Imperial College London

ProfessorMartinHeeney

Faculty of Natural SciencesDepartment of Chemistry

Professor of Organic Materials
 
 
 
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Contact

 

+44 (0)20 7594 1248m.heeney Website

 
 
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Location

 

401GMolecular Sciences Research HubWhite City Campus

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Summary

 

Publications

Publication Type
Year
to

320 results found

Marsh AV, Dyson MJ, Cheetham NJ, Bidwell M, Little M, White AJP, Warriner CN, Swain AC, McCulloch I, Stavrinou PN, Meskers SCJ, Heeney Met al., Correlating the Structural and Photophysical Properties of Ortho , Meta , and Para ‐Carboranyl–Anthracene Dyads, Advanced Electronic Materials, Pages: 2000312-2000312, ISSN: 2199-160X

Journal article

Meindl B, Pfennigbauer K, Stöger B, Heeney M, Glöcklhofer Fet al., 2020, Double ring-closing approach for the synthesis of 2,3,6,7-substituted anthracene derivatives., Journal of Organic Chemistry, Vol: 85, Pages: 8240-8244, ISSN: 0022-3263

A method for the synthesis of 2,3,6,7-substituted anthracene derivatives, one of the most challenging anthracene substitution patterns to obtain, is presented. The method is exemplified by the preparation of 2,3,6,7-anthracenetetracarbonitrile and employs a newly developed, stable, protected 1,2,4,5-benzenetetracarbaldehyde as the precursor. The precursor can be obtained in two scalable synthetic steps from 2,5-dibromoterephthalaldehyde and is converted into the anthracene derivative by a double intermolecular Wittig reaction under very mild conditions, followed by a deprotection and intramolecular double ring-closing condensation reaction.

Journal article

Cong S, Creamer A, Fei Z, Hillman SAJ, Rapley C, Nelson J, Heeney Met al., 2020, Tunable Control of the Hydrophilicity and Wettability of Conjugated Polymers by a Postpolymerization Modification Approach., Macromol Biosci

A facile method to prepare hydrophilic polymers by a postpolymerization nucleophillic aromatic substitution reaction of fluoride on an emissive conjugated polymer (CP) backbone is reported. Quantitative functionalization by a series of monofunctionalized ethylene glycol oligomers, from dimer to hexamer, as well as with high molecular weight polyethylene glycol is demonstrated. The length of the ethylene glycol sidechains is shown to have a direct impact on the surface wettability of the polymer, as well as its solubility in polar solvents. However, the energetics and band gap of the CPs remain essentially constant. This method therefore allows an easy way to modulate the wettability and solubility of CP materials for a diverse series of applications.

Journal article

Lin Y-H, Huang W, Pattanasattayavong P, Lim J, Li R, Sakai N, Panidi J, Hong MJ, Ma C, Wei N, Wehbe N, Fei Z, Heeney M, Labram JG, Anthopoulos TD, Snaith HJet al., 2020, Publisher Correction: Deciphering photocarrier dynamics for tuneable high-performance perovskite-organic semiconductor heterojunction phototransistors., Nat Commun, Vol: 11

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Journal article

Eder S, Yoo D, Nogala W, Pletzer M, Santana Bonilla A, White AJP, Jelfs KE, Heeney M, Choi JW, Glöcklhofer Fet al., Switching between Local and Global Aromaticity in a Conjugated Macrocycle for High‐Performance Organic Sodium‐Ion Battery Anodes, Angewandte Chemie, ISSN: 0044-8249

Journal article

Eder S, Yoo D-J, Nogala W, Pletzer M, Santana Bonilla A, White AJP, Jelfs KE, Heeney M, Choi JW, Glöcklhofer Fet al., 2020, Switching between local and global aromaticity in a conjugated macrocycle for high-performance organic sodium-ion battery anodes., Angewandte Chemie International Edition, ISSN: 1433-7851

Aromatic organic compounds can be used as electrode materials in rechargeable batteries and are expected to advance the development of both anode and cathode materials for sodium-ion batteries (SIBs). However, most aromatic organic compounds assessed as anode materials in SIBs to date exhibit significant degradation issues under fast-charge/discharge conditions and unsatisfying long-term cycling performance. Now, a molecular design concept is presented for improving the stability of organic compounds for battery electrodes. The molecular design of the investigated compound, [2.2.2.2]paracyclophane-1,9,17,25-tetraene (PCT), can stabilize the neutral state by local aromaticity and the doubly reduced state by global aromaticity, resulting in an anode material with extraordinarily stable cycling performance and outstanding performance under fast-charge/discharge conditions, demonstrating an exciting new path for the development of electrode materials for SIBs and other types of batteries.

Journal article

Hodsden T, Thorley KJ, Panidi J, Basu A, Marsh AV, Dai H, White AJP, Wang C, Mitchell W, Glöcklhofer F, Anthopoulos TD, Heeney Met al., 2020, Core fluorination enhances solubility and ambient stability of an IDT‐based n‐type semiconductor in transistor devices, Advanced Functional Materials, Vol: 30, Pages: 1-12, ISSN: 1616-301X

The synthesis of a novel fluorinated n‐type small molecule based on an indacenodithiophene core is reported. Fluorination is found to have a significant impact on the physical properties, including a surprisingly dramatic improvement in solubility, in addition to effectively stabilizing the lowest‐unoccupied molecular orbital energy (−4.24 eV). Single‐crystal analysis and density functional theory calculations indicate the improved solubility can be attributed to backbone torsion resulting from the positioning of the fluorine group in close proximity to the strongly electron‐withdrawing dicyanomethylene group. Organic thin‐film transistors made via blade coating display high electron mobility (up to 0.49 cm2 V−1 s−1) along with good retention of performance in ambient conditions.

Journal article

He Q, Shahid M, Jiao X, Gann E, Eisner F, Wu T, Fei Z, Anthopoulos TD, McNeill CR, Heeney MJet al., 2020, The crucial role of fluorine in fully alkylated ladder type carbazole based non-fullerene organic solar cells, ACS Applied Materials and Interfaces, Vol: 12, Pages: 9555-9562, ISSN: 1944-8244

Two fused ladder type non-fullerene acceptors, DTCCIC and DTCCIC-4F, based on an electron-donating alkylated dithienocyclopentacarbazole core flanked by electron-withdrawing non-fluorinated or fluorinated 1,1-dicyanomethylene-3-indanone (IC or IC-4F), are prepared and utilized in organic solar cells (OSCs). The two new molecules reveal planar structures and strong aggregation behavior, and fluorination is shown to red shift the optical band gap and down shift energy levels. OSCs based on DTCCIC-4F exhibit a power conversion efficiency of 12.6 %, much higher than that of DTCCIC based devices (6.2 %). Microstructural studies reveal that while both acceptors are highly crystalline, bulk heterojunction blends based on the non-fluorinated DTCCIC result in overly coarse domains, while blends based on the fluorinated DTCCIC-4F exhibit a more optimal nanoscale morphology. These results highlight the importance of end group fluorination in controlling molecular aggregation and miscibility.

Journal article

Firdaus Y, He Q, Lin Y, Nugroho FAA, Le Corre VM, Yengel E, Balawi AH, Seitkhan A, Laquai F, Langhammer C, Liu F, Heeney M, Anthopoulos TDet al., 2020, Novel wide-bandgap non-fullerene acceptors for efficient tandem organic solar cells, 10th International Conference on Materials for Advanced Technologies (ICMAT) / Symposium P on Advanced Inorganic Materials and Thin Film Technology for Solar Energy Harvesting and Electronic Application, Publisher: ROYAL SOC CHEMISTRY, Pages: 1164-1175, ISSN: 2050-7488

Conference paper

Leventis A, Chmovzh TN, Knyazeva EA, Han Y, Heeney M, Rakitin OA, Bronstein Het al., 2020, A novel low-bandgap pyridazine thiadiazole-based conjugated polymer with deep molecular orbital levels, POLYMER CHEMISTRY, Vol: 11, Pages: 581-585, ISSN: 1759-9954

Journal article

Chaudhry MU, Panidi J, Nam S, Smith A, Lim J, Tetzner K, Patsalas PA, Vourlias G, Sit W-Y, Firdaus Y, Heeney M, Bradley DDC, Anthopoulos TDet al., 2019, Polymer Light-Emitting Transistors With Charge-Carrier Mobilities Exceeding 1 cm(2) V-1 s(-1), ADVANCED ELECTRONIC MATERIALS, Vol: 6, ISSN: 2199-160X

Journal article

Wu J, Luke J, Lee HKH, Tuladhar PS, Cha H, Jang S-Y, Tsoi WC, Heeney M, Kang H, Lee K, Kirchartz T, Kim J-S, Durrant JRet al., 2019, Tail state limited photocurrent collection of thick photoactive layers in organic solar cells, Nature Communications, Vol: 10, ISSN: 2041-1723

Weanalyseorganic solar cells with four differentphotoactive blends exhibiting differing dependencies ofshort-circuit current upon photoactive layer thickness.These blends and devices are analysedbytransient optoelectronic techniques ofcarrier kinetics and densities, airphotoemission spectroscopyof material energetics, Kelvin probe measurements of work function, Mott-Schottky analyses of apparent doping density and by device modelling. We concludethat,for the device series studied, the photocurrent losswith thick active layersis primarilyassociatedwith the accumulation of photo-generated charge carriers in intra-bandgap tail states.This charge accumulation screens the device internal electricalfield, preventing efficient charge collection. Purification of one studied donor polymer is observed to reduce tail statedistribution anddensity and increase the maximal photoactive thickness forefficient operation. Ourwork suggests that selectingorganic photoactive layerswith a narrow distribution of tail states isa keyrequirement for the fabrication of efficient, high photocurrent, thick organic solar cells.

Journal article

Lami V, Weu A, Zhang J, Chen Y, Fei Z, Heeney M, Friend RH, Vaynzof Yet al., 2019, Visualizing the Vertical Energetic Landscape in Organic Photovoltaics, JOULE, Vol: 3, Pages: 2513-2534, ISSN: 2542-4351

Journal article

He Q, Shahid M, Wu J, Jiao X, Eisner FD, Hodsden T, Fei Z, Anthopoulos TD, McNeill CR, Durrant JR, Heeney Met al., 2019, Fused Cyclopentadithienothiophene acceptor enables ultrahigh short‐circuit current and high efficiency >11% in as‐cast organic solar cells, Advanced Functional Materials, Vol: 29, Pages: 1-7, ISSN: 1616-301X

A new method to synthesize an electron‐rich building block cyclopentadithienothiophene (9H‐thieno‐[3,2‐b]thieno[2″,3″:4′,5′]thieno[2′,3′:3,4]cyclopenta[1,2‐d]thiophene, CDTT) via a facile aromatic extension strategy is reported. By combining CDTT with 1,1‐dicyanomethylene‐3‐indanone endgroups, a promising nonfullerene small molecule acceptor (CDTTIC) is prepared. As‐cast, single‐junction nonfullerene organic solar cells based on PFBDB‐T: CDTTIC blends exhibit very high short‐circuit currents up to 26.2 mA cm−2 in combination with power conversion efficiencies over 11% without any additional processing treatments. The high photocurrent results from the near‐infrared absorption of the CDTTIC acceptor and the well‐intermixed blend morphology of polymer donor PFBDB‐T and CDTTIC. This work demonstrates a useful fused ring extension strategy and promising solar cell results, indicating the great potential of the CDTT derivatives as electron‐rich building blocks for constructing high‐performance small molecule acceptors in organic solar cells.

Journal article

Lin Y-H, Huang W, Pattanasattayavong P, Lim J, Li R, Sakai N, Panidi J, Hong MJ, Ma C, Wei N, Wehbe N, Fei Z, Heeney M, Labram JG, Anthopoulos TD, Snaith HJet al., 2019, Deciphering photocarrier dynamics for tuneable high-performance perovskite-organic semiconductor heterojunction phototransistors, NATURE COMMUNICATIONS, Vol: 10, ISSN: 2041-1723

Journal article

Jang S-Y, Kim I-B, Kang M, Fei Z, Jung E, McCarthy-Ward T, Shaw J, Lim D-H, Kim Y-J, Mathur S, Heeney M, Kim D-Yet al., 2019, Diseleno[3,2-b:2 ',3 '-d]selenophene-Containing High-Mobility Conjugated Polymer for Organic Field-Effect Transistors (vol 6, 1900245, 2019), ADVANCED SCIENCE, Vol: 6

Journal article

Panidi J, Kainth J, Paterson AF, Wang S, Tsetseris L, Emwas AH, McLachlan MA, Heeney M, Anthopoulos TDet al., 2019, Introducing a nonvolatile N-type dopant drastically improves electron transport in polymer and small-molecule organic transistors, Advanced Functional Materials, Vol: 29, Pages: 1-10, ISSN: 1616-301X

KGaA, Weinheim Molecular doping is a powerful yet challenging technique for enhancing charge transport in organic semiconductors (OSCs). While there is a wealth of research on p-type dopants, work on their n-type counterparts is comparatively limited. Here, reported is the previously unexplored n-dopant (12a,18a)-5,6,12,12a,13,18,18a,19-octahydro-5,6-dimethyl- 13,18[1′,2′]-benzenobisbenzimidazo [1,2-b:2′,1′-d]benzo[i][2.5]benzodiazo-cine potassium triflate adduct (DMBI-BDZC) and its application in organic thin-film transistors (OTFTs). Two different high electron mobility OSCs, namely, the polymer poly[[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8- bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2′-bithiophene)] and a small-molecule naphthalene diimides fused with 2-(1,3-dithiol-2-ylidene)malononitrile groups (NDI-DTYM2) are used to study the effectiveness of DMBI-BDZC as a n-dopant. N-doping of both semiconductors results in OTFTs with improved electron mobility (up to 1.1 cm2 V−1 s−1), reduced threshold voltage and lower contact resistance. The impact of DMBI-BDZC incorporation is particularly evident in the temperature dependence of the electron transport, where a significant reduction in the activation energy due to trap deactivation is observed. Electron paramagnetic resonance measurements support the n-doping activity of DMBI-BDZC in both semiconductors. This finding is corroborated by density functional theory calculations, which highlights ground-state electron transfer as the main doping mechanism. The work highlights DMBI-BDZC as a promising n-type molecular dopant for OSCs and its application in OTFTs, solar cells, photodetectors, and thermoelectrics.

Journal article

Musser AJ, Al-Hashimi M, Heeney M, Clark Jet al., 2019, Heavy-atom effects on intramolecular singlet fission in a conjugated polymer, Journal of Chemical Physics, Vol: 151, ISSN: 0021-9606

A chief aim in singlet fission research is to develop new materials concepts for more efficient singlet fission. The typical approaches such as tuning π-overlap and charge-transfer interactions, enhancing delocalization, altering diradical character, or extending the conjugation length have profound effects simultaneously on the singlet and triplet energetics and the couplings between them. While these strategies have resulted in a handful of high-efficiency materials, the complex interplay of these factors makes systematic materials development challenging, and it would be useful to be able to selectively manipulate the properties and dynamics of just part of the singlet fission pathway. Here, we investigate the potential of heteroatom substitution as just such a selective tool. We explore the influence of heavy atoms within the main backbone of polythienylenevinylene and its selenophene and tellurophene derivatives. We find no significant effects on the prompt <300 fs intramolecular singlet fission dynamics but a clear heavy-atom effect on longer time scales.

Journal article

Du T, Xu W, Daboczi M, Kim J, Xu S, Lin C-T, Kang H, Lee K, Heeney MJ, Kim J-S, Durrant JR, McLachlan MAet al., 2019, p-Doping of organic hole transport layers in p–i–n perovskite solar cells: correlating open-circuit voltage and photoluminescence quenching, Journal of Materials Chemistry A, Vol: 7, Pages: 18971-18979, ISSN: 2050-7488

Doping is a widely implemented strategy for enhancing the inherent electronic properties of charge transport layers in photovoltaic (PV) devices. Here, in direct contrast to existing understanding, we find that a reduction in p-doping of the organic hole transport layer (HTL) leads to substantial improvements in PV performance in planar p–i–n perovskite solar cells (PSCs), driven by improvements in open circuit voltage (VOC). Employing a range of transient and steady state characterisation tools, we find that the improvements of VOC correlate with reduced surface recombination losses in less p-doped HTLs. A simple device model including screening of bulk electric fields in the perovskite layer is used to explain this observation. In particular, photoluminescence (PL) emission of complete solar cells shows that efficient performance is correlated to a high PL intensity at open circuit and a low PL intensity at short circuit. We conclude that desirable transport layers for p–i–n PSCs should be charge selective contacts with low doping densities.

Journal article

Choi HH, Paterson AF, Fusella MA, Panidi J, Solomeshch O, Tessler N, Heeney M, Cho K, Anthopoulos TD, Rand BP, Podzorov Vet al., Hall Effect in Polycrystalline Organic Semiconductors: The Effect of Grain Boundaries, ADVANCED FUNCTIONAL MATERIALS, ISSN: 1616-301X

Journal article

Jang SY, Kim IB, Kang M, Fei Z, Jung E, McCarthy-Ward T, Shaw J, Lim DH, Kim YJ, Mathur S, Heeney M, Kim DYet al., 2019, Diseleno[3,2-b:2′,3′-d]selenophene-containing high-mobility conjugated polymer for organic field-effect transistors, Advanced Science, Vol: 6, ISSN: 2198-3844

KGaA, Weinheim The synthesis of a diseleno[3,2-b:2′,3′-d]selenophene (DSS) composed of three fused selenophenes is reported and it is used as a building block for the preparation of a high hole mobility conjugated polymer (PDSSTV). The polymer demonstrates strong intermolecular interactions even in solution, despite steric repulsion between the large Se atom in DSS and adjacent (C β )–H atoms which leads to a partially twisted confirmation PDSSTV. Nevertheless, 2D grazing incidence X-ray diffraction (2D-GIXD) analysis reveals that the polymer tends to align in a highly ordered edge-on orientation after thermal annealing. The polymer demonstrates promising performance in a field-effect transistor device with saturated hole mobility up to 2 cm 2 V −1 s −1 obtained under relatively low gate voltages of −30 V. The ultilization of a Se-containing fused aromatic system, therefore, appears to be a promising avenue for the development of high-performance conjugated polymers.

Journal article

He Q, Shahid M, Panidi J, Marsh AV, Huang W, Daboczi M, Kim J-S, Fei Z, Anthopoulos TD, Heeney Met al., 2019, A versatile star-shaped organic semiconductor based on benzodithiophene and diketopyrrolopyrrole, Journal of Materials Chemistry C, Vol: 7, Pages: 6622-6629, ISSN: 2050-7526

We report the synthesis of a new star-shaped π-conjugated oligomer, BDT(DPP)4, containing a benzodithiophene core and four diketopyrrolopyrrole arms. The thermal, electrochemical and optical properties are characterized and the results complemented by computational studies. The utility of the molecule is demonstrated in both solar cell and field-effect transistor devices. In the former, BDT(DPP)4 displays low efficiency when used as an acceptor in blends with poly(3-hexylthiophene) but exhibits promising performance as a donor, in blends with either a fullerene or a non-fullerene acceptor. In field-effect transistors BDT(DPP)4 exhibits typical p-type transistor behavior, which is in accordance with its better donor performance in solar cell devices.

Journal article

Green JP, Cha H, Shahid M, Creamer A, Durrant JR, Heeney Met al., 2019, Dithieno[3,2-b:2,3-d]arsole-containing conjugated polymers in organic photovoltaic devices, Dalton Transactions, Vol: 48, Pages: 6676-6679, ISSN: 1477-9234

Arsole-derived conjugated polymers are a relatively new class of materials in the field of organic electronics. Herein, we report the synthesis of two new donor polymers containing fused dithieno[3,2-b:2′,3′-d]arsole units and report their application in bulk heterojunction solar cells for the first time. Devices based upon blends with PC71BM display high open circuit voltages around 0.9 V and demonstrate power conversion efficiencies around 4%.

Journal article

Paterson AF, Tsetseris L, Li R, Basu A, Faber H, Emwas A-H, Panidi J, Fei Z, Niazi MR, Anjum DH, Heeney M, Anthopoulos TDet al., 2019, Addition of the lewis acid Zn(C6 F5 )2 enables organic transistors with a maximum hole mobility in excess of 20 cm2 V-1 s-1, Advanced Materials, Vol: 31, ISSN: 0935-9648

Incorporating the molecular organic Lewis acid tris(pentafluorophenyl)borane [B(C6 F5 )3 ] into organic semiconductors has shown remarkable promise in recent years for controlling the operating characteristics and performance of various opto/electronic devices, including, light-emitting diodes, solar cells, and organic thin-film transistors (OTFTs). Despite the demonstrated potential, however, to date most of the work has been limited to B(C6 F5 )3 with the latter serving as the prototypical air-stable molecular Lewis acid system. Herein, the use of bis(pentafluorophenyl)zinc [Zn(C6 F5 )2 ] is reported as an alternative Lewis acid additive in high-hole-mobility OTFTs based on small-molecule:polymer blends comprising 2,7-dioctyl[1]benzothieno [3,2-b][1]benzothiophene and indacenodithiophene-benzothiadiazole. Systematic analysis of the materials and device characteristics supports the hypothesis that Zn(C6 F5 )2 acts simultaneously as a p-dopant and a microstructure modifier. It is proposed that it is the combination of these synergistic effects that leads to OTFTs with a maximum hole mobility value of 21.5 cm2 V-1 s-1 . The work not only highlights Zn(C6 F5 )2 as a promising new additive for next-generation optoelectronic devices, but also opens up new avenues in the search for high-mobility organic semiconductors.

Journal article

Paterson AF, Mottram AD, Faber H, Niazi MR, Fei Z, Heeney M, Anthopoulos TDet al., 2019, Impact of the gate dielectric on contact resistance in high-mobility organic transistors, Advanced Electronic Materials, Vol: 5, 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.

Journal article

Eisner F, Azzouzi M, Fei Z, Hou X, Anthopoulos T, Dennis TJ, Heeney M, Nelson Jet al., 2019, Hybridization of local exciton and charge-transfer states reduces non-radiative voltage losses in organic solar cells, Journal of the American Chemical Society, Vol: 141, Pages: 6362-6374, ISSN: 1520-5126

A number of recent studies have shown that the nonradiative voltage losses in organic solar cells can be suppressed in systems with low energetic offsets between donor and acceptor molecular states, but the physical reasons underpinning this remain unclear. Here, we present a systematic study of 18 different donor/acceptor blends to determine the effect that energetic offset has on both radiative and nonradiative recombination of the charge-transfer (CT) state. We find that, for certain blends, low offsets result in hybridization between charge-transfer and lowest donor or acceptor exciton states, which leads to a strong suppression in the nonradiative voltage loss to values as low as 0.23 V associated with an increase in the luminescence of the CT state. Further, we extend a two-state CT-state recombination model to include the interaction between CT and first excited states, which allows us to explain the low nonradiative voltage losses as an increase in the effective CT to ground state oscillator strength due to the intensity borrowing mechanism. We show that low nonradiative voltage losses can be achieved in material combinations with a strong electronic coupling between CT and first excited states and where the lower band gap material has a high oscillator strength for transitions from the excited state to the ground state. Finally, from our model we propose that achieving very low nonradiative voltage losses may come at a cost of higher overall recombination rates, which may help to explain the generally lower FF and EQE of highly hybridized systems.

Journal article

Eisner FD, Azzouzi M, Fei Z, Hou X, Anthopoulos TD, Dennis TJS, Heeney M, Nelson Jet al., 2019, Hybridization of Local Exciton and Charge-Transfer States Reduces Nonradiative Voltage Losses in Organic Solar Cells., J Am Chem Soc

A number of recent studies have shown that the nonradiative voltage losses in organic solar cells can be suppressed in systems with low energetic offsets between donor and acceptor molecular states, but the physical reasons underpinning this remain unclear. Here, we present a systematic study of 18 different donor/acceptor blends to determine the effect that energetic offset has on both radiative and nonradiative recombination of the charge-transfer (CT) state. We find that, for certain blends, low offsets result in hybridization between charge-transfer and lowest donor or acceptor exciton states, which leads to a strong suppression in the nonradiative voltage loss to values as low as 0.23 V associated with an increase in the luminescence of the CT state. Further, we extend a two-state CT-state recombination model to include the interaction between CT and first excited states, which allows us to explain the low nonradiative voltage losses as an increase in the effective CT to ground state oscillator strength due to the intensity borrowing mechanism. We show that low nonradiative voltage losses can be achieved in material combinations with a strong electronic coupling between CT and first excited states and where the lower band gap material has a high oscillator strength for transitions from the excited state to the ground state. Finally, from our model we propose that achieving very low nonradiative voltage losses may come at a cost of higher overall recombination rates, which may help to explain the generally lower FF and EQE of highly hybridized systems.

Journal article

Ye L, Xiong Y, Chen Z, Zhang Q, Fei Z, Henry R, Heeney M, O'Connor BT, You W, Ade Het al., 2019, Sequential Deposition of Organic Films with Eco-Compatible Solvents Improves Performance and Enables Over 12%-Efficiency Nonfullerene Solar Cells., Adv Mater, Pages: e1808153-e1808153

Casting of a donor:acceptor bulk-heterojunction structure from a single ink has been the predominant fabrication method of organic photovoltaics (OPVs). Despite the success of such bulk heterojunctions, the task ofcontrolling the microstructure in a single casting process has been arduous and alternative approaches are desired. To achieve OPVs with a desirable microstructure, a facile and eco-compatible sequential deposition approach is demonstrated for polymer/small-molecule pairs. Using a nominally amorphous polymer as the model material, the profound influence of casting solvent is shown on the molecular ordering of the film, and thus the device performance and mesoscale morphology of sequentially deposited OPVs can be tuned. Static and in situ X-ray scattering indicate that applying (R)-(+)-limonene is able to greatly promote the molecular order of weakly crystalline polymers and form the largest domain spacing exclusively, which correlates well with the best efficiency of 12.5% in sequentially deposited devices. The sequentially cast device generally outperforms its control device based on traditional single-ink bulk-heterojunction structure. More crucially, a simple polymer:solvent interaction parameter χ is positively correlated with domain spacing in these sequentially deposited devices. These findings shed light on innovative approaches to rationally create environmentally friendly and highly efficient electronics.

Journal article

Reichsöllner E, Creamer A, Cong S, Casey A, Eder S, Heeney M, Glocklhofer Fet al., 2019, Fast and selective post-polymerization modification of conjugated polymers using dimethyldioxirane, Frontiers in Chemistry, Vol: 7, ISSN: 2296-2646

Modification of functional groups attached to conjugated polymer backbones can drastically alter the material properties. Oxidation of electron-donating thioalkyl substituents to electron-withdrawing sulfoxides or sulfones is a particularly effective modification. However, so far, this reaction has not been studied for the modification of conjugated polymers used in organic electronics. Crucial questions regarding selectivity and reaction time waited to be addressed. Here, we show that the reaction is highly selective and complete within just a few minutes when using dimethyldioxirane (DMDO) for the oxidation of thioalkyl substituents attached to the well-investigated conjugated polymers poly(9-(1-octylnonyl)carbazole-alt-4,7-dithienylbenzothiadiazole) (PCDTBT) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT). The selectivity was confirmed by comparison with polymers obtained from pre-oxidized monomers and by control experiments using related polymers without thioalkyl substituents. Using DMDO, the oxidation yields acetone as the only side-product, which reduces the work-up to mere evaporation of solvents and excessive reagent. Our results show that this oxidation is an exciting method for the preparation of electron-deficient conjugated polymers. It may even allow the preparation of electron acceptors for solar cells directly from the electron donors.

Journal article

Sun G, Shahid M, Fei Z, Xu S, Eisner FD, Anthopolous TD, McLachlan MA, Heeney Met 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%.

Journal article

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