Rational molecular engineering of pyrene-based D-Aπ-A-D donor molecules for high-performance photovoltaics

Abstract

In this work, six new donor molecules featuring a D-A-π-A-D architecture have been rationally designed to improve photovoltaic performance through molecular-level engineering. Pyrene is selected as the central donor unit owing to its excellent photophysical characteristics, while thiophene is incorporated as the π-bridge to promote effective charge delocalization. The acceptor segments have been systematically modified to investigate the role of electron-deficient cores in tuning the optoelectronic properties of the proposed molecules. Structural analyses reveal a moderate degree of molecular non-planarity, which is advantageous for suppressing excessive aggregation and enhancing morphological stability. Comprehensive electronic and optical investigations, including molecular electrostatic potential surface (MEPS) and transition density matrix (TDM) analyses, indicate strong intramolecular charge transfer accompanied by intense absorption in the visible region, primarily arising from π-π * and ICT transitions, thus ensuring efficient light harvesting. Furthermore, reduced density gradient (RDG) analysis confirms the dominance of stabilizing non-covalent interactions that contribute to the structural integrity of the systems. Collectively, the designed D-A-π-A-D molecules (S1-S6) demonstrate a favorable combination of stability, charge-transport capability, and broad optical absorption, highlighting their potential for high-performance organic solar cells (OSCs) and related optoelectronic applications.