A Simple Phenyl Group Introduced at the Tail of Alkyl Side Chains of Small Molecular Acceptors: New Strategy to Balance the Crystallinity of Acceptors and Miscibility of Bulk Heterojunction Enabling Highly Efficient Organic Solar Cells

Abstract

Research on fused‐ring small‐molecular‐acceptors (SMAs) has deeply advanced the development of organic solar cells (OSCs). Compared to fruitful studies of ladder‐type cores and end‐caps of SMAs, the exploration of side chains is monotonous. The widely utilized alkyl and aryl side chains usually produce a conflicting association between SMAs' crystallinity and miscibility. Herein, a fresh idea about the modification of side chains is reported to explore the subtle balance between the crystallinity and miscibility. Specifically, a phenyl is introduced to the tail of the alkyl side chain whereby a new acceptor IDIC‐C4Ph is reported. Moderately weakened crystallinity is observed, while maintaining preferred absorption profiles and face‐on orientations. Concurrently, remarkably improved heterojunction morphologies and stacking orientations are detected. PBDB‐T:IDIC‐C4Ph devices exhibit greater efficiency of 11.50% than devices from alky and aryl modified acceptors. Notably, the as‐cast OSCs of PBDB‐TF:IDIC‐C4Ph reveal outstanding FF over 76% with the best efficiency up to 13.23%. The annealed devices reveal further increased efficiency exceeding 14% with the state of the art FF of 78.32%. Overall, an effective but easily navigable approach is demonstrated to modulate the crystallinity of SMAs toward synergistically improved morphologies and molecular orientations of bulk heterojunction enabling highly efficient OSCs.

Unconjugated Side‐Chain Engineering Enables Small Molecular Acceptors for Highly Efficient Non‐Fullerene Organic Solar Cells: Insights into the Fine‐Tuning of Acceptor Properties and Micromorphology

“…The field of organic solar cells (OSCs) grows rapidly in the past few years due to the surge of non‐fullerene acceptors, which have been deemed to replace fullerene‐based acceptors due to their wide absorption ranges, tunable energy levels, and controllable crystallization/aggregation properties . Most of the progresses come from the design and synthesis of novel chemical structures that provide the molecules with properties superior to fullerene‐based acceptors.…”

“…Currently, the prevailing type of small molecule acceptor (SMA) is based on the A‐D‐A structure, that is, an electron‐rich core flanked with two electron‐deficient groups . To further boost the power conversion efficiency (PCE) of a non‐fullerene OSC device, which is proportional to the product of the open‐circuit voltage ( V OC ), the short‐circuit current ( J SC ), and the fill factor (FF), deep insights into the structure–property–performance relationship are needed, particularly for the emerging families of non‐fullerene moieties that have shown great potential in achieving high‐performance OSCs . Some significant achievements have been made to this end.…”

Evaporation‐Free Nonfullerene Flexible Organic Solar Cell Modules Manufactured by An All‐Solution Process

“…ITIC-Th showed longer lamellar packing distance (d 100 ) and shorter π-π stacking distance (d 010 ) than ITIC (in Table S2 in the Supporting Information). [71][72][73][74] As a result, the calculated χ values for PBDB-T and SMD2 showed 0.574 to 0.821 for blended with ITIC, and 0.260 to 0.434 for blended with ITIC-Th. [23,46,56,70] To compare the compatibility the donor polymer and NFA components, the surface tension (γ) was determined and calculated from the contact angles measured using two solvents, water (distilled water) and oil (diiodomethane, DIM) in each pristine film ( Figure S11 and Table S4, Supporting Information).…”

“…[71][72][73][74] As a result, the calculated χ values for PBDB-T and SMD2 showed 0.574 to 0.821 for blended with ITIC, and 0.260 to 0.434 for blended with ITIC-Th. [71,73,77] According to comprehensively the GIWAXS, Flory-Huggins interaction, and DSC results, SMD2 showed a relative high crystallinity compared to PBDB-T, also, ITIC showed a much higher crystallinity than ITIC-Th. A low χ value leads to a too high miscible for the blend films.…”

Recent Progress in Molecular Design of Fused Ring Electron Acceptors for Organic Solar Cells

“…In early 2019, Li et al combined the effect of linear and aromatic alkyl chains in their latest work and introduced phenyl group at the tail of alkyl side‐chain in IDIC to get IDIC‐C4Ph ( A103 , Figure ) . The FREA exhibited similar photophysical properties compared with IDIC , however larger phenyl groups prevent strong fused core stacking led to better morphology and enhanced “face‐on” packing.…”