A series of bowl-shaped PDI dimers designed for organic photovoltaic cells through engineering N-annulated bridge towards potential alternatives of PDI bridged dimer acceptors

- Introducing N-annulation at bay position of PDI dimers may construct bowl-shaped PDI dimers.
- Compared with planar dimers, bowl-shaped PDI dimers possess extended conjugated backbone, flexible electronic structures, complimentary optical absorption with donor and excellent charge transport performance.
- As for PBDTTT-C-T/PDI interface, installed SF and NDT linkers based on N-annulated bridges in PDI dimers exhibit more favorable performance.

Perylene diimides (PDIs) dimer-based non-fullerene acceptors have made significant progress in the field of organic photovoltaics (OPVs) recently. To further render PDI derivatives soluble and tailor self-assembly, the incorporation of N-annulations in PDI dimers becomes an effective strategy in latest researches. Here, we focus on engineering PDI dimers with N-annulated bridges to construct bowl-shaped PDI dimers with the aim of improving efficiency, stereoscopic dimensions and the electron transfer abilities by introducing different functional linkers in N-annulated bridges. Besides some properties relevant to photovoltaic performance of these investigated acceptors were characterized based on density functional theory (DFT) and (time dependent density functional theory) TD-DFT calculations, Marcus semi-classical model was also employed to further estimate the exciton dissociation ability at D/A interface. Our results demonstrate that, compared to planar N-annulated PDI dimers, bowl-shaped PDI dimers possess higher LUMO energy levels, larger open circuit voltage (VOC), complementary optical absorption with the donor PBDTTT-C-T, and more effective charge separation at the interface. Moreover, we highlight that introducing SF and NDT linkers in N-annulated bridges would be more favorable to optical performance. We expect that these modified N-annulated PDI dimers could become potential acceptor materials in OPVs.

Based on the configuration of planar N-annulated PDI dimers, It would be a novel approach to improve the exciton dissociation efficiency that engineering PDI dimers with N-annulated bridges constructing linked bowl shapes. For facilitating more effective efficiency, the aromatic linkers based on N-annulated bridges (π-bridge and D-bridge) were introduced between two PDI based units. Here, D/4 and D/6 exhibit the most excellent optical performance, due to the introduction of expanded conjugated stereoscopic π-bridge SF based on the symmetric bowl shape or the prospective “A-D-A” structure with D-bridge NDT.249