In a significant stride towards optimizing organic photovoltaics (OPVs), researchers have unveiled intricate details on how structural disorder and environmental factors influence the electronic properties of conjugated donor–acceptor (D–A) polymers. The study, led by Leandro R Franco from Chalmers University of Technology and Karlstad University, employs a sophisticated multiscale modeling approach to shed light on these complex interactions, offering valuable insights for the energy sector.
The research, published in the Journal of Physics Energy (JPhys Energy), focuses on the PF5-Y5 polymer, a promising material for solution-processed thin films in OPVs. By combining molecular dynamics (MD) simulations with sequential quantum mechanics/molecular mechanics (s-QM/MM) calculations, Franco and his team have uncovered how structural disorder at the D–A interfaces affects the electronic structure of these polymers.
“Our findings reveal that structural disorder reduces frontier orbital overlap and narrows the fundamental gap by localizing the orbitals,” explains Franco. This localization primarily stems from significant stabilization of the lowest unoccupied molecular orbital (LUMO) on the acceptor unit, enhancing the charge-transfer (CT) character of low-lying singlet and triplet states.
The study highlights the critical role of the chosen quantum mechanics method and the treatment of the environment in QM/MM simulations. Neglecting the anisotropy of the surroundings can significantly impact the description of excited states in D–A materials, a factor that could influence the commercial viability of OPVs.
The research also demonstrates how explicit electrostatic embedding amplifies the CT character and disorder in singlets while preserving triplet localization. This effect contributes to spectral broadening and helps explain a shoulder feature in the visible region, linking it to structural disorder, ambient anisotropy, and CT excitations.
The implications of this work are substantial for the energy sector. By advancing the theoretical understanding of OPVs, the study paves the way for more efficient and cost-effective solar energy solutions. As Franco notes, “This work advances our theoretical understanding of organic photovoltaics by highlighting these interrelated effects, which could guide the design of more efficient materials for solar energy conversion.”
The detailed insights provided by this research could shape future developments in the field, driving innovations in material design and fabrication processes. As the world continues to seek sustainable energy solutions, understanding and mitigating the effects of structural disorder and environmental factors in OPVs will be crucial. This study marks a significant step forward in that direction, offering a clearer path towards harnessing the full potential of organic photovoltaics.