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First-principle total energy calculations were performed to investigate the atomic structures and relative stabilities of two low miller-index surfaces of pyrochlore Y2Zr2O7. The stoichiometric Y2Zr2O7 (110) and (100) surfaces were predicted, with lowest formation energies of 1.20 and 1.47 J/m2, respectively. Based on a thermodynamic defect model, non-stoichiometric Y2Zr2O7 surface energies were further evaluated as a function of environmental oxygen partial pressure (pO2) and temperature (T). With all of the results, we were able to construct the surface phase diagrams for T = 300 and 1400 K. The strong correlation between the structural stabilities and the surface stoichiometry was revealed as varying T and pO2. At a given T, the most stable termination of the (110) surfaces would change from a (Y,Zr)−rich (ns−2Y2Zr6O) to O−rich ones (ns−4O_2 and ns−4O_1) as increasing pO2, while that of the (100) surfaces would change from the stoichiometric (stoi−1Y1Zr_1) to the O−rich one (ns−5O). The critical pO2 value for termination transition moves to its higher end as increasing T. [ABSTRACT FROM AUTHOR]

PEDOT:PSS (poly 3,4-ethylenedioxythiophene-polystyrene sulfonate) film is widely used due to its good electrical conductivity, light transmittance, mechanical flexibility and solution processability. Improving the electrical conductivity and photoelectric stability of PEDOT materials is of great significance to its device applications. In this article, highly conductive PEDOT:PSS films were obtained by spin-coating method after post-treatment by sulfuric acid. The films were placed in air, oxygen, nitrogen and under sun illumination for 30 d to study their photo-electrical stability and aging mechanisms. It indicates that: sunlight is the main factor affecting the stability of photo-electrical properties of thin films, and sulfuric acid treatment removes the excessive PSS component effectively and therefore improves the stability of PEDOT:PSS films. By comparing the absorption spectrum and photoelectron spectroscopy (XPS) of the film before and after aging, it is found that, the film underwent photo-oxidation degradation during the aging process, which directly affects its photoelectrical stability. [ABSTRACT FROM AUTHOR]

Crystalline silicon/compounds heterojunction (SCH) solar cells using oxides or fluorides as the electron or hole transport layers present great low-cost potential. In this paper, c-Si/SnO2 SCH solar cells are based on p-type c-Si substrates and use SnO2, prepared by atomic layer deposition, as the electron transport layers are investigated. By optimizing the SnO2 thickness and the device annealing process, a Voc of 718 mV and an efficiency of 20.1% are achieved on a champion SCH solar cell with an optimized SnO2 thickness of 3 nm. By analyzing the dark J–V curves, transport mechanisms of the silicon/compound heterojunction are investigated. It is proved that a strong inversion layer is induced in the p-type Si substrate, and a high hole barrier exists in the heterojunction region, which makes it a minority-carrier device. The induced inversion layer at the Si surface and the carrier selective transport effect of the SnO2 layer together enable the devices to achieve a high Voc. [ABSTRACT FROM AUTHOR]