Effect of defect densities and band offsets on carrier transport mechanisms in mixed phase silicon/crystalline silicon heterojunction

Thin-film silicon/crystalline silicon heterojunction-type solar cells, combining the low-cost, low-temperature and light-weight of thin-film silicon with the high efficiency and high stability of crystalline silicon (c-Si), are studied widely due to the increased need for terrestrial and satellite applications. A major aspect when dealing with thin-film silicon/crystalline silicon heterojunction solar cells is quality of the silicon film-crystalline silicon hetero-interface. In this study, the carrier transport mechanisms in mixed phase (amorphous and microcrystalline) thin-film silicon/p type crystalline silicon heterojunction for various thin-film thicknesses and SiH₄/H₂ ratios are investigated. The electrical properties are strongly affected by the defect state distribution and the band offset at the hetero-interface. Two carrier transport mechanisms are recognized. The recombination process involving the interface states on the thin-film silicon side dominates at low forward bias (V < 0.4 V), whereas multi-step tunneling capture emission (MTCE) dominates at the high forward bias (0.4 < V < 0.8 V).