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Developing chalcogenide materials for photovoltaic applications
Get PDFLead halide perovskites (LHPs) have shown great potential for optoelectronic applications, including solar cells, photodetectors and light-emitting diodes, but face challenges due to the toxicity of the lead and the limited stability of these materials. These concerns motivate the search for lead-free and more stable alternatives with similar optoelectronic properties to LHPs, and these materials are collectively referred to as ‘perovskite-inspired materials (PIMs)’. Among the studied PIMs, chalcogenide semiconductors based on heavy pnictogen cations (Sb3+ and Bi3+) have gained increasing attention due to the similar electronic structure of Sb3+ and Bi3+ to that of Pb2+, which is believed to be important for the defect tolerance found in LHPs. Chalcogenides also generally have improved stability compared to halide compounds. However, a limitation of pnictogen-based halide and chalcogenide semiconductors is the prevalence of charge-carrier localisation, which severely reduces mobilities and diffusion lengths. Therefore, the discovery of pnictogen-based semiconductors with delocalised chargecarriers, and understanding the principles behind how band-like transport could be found, are important for the future development of these PIMs. In my first project, through optical pump terahertz probe spectroscopy and temperaturedependent mobility measurements, the pnictogen-based semiconductor CuSbSe2 was discovered to have delocalised free charge-carriers, which is different to many other Sb- and Bi-based PIMs explored thus far. Charge-carrier localisation in this family of materials has been so prevalently found that it is being referred to as a “hallmark” of these materials, and fundamentally prevents these materials from reaching their optical limits in efficiency. Therefore, the discovery of delocalised charge-carriers in CuSbSe2 and the understanding of the enabling factors can provide valuable suggestions on how the chemistry of heavy pnictogen-based materials could be changed to avoid this limitation. Through theoretical and experimental studies, I find that the critical factors enabling delocalised charge-carriers are: 1) the presence of regular free volume in the layered structure that can relax the lattice distortions caused by the propagation of acoustic waves in the interlayer gaps, such that bond lengths negligibly change, leading to low deformation potentials; 2) higher electronic dimensionality at band extrema due to quasi-bonding across these interlayer gaps; 3) a low ionic contribution to the dielectric constant compared to the electronic contribution caused by relatively low Born effective charges, as well as the small bandgap (≤ 1.2 e)), thus leading to weak Fröhlich coupling. These findings could be generalisable to other pnictogen-based semiconductors.As CuSbSe2 has been shown to exhibit delocalised charge-carriers, I next investigate two techniques to deposit CuSbSe2 thin films: solution processing and chemical vapour deposition, with the aim of developing these materials into photovoltaics. The novel thiol-amine-based solution processing method is safer than the previously-reported method employing hydrazine as the solvent. Meanwhile, compared to the co-sputtering of metal selenides, which was previously used to achieve the highest efficiency CuSbSe2 solar cells thus far, solution processing may be more cost-effective, since it does not require expensive equipment or vacuum systems. The simpler operation of solution processing also allows the efficient exploration of different parameters. After achieving phase-pure CuSbSe2 thin films via the thiol-amine-based solution processing route, through morphological studies, I found that the heat treatment and the underlayer (compact TiO2, meso-porous TiO2, SnO2 or NiOx) can influence the morphology of solution-processed CuSbSe2 thin films, while the morphology of chemical-vapour-deposited CuSbSe2 thin films is mainly determined by the substrate temperature. Solution-processed CuSbSe2 thin film-based solar cells were all shunted, which can be attributed to the high density of pinholes and small grains present in these films. Some pixels based on C)D CuSbSe2 thin films showed diode-like J-) curves, but exhibited unmeasurable PCEs. This project found that moderate thermal energy input at the beginning of the heat treatment could improve the microscopic morphology of the solution-processed CuSbSe2 thin films. The layer under CuSbSe2 was also found to influence the morphology of the solution-processed CuSbSe2 thin films. To further improve the film morphology, future studies can focus on the underlayers, different solvents (thiols and amines), and heat treatment methods.In the third section, I investigate Sb2S3, grown by chemical bath deposition (CBD). This has been studied for photovoltaics well before the interest in LHPs grew, and has a bandgap (~1.7 e)) that is well-matched with the spectrum from indoor light sources (e.g., white light emitting diodes (WLEDs)). We achieved 17.55%-efficient Sb2S3 indoor photovoltaics (IP)s) under 1000 lux WLED illumination, which was the record value for this material at the time of publication in 2024. However, one key challenge of Sb2S3 photovoltaics is the use of CdS as the buffer layer. Cd is more toxic than Pb, and may impede the commercial development of Sb2S3 photovoltaics. Therefore, in my third project, I focus on developing Cd-free electron transport layers (ETLs). As deposition on CBD-grown SnO2 resulted in discontinuous Sb2S3 films with pinholes, the morphology evolution of Sb2S3 thin films deposited on CdS and SnO2 are compared to understand the fundamental reasons. Microscopic analysis showed that isolated spherical Sb2S3 clusters tend to form on the SnO2 surface. In-depth XPS analysis further reveals that Sb primarily bonds with oxygen on the surface of SnO2, forming Sb2O3, which hinders the heterogeneous nucleation of Sb2S3 on the surface of SnO2, and results in the discontinuous Sb2S3 films. Also, introducing CdS as an interfacial layer between SnO2 and Sb2S3 improved the Sb2S3 film morphology, while significantly reducing the overall Cd content in the device. This suggests that alternative sulphide interfacial layers could optimise Sb2S3 film morphology and enable the development of Cd-free solar cells. Furthermore, our Sb2S3 solar cells exhibited excellent performance under 1-sun illumination, with open-circuit voltage (VOC) values (0.748 )) comparable to the highest reported in the literature (0.796 )). Optical loss analysis identifies device reflection and window layer parasitic absorption as key factors limiting the short-circuit current density, suggesting anti-reflection coatings and more transparent buffer layers as promising strategies for improvement. Overall, this work unravels the mechanisms enabling CdS to outperform SnO2 as the buffer layer for Sb2S3 solar cells, and offers insight into designing more benign buffer layers to improve performance.These three projects not only investigate the fundamental limitations of pnictogen-based chalcogenide semiconductors, such as charge-carrier localisation, but also make contributions to the practical applications and optimisation of these materials as solar absorbers. Based on the understanding of mechanisms enabling delocalised charge-carriers in CuSbSe2, more perovskite-inspired materials with band-like transport can be discovered in the future. Meanwhile, the novel methods to synthesize CuSbSe2 are expected to promote the development of more efficient solar cells with improved safety and cost-efficiency. Moreover, the investigation on the buffer layers for Sb2S3 solar cells highlights the critical properties determining the quality of Sb2S3 films, providing guidance for designing more benign buffer layers. As we have demonstrated the exceptional potential of Sb2S3 solar cells for indoor light harvesting, replacing CdS with other environmentally friendly sulphide buffer layers is expected to contribute to the commercial development of Sb2S3 solar cells for IP). With more efforts and understanding, it is believed that chalcogenide materials can be suitable for sustainable, stable and high-efficiency photovoltaic devices
Conceptualising processes of user learning in domestication theory: what, why, and how?
Get PDFThe idea that users learn about new technologies in order to make them work within their daily lives is an important concept in domestication theory. It offers a way to conceptualise technology-user co-construction across household- and societal-level trajectories, and can be applied to identify policy relevant insights. However, while cognitive, symbolic and practical dimensions of learning in domestication are well established, processes of how users learn remain under-conceptualised. To address this gap, this paper employs process analysis to examine how users learned about a novel lower-carbon home heating technology (smart hybrid heat pumps). Starting from the principle that learning emerges from interactions between elements of technologies and of users’ daily lives, it abductively develops a framework of four learning processes: receiving, experiencing, interpreting and responding. It illustrates how these four interlinked processes give rise to cognitive, symbolic and practical learning, then discusses their role in domestication trajectories and implications for policy
Shifting the discourse on multinational pharmaceutical companies’ climate action to support net zero progress: an adapted argumentative discourse analysis
Get PDFBackground: Up to 55% of health system greenhouse gas emissions are estimated to come from pharmaceuticals, contributing to climate change. There is limited understanding of how pharmaceutical companies mitigate their climate impact. My research explored how multinational pharmaceutical companies approached climate action and what might support net zero progress. Methods: Guided by Maarten Hajer’s argumentative discourse analysis, I analysed data from purposively sampled (a) company documents from three selected multinational pharmaceutical companies, and (b) narrative interviews with twenty-one representatives from these companies, industry groups, and health systems. Argumentative discourse analysis studies the discursive production of meaning about phenomena and the practices through which discourses are produced, reproduced, or transformed. Key analytical concepts include (a) storylines, condensed statements underpinned by various discourses, the ensemble of ideas and concepts through which meaning is ascribed to phenomena; (b) counter-storylines, condensed statements that challenge storylines; (c) discourse-coalitions, actors sharing storylines; and (d) discourse institutionalisation, the solidification of discourse into institutional practices. I extended my analysis with concepts from impression management theory, which sensitised me to the performativity of pharmaceutical company climate action. Findings: I identified four storylines and counter-storylines, underpinned by distinct discourses. (a) Climate action conflicts with patient wellbeing, underpinned by a biomedical discourse prioritising patient care typically via pharmaceuticals, through which pharmaceutical climate impact and inaction was legitimised. A counter-storyline, reflecting planetary health discourse, framed climate action as integral to patient wellbeing. (b) Climate action is contingent on financial viability, advanced by pharmaceutical actors drawing on economic discourse to frame climate action through financial terms. Health system actors challenged this through a counter-storyline, using normative discourse to advocate for climate action regardless of financial viability. (c) Climate action as emissions quantification and disclosure, underpinned by technocratic discourse through which emissions data was framed as vital for compliance and to inform climate action. A counter-storyline, grounded in post-technocratic discourse, critiqued over-reliance on data, urging focus on emissions reduction. (d) Climate action requires more collaboration, drawing on techno-optimist and network governance discourses, climate action was framed as solvable through collective innovation and shared responsibility. Calls for collaboration often remained vague or served to displace responsibility. Conclusion: Dominant discourses, institutionalised in practice, collectively framed pharmaceutical company climate action as conditional on ensuring patient wellbeing, financial viability, access to emissions data, or increased collaboration, thereby delaying and constraining net zero progress. Acceptance, reproduction, and institutionalisation of counter-storylines and alternative discourses by key actors offers potential to support net zero progress, by reframing climate action as interconnected with patient wellbeing, decoupling it from profit, shifting emphasis from quantifying emissions to reducing them, and facilitating productive collaboration
New models for South African consumption, house prices, and mortgage and non-mortgage debt
Get PDFAggregate consumption typically exceeds 60 per cent of GDP and should be pivotal in central bank policy models. Most use semi-structural macro-models, yet consumption is usually inadequately specified. We use a systems approach to estimate new equations for South African consumption, house prices, mortgage and non-mortgage debt, and income forecasting. A credit-augmented consumption function approach introduces a greater role for uncertainty and a key role for credit conditions, and varies the spendability of different wealth components. This provides new insights into the multiple monetary transmission mechanisms, from policy interest rates and credit conditions to aggregate demand, including via non-homogeneous household balance sheet items on consumption. Credit conditions for mortgages and for other debt move quite differently from each other, with implications for consumer spending. Non-mortgage debt covers a larger fraction of total household debt than in advanced market economies, affecting household financial vulnerability. Housing market participants tend to extrapolate recent house price changes when forming expectations of capital gains, so positive shocks to housing demand can feed back onto house prices and consumption and extend boom conditions. House prices and debt can overshoot relative to their fundamentals, affecting financial stability. These findings should benefit future policy modelling in South Africa
Global Hong Kong: Post-2019 Migration and the New Hong Kong Diaspora Edited by Yuk Wah Chan and Yvette To. London and New York: Routledge, 2025. 212 pp. £145.00 (hbk). ISBN 9781032896892
Get PDFEffect of bariatric surgery on non-alcoholic fatty liver disease: an exploratory metabolomics and validation study
Get PDFBACKGROUND: Bariatric surgery presents a significant alleviation for non-alcoholic fatty liver disease (NAFLD), which relies in part on achieving substantial weight loss in post-surgical period. We aimed to understand the effect of bariatric surgery on NAFLD remission via metabolomics and to validate the results in a general population-based cohort.METHODS: In a pilot study, ten patients with NAFLD who underwent bariatric surgery were enrolled. The remission of hepatic steatosis was assessed by MRI-derived proton density fat fraction (PDFF) before and 3-month after surgery. Temporal associations of body mass index (BMI) reduction, alteration in metabolomic biomarkers, and NAFLD remission were quantified by using cross-lagged models, which were then validated in a general population-based cohort (n = 1258).RESULTS: At 3-month after surgery, BMI reduction of 6.9 (SD 1.9) kg/m2 and MRI-PDFF reduction of 9.6% (5.4) (all p-value < 0.001) were achieved. Of the 64 metabolomic biomarkers quantified, 19 biomarkers showed significant differences between pre- and post-surgery (false discovery rate-corrected p-value < 0.05). Temporal associations were observed between BMI reduction and 5 metabolomic biomarkers, while 3 (chenodeoxycholic acid [CDCA], palmitoylcarnitine, and hippuric acid) were further validated in the general population-based cohort. CDCA was able to explain 18% of the association between BMI reduction and NAFLD remission (p-value < 0.05). In the general population-based cohort, Mendelian randomization showed that genetically elevated CDCA level was associated with a higher risk of liver fibrosis.CONCLUSIONS: CDCA is a potential mediator and may predict long-term surgical benefits in liver fibrosis regression
Delivering the Parenting for Lifelong Health Programme with Parents of Young Children in Wales
Get PDFHighlights: What are the main findings? Child behaviour challenges and parenting challenges have risen since COVID-19, especially for low-income families. The cost of delivering parenting interventions can be substantial. What is the implication of the main finding? The Parenting for Lifelong Health programme for parents of Young Children (PLH-YC) is an evidence-based low-cost intervention. Results suggest that the programme is feasible, acceptable, and achieves good outcomes with vulnerable families in Wales. Abstract: Background/Objectives: Based on years of work from high-income countries, the Parenting for Lifelong Health programme for parents of Young Children (PLH-YC) was developed by the first and last authors, as a freely available low-cost programme for low-income families in low- and middle-income countries (LMICs). The initial group-based 12-session programme has since been delivered, adapted, and evaluated across many LMICs and now has a significant body of evidence. Over the last 10 years, early intervention services in the UK have been considerably reduced whilst, exacerbated by the impact of COVID-19, service demands have grown. This paper describes a feasibility trial of the 12-session PLH-YC programme in Wales to explore whether it could recruit and retain parents, and demonstrate improvements in parenting skills and reductions in child behaviour problems. Methods: Two small pre–post trials were conducted in socially disadvantaged communities in Wales, and they were delivered by local parenting practitioners. Of the 20 parents recruited across 3 groups, 17 provided pre- and post-course data and 10 completed qualitative interviews. Results: Retention was good (85%) with mean attendance of 8.7 sessions, and parental and facilitator feedback reported high levels of satisfaction with the programme, with the only recommendation being to make the programme longer and for facilitators to be given more time. Results showed significant benefits to parent-reported parenting practices, child behaviour, and parental mental wellbeing. Conclusions: These preliminary results justify work to develop a rigorous evaluation to establish whether PLH-YC could have a place among parenting-support programmes in the UK
Physical activity (20 min) is a powerful adjunct to insulin for correcting hyperglycaemia in Type 1 diabetes: A paradigm shift
Get PDFMultifunctional Fluidic Units for Emergent, Responsive Robotic Behaviors
Get PDFFluidic circuits have shown significant promise in enabling complex functionality in soft robots with a minimal number of input signals. However, implementing complex behaviors typically involves numerous specialized components, resulting in intricate and nonversatile circuits. To address this challenge, a multifunctional fluidic unit designed to operate flexibly as a valve, sensor, or actuator is introduced. This unit provides an extensive design space that allows precise tuning to achieve the desired functionality. In particular, one configuration integrates all three functions simultaneously, resulting in a self‐sensing oscillating actuator. By assembling multiple units—each customized for specific roles—complex robotic behaviors can be realized. The versatility and effectiveness of this modular approach are demonstrated by creating several robotic systems, including a controlled shaker, a multimodal hopper, and a crawler capable of sensing environmental boundaries. Furthermore, when these units are mechanically coupled via a shared body, it exhibit emergent passive behaviors, such as self‐synchronization—a behavior that is elucidated with a Kuramoto model of networks of oscillators. This study highlights the potential of multifunctionality as a powerful and efficient strategy for realizing embodied intelligence in fluidic robotic systems
Mapping the phenomenology of intranasal 5-MeO-DMT in psychedelic-naïve healthy adults
Get PDF5-Methoxy-N,N-dimethyltryptamine (5-MeO-DMT) is a naturally occurring psychedelic tryptamine. Plants containing 5-MeO-DMT have been used throughout history, and in recent years both synthetic and toad-derived 5-MeO-DMT use is being increasingly reported in naturalistic settings as well as clinical research. However, its subjective effects are not well characterised, and no qualitative research studies have been published to date. In this study, 32 psychedelic-naïve healthy participants from a double-blind, randomised, placebo-controlled, phase 1 trial of the escalating doses of a proprietary formulation of intranasal 5-MeO-DMT (BPL-003) were interviewed using the microphenomenology method shortly after dosing sessions. Microphenomenology is a qualitative research method well-suited to elucidating how subjective effects of this short-acting psychedelic unfold over time. Detailed qualitative and quantitative analysis of interview transcripts revealed a generic time-course of subjective effects, with rapid onset peaking at 8–15 min and gradual return to baseline over 45–60 min. The overall intensity of effects increased with dose and the doses tested were generally well tolerated. 5-MeO-DMT has a distinctive profile of subjective effects relative to published reports of other psychedelics, with a short duration of action, relative lack of visual effects, strong emotional or bodily experiences and the potential to elicit therapeutically relevant content, such as emotional breakthroughs and personal insights. These findings inform therapeutic applications, participant preparation, and future research on 5-MeO-DMT