With the aim of upgrading the power conversion efficiency of organic solar cells (OSCs), four novel non-fullerene, A₁–A₂–D–A₂–A₁-type small molecules were designed that are derivatives of a recently synthesized molecule SBDT-BDD reported for its efficient properties in all-small-molecule OSCs (ASM-OSCs). Optoelectronic properties of the designed molecules were theoretically computed with a selected CAM-B3LYP functional accompanied by the 6-31G(d,p) basis set of density functional theory (DFT), and excited-state calculations were performed through the time-dependent self-consistent field. The parameters of all analyzed molecules describing the charge distribution (frontier molecular orbitals, density of states, molecular electrostatic potential), absorption properties (UV–vis absorption spectra), exciton dynamics (transition density matrix), electron–hole mobilities (reorganization energies), and exciton binding energies were computed and compared. All the designed molecules were found to be superior regarding the aforesaid properties to the reference molecule. Among all molecules, SBDT1 has the smallest band gap (3.88 eV) and the highest absorption maxima with broad absorption in the visible region. SBDT3 has the lowest binding energy (1.51 eV in chloroform solvent) ensuring easier and faster dissociation of excitons to produce free charge-carriers and has the highest open-circuit voltage (2.46 eV) with PC₆₁BM as the acceptor. SBDT1 possesses the highest hole mobility because it has the lowest value of λ₊ (0.0148 eV), and SBDT4 exhibits the highest electron mobility because it has the lowest value of λ_– (0.0146 eV). All the designed molecules are good candidates for ASM-OSCs owing to their superior and optimized properties.

Non-fused ring-based OSCs are an excellent choice, which is attributed to their low cost and flexibility in applications. However, developing efficient and stable non-fused ring-based OSCs is still a big challenge. In this work, with the intent to increase V_oc for enhanced performance, seven new molecules derived from a pre-existing A–D–A type A3T-5 molecule are proposed. Different important optical, electronic and efficiency-related attributes of molecules are studied using the DFT approach. It is discovered that newly devised molecules possess the optimum features required to construct proficient OSCs. They possess a small band gap ranging from 2.22–2.29 eV and planar geometries. Six of seven newly proposed molecules have less excitation energy, a higher absorption coefficient and higher dipole moment than A3T-5 in both gaseous and solvent phases. The A3T-7 molecule exhibited the maximum improvement in optoelectronic properties showing the highest λ_max at 697 nm and the lowest E_x of 1.77 eV. The proposed molecules have lower ionization potential values, reorganization energies of electrons and interaction coefficients than the A3T-5 molecule. The V_oc of six newly developed molecules is higher (V_oc ranging from 1.46–1.72 eV) than that of A3T-5 (V_oc = 1.55 eV). Similarly, almost all the proposed molecules except W6 exhibited improvement in fill factor compared to the A3T-5 reference. This remarkable improvement in efficiency-associated parameters (V_oc and FF) proves that these molecules can be successfully used as an advanced version of terthiophene-based OSCs in the future.

Nonlinear optical (NLO) materials have several uses in many fields such as solid physics, biology, medicine, nuclear physics, and material research. Therefore, a series of nonfullerene-based derivatives (CC10D1–CC10D8) with a D−π–A configuration was planned for the NLO investigation using CC10R as the reference molecule with structural alternations at acceptor moieties. Natural bonding orbital (NBO), UV–vis spectra, frontier molecular orbitals (FMOs), global reactivity parameters (GRPs), transition density matrix (TDM), and density of states (DOS) were analyzed using the M06/6-311G­(d,p) functional in chloroform solvent to understand the NLO responses of CC10R and CC10D1–CC10D8. The highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) band gaps of CC10D1–CC10D6 were illustrated to be lower than that of CC10R, with the larger bathochromic shift (726.408–782.674 nm) resulting in a significant NLO response. Along with the band gap, the FMO method also identified an efficient interfacial charge transfer from D to A moieties via a π-bridge, which was further supported by the DOS and TDM map. Moreover, NBO calculations demonstrated that extended hyperconjugation and strong internal molecular interactions were important in their stabilization. The dipole moment (μ), linear polarizability ⟨α⟩, hyperpolarizability (βtotal), and second-order hyperpolarizability (γtotal.) were studied for CC10R and CC10D1–CC10D8. Among all of the derivatives, CC10D2 was proven to be the most appropriate candidate because of its suitable NLO behavior such as being well-supported by a reduced band gap (2.093 eV) and having a suitable maximum absorption wavelength (782.674 nm). Therefore, CC10D2 was reported to have a greater value of first hyperpolarizability (208 659.330 a.u.) compared with other derivatives and CC10R. For the second hyperpolarizability, a greater value was obtained for CC10R (5.855 × 107 a.u.), and its derivatives showed results comparable to that of the parent chromophore for γtotal. This theoretical framework reveals that structural customization with different acceptor units plays a significant role in obtaining attractive NLO materials for optoelectronic applications.

DFT calculations are carried out to investigate nonlinear optical (NLO) properties of superhalogen (BCl ₄ ) and superalkali (NLi ₄ ) doped graphitic carbon nitride (GCN).