The leaf-templated and oxygen vacancy engineered CaTiO₃ showed excellent structural stability but with loss in morphology for the studied binary phase photocatalytic reactions.

Methylammonium lead halide $\left({\mathrm{MAPbI}}_3\right)$ perovskite has emerged as one of the frontier optoelectronic semiconductors. To avoid lead toxicity, the role of Sn substitution and Pb vacancy (Pb-$⊠)$ are addressed in regulating stability and solar cell efficiency of ${\mathrm{MAPb}}_{1-X-Y}{\mathrm{Sn}}_X{⊠}_Y{\mathrm{I}}_3$ perovskite using hybrid density functional theory (DFT). The role of spin-orbit coupling (SOC) and the electron's self-interaction error are examined carefully. We find to reduce the Pb content from pristine ${\mathrm{MAPbI}}_3$, Sn substitution has a more favorable thermodynamic stability than creating Pb-$⊠$. Moreover, on substituting Sn, due to strong $s\text{−}p$ and $p\text{−}p$ couplings, the lower parts of the conduction band gets shifted downwards, which results in the reduction of the band gap (direct). This further helps us to get a high optical absorption coefficient (redshifted) and maximum solar cell efficiency in ${\mathrm{MAPb}}_{1-X}{\mathrm{Sn}}_X{\mathrm{I}}_3$ for $0<X\le 0.5$.

TiO₂ anatase is considered to play a significant importance in energy and environmental research. However, for developing artificial photosynthesis with TiO₂, the major drawback is its large bandgap of 3.2 eV. Several non-metals have been used experimentally for extending the TiO₂ photo-absorption to the visible region of the spectrum. It’s therefore of paramount importance to provide theoretical guidance to experiment about the kind of defects that are thermodynamically stable at a realistic condition (e.g. Temperature (T), oxygen partial pressure ( $${{\boldsymbol{p}}}_{{{\bf{O}}}_{{\bf{2}}}}$$p O 2 ), doping). However, disentangling the relative stability of different types of defects (viz. substitution, interstitial, etc.) as a function of charge state and realistic T, $${{\boldsymbol{p}}}_{{{\bf{O}}}_{{\bf{2}}}}$$p O 2 is quite challenging. We report here using state-of-the-art first-principles based methodologies, the stability and meta-stability of different non-metal dopants X (X = N, C, S, Se) at various charge states and realistic conditions. The ground state electronic structure is very accurately calculated via density functional theory with hybrid functionals, whereas the finite T and $${{\boldsymbol{p}}}_{{{\bf{O}}}_{{\bf{2}}}}$$p O 2 effects are captured by ab initio atomistic thermodynamics under harmonic approximations. On comparing the defect formation energies at a given T and $${{\boldsymbol{p}}}_{{{\bf{O}}}_{{\bf{2}}}}$$p O 2 (relevant to the experiment), we have found that Se interstitial defect (with two hole trapped) is energetically most favored in the p-type region, whereas N substitution (with one electron trapped) is the most abundant defect in the n-type region to provide visible region photo-absorption in TiO₂. Our finding validates that the most stable defects in X doped TiO₂ are not the neutral defects but the charged defects. The extra stability of $${({\bf{S}}{\bf{e}}{\bf{O}})}_{{\bf{O}}}^{+{\bf{2}}}$$( S e O ) O + 2 is carefully analyzed by comparing the individual effect of bond-making/breaking and the charge carrier trapping energies.

The lead-free double perovskite material (viz. Cs₂AgBiCl₆) has emerged as an efficient and environmentally friendly alternative to lead halide perovskites. To make Cs₂AgBiCl₆ optically active in the visible region of solar spectrum, band gap engineering approach has been undertaken. Using Cs₂AgBiCl₆ as a host, band gap and optical properties of Cs₂AgBiCl₆ have been modulated by alloying with M(I), M(II), and M(III) cations at Ag-/Bi-sites. Here, we have employed density functional theory (DFT) with suitable exchange-correlation functionals in light of spin–orbit coupling (SOC) to determine the stability, band gap and optical properties of different compositions, that are obtained on Ag–Cl and Bi–Cl sublattices mixing. On analyzing 64 combinations within Cs₂AgBiCl₆, we have identified 19 promising configurations having band gap sensitive to solar cell applications. The most suitable configurations with Ge(II) and Sn(II) substitutions have spectroscopic limited maximum efficiency (SLME) of 32.08% and 30.91%, respectively, which are apt for solar cell absorber.