Superalkali halide perovskites with suitable direct band gaps for photovoltaic applications.

The construction of superalkali halide perovskites has attracted attention for the development of new photovoltaic materials, but stable superalkalis have not been found until now. Herein, to construct new three-dimensional superalkali halide perovskites with a MI frame (M = Sn and Pb), a new Li(HO) superalkali cation is designed and selected based on low vertical ionization potential, suitable tolerance factor, small ionic radius and large dissociation energy. High-throughput first-principles calculations show that superalkalis with lower vertical ionization potentials exhibit stronger interactions with the MI frame.

Passivating Lead Halide Perovskites Using Pyridinium Salts with Superhalogen Atoms.

Passivating lead halide perovskites using pyridinium salts has attracted enormous attention, but the excellent surface passivation of the halide perovskites has not been achieved by using only a pyridinium salt until now. Herein, passivating the (001) planes of the cubic CsPbI, CHNHPbI, and NHCHNHPbI perovskites using the pyridinium salts of CNHX (X = Cl, Br, I, PF, ClO, or BF) is systematically studied by high-throughput first-principle calculations and ab initio molecular dynamics simulations. The results show that the excellent surface passivation of the three perovskites is achieved by the pyridinium salt of CNHBF (i.

Quasi-2D lead-free halide perovskite using superalkali cations for red-light-emitting diodes.

Two dimensional halide perovskites have attracted intense attention, but there is no study to consider quasi-2D lead-free perovskites with superalkali cations as potential emitting materials. Herein, the quasi-2D [CH(CH)NH]HOSnBr perovskite is systematically studied by using ab initio molecular dynamics simulation and first principles calculations. The calculated results show that the quasi-2D perovskite has negative formation energy, small effective hole and electron masses, stable dynamics performance, suitable exciton binding energy and direct band gap, and HO superalkali cations that don't agglomerated.

A two-dimensional CdO/CdS heterostructure used for visible light photocatalysis.

Based on hybrid density functional calculations, the geometrical and electronic structures of a two-dimensional (2D) CdO/CdS heterostructure (HT) formed by a CdO monolayer (ML) and a CdS ML are investigated. The formation of the CdO/CdS HT is exothermic, and the CdO/CdS HT shows excellent ability for visible light absorption. The CdO/CdS HT with a rotation angle of 0° possesses the characteristics of type-II band alignment and strong built-in electric field across the interface, which boost the photogenerated carrier separation.

Strain-Tunable Visible-Light-Responsive Photocatalytic Properties of Two-Dimensional CdS/g-C₃N₄: A Hybrid Density Functional Study.

By means of a hybrid density functional, we comprehensively investigate the energetic, electronic, optical properties, and band edge alignments of two-dimensional (2D) CdS/g-C 3 N 4 heterostructures by considering the effect of biaxial strain and pH value, so as to improve the photocatalytic activity. The results reveal that a CdS monolayer weakly contacts with g-C 3 N 4 , forming a type II van der Waals (vdW) heterostructure. The narrow bandgap makes CdS/g-C 3 N 4 suitable for absorbing visible light and the induced built-in electric field between the interface promotes the effective separation of photogenerated carriers.

ZnO/MoX (X = S, Se) composites used for visible light photocatalysis.

Hybrid density functional has been adopted to investigate the structural, electronic, and optical properties of ZnO/MoS and ZnO/MoSe composites as compared with the results of ZnO, MoS, and MoSe monolayers. The results indicate that MoS and MoSe monolayers could contact with monolayer ZnO to form ZnO/MoS and ZnO/MoSe heterostructures through van der Waals (vdW) interactions. The calculated bandgap of ZnO/MoS (ZnO/MoSe) is narrower than that of ZnO or MoS (MoSe) monolayers, facilitating the shift of light absorption edges of the composites towards visible light in comparison with bare ZnO and MoX monolayers.

Double-Hole-Mediated Codoping on KNbO for Visible Light Photocatalysis.

In this theoretical study, the double-hole-mediated codoping strategy has been adopted to improve the photocatalytic activity of cubic KNbO as compared with the corresponding individual doping. The strong double-hole-mediated dopant-dopant coupling significantly reduces the effective bandgaps for the anionic-anionic (N-N, P-P, N-P, C-S) codoped systems with removing the appearing acceptor states above the Fermi level. No dopant-O coupling occurs in the cationic-anionic (V-C, Ti-P, Ti-N, Zr-P, Zr-N, Sc-S, Y-S) codoped systems.

Hybrid Density Functional Study on Mono- and Codoped NaNbO3 for Visible-Light Photocatalysis.

Monodoping with Mo, Cr, and N atoms, and codoping with Mo-N and Cr-N atom pairs, are utilized to adjust the band structure of NaNbO3 , so that NaNbO3 can effectively make use of visible light for the photocatalytic decomposition of water into hydrogen and oxygen, as determined by using the hybrid density functional. Codoping is energetically favorable compared with the corresponding monodoping, due to strong Coulombic interactions between the dopants and other atoms, and the effective band gap and stability for codoped systems increase with decreasing dopant concentration and the distance between dopants. The molybdenum, chromium, and nitrogen monodoped systems, as well as chromium-nitrogen codoped systems, are unsuitable for the photocatalytic decomposition of water by using visible light, because defects introduced by monodoping or the presence of unoccupied states above the Fermi level, which promotes electron-hole recombination processes, suppress their photocatalytic performance.

A hybrid density functional study on the visible light photocatalytic activity of (Mo,Cr)-N codoped KNbO₃.

To improve the photocatalytic performance of KNbO3 for the decomposition of water into hydrogen and oxygen, the electronic structure of KNbO3 should be modified to have a suitable bandgap with band edge positions straddling the water redox level so as to sufficiently absorb visible light. Hybrid density functional theory has been used to calculate the electronic structures of pure, N-, Mo-, and Cr-monodoped, and Mo-N and Cr-N codoped KNbO3. In particular, the influence of the relative positions of Mo-N or Cr-N codopants on the electronic structure of KNbO3 is discussed in detail to account for the possible difference in the photocatalytic activity of the codoped samples prepared by different experimental techniques.