The crystal structure, formation energy, electronic structure, electrical properties and optical properties of anatase TiO2 with various Nb concentrations were studied by first-principles calculations based on density functional theory (DFT) and the Hubbard U correction. Firstly, the crystal structures of TiO2 with various Nb concentrations were optimized successfully. The higher concentrations of Nb facilitate the synthesis of Nb-doped TiO2 systems in an O-rich environment. Furthermore, the band structures and density of states prove that the electronic structure of Nb-doped TiO2 is mainly transformed by the hybridization of Ti 3d, Nb 4d and O 2p states. Next, broadening of the valence band and occupied states at the bottom of the conduction band enhance the conductivity of Nb-doped TiO2, and the conductivity reaches the maximum value at the high Nb-doping concentration of 6.25 at.%. Last but not least, the calculated optical properties show that the absorption edge of Nb-doped TiO2 produces an blue shift. TiO2 with Nb-doping concentration below 14.58 at.% exhibits the high transmittance in the visible region.
Both the passivation and good antireflection effect can improve the power conversion efficiency of the crystalline silicon solar cells. In this study, we simulated and optimized HfO2 single‐layer, SiO2/SiC double‐layer, and MgF2/HfO2/SiC triple‐layer antireflection coatings and obtained the optimal optical parameters based on the optical transfer matrix. In addition, we analyzed the influence of HfO2, SiO2/SiC, and MgF2/HfO2/SiC antireflection coatings on the performance of the crystalline silicon solar cell. The results indicated that the HfO2, SiO2/SiC, and MgF2/HfO2/SiC antireflection coatings increased the power conversion efficiency of the crystalline silicon solar cell from 12.17 % to 17.13 %, 18.57 %, and 18.85 %, respectively. For cost‐saving, the SiO2/SiC double‐layer antireflection coating is a good choice for the crystalline silicon solar cell.
The methylammonium lead iodide (CH 3 NH 3 PbI 3 ) perovskite is a new type of photovoltaic material, which has attracted widespread attention due to its excellent photoelectric properties. Here, the mechanical properties and structural stability of five phases of CH 3 NH 3 PbI 3 under high pressure are studied using first-principles. These works help to improve the understanding of CH 3 NH 3 PbI 3 and predict the new structure. The results show that the two hexagonal phases transform to orthorhombic phase at 1.0 GPa and 2.0 GPa, respectively. The tetragonal phase transforms to cubic phase at 0.3 GPa. Furthermore, in the 2H-phase, Young's modulus (E) decreases with increasing pressure, which means that stiffness decreases with increasing pressure. However, in orthorhombic, tetragonal, and cubic phases, as the pressure increases, E first increases and then decreases. The Pugh's ductility index (G/B) of 2H-phase is greater than 0.57and the one of T-phase is less than 0.57, which proves that the 2H-phase is brittle and the T-phase is tough. The Pugh's ductility index of the other three phases changes around 0.57 with the increase of pressure. As the increase of pressure, only the elastic constant of 4H-phase cannot meet the mechanical stability criteria, and the other four phases can meet.
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