Modulating the Charge Transfer and Optoelectronic Properties of Quinacridone‐Based A–D–A Solar Cell Materials by Benzothiadiazole Derivative Group Acceptors: A <scp>DFT</scp> Study

ABSTRACT This study presents the design and analysis of five acceptor–donor–acceptor (A–D–A) type donor molecules ( QABT1 – QABT5 ) by incorporating 2,1,3‐benzothiadiazole (BT) derivatives as electron‐withdrawing acceptor groups into a synthesized reference molecule ( R ) for organic solar cell (OSC) applications. Density functional theory (DFT) and time‐dependent DFT (TD‐DFT) methods were employed to explore the impact of acceptor modifications on the structural, electronic, optical, charge transport, and photovoltaic properties of the designed molecules. The results indicate that introducing strong electron‐withdrawing groups significantly enhances overall device performance. The structural modifications lead to reduced HOMO–LUMO band gaps (2.02–2.36 eV), facilitating efficient charge transfer (CT) and extending the absorption spectra. All designed molecules exhibit broader and red‐shifted absorption in both gaseous and solvent phases, along with lower optical band gaps and reduced exciton binding energies, improving exciton dissociation and charge transport efficiency compared to the reference molecule. Among the designed molecules, QABT4 and QABT5 emerge as the most promising candidates, exhibiting a small optical band gap (1.75 eV), extended excited‐state lifetime (9.65 ns), and low reorganization energies for electrons ( λ e ∼97 meV) and holes ( λ ℎ ∼120 meV). Additionally, the strong push‐pull mechanism results in efficient intramolecular CT, with above 85% CT excitations. These properties contribute to an enhanced short‐circuit current density (J sc ∼13.73 mA/cm 2 ), high open‐circuit voltage (V oc ∼1.46 V) with minimal energy loss (0.57 eV), and a theoretical power conversion efficiency (PCE) up to ∼18%. These findings underscore QABT4 and QABT5 as promising candidates for high‐performance OSCs, paving the way for next‐generation optoelectronic applications.