Interconnected Morphological and Electronic Structure Properties of the PBDB-T-2F (PM6) Electron Donor in Bulk Organic Semiconductors

The advancement of high-performance wide band-gap polymer donors is crucial for keeping pace with the rapid developments in organic solar cells (OSCs). This study presents a large-scale computational investigation of the correlation between the morphology and electronic structure properties of the PBDB-T-2F (PM6) donor polymer across a range of molecular weights. Our analysis demonstrates that the bulk density of states near the bandgap remains largely invariant with respect to the length of the polymer backbone. The electronic structure is primarily governed by the conformation of the individual polymer chains. This indicates that shorter polymer chains, or those with lower molecular weight, facilitate enhanced transport of holes and excitons. In addition, we observed that low-energy excitons tend to localize in less folded and more planar regions. Moreover, thermal fluctuations play an important role in the dynamic evolution of excitons along the polymer chains. Changes in torsion angles influence intrachain excitonic couplings, which subsequently affect the size, shape, and diffusion length of the excitons. These findings underscore the crucial role that a well-optimized mixture of various chain lengths can play in improving both the efficiency and stability of devices using the PBDB-T-2F (PM6) polymer as an electron donor.