GeTe, as a p-type semiconductor, has been intensively studied in recent years as a promising lead-free midtemperature-range thermoelectric (TE) material. Herein, we report an improved energy conversion efficiency (η) using a two-step TE properties optimization in Mn−Sb co-doped GeTe by engineering electronic structure and lattice dynamics. Mn−Sb co-doping enhances the TE properties of GeTe, as evidenced from both experiments and first-principles-based theoretical calculations. The density functional theory (DFT) calculations indicate that Mn−Sb co-doping improves the band convergence and optimizes the Fermi level position. This in turn helps in enhancing the Seebeck coefficient (α). As a result of the optimized Seebeck coefficient and electrical conductivity (σ), an enhanced power factor (α 2 σ) is obtained for the Mn−Sb co-doped system. Moreover, a significant reduction in the phonon (lattice) thermal conductivity (κ ph ∼ 0.753 W/mK) at 748 K is observed for Ge 0.87 Mn 0.05 Sb 0.08 Te, attributed to the point-defect scattering and reduced phonon group velocity. The synergistic improvement in α and reduction in κ ph result in a maximum figure-of-merit (zT) of 1.67 at 773 K, with an average zT (zT av ) of ∼ 0.9 for Ge 0.87 Mn 0.05 Sb 0.08 Te over a temperature range of 300−773 K, leading to an η of ∼12.7%.

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.

Vacancy-ordered double perovskites (A 2 BX 6 ), being one of the environmentally friendly and stable alternatives to lead halide perovskites, have garnered considerable research attention in the scientific community. However, their thermal transport has not been explored much, despite their potential applications. Here, we explore Cs 2 BI 6 (B = Pt, Pd, Te, Sn) as potential thermoelectric materials using state-of-the-art first-principles-based methodologies, viz., density functional theory combined with many-body perturbation theory (G 0 W 0 ) and spin−orbit coupling. The absence of polyhedral connectivity in vacancy-ordered perovskites gives rise to additional degrees of freedom, leading to lattice anharmonicity. The presence of anharmonic lattice dynamics leads to strong electron−phonon coupling, which is well-captured by the Froḧlich mesoscopic model. The lattice anharmonicity is further studied using ab initio molecular dynamics and the electron localization function. The maximum anharmonicity is observed in Cs 2 PtI 6 , followed by Cs 2 PdI 6 , Cs 2 TeI 6 , and Cs 2 SnI 6 . Also, the computed average thermoelectric figure of merit (zT) for Cs 2 PtI 6 , Cs 2 PdI 6 , Cs 2 TeI 6 , and Cs 2 SnI 6 is 0.88, 0.85, 0.95, and 0.78, respectively, which reveals their promising renewable energy applications.

Exciton binding energy is an important factor in photovoltaics as the formation of excitons influences the charge separation in solar cells. However, a detailed theoretical study of excitonic properties is rather demanding due to huge computational cost. We have systematically applied several state-of-the-art advanced first-principles based methodologies, viz., hybrid density functional theory combined with Spin–Orbit Coupling (SOC), Many Body Perturabtion Theory (MBPT), model-BSE, Wannier–Mott, and Density Functional Perturbation Theory (DFPT) approaches, to understand the excitonic properties by taking a prototypical model system of lead bromide perovskites, viz., APbBr3 [A = CH3NH3+ (MA), HC(NH2)2+ (FA), Cs+]. We show that via conventional procedure using GW/BSE approach along with SOC effect, it is very challenging to converge the BSE calculation to obtain the correct position of the excitonic peak to compute the exciton binding energy (EB) accurately. Therefore, we have employed Wannier–Mott and DFPT approaches to compute EB, where we find that the contribution of ionic dielectric screening is essential. In addition, we have calculated the exciton lifetime, which is in agreement with the trend observed (FAPbBr3 > MAPbBr3 > CsPbBr3) for electron–phonon coupling. The role of cation “A” for achieving the long-lived exciton lifetime is also explained and well understood.

Spin–orbit coupling (SOC) in conjunction with broken inversion symmetry acts as a key ingredient for several intriguing quantum phenomena, viz., Rashba–Dresselhaus (RD) effect. The coexistence of spontaneous polarization and the RD effect in ferroelectric (FE) materials enables the electrical control of spin degrees of freedom. Here, we explore the FE lead halide perovskite CsPbF3 as a potential candidate in the field of spintronics by employing state-of-the-art first-principles-based methodologies, viz., density functional theory (DFT) with semilocal and hybrid functional (HSE06) combined with SOC and many-body perturbation theory (G0W0). For a deeper understanding of the observed spin splitting, the spin textures are analyzed using the k.p model Hamiltonian. We find there is no out-of-plane spin component indicating that the Rashba splitting dominates over Dresselhaus splitting. We also observe that the strength of Rashba spin splitting can be substantially tuned on application of uniaxial strain (±5%). More interestingly, we notice reversible spin textures by switching the FE polarization in CsPbF3 perovskite, making it potent for perovskite-based spintronic applications.