333 results found
Paterson AF, Mottram AD, Faber H, et al., 2019, Impact of the gate dielectric on contact resistance in high-mobility organic transistors, Advanced Electronic Materials, ISSN: 2199-160X
The impact of the gate dielectric on contact resistance in organic thin-film transistors (OTFTs) is investigated using electrical characterization, bias-stress stability measurements, and bandgap density of states (DOS) analysis. Two similar dielectric materials, namely Cytop and poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene] (Teflon AF2400), are tested in top-gate bottom-contact OTFTs. The contact resistance of Cytop-based OTFTs is found to be greater than that of the AF2400-based devices, even though the metal/OSC interface remains identical in both systems. The Cytop devices are also found to perform worse in bias-stress stability tests which, along with the DOS calculations, suggests that charge trapping at the OSC/dielectric interface is more prevalent with Cytop than AF2400. This increased charge trapping at the Cytop OSC/dielectric interface appears to be associated with the higher contact resistance in Cytop OTFTs. Differences in the molecular structure between Cytop and AF2400 and the large difference in the glass transition temperature of the two polymers may be responsible for the observed difference in the transistor performance. Overall, this study highlights the importance of the gate dielectric material in the quest for better performing OTFTs and integrated circuits.
Sun G, Shahid M, Fei Z, et al., 2019, Highly-efficient semi-transparent organic solar cells utilising non-fullerene acceptors with optimised multilayer MoO3/Ag/MoO3 electrodes, Materials Chemistry Frontiers, Vol: 3, Pages: 450-455, ISSN: 2052-1537
We report the optimisation of a semi-transparent solar cell based on a blend of a recently reported high performance donor polymer (PFBDB-T) with a non-fullerene acceptor derivative (C8-ITIC). The performance is shown to strongly depend on the nature of the semi-transparent electrode, and we report the optimal fabrication conditions for a multilayer MoO3/Ag/MoO3 electrode. The effect of deposition rate and layer thickness of both the Ag and the outer MoO3 on transparency and sheet resistance is investigated, and is shown to have a significant impact on the overall device performance. The optimised PFBDB-T:C8-ITIC based devices exhibit an average power conversion efficiency (PCE) of 9.2% with an average visible transmittance (AVT) of 22%.
Karuthedath S, Gorenflot J, Firdaus Y, et al., 2019, Charge and Triplet Exciton Generation in Neat PC70BM Films and Hybrid CuSCN:PC70BM Solar Cells, ADVANCED ENERGY MATERIALS, Vol: 9, ISSN: 1614-6832
Barrit D, Cheng P, Tang MC, et al., 2019, Impact of the Solvation State of Lead Iodide on Its Two-Step Conversion to MAPbI <inf>3</inf> : An In Situ Investigation, Advanced Functional Materials, ISSN: 1616-301X
© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Producing high efficiency solar cells without high-temperature processing or use of additives still remains a challenge with the two-step process. Here, the solution processing of MAPbI 3 from PbI 2 films in N,N-dimethylformamide (DMF) is investigated. In-situ grazing incidence wide-angle X-ray scattering (GIWAXS) measurements reveal a sol–gel process involving three PbI 2 -DMF solvate complexes—disordered (P 0 ) and ordered (P 1 , P 2 )—prior to PbI 2 formation. When the appropriate solvated state of PbI 2 is exposed to MAI (methylammonium Iodide), it can lead to rapid and complete room temperature conversion into MAPbI 3 with higher quality films and improved solar cell performance. Complementary in-situ optical reflectance, absorbance, and quartz crystal microbalance with dissipation (QCM-D) measurements show that dry PbI 2 can take up only one third of the MAI taken up by the solvated-crystalline P 2 phase of PbI 2 , requiring additional annealing and yet still underperforming. The perovskite solar cells fabricated from the ordered P 2 precursor show higher power conversion efficiency (PCE) and reproducibility than devices fabricated from other cases. The average PCE of the solar cells is greatly improved from 13.2(±0.53)% (from annealed PbI 2 ) to 15.7(±0.35)% (from P 2 ) reaching up to 16.2%. This work demonstrates the importance of controlling the solvation of PbI 2 as an effective strategy for the growth of high-quality perovskite films and their application in high efficiency and reproducible solar cells.
Paterson AF, Anthopoulos TD, 2018, Enabling thin-film transistor technologies and the device metrics that matter, Nature Communications, Vol: 9, ISSN: 2041-1723
The field-effect transistor kickstarted the digital revolution that propelled our society into the information age. One member of the now large family of field-effect devices is the thin-film transistor (TFT), best known for its enabling role in modern flat-panel displays. TFTs can be used in all sorts of innovative applications because of the broad variety of materials they can be made from, which give them diverse electrical and mechanical characteristics. To successfully utilize TFT technologies in a variety of rapidly emerging applications, such as flexible, stretchable and transparent large-area microelectronics, there are a number of metrics that matter.
Paterson AF, Lin Y-H, Mottram AD, et al., 2018, The Impact of Molecular p-Doping on Charge Transport in High-Mobility Small-Molecule/Polymer Blend Organic Transistors, ADVANCED ELECTRONIC MATERIALS, Vol: 4, ISSN: 2199-160X
Costa JC, Pouryazdan A, Panidi J, et al., 2018, Low temperature and radiation stability of flexible IGZO TFTs and their suitability for space applications, Pages: 98-101, ISSN: 1930-8876
© 2018 IEEE. In this paper, Low Earth Orbit radiation and temperature conditions are mimicked to investigate the suitability of flexible Indium-Gallium-Zinc-Oxide transistors for lightweight space-wearables. Such wearable devices could be incorporated into spacesuits as unobtrusive sensors such as radiation detectors or physiological monitors. Due to the harsh environment to which these space-wearables would be exposed, they have to be able to withstand high radiation doses and low temperatures. For this reason, the impacts of high energetic electron irradiation with fluences up to 10 12 e - /cm 2 and low operating temperatures down to 78 K, are investigated. This simulates 278 h in a Low Earth Orbit. The threshold voltage and mobility of transistors that were exposed to e-irradiation are found to shift by +0.09 0.05 V and-0.6 0.5 cm 2 V -1 s -1 . Subsequent low temperature exposure resulted in additional shifts of +0.38V and-5.95 cm 2 V -1 s -1 for the same parameters. These values are larger than the ones obtained from non-irradiated reference samples. If this is considered during the systems' design, these devices can be used to unobtrusively integrate sensor systems into space-suits.
Boufflet P, Bovo G, Occhi L, et al., 2018, The influence of backbone fluorination on the dielectric constant of conjugated polythiophenes, Advanced Electronic Materials, Vol: 4, ISSN: 2199-160X
The ability to modify or enhance the dielectric constant of semiconducting polymers can prove valuable for a range of optoelectronic and microelectronic applications. In the case of organic photovoltaics, increasing the dielectric constant of the active layer has often been suggested as a method to control charge generation, recombination dynamics, and ultimately, the power conversion efficiencies. In this contribution, the impact that the degree and pattern of fluorination has on the dielectric constant of poly(3-octylthiophene) (P3OT), a more soluble analogue of the widely studied conjugated material poly(3-hexylthiophene), is explored. P3OT and its backbone-fluorinated analogue, F-P3OT, are compared along with a block and alternating copolymer version of these materials. It is found that the dielectric constant of the polymer thin films increases as the degree of backbone fluorination increases, in a trend consistent with density functional theory calculations of the dipole moment.
Wyatt-Moon G, Georgiadou DG, Zoladek-Lemanczyk A, et al., 2018, Flexible nanogap polymer light-emitting diodes fabricated via adhesion lithography (a-Lith), Journal of Physics: Materials, Vol: 1, ISSN: 2515-7639
We report the development of coplanar green colour organic light-emitting diodes (OLEDs) based on asymmetric nanogap electrodes fabricated on different substrates including glass and plastic. Using adhesion lithography (a-Lith) we pattern Al and Au layers acting as the cathode and anode electrodes, respectively, separated by an inter-electrode distance of <15 nm with an aspect ratio of up to 106. Spin-coating the organic light-emitting polymer poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) on top of the asymmetric Al–Au nanogap electrodes results in green light-emitting nanogap OLEDs with promising operating characteristics. We show that the scaling of the OLED's width from 4 to 200 mm can substantially improve the light output of the device without any adverse effects on the manufacturing yield. Furthermore, it is found that the light-emitting properties in the nanogap area differ from the bulk organic film, an effect attributed to confinement of the conjugated polymer chains in the nanogap channel. These results render a-Lith particularly attractive for low cost facile fabrication of nanoscale light-emitting sources and arrays on different substrates of arbitrary size.
Xu Y, Ji D, Song H, et al., 2018, Light-Matter Interaction within Extreme Dimensions: From Nanomanufacturing to Applications, ADVANCED OPTICAL MATERIALS, Vol: 6, ISSN: 2195-1071
Paterson AF, Singh S, Fallon KJ, et al., 2018, Recent progress in high-mobility organic transistors: a reality check, Advanced Materials, Vol: 30, ISSN: 0935-9648
Over the past three decades, significant research efforts have focused on improving the charge carrier mobility of organic thin‐film transistors (OTFTs). In recent years, a commonly observed nonlinearity in OTFT current–voltage characteristics, known as the “kink” or “double slope,” has led to widespread mobility overestimations, contaminating the relevant literature. Here, published data from the past 30 years is reviewed to uncover the extent of the field‐effect mobility hype and identify the progress that has actually been achieved in the field of OTFTs. Present carrier‐mobility‐related challenges are identified, finding that reliable hole and electron mobility values of 20 and 10 cm2 V−1 s−1, respectively, have yet to be achieved. Based on the analysis, the literature is then reviewed to summarize the concepts behind the success of high‐performance p‐type polymers, along with the latest understanding of the design criteria that will enable further mobility enhancement in n‐type polymers and small molecules, and the reasons why high carrier mobility values have been consistently produced from small molecule/polymer blend semiconductors. Overall, this review brings together important information that aids reliable OTFT data analysis, while providing guidelines for the development of next‐generation organic semiconductors.
Wahyudi W, Cao Z, Kumar P, et al., 2018, Phase Inversion Strategy to Flexible Freestanding Electrode: Critical Coupling of Binders and Electrolytes for High Performance Li-S Battery, ADVANCED FUNCTIONAL MATERIALS, Vol: 28, ISSN: 1616-301X
Heeney MJ, Creamer A, Wood C, et al., 2018, Post-polymerisation functionalisation of conjugated polymer backbones and its application in multi-functional emissive nanoparticles, Nature Communications, Vol: 9, ISSN: 2041-1723
Backbone functionalisation of conjugated polymers is crucial to their performance in many applications, from electronic displays to nanoparticle biosensors, yet there are limited approaches to introduce functionality. To address this challenge we have developed a method for the direct modification of the aromatic backbone of a conjugated polymer, post-polymerisation. This is achieved via a quantitative nucleophilic aromatic substitution (SNAr) reaction on a range of fluorinated electron deficient comonomers. The method allows for facile tuning of the physical and optoelectronic properties within a batch of consistent molecular weight and dispersity. It also enables the introduction of multiple different functional groups onto the polymer backbone in a controlled manner. To demonstrate the versatility of this reaction, we designed and synthesised a range of emissive poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) based polymers for the creation of mono and multifunctional semiconducting polymer nanoparticles (SPNs) capable of two orthogonal bioconjugation reactions on the same surface.
Firdaus Y, Seitkhan A, Eisner F, et al., 2018, Charge Photogeneration and Recombination in Mesostructured CuSCN-Nanowire/PC70BM Solar Cells, SOLAR RRL, Vol: 2, ISSN: 2367-198X
Wijeyasinghe N, Eisner F, Tsetseris L, et al., 2018, p-Doping of Copper(I) Thiocyanate (CuSCN) Hole-Transport Layers for High-Performance Transistors and Organic Solar Cells, ADVANCED FUNCTIONAL MATERIALS, Vol: 28, ISSN: 1616-301X
Eisner F, Seitkhan A, Han Y, et al., 2018, Solution-processed In2O3/ZnO heterojunction electron transport layers for efficient organic bulk heterojunction and inorganic colloidal quantum-dot solar cells, Solar RRL, Vol: 2, ISSN: 2367-198X
We report the development of a solution‐processed In2O3/ZnO heterojunction electron transport layer (ETL) and its application in high efficiency organic bulk‐heterojunction (BHJ) and inorganic colloidal quantum dot (CQD) solar cells. Study of the electrical properties of this low‐dimensional oxide heterostructure via field‐effect measurements reveals that electron transport along the heterointerface is enhanced by more than a tenfold when compared to the individual single‐layer oxides. Use of the heterojunction as the ETL in organic BHJ photovoltaics is found to consistently improve the cell's performance due to the smoothening of the ZnO surface, increased electron mobility and a noticeable reduction in the cathode's work function, leading to a decrease in the cells’ series resistance and a higher fill factor (FF). Specifically, non‐fullerene based organic BHJ solar cells based on In2O3/ZnO ETLs exhibit very high power conversion efficiencies (PCE) of up to 12.8%, and high FFs of over 70%. The bilayer ETL concept is further extended to inorganic lead‐sulphide CQD solar cells. Resulting devices exhibit excellent performance with a maximum PCE of 8.2% and a FF of 56.8%. The present results highlight the potential of multilayer oxides as novel ETL systems and lay the foundation for future developments.
Choi HH, Rodionov YI, Paterson AF, et al., 2018, Accurate Extraction of Charge Carrier Mobility in 4-Probe Field-Effect Transistors, ADVANCED FUNCTIONAL MATERIALS, Vol: 28, ISSN: 1616-301X
Semple J, Georgiadou DG, Wyatt-Moon G, et al., 2018, Large-area plastic nanogap electronics enabled by adhesion lithography, npj Flexible Electronics, Vol: 2, ISSN: 2397-4621
Large-area manufacturing of flexible nanoscale electronics has long been sought by the printed electronics industry. However, the lack of a robust, reliable, high throughput and low-cost technique that is capable of delivering high-performance functional devices has hitherto hindered commercial exploitation. Herein we report on the extensive range of capabilities presented by adhesion lithography (a-Lith), an innovative patterning technique for the fabrication of coplanar nanogap electrodes with arbitrarily large aspect ratio. We use this technique to fabricate a plethora of nanoscale electronic devices based on symmetric and asymmetric coplanar electrodes separated by a nanogap < 15 nm. We show that functional devices including self-aligned-gate transistors, radio frequency diodes and rectifying circuits, multi-colour organic light-emitting nanodiodes and multilevel non-volatile memory devices, can be fabricated in a facile manner with minimum process complexity on a range of substrates. The compatibility of the formed nanogap electrodes with a wide range of solution processable semiconductors and substrate materials renders a-Lith highly attractive for the manufacturing of large-area nanoscale opto/electronics on arbitrary size and shape substrates.
Chaudhry MU, Tetzner K, Lin Y-H, et al., 2018, Low-Voltage Solution-Processed Hybrid Light-Emitting Transistors, ACS APPLIED MATERIALS & INTERFACES, Vol: 10, Pages: 18445-18449, ISSN: 1944-8244
Mottram AD, Pattanasattayavong P, Isakov I, et al., 2018, Electron mobility enhancement in solution-processed low-voltage In2O3 transistorsvia channel interface planarization, AIP ADVANCES, Vol: 8, ISSN: 2158-3226
Squeo BM, Gregoriou VG, Han Y, et al., 2018, alpha,beta-Unsubstituted meso-positioning thienyl BODIPY: a promising electron deficient building block for the development of near infrared (NIR) p-type donor-acceptor (D-A) conjugated polymers, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 6, Pages: 4030-4040, ISSN: 2050-7526
Nam S, Hahm SG, Khim D, et al., 2018, Pronounced Side Chain Effects in Triple Bond-Conjugated Polymers Containing Naphthalene Diimides for n-Channel Organic Field-Effect Transistors, ACS APPLIED MATERIALS & INTERFACES, Vol: 10, Pages: 12921-12929, ISSN: 1944-8244
Sit WY, Eisner FD, Lin YH, et al., 2018, High-efficiency fullerene solar cells enabled by a spontaneously formed mesostructured CuSCN-nanowire heterointerface, Advanced Science, Vol: 5, ISSN: 2198-3844
Fullerenes and their derivatives are widely used as electron acceptors in bulk-heterojunction organic solar cells as they combine high electron mobility with good solubility and miscibility with relevant semiconducting polymers. However, studies on the use of fullerenes as the sole photogeneration and charge-carrier material are scarce. Here, a new type of solution-processed small-molecule solar cell based on the two most commonly used methanofullerenes, namely [6,6]-phenyl-C61-butyric acid methyl ester (PC 60 BM) and [6,6]-phenyl-C71-butyric acid methyl ester (PC 70 BM), as the light absorbing materials, is reported. First, it is shown that both fullerene derivatives exhibit excellent ambipolar charge transport with balanced hole and electron mobilities. When the two derivatives are spin-coated over the wide bandgap p-type semiconductor copper (I) thiocyanate (CuSCN), cells with power conversion efficiency (PCE) of ≈1%, are obtained. Blending the CuSCN with PC 70 BM is shown to increase the performance further yielding cells with an open-circuit voltage of ≈0.93 V and a PCE of 5.4%. Microstructural analysis reveals that the key to this success is the spontaneous formation of a unique mesostructured p-n-like heterointerface between CuSCN and PC 70 BM. The findings pave the way to an exciting new class of single photoactive material based solar cells.
Wijeyasinghe N, Tsetseris L, Regoutz A, et al., 2018, Copper (I) selenocyanate (CuSeCN) as a novel hole-transport layer for transistors, organic solar cells, and light-emitting diodes, Advanced Functional Materials, Vol: 28, ISSN: 1616-301X
The synthesis and characterization of copper (I) selenocyanate (CuSeCN) and its application as a solution-processable hole-transport layer (HTL) material in transistors, organic light-emitting diodes, and solar cells are reported. Density-functional theory calculations combined with X-ray photoelectron spectroscopy are used to elucidate the electronic band structure, density of states, and microstructure of CuSeCN. Solution-processed layers are found to be nanocrystalline and optically transparent ( > 94%), due to the large bandgap of ≥3.1 eV, with a valence band maximum located at -5.1 eV. Hole-transport analysis performed using field-effect measurements confirms the p-type character of CuSeCN yielding a hole mobility of 0.002 cm 2 V -1 s -1 . When CuSeCN is incorporated as the HTL material in organic light-emitting diodes and organic solar cells, the resulting devices exhibit comparable or improved performance to control devices based on commercially available poly(3,4-ethylenedioxythiophene):polystyrene sulfonate as the HTL. This is the first report on the semiconducting character of CuSeCN and it highlights the tremendous potential for further developments in the area of metal pseudohalides.
Fei Z, Eisner FD, Jiao X, et al., 2018, Correction: An alkylated indacenodithieno[3,2-b] thiophene-based nonfullerene acceptor with high crystallinity exhibiting single junction solar cell efficiencies greater than 13% with low voltage losses (vol 30, 2018), Advanced Materials, Vol: 30, ISSN: 0935-9648
Huang W, Lin Y-H, Anthopoulos TD, 2018, High Speed Ultraviolet Phototransistors Based on an Ambipolar Fullerene Derivative, ACS APPLIED MATERIALS & INTERFACES, Vol: 10, Pages: 10202-10210, ISSN: 1944-8244
Lu R, Han Y, Zhang W, et al., 2018, Alkylated indacenodithieno[3,2-b] thiophene-based all donor ladder-type conjugated polymers for organic thin film transistors, Journal of Materials Chemistry C, Vol: 6, Pages: 2004-2009, ISSN: 2050-7534
We report the synthesis of a series of indacenodithieno[3,2-b]thiophene (IDTT) based conjugated polymers by copolymerization with three different electron rich co-monomers [thiophene (T), thieno[3,2-b] thiophene (TT) and dithieno[3,2-b:2′,3′-d]thiophene (DTT)] under Stille coupling conditions. The resulting all-donor polymers show very good solubility in common solvents and exhibit similar optical, thermal and electronic properties. However, the performance of these semiconductors in thin film transistor devices varied and was highly dependent on the nature of the co-monomer. All polymers exhibited unipolar p-type charge transport behaviour, with the mobility values following the trend of IDTT-TT > IDTT-DTT > IDTT-T. The peak saturation mobility value of IDTT-TT was extracted to be 1.1 cm 2 V -1 s -1 , amongst the highest mobility for all-donor conjugated polymers reported to date.
Fei Z, Eisner FD, Jiao X, et al., 2018, An alkylated indacenodithieno[3,2-b]thiophene-based nonfullerene acceptor with high crystallinity exhibiting single junction solar cell efficiencies greater than 13% with low voltage losses, Advanced Materials, Vol: 30, ISSN: 0935-9648
A new synthetic route, to prepare an alkylated indacenodithieno[3,2-b]thiophene-based nonfullerene acceptor (C8-ITIC), is reported. Compared to the reported ITIC with phenylalkyl side chains, the new acceptor C8-ITIC exhibits a reduction in the optical band gap, higher absorptivity, and an increased propensity to crystallize. Accordingly, blends with the donor polymer PBDB-T exhibit a power conversion efficiency (PCE) up to 12.4%. Further improvements in efficiency are found upon backbone fluorination of the donor polymer to afford the novel material PFBDB-T. The resulting blend with C8-ITIC shows an impressive PCE up to 13.2% as a result of the higher open-circuit voltage. Electroluminescence studies demonstrate that backbone fluorination reduces the energy loss of the blends, with PFBDB-T/C8-ITIC-based cells exhibiting a small energy loss of 0.6 eV combined with a high JSCof 19.6 mA cm-2.
Lin Y-H, Pattanasattayavong P, Anthopoulos TD, 2017, Metal-Halide Perovskite Transistors for Printed Electronics: Challenges and Opportunities, ADVANCED MATERIALS, Vol: 29, ISSN: 0935-9648
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