able to obtain fast polycrystalline growth of the intrinsic layer of an n-i-p solar cell. An efficiency of 4.41% is obtained and the fill factor is 0.607. The current density is close to 20 mA/cm² for an i-layer that is only 1.22 μm thick. The cell is deposited on plain stainless steel and thus does not comprise a back reflector