My guess is that the copper oxide would be much cheaper to work into much thinner sheets than silicon, which is also expensive to purify, so although the raw material may be more expensive, the processing costs and volume used might be where the savings are made.
Also, the abstract on the referenced paper seems to indicate that the efficiency of this design is reasonable. I didn't go beyond the paywall to find out more though.
Photovoltaics (PV) are a promising source of clean renewable energy, but current technologies face a cost-to-efficiency trade-off that has slowed widespread implementation.(1, 2) We have developed a PV architecture—screening-engineered field-effect photovoltaics (SFPV)—that in principle enables fabrication of low-cost, high efficiency PV from virtually any semiconductor, including the promising but hard-to-dope metal oxides, sulfides, and phosphides.(3) Prototype SFPV devices have been constructed and are found to operate successfully in accord with model predictions.
You can deposit thin films of silicon on to, say, ordinary glass. Usually, this is done with CVD, although I think epitaxial growth is also a popular technique.
The problem is that this tends to produce amorphous silicon, which is not especially efficient. There is a good deal of work to get to the point where monocrystalline silicon thin film cells are viable outside of the lab, though.
Also, the abstract on the referenced paper seems to indicate that the efficiency of this design is reasonable. I didn't go beyond the paywall to find out more though.
Photovoltaics (PV) are a promising source of clean renewable energy, but current technologies face a cost-to-efficiency trade-off that has slowed widespread implementation.(1, 2) We have developed a PV architecture—screening-engineered field-effect photovoltaics (SFPV)—that in principle enables fabrication of low-cost, high efficiency PV from virtually any semiconductor, including the promising but hard-to-dope metal oxides, sulfides, and phosphides.(3) Prototype SFPV devices have been constructed and are found to operate successfully in accord with model predictions.
http://pubs.acs.org/doi/pdf/10.1021/nl3020022