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This study employed the AMPS-1D software to investigate the relationship between the open-circuit voltage (Voc) and the energy difference between the Highest Occupied Molecular Orbital (HOMO) of the donor and the Lowest Unoccupied Molecular Orbital (LUMO) of the acceptor in P3HT:PCBM bulk heterojunction organic solar cells. The findings indicate a correlation between Voc and the HOMO-LUMO offset up to 1.1 eV, after which Voc remains constant. This behavior is further elucidated using a theorem based on the quasi-Fermi level, which predicts a Voc of 0.64 V, in good agreement with our simulation result of 0.68 V. The Power Conversion Efficiency (PCE) of the solar cell was studied with respect to the active layer thickness, demonstrating an increase in PCE up to 0.40 μm followed by a decrease, yielding a maximum PCE of 5.023%, consistent with the literature. The effect of temperature on PCE was also examined, demonstrating an increase in PCE with decreasing temperature in the range of 150–320 K, with a performance of 6.371% at 150 K. Furthermore, the impact of the optical bandgap on PCE was explored, showing that the PCE increased with a decrease in the optical bandgap of the P3HT:PCBM solar cell, reaching 9.94% when the optical bandgap was 1.5 eV. These findings provide valuable insights into the optimization of the performance of organic solar cells by manipulating key parameters, such as the HOMO-LUMO offset, active layer thickness, temperature, and optical bandgap. [ABSTRACT FROM AUTHOR]

This study investigates the structural and electronic properties of the anatase and rutile TiO2 systems by employing the Quantum Espresso (QE) software using first-principles calculations based on Density Functional Theory (DFT). Optimized lattice constants (a = 3.788, 4.627 a.u. and c = 9.491, 2.979 a.u.) and the internal parameter u (0.209, 0.305), were obtained for anatase and rutile TiO2 phases, respectively. Unit cell volumes were also calculated. Furthermore, the Birch-Murnaghan equation of state was used to obtain the equilibrium volume (937.5, 428.3 a.u.³), the bulk modulus (198.5, 222.5 GPa), and the pressure derivative of the bulk modulus (4.18, 4.37) for both phases. The results are in good agreement with the experimental data and the theoretical results published in other studies. Finally, the energy band gap of both samples was calculated (1.8 and 1.6 eV, respectively) and compared with published results obtained from the Density Of Electron States (DOS). [ABSTRACT FROM AUTHOR]