Oligomeric Acceptor Enables High‐Performance and Robust All‐Polymer Solar Cells with 17.4% Efficiency

Abstract

(2 of 10)that of SMAs limits the short-circult current densities (J SC s), and the unfavorable morphology caused by large conjugated lengths ang high molecular weights of P A and P D materials tends to suppress the fill factors (FFs). [38][39][40][41][42] To solve these issues, "polymerized small molecule acceptor" (PSMA) strategy, [43,44] ternary strategy, [45] and device engineering [30,31,33,46] are considered as efficient approaches to be developed continually. Among various device optimization methods, fabricating the ternary blends has been proved as an advantageous and simple strategy to uplift device performance. It is worth noting that the third component plays an important role in enhancing light absorption, facilitating charge transfer, and optimizing nanoscale morphology in the ternary systems. [34,47] In previous work on all-PSCs, the third components could be P D s, P A s, or small molecule acceptors. [26,29,34,48,49] For example, the strategy of choosing a similar P A to the host one in chemical structure as the third component was reported by Min et al., which improved PCE and stability simultaneously. [24] Recently, Hou and co-workers introduced PM6 with a high molecular weight into the all-PSCs system to afford efficient pathways for charge transport and mechanical stress dissipation, so that the ternary device demonstrated the PCE of 18.2% with outstanding mechanical properties. [26] However, because of the difficulty to alter morphology in all-PSCs devices, it is rather challenging to find proper third components, especially a universal one. Recently, Wei et al. reported a "N-π-N" type oligomeric acceptor, which falls in between SMA and P A and inherited the advantages of both them. Compared to its corresponding SMA, it performed higher tolerance for additive contents, as well as superior stability. While compared to its polymeric counterparts, it could obtain definite molecular structure, increased extinction coefficient, and absence of chains entanglements. [42] However, the oligomeric acceptors have not been considered to introduce in all-PSCs systems so far. [40,[50][51][52][53] Based on this point, it is urgent and significative to study the influence of an oligomeric acceptor as the third component on the performance and mechanical robustness in all-PSCs systems.With these in mind, we designed and synthesized a polymer acceptor (named PZC24) through linking CH-series SMA [54][55][56] by the fluoro-substituted thiophene π bridge. By blending PZC24 with the polymer donor PM6, a decent PCE of 16.82% is achieved. Furthermore, an "N-π-N" type oligomeric acceptor (CH-D1), which has the same core blocks (N type) and linking units (π bridge) as PZC24, was designed and added in PM6:PZC24 system as the third component. Based on the same structure, CH-D1 can be referred as "twins" molecule with PZC24. Therefore, this ternary strategy avoids the complicated selection and additional synthesis for the third component. More importantly, the introduction of CH-D1 leads to stronger crystallinity and more...

Biaxially Conjugated Materials for Organic Solar Cells

“…Moreover, the PM6: NFA9 blend exhibits decent thermal stability in devices (Figure C), suggesting excellent morphological stability. They further revealed that the dimer ( NFA14 ) of Qx-based acceptors is much more stable than the relevant polymer (poly-NFA14) in PM6-based OSCs under photoaging (Figure D) . Our group unraveled how the local isomerization of substitutions on cross-conjugated side groups influences the geometry and noncovalent interactions of molecules, thereby having great impact on the device stability .…”

“…Chen et al further developed a series of dimer-like acceptors based on biaxially conjugated CH-series molecules. They used a “terminal coupling” strategy to synthesize a horizontally linked dimer NFA14 , achieving a decent PCE of 16.62% when coupled with PM6 . Besides, they employed a “core fusing” strategy to obtain a vertically coupled dimer NFA15 that has a symmetrical and coplanar conjugated skeleton .…”

“…Copyright 2023, Springer Nature. Figure D is reprinted with permission from ref . Copyright 2023, Wiley-VCH GmbH.…”

Two-Dimensional Conjugation Extended CH-Series Acceptors with a Distinctive A–D–A Character

“…However, the long-term stability of OSCs is expected to get a striking improvement due to greatly suppressed molecular diffusion in blended films . Note that the most conventional way to build dimer acceptors is “terminal coupling” through end units (brominated 2-(3-oxo-2,3-dihydro-1 H -inden-1-ylidene)­malononitrile groups) of small molecular acceptors at present, just like plenty of dimer acceptors based on Y-series molecular backbones − or CH-D1 in Figure . However, this strategy to construct dimer acceptors will bring about several unavoidable shortcomings: (1) Inferior intermolecular packings, especially for the “E/E” mode .…”

Conjugated versus Nonconjugated Polymerized Small-Molecule Acceptors. Photovoltaic Response and Mechanical Properties

“…Mechanical robustness is one of the most attractive properties of all-polymer blend films. Most polymer acceptors consist of large fused rings and fully conjugated backbones to ensure efficient charge transport and strong light absorption. − However, the backbone in fully conjugated polymers is typically very rigid which favors strong, structurally regular aggregation which often leads to brittle polymer acceptors and BHJ blend films . Few all-PSC studies have introduced nonconjugated units into the polymer backbone to understand their effect on the optical, electronic, and mechanical properties, − and fewer studies have systematically addressed the effect of polymer acceptor conjugation length on the mechanical robustness of the corresponding films and blends .…”