The Si:WO 3 heterostructure is expected to have suitable band alignment for the Z-scheme water splitting, but the heterostructure interfaces have been scarcely studied. In this work, a series of interfaces between the WO 3 (100) and Si (001) surfaces, which have a small lattice-mismatch, are studied using ab initio calculations. When there is no atom diffusion across the interface, a Si-O bonded interface with Si dimers is the most stable. Analysis of the electronic structure shows that the interfacial Si and O atoms are fully saturated, leading to a clean interface without localized gap states. O diffusion from WO 3 into Si is found to be thermodynamically possible, but it does not affect the full bond saturation of the interfacial atoms. A type-II band alignment exists between Si and WO 3 , with the WO 3 conduction band about 0.5 eV higher than the Si valence band, which is not influenced by O diffusion. A band diagram is plotted for the Si:WO 3 heterostructure to evaluate its photocatalytic capability, and the influence of the small Schottky barrier and the interface amorphous layer is discussed.
Ferroelectric size effects in multiferroic BiFeO 3 have been studied using a host of complementary measurements. The structure of such epitaxial films has been investigated using atomic force microscopy, transmission electron microscopy, and x-ray diffraction. The crystal structure of the films has been identified as a monoclinic phase, which suggests that the polarization direction is close to ͗111͘. Such behavior has also been confirmed by piezoforce microscopy measurements. That also reveals that the ferroelectricity is down to at least 2 nm.
The synthesis route based on co-electroplating of copper, zinc, tin, and chalcogen precursor plus post-chalcogenization demonstrates the tremendous potential to realize industrial manufacture of earthabundant kesterite materials for sustainable photovoltaics. Exploration of appropriate annealing temperature is significant to gain insight into the crystallization of kesterite solar materials on the back contacts based on transparent conducting oxides in bifacial device. The Cu 2 ZnSn(S x , Se 1−x ) 4 (CZTSSe) absorber films have been fabricated by post-selenizing coelectroplated metal−sulfide precursors on ITO substrate at 500, 525, and 550 °C. Experimental proof, including electron microscopies, X-ray diffraction, optical transmission/reflection spectra, polarized Raman, and IR techniques, is presented for the interfacial reaction between the ITO back contact and CZTSSe absorber. This reaction contributes to substitutional diffusion of In into CZTSSe (CZTISSe) to a considerable extent and formation of a SnO 2 interfacial layer when the temperature is higher than 500 °C. In incorporation does not much change the optical absorption, band gap, and phonon spectra of CZTSSe; whereas, it leads to lattice expansion more or less. The bifacial kesterite solar devices are successfully fabricated, and the device performance is analyzed and discussed.
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