Amorphous silicon oxide containing nanocrystalline silicon grain (nc-SiOx:H) films are prepared by a plasma-enhanced chemical vapor deposition technique at different negative substrate bias voltages. The influence of the bias voltage applied to the substrate on the microstructure is investigated. The analysis of x-ray diffraction spectra evidences the in situ growth of nanocrystalline Si. The grain size can be well controlled by varying the substrate bias voltage, and the largest size is obtained at 60 V. Fourier transform infrared spectra studies on the microstructure evolutions of the nc-SiOx:H films suggest that the absorption peak intensities, which are related to the defect densities, can be well controlled. It can be attributed to the fact that the negative bias voltage provides a useful way to change the energies of the particles in the deposition process, which can provide sufficient driving force for the diffusion and movement for the species on the growing surface and effectively passivate the dangling bonds. Also the larger grain size and lower band gap, which will result in better photosensitivity, can also be obtained with a moderate substrate bias voltage of 60 V.

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Microcrystalline silicon (µc-Si:H) solar cell with graded band gap microcrystalline silicon oxide (µc-SiO x :H) buffer layer is prepared by plasma enhanced chemical vapor deposition and exhibits improved performance compared with the cell without it. The buffer layer moderates the band gap mismatch by reducing the barrier of the p/i interface, which promotes the nucleation of the i-layer and effectively eliminates the incubation layer, and then enhances the collection efficiency of the cell in the short wavelength region of the spectrum. The p/i interface defect density also decreases from 2.2 × 10 12 cm −2 to 5.0 × 10 11 cm −2 . This graded buffer layer allows to simplify the deposition process for the µc-Si:H solar cell application.

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Oxide thermoelectric materials have been considered to be potential candidates in high-temperature thermoelectric power generation, however, their high thermal conductivity renders them inferior to the conventional thermoelectric materials and limit their practical application. In this paper, we successfully reduce the thermal conductivity of CdO polycrystals through Ca2+ doping, and the improvement in ZT is also obtained due to the low thermal conductivity. Cd1-xCaxO (x=0, 0.01, 0.03, 0.08) polycrystals are synthesized by adding CaCO3 into CdO via conventional solid-state reaction method and their high-temperature thermoelectric properties are studied. XRD results reveal that all samples are composed of CdO polycrystals, and the lattice parameters increase with Ca2+ content due to the larger radius of Ca2+ as compared with that of Cd2+. Addition of CaCO3 can induce the formation of point defects as well as pores in the CdO polycrystals, thus inhibits the grain growth of CdO and induces the increase of grain boundaries. The main electron carriers in CdO are reported to be shallow level donor impurities formed by oxygen vacancies; as the Ca2+ concentration in Cd1-xCaxO increases, the conduction band minimum of the samples shifts upward and the level of donor impurity becomes deeper, finally resulting in the decrease of electron carrier concentration. Meanwhile, the reduced carrier concentration in the doped samples leads to the increase of both the electrical resistivity ρ and the absolute Seebeck coefficient |S|, while the electrical thermal conductivity κ e will decrease with increasing Ca content. Investigations on the thermal properties of the obtained samples demonstrate that the introduction of Ca2+ is effective to suppress the thermal conductivity. The increment of pores and grain boundaries in the doped samples will enhance the long-wavelength phonon scattering, resulting in the decrease of phonon thermal conductivity κ p. Furthermore, the point defects, which come from the mass and size differences between Ca and Cd atoms, also act as scattering centers and lead to a considerable decrease in phonon thermal conductivity. Due to the simultaneous reduction of both electrical and phonon thermal conductivity, the total thermal conductivity κ may substantially be suppressed, for example, the total thermal conductivity of Cd0.95Ca0.05O reaches 2.2 W·m-1·K-1 at 1000 K, a remarkable decrease as compared with pristine CdO, which is 3.6 W·m-1·K-1 measured at the same temperature. Benefiting from the drastically reduced thermal conductivity, Cd0.99Ca0.01O polycrystals can achieve a high ZT of 0.42 at 1000 K, 27% higher than the pure CdO, which is one of the best n-type oxide TE materials reported so far.