First-principles studies on structural, electronic and optical properties of Fe-doped NiS2 counter electrode for Dye- sensitised solar cells using DFT+U / Nur Aisyah Ab Malik Marwan …[et al.]

The structural, electronic, and optical properties of nickel disulfide (NiS2) and iron (Fe)-doped NiS2 were computed by using first-principles calculations through the density functional theory (DFT) method. The Fe was used as a dopant element to understand the behaviour and the key mechanism of Fe-doped NiS2 as a counter electrode in dye-sensitised solar cells (DSSC). The results indicated that the structural properties of the NiS2 as the cubic crystal structure with the space group Pa3 (205) (pyrite structure type) agree with experimental data. The density of states (DOS) of NiS2 and Fe-doped NiS2 shows a gapless bandgap due to Mott-Hubbard insulator behavior. As for optical properties, the optical absorption of NiS2 is shifted towards the infrared (IR) region when doping with Fe while the conductivity of Fe-doped NiS2 is slightly higher in conductivity. These optical properties show that Fe-doped NiS2 is suitable for the photocatalytic activity and may provide an excellent electron charge transfer for a counter electrode in DSSC

First-Principles Study on Structural and Electronic Properties of Cubic (Pm3m) And Tetragonal (P4mm) ATiO₃ (A=Pb, Sn) / Nurakma Natasya Md Jahangir Alam …[et al.]

This work focuses on exploring lead-free ferroelectric materials that have a comparable unique ns2 solitary pair electrons with Pb (II), for example, Sn (II) using the first-principles study. All counts were performed dependent on ultrasoft pseudopotential of Density Functional Theory (DFT) that has been executed in the Cambridge Serial Total Energy Package (CASTEP). The convergence test for cut-off energy and k-point was performed to measure the accuracy of the calculations. It is shown that the structures have threshold energy of 350 eV and k-point of 4x4x4 with Monkhorst Pack. The structural properties for both cubic and tetragonal structures ATiO3 (Pb, Sn) have shown the comparable value of the lattice parameter that was in agreement with previous work. Generalised gradient approximation (GGA) PBE displays the most exact qualities for cross-section parameters concerning exploratory qualities for both cubic PbTiO₃ while GGA-PBEsol functional is the best functional approximation for tetragonal PTO. The electronic band structure and density of states show the presence of hybridizations between anion O 2p and cation Pb 6s/Sn 5s unique solitary pair in tetragonal PTO and SnTO stage. The calculations have shown that both cubic and tetragonal structure of ATiO3 (A=Pb, Sn) has an indirect bandgap of 1.169 eV, 1.164 eV, 1.703 eV, and 1.016 eV respectively. It is shown that tetragonal structures have a higher value of bandgap compared to cubic structures