Impact of solvent processing on the PM6/Y6 morphology and charge transfer in organic solar cells

Abstract

Solvent treatment can dramatically impact the electronic donor/acceptor (D/A) bulk heterojunction morphology of organic solar cells (OSCs). By a combination of molecular dynamic simulations with density functional theory, we investigated the local morphology and conjugated conducting network dependent on the solvent-treatment approach of PM6/Y6 (D/A) thin films, including the D/A interface, D/D domain, and A/A domain. We found that the charge-transfer rate was as high as 10¹² s⁻¹ for exciton dissociation at the D/A interface, which was in good agreement with experimental measurements (10¹² s⁻¹). The electron-transport rate (10¹² s⁻¹) in the A/A stacking configuration was one order of magnitude higher than the hole-transport rate (10¹¹ s⁻¹) in the D/D stacking configuration. This implied that hole transport in the D/D domain should be further improved in order to balance the negative and positive charge-carrier transport. Moreover, the chloroform-treated bulk heterojunction was found to be the most suitable for exciton dissociation at the D/A interface and for conjugated conducting networks in both the D/D and A/A domains, since the chloroform-treatment process promotes the distribution of strong electronic coupling, which favors exciton dissociation and charge transport. This work provides an understanding of how solvent treatment impacts the bulk heterojunction morphology and charge-transfer/transport properties of high-performance OSCs.