Ionization potentials (IPs) and electron affinities (EAs) are important quantities input into most models for calculating the open-circuit voltage (V_oc) of organic solar cells. We assess the semi-empirical density-functional tight-binding (DFTB) method with the third-order self-consistent charge (SCC) correction and the 3ob parameter set (the third-order DFTB (DFTB3) organic and biochemistry parameter set) against experiments (for smaller molecules) and against first-principles GW (Green’s function, G, times the screened potential, W) calculations (for larger molecules of interest in organic electronics) for the calculation of IPs and EAs. Since GW calculations are relatively new for molecules of this size, we have also taken care to validate these calculations against experiments. As expected, DFTB is found to behave very much like density-functional theory (DFT), but with some loss of accuracy in predicting IPs and EAs. For small molecules, the best results were found with ΔSCF (Δ self-consistent field) SCC-DFTB calculations for first IPs (good to ± 0.649 eV). When considering several IPs of the same molecule, it is convenient to use the negative of the orbital energies (which we refer to as Koopmans’ theorem (KT) IPs) as an indication of trends. Linear regression analysis shows that KT SCC-DFTB IPs are nearly as accurate as ΔSCF SCC-DFTB eigenvalues (± 0.852 eV for first IPs, but ± 0.706 eV for all of the IPs considered here) for small molecules. For larger molecules, SCC-DFTB was also the ideal choice with IP/EA errors of ± 0.489/0.740 eV from ΔSCF calculations and of ± 0.326/0.458 eV from (KT) orbital energies. Interestingly, the linear least squares fit for the KT IPs of the larger molecules also proves to have good predictive value for the lower energy KT IPs of smaller molecules, with significant deviations appearing only for IPs of 15–20 eV or larger. We believe that this quantitative analysis of errors in SCC-DFTB IPs and EAs may be of interest to other researchers interested in DFTB investigation of large and complex problems, such as those encountered in organic electronics.

This paper explores a novel group of D-π-A configurations that has been specifically created for organic solar cell applications. In these material compounds, the phenothiazine, the furan, and two derivatives of the thienyl-fused IC group act as the donor, the π-conjugated spacer, and the end-group acceptors, respectively. We assess the impact of substituents by introducing bromine atoms at two potential substitution sites on each end-group acceptor (EG1 and EG2). With the donor and π-bridge held constant, we have employed density functional theory and time-dependent DFT simulations to explore the photophysical and optoelectronic properties of tailored compounds (M1–M6). We have demonstrated how structural modifications influence the optoelectronic properties of materials for organic solar cells. Moreover, all proposed compounds exhibit a greater V_oc exceeding 1.5 V, a suitable HOMO-LUMO energy gap (2.14–2.30 eV), and higher dipole moments (9.23–10.90 D). Various decisive key factors that are crucial for exploring the properties of tailored compounds—frontier molecular orbitals, transition density matrix, electrostatic potential, open-circuit voltage, maximum absorption, reduced density gradient, and charge transfer length (D_index)—were also explored. Our analysis delivers profound insights into the design principles of optimizing the performance of organic solar cell applications based on halogenated material compounds.

A new copolymer has been studied, which is formed by Poly(2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) and poly(3-hexylthiophene) (P3HT). The choice of these π-conjugated polymers was based on their semiconductor characters and their great applicability in electronic organic devices. The structure and vibrational and optoelectronic properties were simulated by calculations based on DFT, TD-DFT, and ZINDO. This material shows original and unique properties compared to the basic homopolymers. Thus, the obtained results reveal that this copolymer can be mixed with the (6,6)-phenyl C61 butyric acid methyl ester (PCBM) to give existence to a new composite that can be used as an active layer for an organic solar cell.