Abstract
Carrier recombination at the metal contact regions has now become a critical obstacle to the advancement of high efficiency diffused junction silicon solar cells. The insertion of a thin dielectric interlayer - forming a metal-insulator-semiconductor (MIS) contact - is a known approach to reduce contact recombination. However, an insulator thickness less than 25 angstrom is usually required for current transport, making it difficult to simultaneously achieve good surface passivation. This paper compares standard MIS contacts to a newly developed contact structure, involving hydrogenated amorphous silicon (a-Si:H) over-layers. The contact structures are trialed on both n(+) and p(+) lightly diffused surfaces, with SiO2 and Al2O3 insulator layers, respectively. In both cases significant improvements in the carrier-selectivity of the contacts is achieved with the addition of the a-Si: H over-layers. Simulations of idealized cell structures are used to highlight the performance and technological benefits of these carrier-selective structures over standard locally diffused contacts.