Relation between charge carrier mobility and lifetime in organic photovoltaics

The relationship between charge carrier lifetime and mobility in a bulk heterojunction based organic solar cell, utilizing diketopyrrolopyrole- naphthalene co-polymer and PC71BM in the photoactive blend layer, is investigated using the photoinduced charge extraction by linearly increasing voltage technique. Light intensity, delay time, and temperature dependent experiments are used to quantify the charge carrier mobility and density as well as the temperature dependence of both. From the saturation of photoinduced current at high laser intensities, it is shown that Langevin-type bimolecular recombination is present in the studied system. The charge carrier lifetime, especially in Langevin systems, is discussed to be an ambiguous and unreliable parameter to determine the performance of organic solar cells, because of the dependence of charge carrier lifetime on charge carrier density, mobility, and type of recombination. It is revealed that the relation between charge mobility (μ) and lifetime (τ) is inversely proportional, where the μτ product is independent of temperature. The results indicate that in photovoltaic systems with Langevin type bimolecular recombination, the strategies to increase the charge lifetime might not be beneficial because of an accompanying reduction in charge carrier mobility. Instead, the focus on non-Langevin mechanisms of recombination is crucial, because this allows an increase in the charge extraction rate by improving the carrier lifetime, density, and mobility simultaneously. © 2013 AIP Publishing LLC.

Mobility in the child (and carer) friendly city : SEQ vs. Stockholm

The rationale for providing state subsidised public transport has changed over time from a social obligation to provide transport options for those without access to private transport to an environmental and economic imperative to minimize congestion and greenhouse gas emissions. In many jurisdictions this shift has seen a greater focus on the provision of peak hour commuter services and a shift in the demographic profile of the riding public and a significant increase in the number of commuter passengers relative to others. The scheduling of commuter services is not geared to meet the needs of children and their generally female carers who often need to engage in trip chaining and travel outside peak commuting periods and on weekends. In addition to service scheduling difficulties, transport infrastructure, both on-board and supporting infrastructure such as bus stops, train stations and connecting footpaths often do not support children and their carers to use public transport services. Combined with a negative attitude by passengers and service providers, such as bus drivers, which may see children, babies and young people as out of place and unwelcome on commuter services, these issues conspire to hinder the use of public transport by children and their carers. Overlaying feminist geography analysis and insights and child-friendly cities objectives, this paper proposes some basic criteria for the provision of public transport services and supporting infrastructure which meets the needs of children, babies and their carers and juxtaposes the achievement of these in South East Queensland, Australia and Stockholm, Sweden.

The Journey of Becoming Involved in Urban Spaces by Children with Diverse Mobility

Participation is a word frequently espoused in the literature of childhood and urban studies. It has also been made sacrosanct through the Convention on the Rights of the Child and other rights-based policy and programming. Despite this importance, what it means and how it is experienced in the everyday lives of children with diverse abilities is not well understood. This chapter provides insight into the everyday experiences of participation by ten children 9-12 years of age, who have diverse personal mobility from various physical conditions that affect muscle and movement differently, including: Muscular Dystrophy, Cerebral Palsy, and Autoimmune Rheumatic Diseases. The children participants live in the outer suburbs and inner regions of south-east Queensland, Australia. The chapter discusses a new way of understanding and theorising participation as a journey of becoming involved. This knowledge emerged through the children’s body-space-time routines (body ballets) and their descriptions of inhabiting urban space. This chapter also establishes how body-space-context interplays shape the experiences of becoming and being involved in everyday life, as well as the preconceptions of body embed in space which divide and constrain children and families actualisation of full and genuine participation.

Learned stochastic mobility prediction for planning with control uncertainty on unstructured terrain

Motion planning for planetary rovers must consider control uncertainty in order to maintain the safety of the platform during navigation. Modelling such control uncertainty is difficult due to the complex interaction between the platform and its environment. In this paper, we propose a motion planning approach whereby the outcome of control actions is learned from experience and represented statistically using a Gaussian process regression model. This mobility prediction model is trained using sample executions of motion primitives on representative terrain, and predicts the future outcome of control actions on similar terrain. Using Gaussian process regression allows us to exploit its inherent measure of prediction uncertainty in planning. We integrate mobility prediction into a Markov decision process framework and use dynamic programming to construct a control policy for navigation to a goal region in a terrain map built using an on-board depth sensor. We consider both rigid terrain, consisting of uneven ground, small rocks, and non-traversable rocks, and also deformable terrain. We introduce two methods for training the mobility prediction model from either proprioceptive or exteroceptive observations, and report results from nearly 300 experimental trials using a planetary rover platform in a Mars-analogue environment. Our results validate the approach and demonstrate the value of planning under uncertainty for safe and reliable navigation.

A/Effective connections : mobility, technology and well-being

This article investigates the significance of internet communication technologies for mediating affect in ways that help promote feelings of well-being among recently arrived migrants from culturally and linguistically diverse communities (CALD) in Australia. It is based on a qualitative study that focuses on the internet's communicative capabilities for maintaining kinship ties in homeland countries, and for forging new connections in the host city of Brisbane during the early re-settlement period. Through the experience of ‘presence’ and affective communities, it emphasizes the ways in which visually mediated interaction helps to combat feelings of social isolation and loneliness. The study finds that internet use is creating new forms of sociality among migrants and plays a key role in the re-settlement period. It highlights the importance of publicly available computers and training for migrants.

Migrants, refugees and mobility : how useful are information communication technologies in the first phase of resettlement?

The rate at which people move and resettle around the world is unprecedented. Mobility and resettlement is now greatly assisted by the use of inexpensive internet communication technologies (ICTs) for a wide variety of functions: to communicate locally and across territories, for localised information seeking, geo – locational mapping and for forging new social connections in host countries and cities. This article is based on a qualitative study of newly arrived migrants and mobile people from non English speaking backgrounds (NESB) to the city of Brisbane, Australia and investigates how the internet is used to assist the initial period of settling into the city. As increasing amounts of essential information is placed online, the study asks how people from NESB communities manage to negotiate the types of information they require during the early stages of resettlement, given varying levels of access to ICTs, digital and language literacy. The study finds that the internet is widely used for specific location information seeking (such as accommodation and job-seeking), but this is often supplemented with other non-mediated sources of information. The study identified implications for social policy in regard to the resourcing and access of information. While findings are specific to the study location, it is feasible that the patterns of internet use for resettlement have relevance in a broader context.

Design of high mobility DPP-based polymer semiconductors for organic thin film transistors

π-Conjugated polymers are the most promising semiconductor materials to enable printed organic thin film transistors (OTFTs) due to their excellent solution processability and mechanical robustness. However, solution-processed polymer semiconductors have shown poor charge transport properties mainly originated from the disordered polymer chain packing in the solid state as compared to the thermally evaporated small molecular organic semiconductors. The low charge carrier mobility, typically < 0.1 cm2 /V.s, of polymer semiconductors poses a challenge for most intended applications such as displays and radio-frequency identification (RFID) tags. Here we present our recent results on the dike topyrrolopyrrole (DPP)-based polymers and demonstrate that when DPP is combined with appropriate electron donating moieties such as thiophene and thienothiophene, very high charge carrier mobility values of ~1 cm2/V.s could be achieved.

Characterization of acyl chain position in unsaturated phosphatidylcholines using differential mobility-mass spectrometry

Glycerophospholipids (GPs) that differ in the relative position of the two fatty acyl chains on the glycerol backbone (i.e., sn-positional isomers) can have distinct physicochemical properties. The unambiguous assignment of acyl chain position to an individual GP represents a significant analytical challenge. Here we describe a workflow where phosphatidylcholines (PCs) are subjected to ESI for characterization by a combination of differential mobility spectrometry and MS (DMS-MS). When infused as a mixture, ions formed from silver adduction of each phospholipid isomer {e.g., [PC (16:0/18:1) + Ag]+ and [PC (18:1/16:0) + Ag]+} are transmitted through the DMS device at discrete compensation voltages. Varying their relative amounts allows facile and unambiguous assignment of the sn-positions of the fatty acyl chains for each isomer. Integration of the well-resolved ion populations provides a rapid method (< 3 min) for relative quantification of these lipid isomers. The DMS-MS results show excellent agreement with established, but time-consuming, enzymatic approaches and also provide superior accuracy to methods that rely on MS alone. The advantages of this DMS-MS method in identification and quantification of GP isomer populations is demonstrated by direct analysis of complex biological extracts without any prior fractionation.

Adsorption and mobility of metals in build-up on road surfaces

The study investigated the adsorption and bioavailability characteristics of traffic generated metals common to urban land uses, in road deposited solids particles. To validate the outcomes derived from the analysis of field samples, adsorption and desorption experiments were undertaken. The analysis of field samples revealed that metals are selectively adsorbed to different charge sites on solids. Zinc, copper, lead and nickel are adsorbed preferentially to oxides of manganese, iron and aluminium. Lead is adsorbed to organic matter through chemisorption. Cadmium and chromium form weak bonding through cation exchange with most of the particle sizes. Adsorption and desorption experiments revealed that at high metal concentrations, chromium, copper and lead form relatively strong bonds with solids particles while zinc is adsorbed through cation exchange with high likelihood of being released back into solution. Outcomes from this study provide specific guidance for the removal of metals from stormwater based on solids removal.

Better health outcomes for people with physical disabilities in China through audits of mobility related access : a research and implementation need

China has 85 million people with disabilities, 30% of whom have a physical disability(1). Up to 2006, overall disability rates increased by 0.5% per year, more for males and in rural areas, and rates of physical disability increased by 11.2% per year(2). With population ageing the proportion of people with disability will increase even faster. In May 2014 the 67th World Health Assembly adopted a resolution endorsing the WHO Global Disability Action Plan 2014–2021. One of its three objectives is “to remove barriers and improve access to health services and programmes”. Access to transport contributes to positive health outcomes both directly and indirectly (e.g. access to economic opportunities, which is associated with better health)(3). However, once people with physical disabilities leave their dwellings they are confronted with physical barriers to their mobility, ranging from the condition/provision of paths to the cost/availability of transport and access to buildings. In addition, their mobility restrictions increase their vulnerability as road users, exposing them to a higher risk of injury through road crashes. QUT's School of Public Health and Social Work (PHSW) and and Centre for Accident Research and Road Safety-Queensland (CARRS-Q) CARRS-Q have been collaborating on development of a combined disability audit and road safety access tool that can identify transport barriers and safety issues along the routes taken by people with disabilities, to enable prioritisation of actions to address these issues. There are also spin-off benefits for other road users from addressing the rising toll of disability through road crashes in China(4). The tool has undergone initial proof-of-concept testing in India and Viet Nam, and is currently being assessed in Cambodia and Laos. Given the rapid development of China, increases in rates of physical disability and the impacts of an ageing population, it is proposed to establish collaborative research through the Australia-China Centre for Public Health to (1) tailor the combined road safety audit and disability access tool for use in China; (2) evaluate its use on a sample of routes; (3) develop plans for changes to the routes in consultation with local authorities; (4) evaluate the effectiveness of implemented changes in terms of access and health. 1. Zheng, Q, et al, 2014. Health and Quality of Life Outcomes, 12:25. 2. Zheng, X, et al, 2011. Bull World Health Org, 89:788–797. 3. Götschi, T & Kahlmeier, S, 2011. Integrated Transport, Health, and Sustainability Assessment (INTHESA): Final Report. Institute of Social and Preventive Medicine, University of Zurich. 4. Lin, T, et al, 2013. J Public Health, 35:541–547.

The limits to public service : rural communities, professional families, and work mobility

Australia faces an ongoing challenge recruiting professionals to staff essential human services in rural and remote communities. This paper identifies the private limits to the implicit service contract between professions and such client populations. These become evident in how private solutions to competing priorities within professional families inform their selective mobility and thus create the public problem for such communities. The paper reports on a survey of doctors, nurses, teachers and police with responsibility for school-aged children in Queensland that plumbed the strength of neoliberal values in their educational strategy and their commitment to the public good in career decisions. The quantitative analysis suggested that neoliberal values are not necessarily opposed to a commitment to the public good. However, the qualitative analysis of responses to hypothetical career opportunities in rural and remote communities drew out the multiple intertwined spatial and temporal limits to such public service, highlighting the priority given to educational strategy in these families’ deliberations. This private/public nexus poses a policy problem on multiple institutional fronts.

Time-independent charge carrier mobility in a model polymer:fullerene organic solar cell

The technique of photo-CELIV (charge extraction by linearly increasing voltage) is one of the more straightforward and popular approaches to measure the faster carrier mobility in measurement geometries that are relevant for operational solar cells and other optoelectronic devices. It has been used to demonstrate a time-dependent photocarrier mobility in pristine polymers, attributed to energetic relaxation within the density of states. Conversely, in solar cell blends, the presence or absence of such energetic relaxation on transport timescales remains under debate. We developed a complete numerical model and performed photo-CELIV experiments on the model high efficiency organic solar cell blend poly[3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-naphthalene] (PDPP-TNT):[6,6]-phenyl-C71-butyric-acid-methyl-ester (PC70BM). In the studied solar cells a constant, time-independent mobility on the scale relevant to charge extraction was observed, where thermalisation of photocarriers occurs on time scales much shorter than the transit time. Therefore, photocarrier relaxation effects are insignificant for charge transport in these efficient photovoltaic devices.

Impact of Mobility Constraints on Epidemic Broadcast in DTNs

In this paper, we investigate the effect of mobility constraints on epidemic broad-cast mechanisms in DTNs (Delay-Tolerant Networks). Major factors affecting epidemic broadcast performances are its forwarding algorithm and node mobility. The impact of forwarding algorithm and node mobility on epidemic broadcast mechanisms has been actively studied in the literature, but those studies use generally unconstrained mobility models. The objective of this paper is therefore to quantitatively investigate the effect of mobility constraints on epidemic broadcast mechanisms. We evaluate the performances of P-BCAST (PUSH-based BroadCast), SA-BCAST (Self-Adaptive BroadCast), and HP-BCAST (History-based P-BCAST) with a random waypoint mobility model with mobility constraints.