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.