Title: Titanium dioxide hole-blocking layer in ultra-thin-film crystalline silicon solar cells,
Abstract: One of the remaining obstacles to approaching the theoretical efficiency
limit of crystalline silicon (c-Si) solar cells is the exceedingly high
interface recombination loss for minority carriers at the Ohmic contacts. In
ultra-thin-film c-Si solar cells, this contact recombination loss is far more
severe than for traditional thick cells due to the smaller volume and higher
minority carrier concentration of the former. This paper presents a novel
design of an electron passing (Ohmic) contact to n-type Si that is
hole-blocking with significantly reduced hole recombination. This contact is
formed by depositing a thin titanium dioxide (TiO2) layer to form a silicon
metal-insulator-semiconductor (MIS) contact. A 2 {\mu}m thick Si cell with this
TiO2 MIS contact achieved an open circuit voltage (Voc) of 645 mV, which is 10
mV higher than that of an ultra-thin cell with a metal contact. This MIS
contact demonstrates a new path for ultra-thin-film c-Si solar cells to achieve
high efficiencies as high as traditional thick cells, and enables the
fabrication of high-efficiency c-Si solar cells at a lower cost.