Unraveling the Structure–Property–Performance Relationships of Fused-Ring Nonfullerene Acceptors: Toward a C-Shaped ortho-Benzodipyrrole-Based Acceptor for Highly Efficient Organic Photovoltaics

Abstract

The high-performance Y6-based nonfullerene acceptors (NFAs) feature a C-shaped A-DA'D-A-type molecular architecture with a central electron-deficient thiadiazole (Tz) A' unit. In this work, we designed and synthesized a new A-D-A-type NFA, termed CB16, having a C-shaped ortho-benzodipyrrole-based skeleton of Y6 but with the Tz unit eliminated. When processed with nonhalogenated xylene without using any additives, the binary PM6:CB16 devices display a remarkable power conversion efficiency (PCE) of 18.32% with a high open-circuit voltage (V oc ) of 0.92 V, surpassing the performance of the corresponding Y6-based devices. In contrast, similarly synthesized SB16, featuring an S-shaped parabenzodipyrrole-based skeleton, yields a low PCE of 0.15% due to the strong side-chain aggregation of SB16. The C-shaped A-D N B N D-A skeleton in CB16 and the Y6-series NFAs constitutes the essential structural foundation for achieving exceptional device performance. The central Tz moiety or other A' units can be employed to finely adjust intermolecular interactions. The single-crystal X-ray structure reveals that ortho-benzodipyrrole-embedded A-D N B N D-A plays an important role in the formation of a 3D elliptical network packing for efficient charge transport. Solution structures of the PM6:NFAs detected by small-and wide-angle X-ray scattering (SWAXS) indicate that removing the Tz unit in the C-shaped skeleton could reduce the self-packing of CB16, thereby enhancing the complexing and networking with PM6 in the spin-coating solution and the subsequent device film. Elucidating the structure−property−performance relationships of A-DA'D-A-type NFAs in this work paves the way for the future development of structurally simplified A-D-A-type NFAs.

Cyclization Engineering of Electron-Deficient Maleimide Unit for Nonfused Ring Electron Acceptors Enables Efficient Organic Solar Cells

“…The LUMO and HOMO energy levels of PI-DTS and DPI-DTS are determined to be −3.94/5.43 eV and −3.90/5.63 eV, respectively, and the band gap derived from electrochemical method of PI-DTS is small, consistent with the DFT results. It is noteworthy that the negligible difference in HOMO energy levels between PI-DTS and PM6 is unfavorable for charge separation, consequently leading to lower exciton dissociation efficiency for these materials based device. , …”

New Avenues for Organic Solar Cells Using Intrinsically Charge-Generating Materials

“…Theoretical and experimental studies have found that these configurations are beneficial for exciton and charge transport in Y6 and these pairs also had the largest couplings for exciton-to-CT conversion . The design of structural derivatives that promote these types of interactions is an exciting avenue for exploration, with early studies revealing positive effects on device performance. , …”

“… 13 The design of structural derivatives that promote these types of interactions is an exciting avenue for exploration, with early studies revealing positive effects on device performance. 46 , 47 …”

C-Shape or S-Shape? The Molecular Geometry Control of Fused-Ring Nonfullerene Acceptors for Lower Energy Loss in Organic Solar Cells

“…Organic solar cells (OSCs) have garnered significant attention for their advantageous features, such as flexibility, light weight, and suitability for large-area manufacturing. − Recently, owing to the innovation of fused-ring nonfullerene acceptors (FRNFAs), particularly the state-of-the-art Y-series acceptors, the power conversion efficiency (PCE) of OSCs has experienced a noteworthy breakthrough, resulting in an impressive PCE surpassing 19%. − To date, significant endeavors have been dedicated to investigate the association between the structure–property–performance relationship of NFAs through the molecular modifications on the central fused-ring units, − side chains, ,− and terminal groups. − Among them, the impact of isomeric molecular geometry on device performance has been less reported. − Of note, to achieve further PCE improvement of OSCs, it is crucial not only to focus on molecular optimization of FRNFAs but also to elucidate the underlying structural mechanisms responsible for the outstanding performance, which will serve as a guide for future molecular design.…”