Enhancing Power Conversion Efficiency Above 17% Through End-group Engineering of thieno[3,2-b]thiophene and 2,4,6-triisopropylphenyl-based Nonfused-ring Electron Acceptors for Organic Photovoltaics: A DFT Insight

Fused-ring electron acceptors (FREAs) have been pivotal in advancing the performance of organic solar cells (OSCs). However, challenges such as high production costs, synthetic complexity and limited scalability hinder their widespread industrial adoption. Nonfused-ring electron acceptors (NFREAs) present a promising alternative, offering more cost-effective and scalable photovoltaic solutions. Despite this, the power conversion efficiencies (PCEs) of NFREA-based OSCs still have significant potential for improvement. In this study, we explore the design of eight novel acceptor–donor–acceptor (A–D–A) NFREAs, referred to as TTS1–TTS8, achieved through end-group engineering of thieno[3,2-b]thiophene (TT) as the primary electron-donating unit, with 2,4,6-triisopropylphenyl (TIP) incorporated to provide steric hindrance. Density functional theory (DFT) and time-dependent DFT (TD-DFT) simulations provide insights into the impact of end-capping modifications on the photovoltaic properties of TTS1–TTS8. The optimization of these compounds through structural modifications has led to notable improvements in their photovoltaic performance. Among the developed series, the TTS8 compound exhibits a remarkable PCE of 17%, surpassing the theoretical limit of the reference molecule TTS-4F (12%). These molecules show increased binding energies ([Formula: see text]0.299 eV), broadened absorption profiles (λ max = 702–792 nm), reduced energy gaps (1.98–1.90 eV) and enhanced open-circuit voltages (V oc = 1.21–1.53 V). Further characterization through transition dipole moments (TDMs), electron density distributions (EDDs), molecular electrostatic potentials (MEPs), frontier molecular orbitals (FMOs) and reorganization energies ([Formula: see text] = 0.0061–0.0073 [Formula: see text], [Formula: see text] = 0.0064–0.0076 [Formula: see text] corroborates these improvements. Furthermore, the charge transfer analysis of TTS7/PM6 found a significant charge shifting at the HOMO (PM 6 ) to LUMO (TTS7) interface. TTS8, in particular, stands out with its superior PCE, V oc of 1.53 V, 59% fill factor and excellent efficiency, making it a promising candidate for next-generation solar cell applications. These results highlight the potential of the TTS1–TTS8 series in advancing the development of high-performance and sustainable organic solar cells.