Thin film micro- and polycrystalline silicon nip cells on stainless steel made by hot-wire chemical vapour deposition

Hot-wire chemical vapour deposition (HWCVD) with two tantalum filaments has been employed to deposit highly crystalline microcrystalline silicon (μc-Si:H) for use in the bottom cell of multijunction solar cells. The material was compared to previously developed poly2 material, which is deposited under slightly different conditions. The present material has smaller crystallites, which show a less preferential (220) orientation, and has a lower crystalline volume fraction (80%). A higher oxygen content, suggesting a less compact structure, and well-passivated grain boundaries were observed. A single junction nip-configured solar cell, in which a 1.1-μm-thick layer of the material was incorporated as absorber layer, showed a higher Voc and FF (0.412 V and 0.664) and a lower Jsc (16.08 mA/cm2) than the best poly2-containing cell. The lower Jsc is a result of poorer light-trapping due to the reduced (220) orientation and size of the materials crystallites.