A high solar cell efficiency of 32%, water-splitting for hydrogen generation, optoelectronics, and super-exchange...

Recently, double perovskite oxides (DPO) have gained much interest due to their wide range of technological applications in various demanding fields of energy conversion. Here, we present a comprehensive theoretical study of several physical properties of a lead-free Ba₂MnTiO₆ DPO. The structural stability is validated by computing the formation enthalpy, elastic parameters, and phonon dispersion curves. Additionally, the ab initio molecular dynamics simulations carried out indicate stable energy oscillations without any drifting and structural degradation, further confirming the thermal stability of the structure. Alongside this, a quasi-harmonic Debye approximation shows that the material is thermodynamically stable. Interestingly, a direct energy gap of 1.236 eV is predicted, rendering the compound appropriate for visible light-driven applications. The magnetic ground state of the motif is antiferromagnetic, characterized by strong superexchange coupling in the partially occupied Mn t_2g-t_2g orbitals having a spin-moment of 2.554µ _B, which is attributed to the 3d³ state with . The onset of the optical absorption at around 1.23 eV coincides well with the calculated E _g value, while there is a sharp optical absorption peak within the visible/visible-ultraviolet range up to about 23 × 10⁴/63 × 10⁴ cm^-1 at 2.2/3.2 eV. Strikingly, the extraordinary Spectroscopic Limited Maximum Efficiency (SLME) of 32.28% is based on the optimized conditions of important device parameters, which are characterized by significant open-circuit voltage (V _oc = 0.945 V), accompanied by a large fill factor (FF = 0.877), which are backed up by the small saturation current density (J ₀ = 5.17 × 10^-18 A cm^-2) and enhanced short circuit current density (J _sc = 38.95 mA cm^-2), reflecting its strong photovoltaic performance. Moreover, band edge alignment illustrates that the system displays hydrogen production for a higher pH state. Ultimately, the thermoelectric analysis shows that there is a significant power factor of 6.54 W mK^-2 s^-1 and a figure of merit value of 0.63 at 1200 K, which enhances its potential for energy conversion applications. In conclusion, these results demonstrate that Ba₂MnTiO₆ is a versatile and efficient material for solar energy conversion, hydrogen generation by photocatalysis, and energy harvesting technologies.