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Journal articlePaterson AF, Faber H, Savva A, et al., 2019,
On the Role of Contact Resistance and Electrode Modification in Organic Electrochemical Transistors.
, Adv Mater, Pages: e1902291-e1902291Contact resistance is renowned for its unfavorable impact on transistor performance. Despite its notoriety, the nature of contact resistance in organic electrochemical transistors (OECTs) remains unclear. Here, by investigating the role of contact resistance in n-type OECTs, the first demonstration of source/drain-electrode surface modification for achieving state-of-the-art n-type OECTs is reported. Specifically, thiol-based self-assembled monolayers (SAMs), 4-methylbenzenethiol (MBT) and pentafluorobenzenethiol (PFBT), are used to investigate contact resistance in n-type accumulation-mode OECTs made from the hydrophilic copolymer P-90, where the deliberate functionalization of the gold source/drain electrodes decreases and increases the energetic mismatch at the electrode/semiconductor interface, respectively. Although MBT treatment is found to increase the transconductance three-fold, contact resistance is not found to be the dominant factor governing OECT performance. Additional morphology and surface energy investigations show that increased performance comes from SAM-enhanced source/drain electrode surface energy, which improves wetting, semiconductor/metal interface quality, and semiconductor morphology at the electrode and channel. Overall, contact resistance in n-type OECTs is investigated, whilst identifying source/drain electrode treatment as a useful device engineering strategy for achieving state of the art n-type OECTs.
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Journal articleBristow H, Thorley KJ, White AJP, et al., 2019,
Impact of Nonfullerene Acceptor Side Chain Variation on Transistor Mobility
, ADVANCED ELECTRONIC MATERIALS, ISSN: 2199-160X -
Journal articleCha H, Fish G, Luke J, et al., 2019,
Suppression of Recombination Losses in Polymer:Nonfullerene Acceptor Organic Solar Cells due to Aggregation Dependence of Acceptor Electron Affinity
, ADVANCED ENERGY MATERIALS, Vol: 9, ISSN: 1614-6832 -
Conference paperKhan J, Ugur E, Aydin E, et al., 2019,
Probing Carrier Extraction from Lead Halide Perovskite to Polymeric Charge Transport Layers by Ultrafast Transient Absorption Spectroscopy
, nanoGe Fall Meeting 2019, Publisher: Fundació Scito -
Journal articleWang S-J, Venkateshvaran D, Mahani MR, et al., 2019,
Long spin diffusion lengths in doped conjugated polymers due to enhanced exchange coupling (vol 2, pg 98, 2019)
, NATURE ELECTRONICS, Vol: 2, Pages: 313-313, ISSN: 2520-1131 -
Journal articleMcCulloch I, 2019,
New synthetic methodology paves the way to prepare electron deficient semiconducting mesopolymers with very high performance
, SCIENCE CHINA-CHEMISTRY, Vol: 62, Pages: 885-886, ISSN: 1674-7291 -
Journal articleThomas TH, Harkin DJ, Gillett AJ, et al., 2019,
Short contacts between chains enhancing luminescence quantum yields and carrier mobilities in conjugated copolymers
, NATURE COMMUNICATIONS, Vol: 10, ISSN: 2041-1723- Author Web Link
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- Citations: 49
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Journal articleWadsworth A, Bristow H, Hamid Z, et al., 2019,
End Group Tuning in Acceptor–Donor–Acceptor Nonfullerene Small Molecules for High Fill Factor Organic Solar Cells
, Advanced Functional Materials, Pages: 1808429-1808429, ISSN: 1616-301X -
Journal articleHu H, Deng W, Qin M, et al., 2019,
Charge carrier transport and nanomorphology control for efficient non-fullerene organic solar cells
, Materials Today Energy, Vol: 12, Pages: 398-407, ISSN: 2468-6069 -
Journal articleGhasemi M, Hu H, Peng Z, et al., 2019,
Delineation of Thermodynamic and Kinetic Factors that Control Stability in Non-fullerene Organic Solar Cells
, JOULE, Vol: 3, Pages: 1328-1348, ISSN: 2542-4351 -
Journal articleMoser M, Thorley KJ, Moruzzi F, et al., 2019,
Highly selective chromoionophores for ratiometric Na+ sensing based on an oligoethyleneglycol bridged bithiophene detection unit
, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 7, Pages: 5359-5365, ISSN: 2050-7526 -
Journal articleNikolka M, Broch K, Armitage J, et al., 2019,
High-mobility, trap-free charge transport in conjugated polymer diodes
, Nature Communications, Vol: 10, ISSN: 2041-1723Charge transport in conjugated polymer semiconductors has traditionally been thought to be limited to a low-mobility regime by pronounced energetic disorder. Much progress has recently been made in advancing carrier mobilities in field-effect transistors through developing low-disorder conjugated polymers. However, in diodes these polymers have to date not shown much improved mobilities, presumably reflecting the fact that in diodes lower carrier concentrations are available to fill up residual tail states in the density of states. Here, we show that the bulk charge transport in low-disorder polymers is limited by water-induced trap states and that their concentration can be dramatically reduced through incorporating small molecular additives into the polymer film. Upon incorporation of the additives we achieve space-charge limited current characteristics that resemble molecular single crystals such as rubrene with high, trap-free SCLC mobilities up to 0.2 cm2/Vs and a width of the residual tail state distribution comparable to kBT.
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Journal articleBabics M, Duan T, Balawi AH, et al., 2019,
Negligible Energy Loss During Charge Generation in Small-Molecule/Fullerene Bulk-Heterojunction Solar Cells Leads to Open-Circuit Voltage over 1.10 V
, ACS APPLIED ENERGY MATERIALS, Vol: 2, Pages: 2717-2722, ISSN: 2574-0962 -
Journal articleLuke J, Speller EM, Wadsworth A, et al., 2019,
Twist and degrade – Impact of molecular structure on the photostability of non-fullerene acceptors and their photovoltaic blends
, Advanced Energy Materials, Vol: 9, Pages: 1-14, ISSN: 1614-6832Non-fullerene acceptors (NFAs) dominate organic photovoltaic (OPV) research due to their promising efficiencies and stabilities. However, there is very little investigation into the molecular processes of degradation, which is critical to guiding design of novel NFAs for long-lived, commercially viable OPVs. Here we investigate the important role of molecular structure and conformation on NFA photostability in air by comparing structurally similar but conformationally different promising NFAs; planar O-IDTBR and non-planar O-IDFBR. We identify a three-phase degradation process: (i) initial photo-induced conformational change (i.e. torsion about the Core-BT dihedral), induced by non-covalent interactions with environmental molecules, (ii) followed by photo-oxidation and fragmentation, leading to chromophore bleaching and degradation product formation, and (iii) finally complete chromophore bleaching.Initial conformational change is a critical prerequisite for further degradation, providing fundamental understanding of the relative stability of IDTBR and IDFBR, where the alreadytwisted IDFBR is more prone to degradation. When blended with the donor polymer P3HT, both NFAs exhibit improved photostability whilst the photostability of the polymer itself is significantly reduced by the more miscible twisted NFA. Our findings elucidate the important role of NFA molecular structure on photostability of OPV systems, and provide vital insights into molecular design rules for intrinsically photostable NFAs.
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Journal articleSpeller EM, Clarke AJ, Aristidou N, et al., 2019,
Toward improved environmental stability of polymer:fullerene and polymer:non-fullerene organic solar cells: a common energetic origin of light and oxygen induced degradation
, ACS Energy Letters, Vol: 4, Pages: 846-852, ISSN: 2380-8195With the emergence of nonfullerene electron acceptors resulting in further breakthroughs in the performance of organic solar cells, there is now an urgent need to understand their degradation mechanisms in order to improve their intrinsic stability through better material design. In this study, we present quantitative evidence for a common root cause of light-induced degradation of polymer:nonfullerene and polymer:fullerene organic solar cells in air, namely, a fast photo-oxidation process of the photoactive materials mediated by the formation of superoxide radical ions, whose yield is found to be strongly controlled by the lowest unoccupied molecular orbital (LUMO) levels of the electron acceptors used. Our results elucidate the general relevance of this degradation mechanism to both polymer:fullerene and polymer:nonfullerene blends and highlight the necessity of designing electron acceptor materials with sufficient electron affinities to overcome this challenge, thereby paving the way toward achieving long-term solar cell stability with minimal device encapsulation.
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