PDT-S-T: a new polymer with optimized molecular conformation for controlled aggregation and π-π stacking and its application in efficient photovoltaic devices.

The correlation among molecular conformation, the crystallinity of the morphology, propensity for π-π stacking, J- versus H-aggregation, and photovoltaic performance have been studied based on two newly designed polymers, PBDTTT-S-T and PDT-S-T. The results show that more linear backbone structure is helpful to improve photovoltaic properties of the polymer, and therefore, molecular conformation should be considered for molecular design of photovoltaic polymers.