Impactof the Siloxane-Terminated Side Chain on PhotovoltaicPerformances of the Dithienylbenzodithiophene–Difluorobenzotriazole-BasedWide Band Gap Polymer Donor in Non-Fullerene Polymer Solar Cells

To thoroughly disclose the role of the siloxane-terminated side chain with different substituent positions, three difluorobenzotriazole–dithienylbenzodithiophene (FTAZ–BDTT)-based polymers PBZ-1Si, PBZ-2Si, and PBZ-3Si with the siloxane-terminated side chain on the FTAZ unit (PBZ-1Si), on the BDTT unit (PBZ-2Si), and both on BDTT and FTAZ units (PBZ-3Si), respectively, were synthesized. The different side chain substitutions have slight influences on absorption behavior, thermal stability, and frontier molecular orbitals but have shown a great effect on the aggregation of the polymers. Grazing-incidence wide-angle X-ray scattering measurements reveal that, relative to PBZ-1Si with branched alkyl on the BDTT unit, polymers PBZ-2Si and PBZ-3Si, bearing the siloxane-terminated side chains on the BDTT unit, exhibit smaller π–π stacking distances and larger crystal coherence lengths, suggesting that adopting the siloxane-terminated side chain on the BDTT unit can promote the interchain π–π interaction and the ...