Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.

The technology behind a large area array of flexible solar cells with a unique design and semitransparent blue appearance is presented. These modules are implemented in a solar tree installation at the German pavilion in the EXPO2015 in Milan/IT. The modules show power conversion efficiencies of 4.5% and are produced exclusively using standard printing techniques for large-scale production.

We have investigated the effects of thin-film morphology on the photovolatic performance for a series of donor–acceptor copolymers based on benzodithiophene donor and benzothiadiazole acceptor units. Photovoltaic devices incorporating polymer:fullerene blends show highest efficiencies (up to 6%) for those polymers exhibiting the least degree of crystallinity in X-ray diffraction patterns and a corresponding lowest surface roughness in thin films. We find that the existence of such crystalline domains in thin polymer films correlates well with spectral signatures of polymer chain aggregates already present in solution prior to casting of the film. Polymer solubility and casting conditions therefore appear to be crucial factors for enhancing efficiencies of photovoltaic devices based on such donor–acceptor copolymers. To examine why the presence of crystallite domains lowers device efficiencies, we measured exciton diffusion lengths by modeling the time-dependent photoluminescence from thin polymer films de...

While organic semiconductors used in polymer:fullerene photovoltaics are generally not intentionally doped, significant levels of unintentional doping have previously been reported in the literature. Here, we explain the differences in photocurrent collection between standard (transparent anode) and inverted (transparent cathode) low band-gap polymer:fullerene solar cells in terms of unintentional p-type doping. Using capacitance/voltage measurements, we find that the devices exhibit doping levels of order 10 16 cm −3 , resulting in space-charge regions ~100 nm thick at short circuit. As a result, low field regions form in devices thicker than 100 nm. Because more of the light is absorbed in the low field region in standard than in inverted architectures, the losses due to inefficient charge collection are greater in standard architectures. Using optical modelling, we show that the observed trends in photocurrent with device architecture and thickness can be explained if only charge carriers photogenerated in the depletion region contribute to the photocurrent.

To enable the integration of organic transistors into flexible displays we have developed passive materials for a robust, layer-to-layer compatible device stack to be manufactured using a variety of industrially applicable coating and printing processes. The solution processable materials for the OSC protection and the passivation material are designed for good interlayer adhesion and OTFT stability. The 365 nm UV-curable protection layers for the OSC are compatible with fabrication processes commonly used in the display industry, e.g., sputtering of metals. Fabrication of ink-jet printed devices is demonstrated with usage of a passive material suitable for further pixel integration. The bias stress and ambient stability was shown for the integrated stacks of transistors with the carrier mobility greater than that of amorphous silicon. We further demonstrate the development of formulations, suitable for high throughput roll-to-roll processing of soluble small molecule semiconductors allowing a high degree of structural order in the final solid film. Transistor mobility <2 cm2/V·s is achieved with a range of viscosity values compatible with flexographic printing. Fine pattern of OSC is demonstrated with flexographic printing by adjusting the viscosity of the formulation. Uniform layers are achieved with coating and printing techniques and uniformity values are sufficient for display application.

Organic complementary inverters and ring oscillators based on polyelectrolyte-gated thin-film transistors are demonstrated. Detrimental electrochemical doping is suppressed by using polyanionic and polycationic gate insulators in the p- and n-channel transistors, respectively. The circuits operate at supply voltages between 0.2 V and 1.5 V, have a static power consumption of less than 2.5 nW per logic gate and show propagation delays down to 0.26 ms per stage.

The synthesis of a new conjugated material is reported; BDHTT–BBT features a central electron-deficient benzobisthiazole capped with two 3,6-dihexyl-thieno[3,2-b]thiophenes. Cyclic voltammetry was used to determine the HOMO (−5.7 eV) and LUMO (−2.9 eV) levels. The solid-state properties of the compound were investigated by X-ray diffraction on single-crystal and thin-film samples. OFETs were constructed with vacuum deposited films of BDHTT–BBT. The films displayed phase transitions over a range of temperatures and the morphology of the films affected the charge transport properties of the films. The maximum hole mobility observed from bottom-contact, top-gate devices was 3 × 10−3 cm2 V−1s−1, with an on/off ratio of 104–105 and a threshold voltage of −42 V. The morphological and self-assembly characteristics versus electronic properties are discussed for future improvement of OFET devices.

The mass production technique of gravure contact printing is used to fabricate state-of-the art polymer field-effect transistors (FETs). Using plastic substrates with prepatterned indium tin oxide source and drain contacts as required for display applications, four different layers are sequentially gravure-printed: the semiconductor poly(3-hexylthiophene-2,5-diyl) (P3HT), two insulator layers, and an Ag gate. A crosslinkable insulator and an Ag ink are developed which are both printable and highly robust. Printing in ambient and using this bottom-contact/top-gate geometry, an on/off ratio of >10(4) and a mobility of 0.04 cm(2) V-1 s(-1) are achieved. This rivals the best top-gate polymer FETs fabricated with these materials. Printing using low concentration, low viscosity ink formulations, and different P3HT molecular weights is demonstrated. The printing speed of 40 m min(-1) on a flexible polymer substrate demonstrates that very high-volume, reel-to-reel production of organic electronic devices is possible.

The morphology, optical properties, and photoconductance of blends of the poly(thienothiophene) derivatives poly(3,6-dialkylthieno[3,2-b]thiophene-co-bithiophene) (pATBT), poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (pBTTT), and poly(2,5-bis(3-dodecylthiophen-2-yl)thieno[2,3-b]thiophene) (pBTCT) with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were studied. After thermal annealing, the pATBT:PCBM blend exhibits formation of phase-segregated polymer and PCBM domains. Annealing of pBTTT:PCBM and pBTCT:PCBM yields a layered structure with PCBM molecules intercalated between layers of pi-stacked polymers. In the intercalated systems the photoluminescence is almost completely quenched, in contrast to the phase-segregated pATBT:PCBM blend. The higher degree of exciton quenching in the intercalated systems likely results in a higher initial yield of charges. However, on longer time scales (>10 ns), the microwave photoconductance for the layered systems is lower than for pATBT:PCBM blend systems. This is likely due to restricted motion of charges in intercalated systems, which reduces the yield of free charge carriers or enhances the charge carrier recombination.

In this paper, we use transient absorption spectroscopy to examine the charge photogeneration yields of a series of low band gap polythiophenes and polyselenophenes in blend films with 6,6-phenyl C61-butyric acid methyl ester (PCBM). The polymers are selected to have approximately matched ionization potentials, allowing us to focus upon the importance of the polymer lowest unoccupied molecular orbital (LUMO) level in determining photogeneration efficiency. Data are collected as a function of PCBM composition. A correlation is observed between the yield of dissociated polarons, as measured by the amplitude of the transient absorption signal, and the polymer LUMO level. Lower band gap polyselenophenes produce lower polaron yields, in quantitative agreement with a previously proposed model in which the excess thermal energy of initially generated bound radical pairs determines their dissociation efficiency. Increasing the PCBM concentration from 5 to 50 wt % results in an increase in charge photogeneration. Photoluminescence data demonstrate that this dependence is not primarily associated with an increase in exciton quenching; instead, this increase is assigned to the additional influence of PCBM domain size and/or electron mobility on the dissociation efficiency of the bound radical pairs. These observations are then discussed in terms of their implications for the development of polymer semiconductor materials for organic photovoltaics, and in particular the development of guidelines for the design of polymers for efficiency charge photogeneration in such devices.

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTUnderstanding the Influence of Morphology on Poly(3-hexylselenothiophene):PCBM Solar CellsAmy M. Ballantyne, Toby A. M. Ferenczi, Mariano Campoy-Quiles, Tracey M. Clarke, Andrea Maurano, Kien Hon Wong, Weimin Zhang, Natalie Stingelin-Stutzmann, Ji-Seon Kim, Donal D. C. Bradley, James R. Durrant, Iain McCulloch, Martin Heeney, Jenny Nelson*, Steve Tierney, Warren Duffy, Christian Mueller, and Paul SmithView Author Information Imperial College London, London SW7 2AZ, United Kingdom Merck Chemicals, Chilworth Science Park, University Parkway, Southampton SO16 7QD, United Kingdom Department of Materials, ETH Zurich, Switzerland*To whom correspondence should be addressed. E-mail: [email protected]Cite this: Macromolecules 2010, 43, 3, 1169–1174Publication Date (Web):January 13, 2010Publication History Received9 November 2009Revised3 January 2010Published online13 January 2010Published inissue 9 February 2010https://pubs.acs.org/doi/10.1021/ma902477hhttps://doi.org/10.1021/ma902477hrapid-communicationACS PublicationsCopyright © 2010 American Chemical SocietyRequest reuse permissionsArticle Views3683Altmetric-Citations88LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Crystallinity,Mobility,Organic polymers,Polymer films,Polymers Get e-Alerts

The morphology and the optoelectronic properties of films of poly(dialkylthieno[3,2-b]thiophene-cobithiophene) (pDA2T) and blends of this polymer with [6, 6]-phenyl C-61-butyric acid methyl ester (PCBM) is investigated. Upon spin-coating of the blend a thin film is formed containing both PCBM and the polymer in nanocrystalline form. On annealing, phase separation occurs, leading to formation of the PCBM-rich domains embedded in a polymer-rich matrix. The electrodeless time-resolved microwave conductivity technique is used to study the photogeneration of charge carriers and their decay over time. The photoconductance increases dramatically on adding PCBM to the polymer. Annealing of the blend reduces the photogeneration yield of char-e carriers. due to the smaller interfacial area between pDA2T and PCBM. The phase separation of the polymer and PCBM after annealing retards recombination of charge carriers, which is beneficial for charge collection in a solar cell. The magnitude of the photoconductance of the pDA2T:PCBM blend is comparable to that for a P3HT:PCBM blend. The above findings, together with the smaller energy loss involved in electron transfer from pDA2T to PCBM, as compared to blends of P3HT and PCBM, make pDA2T a promising material for photovoltaic applications.

We report herein a comparison of the photophysics of a series of polythiophenes with ionization potentials ranging from 4.8 to 5.6 eV as pristine films and when blended with 5 wt % 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]C61 (PCBM). Three polymers are observed to give amorphous films, attributed to a nonplanar geometry of their backbone while the other five polymers, including poly(3-hexylthiophene), give more crystalline films. Optical excitation of the pristine films of the amorphous polymers is observed by transient absorption spectroscopy to give rise to polymer triplet formation. For the more crystalline pristine polymers, no triplet formation is observed, but rather a short-lived (approximately 100 ns), broad photoinduced absorption feature assigned to polymer polarons. For all polymers, the addition of 5 wt % PCBM resulted in 70-90% quenching of polymer photoluminescence (PL), indicative of efficient quenching of polythiophene excitons. Remarkably, despite this efficient exciton quenching, the yield of dissociated polymer+ and PCBM- polarons, assayed by the appearance of a long-lived, power-law decay phase assigned to bimolecular recombination of these polarons, was observed to vary by over 2 orders of magnitude depending upon the polymer employed. In addition to this power-law decay phase, the blend films exhibited short-lived decays assigned, for the amorphous polymers, to neutral triplet states generated by geminate recombination of bound radical pairs and, for the more crystalline polymers, to the direct observation of the geminate recombination of these bound radical pairs to ground. These observations are discussed in terms of a two-step kinetic model for charge generation in polythiophene/PCBM blend films analogous to that reported to explain the observation of exciplex-like emission in poly(p-phenylenevinylene)-based blend films. Remarkably, we find an excellent correlation between the free energy difference for charge separation (deltaG(CS)rel) and yield of the long-lived charge generation, with efficient charge generation requiring a much larger deltaG(CS)rel than that required to achieve efficient PL quenching. We suggest that this observation is consistent with a model where the excess thermal energy of the initially formed polaron pairs is necessary to overcome their Coulombic binding energy. This observation has important implications for synthetic strategies to optimize organic solar cell performance, as it implies that, at least devices based on polythiophene/PCBM blend films, a large deltaG(CS)rel (or LUMO level offset) is required to achieve efficient charge dissociation.

Fabrication of thin film transistors (TFT's) for display applications by IJ printing involves many individual but interrelated Processes from the design of organic semiconductor materials (OSCs), development of stable formulations that can be jetted reliably, the design of patterned substrates together with electrodes and other structures, pre and post treatment processes to ensure correct semiconductor and dielectric layer formation together with optimization of the deposition and drying process. Each of these steps has to be designed to fit the complete manufacturing process, independently developed and then optimized for the total device. In this paper we describe some aspects of this development cycle leading to commercially available ink jet printable organic semiconductor and dielectric inks using polymers and small molecules for TFT fabrication in displays and other device applications including:What is required from OSC materials and processes?How can we IJ print and process OSCs?Examples of IJ printed TFT performance we obtain.

The synthesis of regioregular poly(3-hexyl)selenophene is reported, and its optical and electrical properties are compared to those of regioregular poly(3-hexyl)thiophene.

A common strategy to improve the electrical performance of organic field effect transistors is to optimize the charge carrier mobility of the semiconducting thin film. Polymer semiconductor transport properties have shown a dependence on the chain length, due principally to the strong influence of molecular weight on the thin film microstructure. In this work, we report on a study of the influence of increasing molecular weight of poly(2,5-bis(3-docecylthiophen-2-yl)thieno[3,2-b]thiophenes) (pBTTT-C12) on the polymer bulk thermal properties, thin film microstructure and the electrical performance of thin film field effect transistor devices. Clear differences can be observed within a number average molecular weight range of 8,000 - 18,000 Dalton. A Liquid crystalline phase was only observed at the highest molecular weight, different thin film morphology was observed within the molecular weight range, and the field effect mobility was shown to increase with increasing molecular weight.

Efficient triplet formation is observed for films of high ionisation potential polythiophenes blended with a fullerene derivative, and assigned to formation via geminate charge recombination of bound radical ion pair states.

Organic semiconductors that can be fabricated by simple processing techniques and possess excellent electrical performance, are key requirements in the progress of organic electronics. Both high semiconductor charge-carrier mobility, optimized through understanding and control of the semiconductor microstructure, and stability of the semiconductor to ambient electrochemical oxidative processes are required. We report on new semiconducting liquid-crystalline thieno[3,2-b ]thiophene polymers, the enhancement in charge-carrier mobility achieved through highly organized morphology from processing in the mesophase, and the effects of exposure to both ambient and low-humidity air on the performance of transistor devices. Relatively large crystalline domain sizes on the length scale of lithographically accessible channel lengths (∼200 nm) were exhibited in thin films, thus offering the potential for fabrication of single-crystal polymer transistors. Good transistor stability under static storage and operation in a low-humidity air environment was demonstrated, with charge-carrier field-effect mobilities of 0.2–0.6 cm2 V−1 s−1 achieved under nitrogen.

The development of p-type semiconducting polymers demonstrating good stability under ambient operation is of importance for the development of low cost, printed electronics. We present here the synthesis and full characterisation of two soluble terthiophene polymers, and examine the effect of introducing a fused aromatic heterocycle, thieno[2,3-b]thiophene, into a terthiophene polymer backbone. This heterocycle contains a cross-conjugated central double bond, and its inclusion was shown to have a marked influence on the optical, thermal and electrical properties of the terthiophene polymer. Transistors were fabricated from both polymers, and the operation and storage lifetime under ambient operation was compared.

Organic thin film transistor (OTFT) gas sensors fabricated with an array of different active materials are monitored for shifts in performance characteristics during continuous operation over many days in both inert and ambient environments. We analyze the different patterns of degradation behavior observed in different materials and discuss approaches to decoupling a device’s sensor response from its stress response.