From Molecular Design to Device Performance: <scp>DFT</scp> and <scp>TD</scp> ‐ <scp>DFT</scp> Insights into Small‐Molecule Organic Solar Cells

ABSTRACT Organic solar cells (OSCs), notably small‐molecules OSCs (SMOSCs), have gained considerable attention as promising photovoltaic technologies because of their well‐defined molecular structures, high batch reproducibility, and tunable electronic properties. Density functional theory (DFT) and time‐dependent DFT (TD‐DFT) have become powerful computational methods for investigating performance mechanisms and assisting high‐performance materials design. This review provides a comprehensive overview of recent advances in DFT‐guided design approaches for SMOSCs, emphasizing the role of computational parameters derived from DFT calculations in establishing robust structure–property–performance relationships. It further discusses fundamental theoretical and methodological aspects of DFT‐based modeling and analyzes the influence of frontier orbital energies, optical absorption properties, donor‐acceptor interfacial energetics, and charge‐transport descriptors on essential device parameters, like open‐circuit voltage, short‐circuit current density, and power conversion efficiency. Special attention is devoted to recent advances in small‐molecule donors and non‐fullerene acceptors for their role in improving device efficiency. By combining computational and experimental insights, it demonstrates the pivotal role of DFT‐based approaches in accelerating materials discovery and guiding molecular architecture optimization. These perspectives are aimed to support the rational design of next‐generation high‐performance organic photovoltaic systems.