Heterojunction solar cells formed by nanocrystalline Si films on fine-grained multicrystalline Si substrates were 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 were assessed using 1D and 2D device simulations. The grain boundary in fine-grained multicrystalline Si was modelled in two ways: as a defective surface with continuous defect distribution throughout the band-gap, and as a hypothetical sheet with a certain recombination velocity for electrons and holes. The SR and I–V characteristics of HJs were exploited to characterize grain boundary effects on the photovoltaic properties of the solar cells and photodetectors. Simulation results showed noticeable differences on the dark I–V and SR of on- and off-grain boundary HJs. Grain boundary effects became important when fine-grained multicrystalline substrates were used. Measurement results of tiny test structures fabricated on the grain boundary showed consistently inferior dark I–V and SR characteristics compared to those fabricated away from the grain and permitted quantification of recombination at the grain boundary.

Modelling of Grain Boundary Effects in Nanocrystalline/Multicrystalline Silicon Heterojunction Solar Cells. M.Farrokh-Baroughi, S.Sivoththaman: Semiconductor Science and Technology, 2006, 21, 979-86