In this tutorial review, different film microstructures, commonly termed morphologies, into which the organic semiconductor polymers self-assemble macroscopically are presented, together with their ...corresponding influence on charge carrier mobility and hence transistor behaviour. It will be clarified how various chemical design approaches and solution processing methods enable the manipulation of polymer morphology, leading to improvements in transistor performance. Ultimately, it is illustrated that the directional alignment of polymers form oriented fiber-like films, yielding one of the highest mobilities reported so far for polymer transistors. Based on these observations, a prediction is made concerning which kind of morphology is expected to reach the best charge carrier mobility.
We report a blue dye, coded as R6, which features a polycyclic aromatic hydrocarbon, 9,19-dihydrobenzo1′,10′phenanthro3′,4′:4,5thieno3,2-bbenzo1,10phenanthro3,4-dthiophene, coupled with a ...diarylamine electron donor and 4-(7-ethynylbenzoc1,2,5thiadiazol-4-yl)benzoic acid acceptor. Dye R6 displays a brilliant sapphire color in a sensitized TiO2 mesoporous film with a Co(II/III) tris(bipyridyl)-based redox electrolyte. The R6 based dye-sensitized solar cell achieves an impressive power conversion efficiency of 12.6% under standard air mass 1.5 global, 100 mW cm–2, and shows a remarkable photostability.
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Good Co‐op: A novel cyclopentadithiophene‐bridged donor–acceptor dye applied as sensitizer in mesoscopic dye‐sensitized solar cells, in conjunction with the cobalt complexes CoII(bpy)3(B(CN)4)2 and ...CoIII(bpy)3(B(CN)4)3 as redox couple, yields high power conversion efficiencies (up to 9.6 %) under standard AM 1.5G solar irradiation. The results confirm that cobalt complexes are legitimate alternatives to the commonly used I−/I3− redox shuttle when used with judiciously engineered organic sensitizers.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co (II/III) tris(bipyridyl)—based ...redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.
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A replacement for gold as the hole‐injecting metal in organic electronic devices is presented: patterned graphene electrodes prepared from graphite oxide sheets by oxygen plasma etching. ...Solution‐processed organic FETs with poly(3‐hexylthiophene) as the semiconductor and these graphene electrodes are shown to perform as well as or even better than devices with gold contacts.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this article, the design paradigm involving molecular weight, alkyl substituents, and donor−acceptor interaction for the ...poly2,6-(4,4-bis-alkyl-4H-cyclopenta2,1-b;3,4-b′-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole) (cyclopentadithiophene−benzothiadiazole) donor−acceptor copolymer (CDT−BTZ) toward field-effect transistors (FETs) with ultrahigh mobilities is presented and discussed. It is shown that the molecular weight plays a key role in improving hole mobilities, reaching an exceptionally high value of up to 3.3 cm2 V−1 s−1. Possible explanations for this observation is highlighted in conjunction with thin film morphology and crystallinity. Hereby, it is found that the former does not change, whereas, at the same time, crystallinity improved with ever growing molecular weight. Furthermore, other important structural design factors such as alkyl chain substituents and donor−acceptor interaction between the polymer backbones potentially govern intermolecular stacking distances crucial for charge transport and hence for device performance. In this aspect, for the first time we attempt to shed light onto donor−acceptor interactions between neighboring polymer chains with the help of solid state nuclear magnetic resonance (NMR). On the basis of our results, polymer design principles are inferred that might be of relevance for prospective semiconductors exhibiting hole mobilities even exceeding 3 cm2 V−1 s−1.
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Four new DTS−BTD copolymers (P1−P4) differing by the concentration of electron-donating and -withdrawing substituents along the backbone have been synthesized and characterized by 2D-WAXS and in ...bottom-contact FETs. While all copolymers can self-assemble into lamellar superstructures, only P2 and P4 show a propensity to π-stack. P4 exhibits a hole mobility as high as 0.02 cm2 V−1 s−1 in excellent agreement with the close π-stacking and lamellar distances found by structural analysis (0.36 and 1.84 nm, respectively) and absorbs homogenously across the entire visible spectrum as solar cell applications require.
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The influence of molecular packing on the performance of polymer organic field‐effect transistors is illustrated in this work. Both close π‐stacking distance and long‐range order are important for ...achieving high mobilities. By aligning the polymers from solution, long‐range order is induced, yielding hole mobilities of up to µsat = 1.4 cm2 V−1 s−1 and current on/off ratios Ion/Ioff of 105.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
We present a solution processed organic field-effect transistor based on a benzothiadiazole (BTZ)−cyclopentadithiophene (CDT) copolymer with mobilities as high as 0.17 cm2/Vs and an on/off ratio of ...105. This pronounced performance together with the lack of macroscopic order in the thin film makes this conjugated copolymer an attractive candidate for low-cost organic electronics due to its facile processing.
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We highlight the effect of the interfacial charge-transfer resistance at the counter electrode in dye-sensitized solar cells based on two cobalt redox shuttles, namely cobalt(iii/ii) tris(2,2prime or ...minute-bipyridine) and cobalt(iii/ii) tris(1,10-phenanthroline). Highly porous counter electrodes based on poly(3,4-ethylenedioxythiophene) (PEDOT) prepared by electro-oxidative polymerization are compared to the typically employed platinized FTO glass, with the former showing much lower charge transfer resistances for both cobalt complexes, leading to improved fill factors and to linear response of the short circuit photo-current density to light intensity up to one sun. Based on these findings, an excellent power conversion efficiency of 10.3% was achieved with a recently reported organic sensitizer and PEDOT as counter electrode.
