Imperial College London

ProfessorIainMcCulloch

Faculty of Natural SciencesDepartment of Chemistry

Chair in Polymer Materials
 
 
 
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Contact

 

+44 (0)20 7594 5669i.mcculloch

 
 
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Location

 

RCS 1 M229ChemistrySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

417 results found

Lin Y, Adilbekova B, Firdaus Y, Yengel E, Faber H, Sajjad M, Zheng X, Yarali E, Seitkhan A, Bakr OM, El-Labban A, Schwingenschlogl U, Tung V, McCulloch I, Laquai F, Anthopoulos TDet al., 2019, 17% Efficient Organic Solar Cells Based on Liquid Exfoliated WS2 as a Replacement for PEDOT:PSS, ADVANCED MATERIALS, ISSN: 0935-9648

Journal article

Seitkhan A, Neophytou M, Kirkus M, Abou-Hamad E, Hedhili MN, Yengel E, Firdaus Y, Faber H, Lin Y, Tsetseris L, McCulloch I, Anthopoulos TDet al., 2019, Use of the Phen-NaDPO:Sn(SCN)(2) Blend as Electron Transport Layer Results to Consistent Efficiency Improvements in Organic and Hybrid Perovskite Solar Cells, ADVANCED FUNCTIONAL MATERIALS, ISSN: 1616-301X

Journal article

Zheng Y, Wang G-JN, Kang J, Nikolka M, Wu H-C, Tran H, Zhang S, Yan H, Chen H, Yuen PY, Mun J, Dauskardt RH, McCulloch I, Tok JB-H, Gu X, Bao Zet al., 2019, An Intrinsically Stretchable High-Performance Polymer Semiconductor with Low Crystallinity, ADVANCED FUNCTIONAL MATERIALS, ISSN: 1616-301X

Journal article

Liao H, Xiao C, Ravva MK, Yao L, Yu Y, Yang Y, Zhang W, Zhang L, Li Z, McCulloch I, Yue Wet al., 2019, Fused Pyrazine- and Carbazole-Containing Azaacenes: Synthesis and Properties, CHEMPLUSCHEM, ISSN: 2192-6506

Journal article

Wustoni S, Combe C, Ohayon D, Akhtar MH, McCulloch I, Inal Set al., 2019, Membrane-Free Detection of Metal Cations with an Organic Electrochemical Transistor, ADVANCED FUNCTIONAL MATERIALS, ISSN: 1616-301X

Journal article

Khan JI, Ashraf RS, Alamoudi MA, Nabi MN, Mohammed HN, Wadsworth A, Firdaus Y, Zhang W, Anthopoulos TD, McCulloch I, Laquai Fet al., 2019, P3HT Molecular Weight Determines the Performance of P3HT:O-IDTBR Solar Cells, SOLAR RRL, Vol: 3, ISSN: 2367-198X

Journal article

Savva A, Ohayon D, Surgailis J, Paterson AF, Hidalgo TC, Chen X, Maria IP, Paulsen BD, Petty AJ, Rivnay J, McCulloch I, Inal Set al., 2019, Solvent Engineering for High-Performance n-Type Organic Electrochemical Transistors, ADVANCED ELECTRONIC MATERIALS, Vol: 5, ISSN: 2199-160X

Journal article

Schott S, Chopra U, Lemaur V, Melnyk A, Olivier Y, Di Pietro R, Romanov I, Carey RL, Jiao X, Jellett C, Little M, Marks A, McNeill CR, McCulloch I, McNellis ER, Andrienko D, Beljonne D, Sinova J, Sirringhaus Het al., 2019, Polaron spin dynamics in high-mobility polymeric semiconductors, NATURE PHYSICS, Vol: 15, Pages: 814-+, ISSN: 1745-2473

Journal article

Paterson AF, Faber H, Savva A, Nikiforidis G, Gedda M, Hidalgo TC, Chen X, McCulloch I, Anthopoulos TD, Inal Set al., On the Role of Contact Resistance and Electrode Modification in Organic Electrochemical Transistors., Adv Mater, Pages: e1902291-e1902291

Contact 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.

Journal article

Bristow H, Thorley KJ, White AJP, Wadsworth A, Babics M, Hamid Z, Zhang W, Paterson AF, Kosco J, Panidi J, Anthopoulos TD, McCulloch Iet al., Impact of Nonfullerene Acceptor Side Chain Variation on Transistor Mobility, ADVANCED ELECTRONIC MATERIALS, ISSN: 2199-160X

Journal article

Cha H, Fish G, Luke J, Alraddadi A, Lee HH, Zhang W, Dong Y, Limbu S, Wadsworth A, Maria IP, Francas L, Sou HL, Du T, Kim J-S, McLachlan MA, McCulloch I, Durrant JRet 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

Journal article

Wang S-J, Venkateshvaran D, Mahani MR, Chopra U, McNellis ER, Di Pietro R, Schott S, Wittmann A, Schweicher G, Cubukcu M, Kang K, Carey R, Wagner TJ, Siebrecht JNM, Wong DPGH, Jacobs IE, Aboljadayel RO, Ionescu A, Egorov SA, Mueller S, Zadvorna O, Skalski P, Jellett C, Little M, Marks A, McCulloch I, Wunderlich J, Sinova J, Sirringhaus Het 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 article

McCulloch 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 article

Thomas TH, Harkin DJ, Gillett AJ, Lemaur V, Nikolka M, Sadhanala A, Richter JM, Armitage J, Chen H, McCulloch I, Menke SM, Olivier Y, Beljonne D, Sirringhaus Het al., 2019, Short contacts between chains enhancing luminescence quantum yields and carrier mobilities in conjugated copolymers, NATURE COMMUNICATIONS, Vol: 10, ISSN: 2041-1723

Journal article

Wadsworth A, Bristow H, Hamid Z, Babics M, Gasparini N, Boyle CW, Zhang W, Dong Y, Thorley KJ, Neophytou M, Ashraf RS, Durrant JR, Baran D, McCulloch Iet al., 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 article

Hu H, Deng W, Qin M, Yin H, Lau T-K, Fong PWK, Ren Z, Liang Q, Cui L, Wu H, Lu X, Zhang W, McCulloch I, Li Get 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 article

Ghasemi M, Hu H, Peng Z, Rech JJ, Angunawela I, Carpenter JH, Stuard SJ, Wadsworth A, McCulloch I, You W, Ade Het 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 article

Moser M, Thorley KJ, Moruzzi F, Ponder JF, Maria IP, Giovannitti A, Inal S, McCulloch Iet 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 article

Nikolka M, Broch K, Armitage J, Hanifi D, Nowack PJ, Venkateshvaran D, Sadhanala A, Saska J, Mascal M, Jung S-H, Lee J-K, McCulloch I, Salleo A, Sirringhaus Het al., 2019, High-mobility, trap-free charge transport in conjugated polymer diodes, Nature Communications, Vol: 10, ISSN: 2041-1723

Charge 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.

Journal article

Babics M, Duan T, Balawi AH, Liang R-Z, Cruciani F, Carja I-D, Gottlieb D, McCulloch I, Vandewal K, Laquai F, Beaujuge PMet 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 article

Luke J, Speller EM, Wadsworth A, Wyatt MF, Dmiitrov S, Lee HKH, Li Z, Tsoi WC, McCulloch I, Bagnis D, Durrant JR, Kim J-Set 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: 1614-6832

Non-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.

Journal article

Speller EM, Clarke AJ, Aristidou N, Wyatt MF, Francàs L, Fish G, Cha H, Lee HKH, Luke J, Wadsworth A, Evans AD, McCulloch I, Kim JS, Haque SA, Durrant JR, Dimitrov SD, Tsoi WC, Li Zet 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: 2380-8195

With 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.

Journal article

Dimitrov SD, Azzouzi M, Wu J, Yao J, Dong Y, Tuladhar PS, Schroeder BC, Bittner ER, McCulloch I, Nelson J, Durrant JRet al., 2019, Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends., J Am Chem Soc, Vol: 141, Pages: 4634-4643

Despite performance improvements of organic photovoltaics, the mechanism of photoinduced electron-hole separation at organic donor-acceptor interfaces remains poorly understood. Inconclusive experimental and theoretical results have produced contradictory models for electron-hole separation in which the role of interfacial charge-transfer (CT) states is unclear, with one model identifying them as limiting separation and another as readily dissociating. Here, polymer-fullerene blends with contrasting photocurrent properties and enthalpic offsets driving separation were studied. By modifying composition, film structures were varied from consisting of molecularly mixed polymer-fullerene domains to consisting of both molecularly mixed and fullerene domains. Transient absorption spectroscopy revealed that CT state dissociation generating separated electron-hole pairs is only efficient in the high energy offset blend with fullerene domains. In all other blends (with low offset or predominantly molecularly mixed domains), nanosecond geminate electron-hole recombination is observed revealing the importance of spatially localized electron-hole pairs (bound CT states) in the electron-hole dynamics. A two-dimensional lattice exciton model was used to simulate the excited state spectrum of a model system as a function of microstructure and energy offset. The results could reproduce the main features of experimental electroluminescence spectra indicating that electron-hole pairs become less bound and more spatially separated upon increasing energy offset and fullerene domain density. Differences between electroluminescence and photoluminescence spectra could be explained by CT photoluminescence being dominated by more-bound states, reflecting geminate recombination processes, while CT electroluminescence preferentially probes less-bound CT states that escape geminate recombination. These results suggest that apparently contradictory studies on electron-hole separation can be exp

Journal article

Wadsworth A, Moser M, Marks A, Little M, Gasparini N, Brabec C, Baran D, McCulloch Iet al., 2019, Critical review of the molecular design progress in non-fullerene electron acceptors towards commercially viable organic solar cells, Chemical Society Reviews, Vol: 48, Pages: 1596-1625, ISSN: 1460-4744

Fullerenes have formed an integral part of high performance organic solar cells over the last 20 years, however their inherent limitations in terms of synthetic flexibility, cost and stability have acted as a motivation to develop replacements; the so-called non-fullerene electron acceptors. A rapid evolution of such materials has taken place over the last few years, yielding a number of promising candidates that can exceed the device performance of fullerenes and provide opportunities to improve upon the stability and processability of organic solar cells. In this review we explore the structure–property relationships of a library of non-fullerene acceptors, highlighting the important chemical modifications that have led to progress in the field and provide an outlook for future innovations in electron acceptors for use in organic photovoltaics.

Journal article

Wang SJ, Venkateshvaran D, Mahani MR, Chopra U, McNellis ER, Di Pietro R, Schott S, Wittmann A, Schweicher G, Cubukcu M, Kang K, Carey R, Wagner TJ, Siebrecht JNM, Wong DPGH, Jacobs IE, Aboljadayel RO, Ionescu A, Egorov SA, Mueller S, Zadvorna O, Skalski P, Jellett C, Little M, Marks A, McCulloch I, Wunderlich J, Sinova J, Sirringhaus Het al., 2019, Long spin diffusion lengths in doped conjugated polymers due to enhanced exchange coupling, Nature Electronics, Vol: 2, Pages: 98-107

© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Carbon-based semiconductors such as conjugated organic polymers are of potential use in the development of spintronic devices and spin-based information processing. In particular, these materials offer a low spin–orbit coupling strength due to their relatively light constituent chemical elements, which should, in principle, favour long spin diffusion lengths. However, organic polymers are relatively disordered materials and typically have a carrier mobility that is orders of magnitude lower than crystalline inorganic materials. As a result, small spin diffusion lengths of around 50 nm have typically been measured using vertical organic spin valves. Here, we report measuring spin diffusion lengths in doped conjugated polymers using a lateral spin transport device architecture, which is based on spin pumping injection and inverse spin Hall detection. The approach suggests that long spin diffusion lengths of more than 1 μm and fast spin transit times of around 10 ns are possible in conjugated polymer systems when they have a sufficiently high spin density (around 10 20 cm −3 ). We explain these results in terms of an exchange-based spin diffusion regime in which the exchange interactions decouple spin and charge transport.

Journal article

Moia D, Giovannitti A, Szumska AA, Maria IP, Rezasoltani E, Sachs M, Schnurr M, Barnes PRF, McCulloch I, Nelson Jet al., Design and evaluation of conjugated polymers with polar side chains as electrode materials for electrochemical energy storage in aqueous electrolytes, Energy & Environmental Science, ISSN: 1754-5692

<p>Solution processable p-type and n-type conjugated polymers with polar side chains enable fast charging in aqueous electrolytes and 1.4 V cell voltage.</p>

Journal article

Tan CH, Wadsworth A, Gasparini N, Wheeler S, Holliday S, Ashraf RS, Dimitrov SD, Baran D, McCulloch I, Durrant JRet al., 2019, Excitation Wavelength-Dependent Internal Quantum Efficiencies in a P3HT/Nonfullerene Acceptor Solar Cell, Journal of Physical Chemistry C, Vol: 123, Pages: 5826-5832, ISSN: 1932-7447

© 2018 American Chemical Society. Solar cells based on blends of the donor polymer, P3HT, with the nonfullerene acceptor, O-IDTBR, have been shown to exhibit promising efficiencies and stabilities for low-cost organic photovoltaic devices. We focus herein on the charge separation and recombination dynamics in such devices. By employing selective wavelength excitations of P3HT and O-IDTBR, we show that photoexcitation of P3HT results in lower internal quantum efficiency (IQE) for photocurrent generation than that observed for photoexcitation of O-IDTBR. Transient absorption and photoluminescence quenching studies indicate that this lower IQE results primarily from higher geminate recombination losses of photogenerated charges following P3HT excitation compared with O-IDTBR excitation, rather than from differences in exciton separation efficiency. These higher geminate recombination losses result in lower photocurrent generation efficiency at short circuit upon selective excitation of the P3HT donor, when compared with O-IDTBR excitation.

Journal article

Thiburce Q, Giovannitti A, McCulloch I, Campbell AJet al., 2019, Nanoscale ion-doped polymer transistors, Nano Letters, Vol: 19, Pages: 1712-1718, ISSN: 1530-6984

Organic transistors with submicron dimensions have been shown to deviate from the expected behaviour due to a variety of so-called 'short-channel' effects, resulting in nonlinear output characteristics and a lack of current saturation, considerably limiting their use. Here, using an electrochemically-doped polymer in which ions are dynamically injected and removed from the bulk of the semiconductor, we show that devices with nanoscale channel lengths, down to 50 nm, exhibit output curves with well-defined linear and saturation regimes. Additionally, they show very large on-currents on par with their microscale counterparts, large on-to-off ratios of 108, and record-high width-normalised transconductances above 10 S m-1. We believe this work paves the way for the fabrication of high-gain, high-current polymer integrated circuits such as sensor arrays operating at voltages below |1 V| and prepared using simple solution processing methods.

Journal article

Dong Y, Cha H, Zhang J, Pastor E, Tuladhar PS, McCulloch I, Durrant JR, Bakulin AAet al., 2019, The binding energy and dynamics of charge-transfer states in organic photovoltaics with low driving force for charge separation, Journal of Chemical Physics, Vol: 150, ISSN: 0021-9606

Recent progress in organic photovoltaics (OPVs) has been enabled by optimization of the energetic driving force for charge separation, and thus maximization of open-circuit voltage, using non-fullerene acceptor (NFA) materials. In spite of this, the carrier dynamics and relative energies of the key states controlling the photophysics of these systems are still under debate. Herein, we report an in-depth ultrafast spectroscopic study of a representative OPV system based on a polymer donor PffBT4T-2OD and a small-molecule NFA EH-IDTBR. Global analysis of the transient absorption data reveals efficient energy transfer between donor and acceptor molecules. The extracted kinetics suggest that slow (∼15 ps) generation of charge carriers is followed by significant geminate recombination. This contrasts with the "reference" PffBT4T-2OD:PC71BM system where bimolecular recombination dominates. Using temperature-dependent pump-push-photocurrent spectroscopy, we estimate the activation energy for the dissociation of bound charge-transfer states in PffBT4T-2OD:EH-IDTBR to be 100 ± 6 meV. We also observe an additional activation energy of 14 ± 7 meV, which we assign to the de-trapping of mobile carriers. This work provides a comprehensive picture of photophysics in a system representing new generation of OPV blends with a small driving force for charge separation.

Journal article

Gasparini N, Salleo A, McCulloch I, Baran Det al., 2019, The role of the third component in ternary organic solar cells, Nature Reviews Materials

© 2019, Springer Nature Limited. Ternary organic solar cells (TSCs) contain a single three-component photoactive layer with a wide absorption window, which is obtained without the need for multiple stacks. Subsequently, TSCs have attracted great interest in the photovoltaics field. Through careful selection of the three (or more) active components that form the photoactive layer, all photovoltaic parameters can be simultaneously enhanced within a TSC — a strategy that has resulted in record efficiencies for single-junction solar cells. In this Review, we outline key developments in TSCs, with a focus on the central role of the third component in achieving record efficiencies. We analyse the effects of the third component on the nanomorphology of the bulk heterojunction and the photovoltaic parameters of TSCs. Moreover, we discuss the charge-transfer and/or energy-transfer mechanisms and nanomorphology models that govern the operation of TSCs. We consider both polymer and small-molecule donors as well as fullerenes and recently developed non-fullerene acceptors. In addition, we summarize the recent success of TSCs in mitigating the stability issues of binary solar cells. Finally, we provide a perspective on the advantages of ternary blends and suggest design strategies for highly efficient and stable devices for commercial photovoltaics.

Journal article

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