Organic semiconductors with higher carrier mobility and better transparency have been actively pursued for numerous applications, such as flat-panel display backplane and sensor arrays. The carrier ...mobility is an important figure of merit and is sensitively influenced by the crystallinity and the molecular arrangement in a crystal lattice. Here we describe the growth of a highly aligned meta-stable structure of 2,7-dioctyl1benzothieno3,2-b1benzothiophene (C8-BTBT) from a blended solution of C8-BTBT and polystyrene by using a novel off-centre spin-coating method. Combined with a vertical phase separation of the blend, the highly aligned, meta-stable C8-BTBT films provide a significantly increased thin film transistor hole mobility up to 43 cm(2) Vs(-1) (25 cm(2) Vs(-1) on average), which is the highest value reported to date for all organic molecules. The resulting transistors show high transparency of >90% over the visible spectrum, indicating their potential for transparent, high-performance organic electronics.
A new semiconducting polymer, PDPP3T, with alternating diketopyrrolopyrrole and terthiophene units is presented. PDPP3T has a small band gap of 1.3 eV and exhibits nearly balanced hole and electron ...mobilities of 0.04 and 0.01 cm2 V−1 s−1, respectively, in field-effect transistors (FETs). By the combination of two identical ambipolar transistors, an inverter was constructed that exhibits a gain of ∼30. When PDPP3T was combined with 60PCBM or 70PCBM in a 1:2 weight ratio, photovoltaic cells were made that provide a photoresponse up to 900 nm and an AM1.5 power conversion efficiency of 3.8 or 4.7%, respectively. In contrast to the almost constant FET mobility, the efficiency of the photovoltaic cells was found to be strongly dependent on the molecular weight of PDPP3T and the use of diiodooctane as a processing agent.
For organic semiconductors to find ubiquitous electronics applications, the development of new materials with high mobility and air stability is critical. Despite the versatility of carbon, ...exploratory chemical synthesis in the vast chemical space can be hindered by synthetic and characterization difficulties. Here we show that in silico screening of novel derivatives of the dinaphtho2,3-b:2',3'-fthieno3,2-bthiophene semiconductor with high hole mobility and air stability can lead to the discovery of a new high-performance semiconductor. On the basis of estimates from the Marcus theory of charge transfer rates, we identified a novel compound expected to demonstrate a theoretic twofold improvement in mobility over the parent molecule. Synthetic and electrical characterization of the compound is reported with single-crystal field-effect transistors, showing a remarkable saturation and linear mobility of 12.3 and 16 cm(2) V(-1) s(-1), respectively. This is one of the very few organic semiconductors with mobility greater than 10 cm(2) V(-1) s(-1) reported to date.
Organic single‐crystalline p‐n junctions are grown from mixed solutions. First, C60 crystals (n‐type) form and, subsequently, C8‐BTBT crystals (p‐type) nucleate heterogeneously on the C60 crystals. ...Both crystals continue to grow simultaneously into single‐crystalline p‐n junctions that exhibit ambipolar charge transport characteristics. This work provides a platform to study organic single‐crystalline p‐n junctions.
Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5′bis(4-alkylphenyl)-2,2′-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical ...structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified SiO2 surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd–even effect in the strength of the intermolecular electronic coupling.
A conjugated polymer (PBTTQ) that consists of alternating electron-rich bithiophene and electron-deficient thiadiazoloquinoxaline units was synthesized via Yamamoto polymerization with Ni(cod)2 and ...provides a band gap of 0.94 eV. This represents one of the smallest band gaps obtained for a soluble conjugated polymer. When applied in a bulk heterojunction solar cell together with 84PCBM as the electron acceptor, the polymer affords a response up to 1.3 μm.
Three small band gap copolymers based on alternating dithiophene and thienopyrazine units were synthesized via Yamamoto coupling and applied in bulk heterojunction solar cells as donor together with ...PCBM (6,6-phenyl C61 butyric acid methyl ester) as acceptor. The polymers have an optical band gap of about 1.3eV in the solid state and only vary by the chemical nature of the solubilizing side chains. The nature of the side chain has a major effect on solubility and processability of the polymer. Using n-butoxymethyl side chains a soluble, easy to process polymer was obtained that gave the best photovoltaic performance. With short-circuit currents up to 5.2mA/cm2 an efficiency of 0.8% was achieved under estimated standard solar light conditions (AM1.5G, 100mW/cm2) with spectral response up to 950nm.
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Developing new acceptor materials as alternatives to fullerene acceptors remains a challenge in the field of organic photovoltaics. We report on the synthesis and optoelectronic properties of three ...acceptor polymers bearing diketopyrrolopyrrole units in the main chain (PA, PB and PC). Their performance as the acceptor material in bulk heterojunction solar cells using P3HT as the donor material has been tested. The solar cells show relatively high open-circuit voltages (≥0.9 V) but low fill factors and short-circuit current densities limit the photovoltaic device performance. Formation of free charge carriers and low electron mobility are identified as the major obstacles. In blends of P3HT with PA or PB charge formation is limited, while for the P3HT:PC blend photogenerated charges recombine into the PC triplet state before they can separate, unless assisted by a reverse electric field.
The properties of a mixed CdTe quantum dot/tetrahydro‐4H‐thiopyran‐4‐ylidene‐functionalized polythiophene system are reported. This system was prepared by exposing trioctylphosphine (TOP)‐capped CdTe ...quantum dots to the polythiophene in solution. Strong fluorescence emission quenching and shortening of the fluorescence emission lifetimes of both the polythiophene and the quantum dots occur when they are mixed, indicating the occurrence of photoinduced charge separation. Photoinduced absorption spectroscopy reveals a considerable decrease in the population of the polythiophene triplet excited state in the mixed system. These results demonstrate that between the quantum dots and the polythiophene there is both physical and electronic contact, which is mediated by the tetrahydro‐4H‐thiopyran‐4‐ylidene side chains.
Assemblies of CdTe quantum dots and a polythiophene are created by functionalizing the latter with tetrahydrothiopyran‐4‐ylidene side chains (see picture). As shown by the occurrence of photoinduced charge separation, electronic contact between quantum dots and a semiconducting polymer is achieved in this way.
The synthesis and photovoltaic performance of poly3-(
n-butoxymethyl)-thiophene (P3BMT) is reported. Incorporation of a
n-butoxymethyl side chain, instead of an alkyl chain as in ...poly(3-hexylthiophene) (P3HT) may increase the oxidation potential via an inductive effect, leading to an increase in open-circuit voltage (
V
oc) in bulk heterojunction solar cells. Applying the Grignard metathesis polymerization route afforded highly regioregular P3BMT with >
95% HT coupling. In solution, the optical and electrochemical properties of P3BMT are nearly identical to those of P3HT. However, the absorption data in the film point to a lesser degree of 3D ordering. The ether functionality appears to prevent a close packing of the chains. The best bulk heterojunction solar cells made from P3BMT with 6,6-phenyl-C
61-butyric acid methyl ester (PCBM) as acceptor had
V
oc
=
0.71 V, which is indeed ∼
0.1 V higher than that of P3HT:PCBM cells. As a result of the lower 3D ordering, the short-circuit current (
J
sc
=
4.16 mA/cm
2) is less. In combination with a fill factor of 0.57, a maximum power conversion efficiency of 1.68% was obtained.
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