We design and synthesize four fused-ring electron acceptors based on 6,6,12,12-tetrakis(4-hexylphenyl)-indacenobis(dithieno3,2-b;2′,3′-dthiophene) as the electron-rich unit and ...1,1-dicyanomethylene-3-indanones with 0–2 fluorine substituents as the electron-deficient units. These four molecules exhibit broad (550–850 nm) and strong absorption with high extinction coefficients of (2.1–2.5) × 105 M–1 cm–1. Fluorine substitution downshifts the LUMO energy level, red-shifts the absorption spectrum, and enhances electron mobility. The polymer solar cells based on the fluorinated electron acceptors exhibit power conversion efficiencies as high as 11.5%, much higher than that of their nonfluorinated counterpart (7.7%). We investigate the effects of the fluorine atom number and position on electronic properties, charge transport, film morphology, and photovoltaic properties.
Non-fullerene polymer solar cells (PSCs) with solution-processable n-type organic semiconductor (n-OS) as acceptor have seen rapid progress recently owing to the synthesis of new low bandgap n-OS, ...such as ITIC. To further increase power conversion efficiency (PCE) of the devices, it is of a great challenge to develop suitable polymer donor material that matches well with the low bandgap n-OS acceptors thus providing complementary absorption and nanoscaled blend morphology, as well as suppressed recombination and minimized energy loss. To address this challenge, we synthesized three medium bandgap 2D-conjugated bithienyl-benzodithiophene-alt-fluorobenzotriazole copolymers J52, J60, and J61 for the application as donor in the PSCs with low bandgap n-OS ITIC as acceptor. The three polymers were designed with branched alkyl (J52), branched alkylthio (J60), and linear alkylthio (J61) substituent on the thiophene conjugated side chain of the benzodithiophene (BDT) units for studying effect of the substituents on the photovoltaic performance of the polymers. The alkylthio side chain, red-shifted absorption down-shifted the highest occupied molecular orbital (HOMO) level and improved crystallinity of the 2D conjugated polymers. With linear alkylthio side chain, the tailored polymer J61 exhibits an enhanced J SC of 17.43 mA/cm2, a high V OC of 0.89 V, and a PCE of 9.53% in the best non-fullerene PSCs with the polymer as donor and ITIC as acceptor. To the best of our knowledge, the PCE of 9.53% is one of the highest values reported in literature to date for the non-fullerene PSCs. The results indicate that J61 is a promising medium bandgap polymer donor in non-fullerene PSCs.
Scalable production of high-quality heteroatom-modified graphene is critical for microscale supercapacitors but remains a great challenge. Herein, we demonstrate a scalable, single-step ...electrochemical exfoliation of graphite into highly solution-processable fluorine-modified graphene (FG), achieved in an aqueous fluorine-containing neutral electrolyte, for flexible and high-energy-density ionogel-based microsupercapacitors (FG-MSCs). The electrochemically exfoliated FG nanosheets are characterized by atomic thinness, large lateral size (up to 12 μm), a high yield of >70% with ≤3 layers, and a fluorine doping of 3 at%, allowing for large-scale production of FG-MSCs. Our ionogel-based FG-MSCs deliver high energy density of 56 mWh cm–3, by far outperforming the most reported MSCs. Furthermore, the all-solid-state microdevices offer exceptional cyclability with ∼93% after 5000 cycles, robust mechanical flexibility with 100% of capacitance retention bended at 180°, and outstanding serial and parallel integration without the requirement of metal-based interconnects for high-voltage and high-capacitance output. Therefore, these FG-MSCs represent remarkable potential for electronics.
To simultaneously achieve low photon energy loss (E loss) and broad spectral response, the molecular design of the wide band gap (WBG) donor polymer with a deep HOMO level is of critical importance ...in fullerene-free polymer solar cells (PSCs). Herein, we developed a new benzodithiophene unit, i.e., DTBDT-EF, and conducted systematic investigations on a WBG DTBDT-EF-based donor polymer, namely, PDTB-EF-T. Due to the synergistic electron-withdrawing effect of the fluorine atom and ester group, PDTB-EF-T exhibits a higher oxidation potential, i.e., a deeper HOMO level (ca. −5.5 eV) than most well-known donor polymers. Hence, a high open-circuit voltage of 0.90 V was obtained when paired with a fluorinated small molecule acceptor (IT-4F), corresponding to a low E loss of 0.62 eV. Furthermore, side-chain engineering demonstrated that subtle side-chain modulation of the ester greatly influences the aggregation effects and molecular packing of polymer PDTB-EF-T. With the benefits of the stronger interchain π–π interaction, the improved ordering structure, and thus the highest hole mobility, the most symmetric charge transport and reduced recombination are achieved for the linear decyl-substituted PDTB-EF-T (P2)-based PSCs, leading to the highest short-circuit current density and fill factor (FF). Due to the high Flory–Huggins interaction parameter (χ), surface-directed phase separation occurs in the P2:IT-4F blend, which is supported by X-ray photoemission spectroscopy results and cross-sectional transmission electron microscope images. By taking advantage of the vertical phase distribution of the P2:IT-4F blend, a high power conversion efficiency (PCE) of 14.2% with an outstanding FF of 0.76 was recorded for inverted devices. These results demonstrate the great potential of the DTBDT-EF unit for future organic photovoltaic applications.
Fluorinated organic molecules are pervasive within the pharmaceutical and agrochemical industries due to the range of structural and physicochemical properties that fluorine imparts. Currently, the ...most abundant methods for the synthesis of the aryl–CF2 functionality have relied on the deoxyfluorination of ketones and aldehydes using expensive and poorly atom economical reagents. Here, we report a general method for the synthesis of aryl–CF2R and aryl–CF2H compounds through activation of the corresponding trifluoromethyl arene precursors. This strategy is enabled by an endergonic electron transfer event that provides access to arene radical anions that lie outside of the catalyst reduction potential. Fragmentation of these reactive intermediates delivers difluorobenzylic radicals that can be intercepted by abundant alkene feedstocks or a hydrogen atom to provide a diverse array of difluoalkylaromatics.
There is an urgent need for low-cost, resource-friendly, high-energy-density cathode materials for lithium-ion batteries to satisfy the rapidly increasing need for electrical energy storage. To ...replace the nickel and cobalt, which are limited resources and are associated with safety problems, in current lithium-ion batteries, high-capacity cathodes based on manganese would be particularly desirable owing to the low cost and high abundance of the metal, and the intrinsic stability of the Mn4+ oxidation state. Here we present a strategy of combining high-valent cations and the partial substitution of fluorine for oxygen in a disordered-rocksalt structure to incorporate the reversible Mn2+/Mn4+ double redox couple into lithium-excess cathode materials. The lithium-rich cathodes thus produced have high capacity and energy density. The use of the Mn2+/Mn4+ redox reduces oxygen redox activity, thereby stabilizing the materials, and opens up new opportunities for the design of high-performance manganese-rich cathodes for advanced lithium-ion batteries.
The activation of carbon–fluorine (C−F) bonds is an important topic in synthetic organic chemistry. Metal‐mediated and ‐catalyzed elimination of β‐ or α‐fluorine proceeds under milder conditions than ...oxidative addition to C−F bonds. The β‐ or α‐fluorine elimination is initiated from organometallic intermediates having fluorine substituents on carbon atoms β or α to metal centers, respectively. Transformations through these elimination processes (C−F bond cleavage), which are typically preceded by carbon–carbon (or carbon–heteroatom) bond formation, have been increasingly developed in the past five years as C−F bond activation methods. In this Minireview, we summarize the applications of transition‐metal‐mediated and ‐catalyzed fluorine elimination to synthetic organic chemistry from a historical perspective with early studies and from a systematic perspective with recent studies.
Eliminate to activate: Metal‐mediated and ‐catalyzed elimination of β‐ or α‐fluorine proceeds under mild conditions, starting from organometallic intermediates with fluorine substituents on the carbon atoms β or α to the metal centers, respectively. Recently, these elimination processes have been used in the development of a variety of methods for activating C−F bonds.
The development of semiconducting polymers is imperative to improve the performance of polymer-based solar cells (PSCs). In this study, new semiconducting polymers based on ...naphtho1,2-c:5,6-c′bis1,2,5thiadiazole (NTz), PNTz4TF2 and PNTz4TF4, having 3,3′-difluoro-2,2′-bithiophene and 3,3′,4,4′-tetrafluoro-2,2′-bithiophene, respectively, are designed and synthesized. These polymers possess a deeper HOMO energy level than their counterpart, PNTz4T, which results in higher open-circuit voltages in solar cells. This concequently reduces the photon energy loss that is one of the most important issues surrounding PSCs. The PNTz4TF4 cell exhibits up to 6.5% power conversion efficiency (PCE), whereas the PNTz4TF2 cell demonstrates outstanding device performance with as high as 10.5% PCE, which is quite high for PSCs. We further discuss the performances of the PSCs based on these polymers by correlating the charge generation and recombination dynamics with the polymer structure and ordering structure. We believe that the results provide new insights into the design of semiconducting polymers and that there is still much room for improvement of PSC efficiency.
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