Because of their elasticity, light weight, little cost, and wide-area applications, besides a notable increase in power conversion efficiency (PCE), organic solar cells (OSCs) have recently caught the concern of numerous researchers. In the current project, we created a variety of organic small compounds as donor materials by using Gaussian 09. Our design approach entails swapping the core part, which is benzothiadiazole (BT), based on a derivative of oxadiazole, as the terminals on both sides of the prototype compound (RM) with a variety of fragments to improve the electronic and optic characterization and performance for PCE in OSCs. Careful theoretical consideration under density-functional theory (DFT) and time-dependent density functional theory (TD-DFT) at the B3LYP/6-31G(d,p) basis set was made to find the maximum absorption wavelength λmax, the efficiency of light harvesting (LHE), excitation energy (EX), highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LOMO) levels, energy band gap (Eg), dipole moment (ρ), the density of state (DOS), ionization potential (IP), electron affinity (EA), fill factor (FF), and open circuit voltage (Voc) of molecules RM and TS studied in a methodical manner. Calculated values revealed that proposed compounds T1—T4 can be encouraging materials for manufacturing OSCs as a donor tiny compound with acceptor PC61BM to predict a rise in PCE owing to their possession of proper values for some optical and electronic features, like the lowest HOMO level, narrower band gaps, and a greater absorption wavelength compared with the reference model RM.