Recent progress in the understanding and manipulation of morphology in polymer: fullerene photovoltaic cells

Provisional chapterFullerene-based organic photovoltaic devices (OPVs) have attracted increasing interest as a low-cost, lightweight, flexible and easy to process alternative to the silicon-based solar cells. Currently the most efficient fullerene-based OPV devices, although improving dramatically in the last few years, are still a long way from a technologically useful efficiency. The performance of current OPV devices is assumed to exist due to the phase separation of the donor (D) and acceptor (A) materials into co-continuous networks of D and A rich phases, forming the so-called Bulk-Hetero-Junctions (BHJ). A typical BHJ active layer in an OPV device is a thin film mixture of a conjugated donor polymer such as regioregular poly(3-hexyl-thiophene) (P3HT), and a functionalized acceptor fullerene such as [6,6]-phenyl C61-butyric acid methyl ester (PCBM). The morphology of these BHJ films has proven to be extremely important in determining the optoelectronic properties of the corresponding devices. However, the correlations between the structure of these donor/acceptor materials from atomic to microscopic length scales, the resulting optoelectronic properties, and the device performance are still not understood from first principles. The understanding and manipulation of this polymer-fullerene morphology has therefore been the focus of intense electronic and optoelectronic polymer-device research, using a broad range of techniques, yet the results from these studies are less than definitive and, in some cases, contradictory. In this chapter, some of these most relevant studies in the understanding and manipulation of the polymer-fullerene morphology are reviewed

Solid state processing of conjugated polymer-fullerene blends

If the future global future energy needs are to be met, renewable energies must be exploited. The possibility of cheap, but efficient organic or polymer based photovoltaic (OPV) devices are among the competing technologies, which are actively being studied. To date the most efficient OPV devices are based on conjugated polymer-fullerene bulk heterojunctions (BHJ). The choice of polymer and fullerene is a balance of electronic (donor-acceptor) properties, but due to the nature of the solubility of the species, also includes solubilising ligands. Whilst these ligands certainly induce improved solution processability, they can also affect the electronic characteristics and also morphology of the polymers and fullerenes. However, potentially interesting polymer-fullerene combinations are not being explored due to difficulties in solution processing of the mixtures. We are exploring the use of pressure on the phase behaviour of polymer-fullerene blends, following on from previous workers who showed that melt processing of polymers can be greatly influenced by application of pressure. Under moderate pressure, we have demonstrated that equivalent phase behavior in polymer-fullerene pairs observed by conventional solution processing can be induced in solid-state processing. Using a combination of experiments and molecular modeling we are exploring the effect that pressure plays in inducing phase miscibility in otherwise intractable polymer-fullerene mixtures. To date we have been exploring a number of model-fullerene mixtures, but have demonstrated that the effects of this solid-state processing method are ubiquitous. The results of this fundamental study are expected to lead to alternative methods of processing of conjugated polymers without the need for solvents

Thermodynamic effects in morphological evolution of polymer-fullerene nanocomposites for photovoltaic applications

Polymer based photovoltaic devices promise solar technologies that are inexpensive enough to be widely exploited and therefore provide a significant fraction of the future energy needs. There are many promising polymer-fullerene mixtures that are promising materials candidates for achieving high performance devices, but their exploitation requires and improved understanding of their structure-property relationships. Of particular relevance is the phase behavior of the mixtures. The phase behavior of donor-acceptor materials for photovoltaic applications is of key importance [1,2]: i) to gain a fundamental understanding and control of morphology development in the donor-acceptor blends; ii) to appropriately choose the operating window for thermal annealing; iii) to understand the long-term stability of the blended film morphology and consequently of the photovoltaic performance of the corresponding solar cells. In this work the phase behavior of polymer-fullerene mixtures is being studied using Differential Scanning Calorimetry (DSC), Wide-Angle X-Ray Scattering (WAXS), Small-Angle Neutron Scattering (SANS) and theoretical ab initio Density Functional Theory (DFT) calculations

Flexible low-density polyethylene–BaTiO3 nanoparticle composites for monitoring leakage current in high-tension equipment.

Polymer–nanoparticle composites prepared using a low-density polyethylene (LDPE) matrix with BaTiO3 nanoparticle compositions of 6, 9, 12, and 15 wt % have shown insulating behavior and are evaluated for their applicability as flexible strain sensors. With increasing percentage of the nanoparticles, the LDPE crystallinity decreased from 38.11 to 33.79% and the maximum electrical displacement response was seen to increase from 2.727 × 10–4 to 4.802 × 10–4 C/cm2. The maximum current, remnant current, and coercive field, all increased with the increasing nanoinclusion loading. Furthermore, the interaction radius values derived from the three-dimensional (3D) model of the nanoparticle dispersion state in polymer–nanoparticle composites were found to be correlated with its key properties. The interaction radius values from the simulated 3D model gave a clear basis for comparing the electrical properties of the samples with the effect of the nanoparticles’ functionalization on the dispersion state in the context of the increased NP loading and giving the values of 275, 290, 310, and 300 nm, respectively. The 12 wt % nanoparticulate-loaded sample demonstrates the best overall trade-off of key parameters studied herein. Overall, the results demonstrate that these flexible polymer–nanoparticle composites could be used for strain-based sensors in the high-tension applications

Phase-morphology and molecular structure correlations in model fullerene-polymer nanocomposites

Organic or polymer based photovoltaic devices promise solar technologies that are inexpensive enough to be widely exploited and therefore provide a significant fraction of the future energy needs. There are many promising polymer-fullerene mixtures that are promising materials candidates for achieving high performance device, but their exploitation requires an improved understanding of their structure-property relationships. Of particular relevance is the molecular structural as well as mesoscale phase behaviour. In order to guide the use of electron acceptor fullerenes in these systems we are using multi-scale molecular modelling coupled with neutron and X-ray scattering to determine the structure behavior of model polymer-fullerene mixtures. Neutron scattering is particularly useful for these types of studies since the fullerene generally have a high scattering contrast with respect to most polymers. This natural contrast, enhanced by careful selective deuteration allows us to carefully probe the atomic and molecular interactions in these complex systems. We are studying model polymer systems to establish fullerene-polymer phase behaviour. To establish how fullerene addition changes polymer phase behaviour, using advanced scattering techniques we are studying phase morphology and molecular structure. Control of morphology development is being examined with particular relevance to solid state processing

Practice development plans to improve the primary care management of acute asthma: randomised controlled trial

Background: Our professional development plan aimed to improve the primary care management of acute asthma, which is known to be suboptimal. Methods: We invited 59 general practices in Grampian, Scotland to participate. Consenting practices were randomised to early and delayed intervention groups. Practices undertook audits of their management of all acute attacks (excluding children under 5 years) occurring in the 3 months preceding baseline, 6-months and 12-months study time-points. The educational programme [including feedback of audit results, attendance at a multidisciplinary interactive workshop, and formulation of development plan by practice teams] was delivered to the early group at baseline and to the delayed group at 6 months. Primary outcome measure was recording of peak flow compared to best/predicted at 6 months. Analyses are presented both with, and without adjustment for clustering. Results: 23 consenting practices were randomised: 11 to early intervention. Baseline practice demography was similar. Six early intervention practices withdraw before completing the baseline audit. There was no significant improvement in our primary outcome measure (the proportion with peak flow compared to best/predicted) at either the 6 or 12 month time points after adjustment for baseline and practice effects. However, the between group difference in the adjusted combined assessment score, whilst non-significant at 6 months (Early: 2.48 (SE 0.43) vs. Delayed 2.26 (SE 0.33) p = 0.69) reached significance at 12 m (Early:3.60 (SE 0.35) vs. Delayed 2.30 (SE 0.28) p = 0.02). Conclusion: We demonstrated no significant benefit at the a priori 6-month assessment point, though improvement in the objective assessment of attacks was shown after 12 months. Our practice development programme, incorporating audit, feedback and a workshop, successfully engaged the healthcare team of participating practices, though future randomised trials of educational interventions need to recognise that effecting change in primary care practices takes time. Monitoring of the assessment of acute attacks proved to be a feasible and responsive indicator of quality care

The NIHR collaboration for leadership in applied health research and care (CLAHRC) for greater manchester: combining empirical, theoretical and experiential evidence to design and evaluate a large-scale implementation strategy

Background: In response to policy recommendations, nine National Institute for Health Research (NIHR) Collaborations for Leadership in Applied Health Research and Care (CLAHRCs) were established in England in 2008, aiming to create closer working between the health service and higher education and narrow the gap between research and its implementation in practice. The Greater Manchester (GM) CLAHRC is a partnership between the University of Manchester and twenty National Health Service (NHS) trusts, with a five-year mission to improve healthcare and reduce health inequalities for people with cardiovascular conditions. This paper outlines the GM CLAHRC approach to designing and evaluating a large-scale, evidence- and theory-informed, context-sensitive implementation programme. Discussion: The paper makes a case for embedding evaluation within the design of the implementation strategy. Empirical, theoretical, and experiential evidence relating to implementation science and methods has been synthesised to formulate eight core principles of the GM CLAHRC implementation strategy, recognising the multi-faceted nature of evidence, the complexity of the implementation process, and the corresponding need to apply approaches that are situationally relevant, responsive, flexible, and collaborative. In turn, these core principles inform the selection of four interrelated building blocks upon which the GM CLAHRC approach to implementation is founded. These determine the organizational processes, structures, and roles utilised by specific GM CLAHRC implementation projects, as well as the approach to researching implementation, and comprise: the Promoting Action on Research Implementation in Health Services (PARIHS) framework; a modified version of the Model for Improvement; multiprofessional teams with designated roles to lead, facilitate, and support the implementation process; and embedded evaluation and learning. Summary: Designing and evaluating a large-scale implementation strategy that can cope with and respond to the local complexities of implementing research evidence into practice is itself complex and challenging. We present an argument for adopting an integrative, co-production approach to planning and evaluating the implementation of research into practice, drawing on an eclectic range of evidence sources.Gill Harvey, Louise Fitzgerald, Sandra Fielden, Anne McBride, Heather Waterman, David Bamford, Roman Kislo and Ruth Boade

A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

Meeting abstrac