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Non‐fullerene acceptors have shown great promise for organic solar cells (OSCs). However, challenges in achieving high efficiency molecular system with conformational unicity and effective molecular stacking remain. In this study, we present a new design of non‐fused tetrathiophene acceptor R4T‐1 via employing the encapsulation of tetrathiophene with macrocyclic ring. The single crystal structure analysis reveals that cyclic alkyl side chains can perfectly encapsulate the central part of molecule and generate a conformational stable and planar molecular backbone. Whereas, the control 4T‐5 without the encapsulation restriction displays cis‐ and twisted conformation. As a result, R4T‐1 based OSCs achieved an outstanding power conversion efficiency (PCE) exceeding 15.10 % with a high short‐circuit current density (Jsc) of 25.48 mA/cm2, which is significantly improved by ≈30 % in relative to that of the control. Our findings demonstrate that the macrocyclic encapsulation strategy could assist fully non‐fused electron acceptors (FNEAs) to achieve a high photovoltaic performance and pave a new way for FNEAs design. [ABSTRACT FROM AUTHOR]

The power conversion efficiency of polythiophene organic solar cells is constantly refreshed. Despite the renewed device efficiency, very few efforts have been devoted to understanding how the type of electron acceptor alters the photovoltaic and mechanical properties of these low‐cost solar cells. Herein, the authors conduct a thorough investigation of photovoltaic and mechanical characteristics of a simple yet less‐explored polythiophene, namely poly(3‐pentylthiophene) (P3PT), in three different types of organic solar cells, where ZY‐4Cl, PC71BM, and N2200 are employed as three representative acceptors, respectively. Compared with the reference poly(3‐hexylthiophene) (P3HT)‐based solar cells, P3PT‐based devices, all perform more efficiently. Particularly, the P3PT:ZY‐4Cl blend exhibits the highest efficiency (ca. 10%) among the six combinations and outperforms the prior top‐performance system P3HT:ZY‐4Cl. Furthermore, the blend films based on N2200 exhibit a high crack‐onset strain of ∼38% on average, which is approximately 15‐ and 17‐times higher than those of ZY‐4Cl and PC71BM, respectively. The microstructural origins for the above difference are well elucidated by detailed grazing incidence X‐ray scattering and microscopy analysis. This work not only underlines the potential of P3PT in prolific solar cell research but also demonstrates the superior tensile properties of polythiophene‐based all‐polymer blends for the preparation of stretchable solar cells. [ABSTRACT FROM AUTHOR]

A series of tetrathiophene‐based fully non‐fused ring acceptors (4T‐1, 4T‐2, 4T‐3, and 4T‐4), which can be paired with the star donor polymer PBDB‐T to fabricate highly efficient organic solar cells are developed. Tailoring the size of lateral chains can tune the solubility and packing mode of acceptor molecules in neat and blend films. It is found that the incorporation of 2‐ethylhexyl chains can effectively change the compatibility with the donor polymer PBDB‐T, and an encouraging power conversion efficiency of 10.15% is accomplished by 4T‐3‐based organic solar cells. It also presents good compatibility with the other polymer donor and an even higher power conversion efficiency (PCE) of 12.04% is achieved based on D18:4T‐3 blend, which is the champion PCE for the fully non‐fused acceptors. Importantly, these inexpensive tetrathiophene fully non‐fused ring acceptors provide cost‐effective photovoltaic performance. The results demonstrate a high photovoltaic performance from synthetically inexpensive materials could be achieved by the rational design of non‐fused ring acceptor molecules. [ABSTRACT FROM AUTHOR]

Side-chain engineering has been considered as one of the most promising strategies to optimize non-fullerene acceptors. In this work, we use side-chain engineering to synthesize three fully non-fused electron acceptors (FNEAs) i.e. two symmetric acceptors (4T-BE and 4T-TO) and one asymmetric acceptor (4T-BOE) by different side chain combination onto the tetrathiophene unit, which could effectively tune the molecular conformations, electronic properties, charge carrier transport, film morphology, and photovoltaic properties. From 4T-BE to 4T-BOE and 4T-TO , the molecules present more red-shifted absorption, smaller optical bandgaps, initially rising and then declining LUMO energy levels and stronger intermolecular stacking. When blended with polymer donor PBDB-T, asymmetric 4T-BOE with alkoxy and ester side chains demonstrate a champion PCE of 9.57% with a short-circuit current density (J sc) of 16.28 mA/cm2, an open circuit voltage (V oc) of 0.87 V, and a fill factor (FF) of 67.50%, which was higher than that of the devices based on PBDB-T: 4T-BE and PBDB-T: 4T-TO. These results demonstrate that asymmetric side-chain engineering is an especially crucial and effective approach for the design of highly efficient FNEAs. [Display omitted] • Systematic study on side chain combination of the tetrathiophene-based fully non-fused electron acceptors. • Acceptor with asymmetric side chain functionalization presents moderate planarity, appropriate fibrous morphology and high PCE. • Careful lateral chain selection is crucial for FNEAs design. [ABSTRACT FROM AUTHOR]

Abstract Side-chain engineering could tune the crystallinity, solubility and aggregation styles of fused-ring electron acceptors (FREAs), and thus could influence the morphology and charge carrier mobility of blend films as well as the final device performances. Herein, we developed a novel FREA called spiro -IDT- O -IC , which is composed of a spiro-bridged IDT core and two 1,1-dicyanomethylene-3-indanone (IC) terminal units. Similar acceptor molecule IDT- O -IC with four 4-octyloxyphenyl side chains is also prepared for the control experiment. The absorptions, energy levels, molecular configurations, and electronic wave functions of these two acceptor molecules have been comparatively studied. Polymer solar cells (PSCs) fabricated with PBDB-T: spiro -IDT- O -IC as the active layer demonstrated a PCE of 6.23% with a J sc of 11.76 mA/cm2, a V oc of 0.84 V and an FF of 0.63. To the best of our knowledge, this is the first report that a spiro-bridged ladder type core was used for the fabrication of fused ring acceptors. Graphical abstract Image 1 Highlights • Lateral fluorene introduced into the molecular skeleton in a perpendicular way. • Bulky side chains of spiro -IDT- O -IC to regulate its aggregation in blend films. • First report of a spiro-bridged ladder core used for A-D-A fused ring acceptors. [ABSTRACT FROM AUTHOR]

• Minor terminal and central changes endow DO-2F and FO-N complementary absorption. • Asymmetrical FO-N effectively suppress the self-aggregation of DO-2F. • Acceptor alloy is found between the FO-N and DO-2F. • Alloy state acceptors produce suitable morphology with reduced V nr of 0.23 eV. • FO-N is an excellent third component for highly efficient OSCs of 14.10% Nonfused ring acceptors have shown great potential for future commercial applications of organic solar cells (OSCs) due to their simple structure and low synthetic costs. Herein, a novel asymmetrical nonfused ring acceptor FO-N with one branched lateral chain and one fluoro substituent at the central phenylene core was designed and introduced into PBDB-T : DO-2F binary system to fabricate high-efficiency ternary OSCs. The high-lying LUMO level of FO-N is conducive to improve V oc for ternary devices. More importantly, the introduction of FO-N as the third component can efficiently improve the compatibility of the ternary system via tuning the crystal size and optimizing the blend film morphology, which is beneficial to charge separation and reduced the non-radiative energy loss (Δ E nonrad). Finally, the ternary device achieved a low Δ E nonrad of 0.23 eV and a greatly improved PCE of 14.10% and with a V oc of 0.88 V, a J sc of 21.48 mA/cm2 and an FF of 74.41%. These results imply that the asymmetric nonfused ring acceptor design strategy is an effective way for optimizing the photovoltaic performance of highly crystallized blend system. [ABSTRACT FROM AUTHOR]

Non-fused ring electron acceptors with varied substituents were developed to construct efficient organic solar cells (OSCs). Out-of-plane rigid substituents such as 2-methylphenyl, 2- tert -butylphenyl and diphenylamine were introduced to the central benzene unit to improve the solubility of non-fused ring acceptors and noncovalent interactions such as O⋯S and N⋯S were used to enhance the planarity of molecular backbones. Blend films based on PBDB-T and these acceptors displayed better morphology without oversized aggregates formed. As-cast devices based on SM1 , SM2 and SM3 exhibited power conversion efficiencies of 5.96%, 6.43% and 6.80%, respectively. Image 1 • We designed three non-fused acceptors with varied substituents to construct efficient organic solar cells (OSCs). • Three electron acceptors could form strong intermolecular aggregations in films. • The morphology of blend films based on PBDB-T and acceptors displayed nanofibril network structure. • Simple non-fused acceptors are promising in achieving low-cost and high performance organic solar cells. [ABSTRACT FROM AUTHOR]