Zn 1- x Ge x O y Passivating Interlayers for BaSi 2 Thin-Film Solar Cells.

BaSi 2 is a promising absorber material for next-generation thin-film solar cells (TFSCs). For high-efficiency TFSCs, a suitable interlayer should be found for every light absorber. However, such an interlayer has not been studied for BaSi 2 . In this study, we investigated amorphous Zn 1- x Ge x O y films as interlayers for BaSi 2 . The Zn/Ge atomic ratio in the Zn 1- x Ge x O y film and the optical band gap depend on the substrate temperature during sputtering deposition. A suitable i-Zn 1- x Ge x O y /BaSi 2 heterointerface with spike-type conduction band offset was achieved when Zn 1- x Ge x O y was deposited on BaSi 2 at 50 °C. Furthermore, photoresponsivity measurements revealed that Zn 1- x Ge x O y has an excellent surface passivation effect on BaSi 2 . When the thickness of Zn 1- x Ge x O y was 2 nm, a high photoresponsivity of 0.9 A/W was obtained for a 500 nm thick BaSi 2 layer at a wavelength of 780 nm under an applied bias voltage of 0.5 V between the front and rear electrodes, where the photoresponsivity in the short-wavelength region was significantly improved compared with that of BaSi 2 capped with an amorphous Si layer. X-ray photoelectron spectroscopy revealed that the Zn 1- x Ge x O y films suppressed the oxidation of the BaSi 2 surface, decreasing the carrier recombination rate. This is the first demonstration of passivation interlayers for BaSi 2 with suitable band alignment for carrier transport and surface passivation effects.