Publications
421 results found
Wijeyasinghe N, Regoutz A, Eisner F, et al., 2017, Copper(I) Thiocyanate (CuSCN) Hole-Transport Layers Processed from Aqueous Precursor Solutions and Their Application in Thin-Film Transistors and Highly Efficient Organic and Organometal Halide Perovskite Solar Cells, ADVANCED FUNCTIONAL MATERIALS, Vol: 27, ISSN: 1616-301X
This study reports the development of copper(I) thiocyanate (CuSCN) hole-transport layers (HTLs) processed from aqueous ammonia as a novel alternative to conventional n-alkyl sulfide solvents. Wide bandgap (3.4–3.9 eV) and ultrathin (3–5 nm) layers of CuSCN are formed when the aqueous CuSCN–ammine complex solution is spin-cast in air and annealed at 100 °C. X-ray photoelectron spectroscopy confirms the high compositional purity of the formed CuSCN layers, while the high-resolution valence band spectra agree with first-principles calculations. Study of the hole-transport properties using field-effect transistor measurements reveals that the aqueous-processed CuSCN layers exhibit a fivefold higher hole mobility than films processed from diethyl sulfide solutions with the maximum values approaching 0.1 cm2 V−1 s−1. A further interesting characteristic is the low surface roughness of the resulting CuSCN layers, which in the case of solar cells helps to planarize the indium tin oxide anode. Organic bulk heterojunction and planar organometal halide perovskite solar cells based on aqueous-processed CuSCN HTLs yield power conversion efficiency of 10.7% and 17.5%, respectively. Importantly, aqueous-processed CuSCN-based cells consistently outperform devices based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate HTLs. This is the first report on CuSCN films and devices processed via an aqueous-based synthetic route that is compatible with high-throughput manufacturing and paves the way for further developments.
Green JP, Cryer SJ, Marafie J, et al., 2017, Synthesis of a Luminescent Arsolo[2,3-d:5,4-d']bis(thiazole) Building Block and Comparison to Its Phosphole Analogue, Organometallics, Vol: 36, Pages: 2632-2636, ISSN: 0276-7333
The synthesis of 4-phenyl-4H-arsolo[2,3-d:5,4-d′]bis(thiazole) is reported, and its properties are compared to those of the previously prepared phosphole analogue. By comparison of their single-crystal structures, the harmonic oscillator model of heterocyclic electron delocalization (HOMHED) was used to directly compare the aromatic character of the two systems. The findings demonstrate that, although both compounds can be considered aromatic, the phosphole-containing compound had a greater degree of aromatic character than its arsole analogue. The arsole derivative exhibited excellent stability in ambient air with no formation of the arsole oxide observed upon storage. The absorption and photoluminescence spectra of the arsole derivate were subtly altered in comparison to the phosphole derivative, suggesting that changing pnictogenic atoms in such fused-ring systems to heavier analogues could be a viable way of tuning both the ambient stability and optoelectronic properties of such materials.
Fei Z, Chen L, Han Y, et al., 2017, Alternating 5,5-Dimethylcyclopentadiene and Diketopyrrolopyrrole Copolymer Prepared at Room Temperature for High Performance Organic Thin-Film Transistors, Journal of the American Chemical Society, Vol: 139, Pages: 8094-8097, ISSN: 1520-5126
We report that the inclusion of nonaromatic 5,5-dimethylcyclopentadiene monomer into a conjugated backbone is an attractive strategy to high performance semiconducting polymers. The use of this monomer enables a room temperature Suzuki copolymerization with a diketopyrrolopyrrole comonomer to afford a highly soluble, high molecular weight material. The resulting low band gap polymer exhibits excellent photo and thermal stability, and despite a large π–π stacking distance of 4.26 Å, it demonstrates excellent performance in thin-film transistor devices.
Fei Z, Han Y, Gann E, et al., 2017, Alkylated selenophene-based ladder-type monomers via a facileroute for high performance thin-film transistor applications, Journal of the American Chemical Society, Vol: 139, Pages: 8552-8561, ISSN: 1943-2984
We report the synthesis of two new selenophene-containing ladder-type monomers, cyclopentadiselenophene (CPDS) and indacenodiselenophene (IDSe), via a 2-fold and 4-fold Pd-catalyzed coupling with a 1,1-diborylmethane derivative. Copolymers with benzothiadiazole were prepared in high yield by Suzuki polymerization to afford materials which exhibited excellent solubility in a range of nonchlorinated solvents. The CPDS copolymer exhibited a band gap of just 1.18 eV, which is among the lowest reported for donor–acceptor polymers. Thin-film transistors were fabricated using environmentally benign, nonchlorinated solvents, with the CPDS and IDSe copolymers exhibiting hole mobility up to 0.15 and 6.4 cm2 V–1 s–1, respectively. This high performance was achieved without the undesirable peak in mobility often observed at low gate voltages due to parasitic contact resistance.
Costa L, Al-Hashimi M, Heeney M, et al., 2017, Template-Synthesis of Conjugated Poly(3-Hexylselenophene) (P3HS) Nanofibers Using Femtosecond Laser Machined Fused Silica Templates, MRS ADVANCES, Vol: 2, Pages: 2957-2960, ISSN: 2059-8521
Hu Z, Haws RT, Fei Z, et al., 2017, Impact of backbone fluorination on nanoscale morphology and excitonic coupling in polythiophenes, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, Vol: 114, Pages: 5113-5118, ISSN: 0027-8424
Dey S, Watkins S, Sredojevic D, et al., 2017, Novel transition-metal-free homo-polymerization of Pyrrolo[3,2-d:4,5-d′]Bisthiazole (PBTz) using turbo-Grignard for organic electronics, 253rd National Meeting of the American-Chemical-Society (ACS) on Advanced Materials, Technologies, Systems, and Processes, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Creamer A, Casey A, Marsh AV, et al., 2017, Systematic Tuning of 2,1,3-Benzothiadiazole Acceptor Strength by Monofunctionalization with Alkylamine, Thioalkyl, or Alkoxy Groups in Carbazole Donor-Acceptor Polymers, MACROMOLECULES, Vol: 50, Pages: 2736-2746, ISSN: 0024-9297
A simple route to the preparation of alkylamine, thioalkyl, and alkoxy monofunctionalized 4,7-di(thiophen-2-yl)-2,1,3-benzothiadiazole) based monomers is reported from a common fluorinated precursor. Copolymerization with a carbazole comonomer under Suzuki conditions yielded a series of analogous donor–acceptor copolymers in which the only difference was the nature of the heteroatom (N, O, or S) on the benzothiadiazole core. This was shown to have a significant impact on the wavelength and intensity of the intramolecular charge transfer (ICT) absorption peak due to a combination of electronic and steric factors. Substantial differences were also observed in the solar cell performance of blends with PC71BM, with the octylamino substituted polymer exhibiting significantly lower performance than the other two polymers. This polymer also exhibited a reversible change in the optical spectra upon exposure to acid, suggesting potential as a sensing material.
Casey A, Green JP, Shakya Tuladhar P, et al., 2017, Cyano substituted benzotriazole based polymers for use in organic solar cells, Journal of Materials Chemistry A, Vol: 5, Pages: 6465-6470, ISSN: 2050-7496
A new synthetic route to the electron accepting di-cyano substituted benzo[d][1,2,3]triazole (BTz) monomer 2-(2-butyloctyl)-4,7-di(thiophen-2-yl)-2H-benzotriazole-5,6-dicarbonitrile (dTdCNBTz) is reported. The cyano substituents can be easily introduced to the BTz unit in one step via the nucleophilic aromatic substitution of the fluorine substituents of the fluorinated precursor 2-(2-butyloctyl)-4,7-di(thiophen-2-yl)-2H-benzotriazole-5,6-difluoro (dTdFBTz). Co-polymers were prepared with distannylated benzo[1,2-b:4,5-b′]dithiophene (BDT) monomers containing either 2-ethylhexylthienyl (T-EH) side chains or 2-butyloctylthienyl (T-BO) side chains via Stille coupling to yield the novel medium band gap polymers P1 and P2 respectively. Whilst the organic photovoltaic (OPV) performance of P1 was limited by a lack of solubility, the improved solubility of P2 resulted in promising device efficiencies of up to 6.9% in blends with PC61BM, with high open circuit voltages of 0.95 V.
Rodriquez D, Kim J-H, Root SE, et al., 2017, Comparison of Methods for Determining the Mechanical Properties of Semiconducting Polymer Films for Stretchable Electronics, ACS APPLIED MATERIALS & INTERFACES, Vol: 9, Pages: 8855-8862, ISSN: 1944-8244
Patra D, Lee J, Lee J, et al., 2017, Synthesis of low band gap polymers based on pyrrolo[3,2-d:4,5-d ']bisthiazole (PBTz) and thienylenevinylene (TV) for organic thin-film transistors (OTFTs), JOURNAL OF MATERIALS CHEMISTRY C, Vol: 5, Pages: 2247-2258, ISSN: 2050-7526
Isakov I, Paterson AF, Solomeshch O, et al., 2016, Hybrid complementary circuits based on p-channel organic and n-channel metal oxide transistors with balanced carrier mobilities of up to 10 cm(2)/Vs, Applied Physics Letters, Vol: 109, ISSN: 1077-3118
We report the development of hybrid complementary inverters based on p-channel organic andn-channel metal oxide thin-film transistors (TFTs) both processed from solution at <200 C. For theorganic TFTs, a ternary blend consisting of the small-molecule 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene, the polymer indacenodithiophene-benzothiadiazole (C16IDT-BT) and the p-typedopant C60F48 was employed, whereas the isotype In2O3/ZnO heterojunction was used for the nchannelTFTs. When integrated on the same substrate, p- and n-channel devices exhibited balancedcarrier mobilities up to 10 cm2/Vs. Hybrid complementary inverters based on these devices show highsignal gain (>30 V/V) and wide noise margins (70%). The moderate processing temperaturesemployed and the achieved level of device performance highlight the tremendous potential of the technologyfor application in the emerging sector of large-area microelectronics.
Boufflet P, Casey A, Xia Y, et al., 2016, Pentafluorobenzene end-group as a versatile handle for para fluoro "click" functionalization of polythiophenes, Chemical Science, Vol: 8, Pages: 2215-2225, ISSN: 2041-6520
A convenient method of introducing pentafluorobenzene (PFB) as a single end-group in polythiophene derivatives is reported via in situ quenching of the polymerization. We demonstrate that the PFB-group is a particularly useful end-group due to its ability to undergo fast nucleophilic aromatic substitutions. Using this molecular handle, we are able to quantitatively tether a variety of common nucleophiles to the polythiophene backbone. The mild conditions required for the reaction allows sensitive functional moieties, such as biotin or a cross-linkable trimethoxysilane, to be introduced as end-groups. The high yield enabled the formation of a diblock rod-coil polymer from equimolar reactants under transition metal-free conditions at room temperature. We further demonstrate that water soluble polythiophenes end-capped with PFB can be prepared via the hydrolysis of an ester precursor, and that such polymers are amenable to functionalization under aqueous conditions.
Casey A, Han Y, Gann E, et al., 2016, Vinylene-linked oligothiophene–difluorobenzothiadiazole copolymer for transistor applications, ACS Applied Materials & Interfaces, Vol: 8, Pages: 31154-31165, ISSN: 1944-8244
The synthesis of the novel donor-acceptor monomer 4,7-bis[(E)-2-(5-bromo-3-dodecylylthiophen-2-yl)ethenyl]-5,6-difluoro-2,1,3-benzothiadiazole (FBT-V2T2) is reported. Polymerization with 4,4'-ditetradecyl-5,5'-bistrimethylstannyl-2,2'-bithiophene afforded a highly crystalline polymer that aggregated strongly in solution. Polymer films were well ordered resulting in high performance field-effect transistors with low onset voltages, negligible hysteresis, high channel current on/off ratios and peak hole mobilities of up to 0.5 cm2V-1s-1. Notably the transistors exhibited close to ideal behavior with extracted mobilities almost independent of gate of voltage.
Boufflet P, Wood S, Wade J, et al., 2016, Comparing blends and blocks: Synthesis of partially fluorinated diblock polythiophene copolymers to investigate the thermal stability of optical and morphological properties, Beilstein Journal of Organic Chemistry, Vol: 12, Pages: 2150-2163, ISSN: 1860-5397
The microstructure of the active blend layer has been shown to be a critically important factor in the performance of organic solar devices. Block copolymers provide a potentially interesting avenue for controlling this active layer microstructure in solar cell blends. Here we explore the impact of backbone fluorination in block copolymers of poly(3-octyl-4-fluorothiophene)s and poly(3-octylthiophene) (F-P3OT-b-P3OT). Two block co-polymers with varying block lengths were prepared via sequential monomer addition under Kumada catalyst transfer polymerisation (KCTP) conditions. We compare the behavior of the block copolymer to that of the corresponding homopolymer blends. In both types of system, we find the fluorinated segments tend to dominate the UV–visible absorption and molecular vibrational spectral features, as well as the thermal behavior. In the block copolymer case, non-fluorinated segments appear to slightly frustrate the aggregation of the more fluorinated block. However, in situ temperature dependent Raman spectroscopy shows that the intramolecular order is more thermally stable in the block copolymer than in the corresponding blend, suggesting that such materials may be interesting for enhanced thermal stability of organic photovoltaic active layers based on similar systems.
Han Y, Barnes G, Lin Y-H, et al., 2016, Doping of large ionization potential indenopyrazine polymers via Lewis acid complexation with tris(pentafluorophenyl)borane: a simple method for improving the performance of organic thin-film transistors, Chemistry of Materials, Vol: 28, Pages: 8016-8024, ISSN: 1520-5002
Molecular doping, under certain circumstances, can be used to improve the charge transport in organic semiconductors through the introduction of excess charge carriers which can in turn negate unwanted trap states often present in organic semiconductors. Here, two Lewis basic indenopyrazine copolymers with large ionization potential (5.78 and 5.82 eV) are prepared to investigate the p-doping efficiency with the Lewis acid dopant, tris(pentafluorophenyl)borane, using organic thin-film transistors (OTFTs). The formation of Lewis acid–base complex between the polymer and dopant molecules is confirmed via optical spectroscopy and electrical field-effect measurements, with the latter revealing a dopant-concentration-dependent device performance. By adjusting the amount of p-dopant, the hole mobility can be increased up to 11-fold while the OTFTs’ threshold voltages are reduced. The work demonstrates an alternative doping mechanism other than the traditional charge transfer model, where the energy level matching principle can limit the option of dopants.
Datko B, Thomas A, Fei Z, et al., 2016, Understanding the origins of efficient triplet formation in poly 3-hexylthiophene aggregate nanostructure, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Fei Z, Han Y, Martin J, et al., 2016, Conjugated Copolymers of Vinylene Flanked Naphthalene Diimide, Macromolecules, Vol: 49, Pages: 6384-6393, ISSN: 0024-9297
We report the synthesis of a novel naphthalene diimide (NDI) monomer containing two (tributylstannyl)vinyl groups. The utility of this building block is demonstrated by its copolymerization with five different electron-rich comonomers under Stille conditions. The resulting high molecular weight polymers show red-shifted optical absorptions in comparison to the analogous polymers without the vinylene spacer and a significant increase in the intensity of the low-energy intramolecular charge transfer band. The polymers all exhibit ambipolar behavior in bottom-gate, top-contact organic thin-film transistors. The insertion of a solution-processed barium hydroxide layer between the polymer and the gold electrode led to unipolar behavior with improved electron mobilities.
Paterson AF, Treat ND, Zhang W, et al., 2016, Small Molecule/Polymer Blend Organic Transistors with Hole Mobility Exceeding 13 cm V−1 s−1, Advanced Materials, Vol: 28, Pages: 7791-7798, ISSN: 1521-4095
A ternary organic semiconducting blend composed of a small-molecule, a conjugated polymer, and a molecular p-dopant is developed and used in solution-processed organic transistors with hole mobility exceeding 13 cm(2) V(-1) s(-1) (see the Figure). It is shown that key to this development is the incorporation of the p-dopant and the formation of a vertically phase-separated film microstructure.
Casey A, Dimitrov SD, Shakya-Tuladhar P, et al., 2016, Effect of Systematically Tuning Conjugated Donor Polymer Lowest Unoccupied Molecular Orbital Levels via Cyano Substitution on Organic Photovoltaic Device Performance, Chemistry of Materials, Vol: 28, Pages: 5110-5120, ISSN: 0897-4756
We report a systematic study into the effects of cyano substitution on the electron accepting ability of the common acceptor 4,7-bis(thiophen-2-yl)-2,1,3-benzothiadiazole (DTBT). We describe the synthesis of DTBT monomers with either 0, 1, or 2 cyano groups on the BT unit and their corresponding copolymers with the electron rich donor dithienogermole (DTG). The presence of the cyano group is found to have a strong influence on the optoelectronic properties of the resulting donor–acceptor polymers, with the optical band gap red-shifting by approximately 0.15 eV per cyano substituent. We find that the polymer electron affinity is significantly increased by ∼0.25 eV upon addition of each cyano group, while the ionization potential is less strongly affected, increasing by less than 0.1 eV per cyano substituent. In organic photovoltaic (OPV) devices power conversion efficiencies (PCE) are almost doubled from around 3.5% for the unsubstituted BT polymer to over 6.5% for the monocyano substituted BT polymer. However, the PCE drops to less than 1% for the dicyano substituted BT polymer. These differences are mainly related to differences in the photocurrent, which varies by 1 order of magnitude between the best (1CN) and worst devices (2CN). The origin of this variation in the photocurrent was investigated by studying the charge generation properties of the photoactive polymer–fullerene blends using fluorescence and transient absorption spectroscopic techniques. These measurements revealed that the improved photocurrent of 1CN in comparison to 0CN was due to improved light harvesting properties while maintaining a high exciton dissociation yield. The addition of one cyano group to the BT unit optimized the position of the polymer LUMO level closer to that of the electron acceptor PC71BM, such that the polymer’s light harvesting properties were improved without sacrificing either the exciton dissociation yield or device VOC. We also identify that the dr
Kang K, Watanabe S, Broch K, et al., 2016, 2D coherent charge transport in highly ordered conducting polymers doped by solid state diffusion, Nature Materials, Vol: 15, Pages: 896-902, ISSN: 1476-4660
Doping is one of the most important methods to control charge carrier concentration in semiconductors. Ideally, the introduction of dopants should not perturb the ordered microstructure of the semiconducting host. In some systems, such as modulation-doped inorganic semiconductors or molecular charge transfer crystals, this can be achieved by spatially separating the dopants from the charge transport pathways. However, in conducting polymers, dopants tend to be randomly distributed within the conjugated polymer, and as a result the transport properties are strongly affected by the resulting structural and electronic disorder. Here, we show that in the highly ordered lamellar microstructure of a regioregular thiophene-based conjugated polymer, a small-molecule p-type dopant can be incorporated by solid state diffusion into the layers of solubilizing side chains without disrupting the conjugated layers. In contrast to more disordered systems, this allows us to observe coherent, free-electron-like charge transport properties, including a nearly ideal Hall effect in a wide temperature range, a positive magnetoconductance due to weak localization and the Pauli paramagnetic spin susceptibility.
Green J, Han Y, Kilmurray R, et al., 2016, An Air-Stable Semiconducting Polymer Containing Dithieno[3,2-b:2′,3′-d]arsole, Angewandte Chemie - International Edition, Vol: 55, Pages: 7148-7151, ISSN: 1433-7851
Arsole-containing conjugated polymers are a practically unexplored class of materials despite the high interest in their phosphole analogues. Herein we report the synthesis of the first dithieno[3,2-b;2′,3′-d]arsole derivative, and demonstrate that it is stable to ambient oxidation in its +3 oxidation state. A soluble copolymer is obtained by a palladium-catalyzed Stille polymerization and demonstrated to be a p-type semiconductor with promising hole mobility, which was evaluated by field-effect transistor measurements.
Green JP, Han Y, Kilmurray R, et al., 2016, An air-stable semiconducting polymer containing Dithieno[3,2- b :2′,3′- d ]arsole, Angewandte Chemie, Vol: 128, Pages: 7264-7267, ISSN: 0044-8249
Arsole-containing conjugated polymers are a practically unexplored class of materials despite the high interest in their phosphole analogues. Herein we report the synthesis of the first dithieno[3,2-b;2′,3′-d]arsole derivative, and demonstrate that it is stable to ambient oxidation in its +3 oxidation state. A soluble copolymer is obtained by a palladium-catalyzed Stille polymerization and demonstrated to be a p-type semiconductor with promising hole mobility, which was evaluated by field-effect transistor measurements.
Bannock JH, Xu W, Baïssas T, et al., 2016, Rapid flow-based synthesis of poly(3-hexylthiophene) using 2-methyltetrahydrofuran as a bio-derived reaction solvent, European Polymer Journal, Vol: 80, Pages: 240-246, ISSN: 1873-1945
We report the synthesis of poly(3-hexylthiophene) (P3HT) by Grignard metathesis (GRIM) polymerization using the bio-derived ‘green’ solvent 2-methyltetrahydrofuran (2-MeTHF). Using a standard flask-based reaction, the molecular weight distribution, regioregularity and product yield were found to be similar to those obtained under equivalent conditions using tetrahydrofuran (THF) as a reaction solvent. The synthesis was subsequently adapted to a novel “tube-in-shell” droplet-based flow reactor, using a newly developed high-solubility catalyst derived from nickel(II) bromide ethylene glycol dimethyl ether complex (Ni(dme)Br2) and 1,3-bis(diphenylphosphino)propane (dppp). Use of the new catalyst together with an increased reaction temperature of 65 oC (enabled by the higher boiling point of 2-MeTHF) resulted in an approximate four-fold increase in reaction rate compared to a standard THF- based synthesis at 55 oC, with full conversion reached within one minute. The purified flow- synthesized polymer had an Mw of 46 kg mol-1, a low PDI of 1.4, and a regioregularity of 93 %, indicating the suitability of flow-based GRIM polymerization in 2-MeTHF for the high- throughput synthesis of high quality P3HT.
Bannock JH, Treat N, Chabinyc M, et al., 2016, The influence of polymer purification on the efficiency of poly(3-hexylthiophene):fullerene organic solar cells, Scientific Reports, Vol: 6, ISSN: 2045-2322
We report the influence of different polymer purification procedures on the photovoltaic performance ofbulk heterojunction solar cells formed from binary blends of poly(3-hexylthiophene) (P3HT) andfullerenes. Selective Soxhlet extractions and metal scavenging agents were used to remove residualmonomer, magnesium salt by-products and catalyst from high-weight P3HT (Mw 121 kg/mol, PDI 1.8,RR 99%) synthesised by the Grignard metathesis (GRIM) polymerization route. Using phenyl-C61-butyric acid methyl ester (PC60BM) as an electron acceptor, we observed an increase in average powerconversion efficiency from 2.3 to 4.8 % in going from crude to fully purified material. Using indene-C60bisadduct (IC60BA) in place of PC60BM, we observed a further increase to an average value of 6.6 %,which is high for a bulk heterojunction formed from a binary blend of P3HT and C60 fullerene derivatives.
Dey S, Al Qaradawi S, Bazzi H, et al., 2016, Fused pyrrolo[3,2-d:4,5-d′]bisthiazole-based n-type copolymers, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Heeney M, 2016, Post-polymerization modification of conjugated polymers, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Kassar T, Gueldal NS, Berlinghof M, et al., 2016, Real-Time Investigation of Intercalation and Structure Evolution in Printed Polymer:Fullerene Bulk Heterojunction Thin Films, ADVANCED ENERGY MATERIALS, Vol: 6, ISSN: 1614-6832
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Dimitrov SD, Schroeder BC, Nielsen CB, et al., 2016, Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells, Polymers, Vol: 8, ISSN: 2073-4360
The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.
Cachelin P, Green JP, Peijs T, et al., 2016, Optical acetone vapor sensors based on chiral nematic liquid crystals and reactive chiral dopants, Advanced Optical Materials, Vol: 4, Pages: 592-596, ISSN: 2195-1071
Accurate monitoring of exposure to organic vapors, such as acetone, is an important part of maintaining a safe working environment and adhering to long- and short-term exposure limits. Here, a novel acetone vapor detection system is described based on the use of a reactive chiral dopant in a nematic liquid crystal thin film, which can accurately monitor the total exposure over a given time frame through changes in the reflection band of the film. It is found that films exposed to 1000 parts per million by volume (ppmv) of acetone vapor for 2 h exhibit a shift in reflection band of 12 nm, with smaller shifts observed at lower concentrations of acetone. Such sensors have potential applications in industrial hygiene.
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