High-quality heterojunction diodes with near-unity ideality factor were fabricated by direct deposition of a (n(+)) nanocrystalline silicon film on top of fine-grained (p) multicrystalline silicon substrates. A very good ideality factor of 1.08 was achieved using a single-diode model in the medium forward-bias regime. Current-voltage (IV) characteristics of the diodes measured in the dark show that the recombination at the heterointerface is much less than the recombination at the space-charge region in the low forward-bias regime confirming the fact that the junction quality is good and is suitable for photovoltaic applications. Internal quantum efficiency measurements performed on these cells show a high (> 70%) blue response partly due to a high transparency of the n(+) nanocrystalline material. Illuminated IV of the heterojunction solar cells show a high fill factor of 78% - 79% and an acceptable open circuit voltage of 550 mV for a simple structure without a rear-surface passivation or transparent conductive oxide. (c) 2006 American Vacuum Society.