Abstract
Alkaline-earth metallic dopant can improve the performance of anatase TiO2 in photocatalysis and solar cells. Aiming to understand doping mechanisms, the dopant formation energies, electronic structures, and optical properties for Be, Mg, Ca, Sr, and Ba doped anatase TiO2 are investigated by using density functional theory calculations with the HSE06 and PBE functionals. By combining our results with those of previous studies, the HSE06 functional provides a better description of electronic structures. The calculated formation energies indicate that the substitution of a lattice Ti with an AEM atom is energetically favorable under O-rich growth conditions. The electronic structures suggest that, AEM dopants shift the valence bands (VBs) to higher energy, and the dopant-state energies for the cases of Ca, Sr, and Ba are quite higher than Fermi levels, while the Be and Mg dopants result into the spin polarized gap states near the top of VBs. The components of VBs and dopant-states support that the AEM dopants are active in inter-band transitions with lower energy excitations. As to optical properties, Ca/Sr/Ba are more effective than Be/Mg to enhance absorbance in visible region, but the Be/Mg are superior to Ca/Sr/Ba for the absorbance improvement in near-IR region.
Highlights
Titanium dioxide (TiO2 ) has been widely applied in the systems of pigment, photocatalysis, hydrogen storage and production, novel solar cells, and so on [1,2,3,4,5,6,7,8,9,10], because TiO2 has many merits, including nontoxicity, high stability, abundant resource, etc. [11,12]
The substitution effects of alkaline-earth metallic (AEM) dopant on structures can be seen from the local geometries around
‚ Viewing from methodology, by combining the previous studies with our results, including band gaps and the dopant states, HSE06 provides a better description of the electronic structures
Summary
Titanium dioxide (TiO2 ) has been widely applied in the systems of pigment, photocatalysis, hydrogen storage and production, novel solar cells, and so on [1,2,3,4,5,6,7,8,9,10], because TiO2 has many merits, including nontoxicity, high stability, abundant resource, etc. [11,12]. The modification of electronic structures and related properties for anatase TiO2 is very important for the applications of TiO2 nano-materials. It had been reported that the photocatalytic properties of TiO2 were enhanced by alkaline-earth metallic dopant, such as Be [15,16], Ca [17], and Sr [18]. The outperformance of perovskite solar cells with thin dense Mg-doped TiO2 as hole-blocking layers was reported [20,21]. Alkaline-earth metallic (AEM) dopant can improve the performance of TiO2 in photocatalysis and solar cells. The improved performance of perovskite solar cells with Mg-doped anatase TiO2 was attributed to the better properties of Mg-modulated TiO2 as compared to TiO2 , such as upshifted CB minimum and downshifted valence band (VB) maximum, etc. It is necessary to study on the doping mechanism of AEM-doped anatase TiO2
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