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A thin-film a-Si:H pin detector was developed for selective detection of UVA (320-400 nm) radiation. In order for the fabrication technology to be transferable onto flexible substrates, all of the processing steps were conducted at temperatures less than 125 • C. The measured saturation current as low as 2 pA cm −2 and the ideality factor of 1.47 show that the pin diodes have a good quality i-layer as well as p-i and n-i interfaces. The film thicknesses were optimized to suppress the detector sensitivity in the visible spectral range, and the peak of spectral response was observed at 410 nm. The selectivity estimated from the ratio of the photocurrent generated by UVA absorption to the total photocurrent is 21%.

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 550mV for a simple structure without a rear-surface passivation or transparent conductive oxide.

Heterojunction solar cells formed by nanocrystalline silicon films on fine-grained multicrystalline silicon substrates are simulated in the presence of grain boundaries. The effects of grain boundaries on the dark and illuminated current-voltage (I -V ) characteristics and spectral response (SR) of heterojunction (HJ) solar cells are assessed using 1D and 2D device simulations. The grain boundary in fine-grained multicrystalline silicon is modelled in two ways: as a defective surface with continuous defect distribution throughout the bandgap, and as a hypothetical sheet with a certain recombination velocity for electrons and holes. The SR and I -V characteristics of HJs are exploited to characterize grain boundary effects on the photovoltaic properties of the solar cells and photodetectors. Simulation results show noticeable differences on the dark I -V and SR of on-and off-grain boundary HJs. Grain boundary effects become important when fine-grained multicrystalline substrates are used. Measurement results of tiny test structures fabricated on the grain boundary show consistently inferior dark I -V and SR characteristics compared to those fabricated away from the grain and allow us to quantify the recombination at the grain boundary.

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