Impact of different aromatic side units on benzodithiophene on the optical, electronic, and photovoltaic properties for organic solar cell applications

This study investigates the influence of different aromatic side groups on the 2D-benzodithiophene (BDT) unit in donor–acceptor conjugated polymers for organic solar cell (OSC) applications. Three new polymers, P1, P2, and P3, featuring phenyl, thienyl, and thienothienyl side chains on the 2D-BDT backbone, respectively, were synthesized using the Stille cross-coupling reaction. The benzotriazole (BTz) unit served as the electron acceptor with a selenophene π-bridge to enhance electronic interactions. The optical band gaps were determined to be 1.79 eV, 1.74 eV, and 1.73 eV for P1, P2, and P3, respectively. OSCs fabricated using these polymers and PC₇₁BM as the acceptor showed the best performance for the thienyl-substituted polymer (P2), achieving a PCE of 4.34 % with a J_SC of 10.08 mA/cm², an V_OC of 0.67 V, and a FF of 64 %. Compared to P1 and P3, the P2-based blend exhibited a more defined interpenetrating network with PC₇₁BM, enhancing charge transport and promoting exciton dissociation due to its thinner active layer and optimized morphology. These findings highlight the importance of side-chain engineering in improving the optoelectronic properties, morphology, and photovoltaic performance of OSCs. This study highlights the critical role of side-chain engineering in tuning the optoelectronic properties, morphology, and performance of OSCs. The findings emphasize that thienyl side chains in P2 facilitate better π–π stacking and molecular organization, resulting in superior device performance compared to phenyl and thienothienyl-substituted counterparts.