Visible-light-transparent p-type NiO films were deposited by reactive RF sputtering under unintentional heating. An optical transmittance of >80% was obtained in the wavelength range of 500–800 nm when the films were deposited under a very low O2 fraction in the gas phase O2/(Ar+ O2) = 0.5%. This result may reflect a decrease in the concentration of Ni vacancies due to the increase in their formation energy under oxygen-poor deposition conditions. Heterostructure pn junctions consisting of p-type NiO and n-type ZnO layers were also deposited. We eventually observed a slight but noticeable photovoltaic effect.

The optical and electrical properties of proton irradiated Cu(In,Ga)Se 2 (CIGS) solar cells and the composed thin films such as transparent conducting oxide (TCO) and CIGS were investigated. The transmittance and resistivity of TCO window layers remained constant for a fluence of up to 3 Â 10 15 cm À2 . For CIGS thin films, the photoluminescence (PL) peak intensity tended to decrease, possibly because the number of nonradiative recombination centers increased under proton irradiation. In addition, the PL spectra of irradiated CIGS solar cells suggested that the CIGS absorber layer and/or the depletion layer around the CdS/CIGS interface are more prone to degrade than other layers. These results constitute the first step in clarifying the degradation mechanism of CIGS solar cells. #

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