Regulation of the luminescence mechanism of two-dimensional tin halide perovskites

Two-dimensional (2D) Sn-based perovskites are a kind of non-toxic environment-friendly luminescent material. However, the research on the luminescence mechanism of this type of perovskite is still very controversial, which greatly limits the further improvement and application of the luminescence performance. At present, the focus of controversy is defects and phonon scattering rates. In this work, we combine the organic cation control engineering with temperature-dependent transient absorption spectroscopy to systematically study the interband exciton relaxation pathways in layered A2SnI4 (A = PEA+, BA+, HA+, and OA+) structures. It is revealed that exciton-phonon scattering and exciton-defect scattering have different effects on exciton relaxation. Our study further confirms that the deformation potential scattering by charged defects, not by the non-polar optical phonons, dominates the excitons interband relaxation, which is largely different from the Pb-based perovskites. These results enhance the understanding of the origin of the non-radiative pathway in Sn-based perovskite materials.

Metal–Insulator Transition in Doped Barium Plumbates

Solid solutions in the Ba(Pb1−xSrx)O3−z system were prepared by aliovalent substitution of Pb4+ by Sr2+ ions to investigate the effect of cation stoichiometry on thermal and electrical properties as x was varied between 0 and 0.4, in the temperature range 300–523 K. The starting compound, barium plumbate (BaPbO3), has a perovskite structure and is known to exhibit metallic conductivity due to an overlap of the O2p nonbonding and the Pb–O spσ antibonding band, which is partially filled by the available electrons. The large difference in the ionic radii between the Pb4+ and Sr2+ ions introduces significant strain into the (Pb/Sr)O6 octahedra of the perovskite structure. Additionally, charged defects are created on account of the different oxidation states of the Pb4+ and Sr2+ ions. Evidence of a metal to insulator transition (MIT) of the Mott–Hubbard type has been observed at a critical concentration of Sr2+ ions.

Electron-deficient 4-nitrophthalonitrile passivated efficient perovskite solar cells with efficiency exceeding 22%

We proved that electron-deficient 4-nitrophthalonitrile with σ–π accepting NO2 and –CN can passivate the charged defects in perovskite solar cells, which achieve a power conversion efficiency (PCE) of 22.1% and improved stability.

Theoretical insights of codoping to modulate electronic structure of $$\hbox {TiO}_2$$ and $$\hbox {SrTiO}_3$$ for enhanced photocatalytic efficiency

$$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 are well known materials in the field of photocatalysis due to their exceptional electronic structure, high chemical stability, non-toxicity and low cost. However, owing to the wide band gap, these can be utilized only in the UV region. Thus, it’s necessary to expand their optical response in visible region by reducing their band gap through doping with metals, nonmetals or the combination of different elements, while retaining intact the photocatalytic efficiency. We report here, the codoping of a metal and a nonmetal in anatase $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 for efficient photocatalytic water splitting using hybrid density functional theory and ab initio atomistic thermodynamics. The latter ensures to capture the environmental effect to understand thermodynamic stability of the charged defects at a realistic condition. We have observed that the charged defects are stable in addition to neutral defects in anatase $$\hbox {TiO}_2$$ TiO 2 and the codopants act as donor as well as acceptor depending on the nature of doping (p-type or n-type). However, the most stable codopants in $$\hbox {SrTiO}_3$$ SrTiO 3 mostly act as donor. Our results reveal that despite the response in visible light region, the codoping in $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 cannot always enhance the photocatalytic activity due to either the formation of recombination centers or the large shift in the conduction band minimum or valence band maximum. Amongst various metal-nonmetal combinations, $$\hbox {Mn}_\text {Ti}\hbox {S}_\text {O}$$ Mn Ti S O (i.e. Mn is substituted at Ti site and S is substituted at O site), $$\hbox {S}_\text {O}$$ S O in anatase $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {Mn}_\text {Ti}\hbox {S}_\text {O}$$ Mn Ti S O , $$\hbox {Mn}_\text {Sr}\hbox {N}_\text {O}$$ Mn Sr N O in $$\hbox {SrTiO}_3$$ SrTiO 3 are the most potent candidates to enhance the photocatalytic efficiency of anatase $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 under visible light irradiation.

Investigation of Local Conduction Mechanisms in Ca and Ti-Doped BiFeO3 Using Scanning Probe Microscopy Approach

In this work we demonstrate the role of grain boundaries and domain walls in the local transport properties of n- and p-doped bismuth ferrites, including the influence of these singularities on the space charge imbalance of the energy band structure. This is mainly due to the charge accumulation at domain walls, which is recognized as the main mechanism responsible for the electrical conductivity in polar thin films and single crystals, while there is an obvious gap in the understanding of the precise mechanism of conductivity in ferroelectric ceramics. The conductivity of the Bi0.95Ca0.05Fe1−xTixO3−δ (x = 0, 0.05, 0.1; δ = (0.05 − x)/2) samples was studied using a scanning probe microscopy approach at the nanoscale level as a function of bias voltage and chemical composition. The obtained results reveal a distinct correlation between electrical properties and the type of charged defects when the anion-deficient (x = 0) compound exhibits a three order of magnitude increase in conductivity as compared with the charge-balanced (x = 0.05) and cation-deficient (x = 0.1) samples, which is well described within the band diagram representation. The data provide an approach to control the transport properties of multiferroic bismuth ferrites through aliovalent chemical substitution.