• Energy Research
• Embargo close
• GB close
• DE close
• US close
• RU close

Over the past decade, lead-halide perovskites (LHPs) have demonstrated significant potential in terms of their performance across a wide range of optoelectronic devices, including solar cells, photodetectors and light-emitting diodes. However, the toxicity of lead and instability issue of LHPs are still concerns for their widespread implementation. These successes, but also the challenges of LHPs have motivated great efforts across multiple disciplines to search for lead-free and stable alternatives that can have similar optoelectronic properties to LHPs, namely ‘perovskite-inspired materials (PIMs)’. With the deeper understanding of defect tolerance displayed in LHPs, a large number of PIMs have been identified until now. Among all the identified PIMs, ternary chalcogenides or ABZ2 materials, are believed to be one of the most promising alternatives so far, owing to their simple fabrication protocols, strong absorption and high stability in air. Particularly, AgBiS2 solar cells have demonstrated the highest efficiency (9.17%) among all bismuth-based solar cells. Nevertheless, studies into ternary chalcogenides are mostly limited to AgBiS2 photovoltaics, and the investigations into other potential ABZ2 materials or broader applications are rare so far. Therefore, this thesis will aim to investigate the optoelectronic properties of another promising while rarely investigated ABZ2 material – NaBiS2, and also the potential of AgBiS2 as near-infrared (NIR) photodetectors. In the first project of this thesis, NaBiS2 nanocrystals (NCs) have been shown to exhibit extremely strong absorption, along with a comparatively sharp absorption onset. However, optical-pump-terahertz-probe (OPTP) measurements indicated that most free charge-carriers in NaBiS2 NCs will be localised within a few picoseconds. These localised charge-carriers only exhibited low mobility of around 0.03 cm2 V-1 s-1 and could not transport effectively even though they might be rather long-lived in NaBiS2 and unaffected by intentionally-introduced defects. With help from density functional theory (DFT) calculations, all of these unusual characteristics in NaBiS2 have been shown to closely associate with intrinsic cation disorder, which was also observed in AgBiS2. Although post-annealing is effective for improving cation inhomogeneity and enhancing absorption in AgBiS2, its effect on NaBiS2 was found to be rather minor, which also indicated that the charge-carrier localisation process in NaBiS2 could not be significantly mitigated after annealing. Based on the fundamental insights acquired in the first project, the possibility of further improving charge-carrier transport in NaBiS2 NCs through ligand exchange treatment was investigated in my second project. Using a variety of correlated spectroscopic characterisation techniques, I found that NaBiS2 NCs treated by inorganic iodide ligands had enhanced sum mobility and surface photovoltage (SPV) signals, which implies an improvement in the macroscopic charge-carrier transport. However, the ultrafast localisation process was still observed in these iodide-treated NaBiS2 NCs, suggesting that their cation disorder was not greatly changed. At the same time, the defect capture rates were also found to be lower in the iodide-treated NaBiS2 NCs based on my two proposed models for describing charge-carrier dynamics. As a result, solar cells based on these iodide-treated NaBiS2 NCs could exhibit a peak external quantum efficiency (EQE) value over 50%, along with a power conversion efficiency exceeding 0.7%. Although this is an order of magnitude larger than previous reports, I found ion migration to be a limiting factor for NaBiS2 devices from temperature-dependent transient current measurements, where a low activation energy of only 88 meV was extracted. In my third project, AgBiS2 photodetectors were fabricated and characterised in depth. Aside from the broadband photo-response across from ultra-violet (UV) to near-infrared (NIR) region, AgBiS2 photodetectors have demonstrated an extremely high cut-off frequency (f-3dB) on MHz order, indicating their great potential in applications requiring fast device response such as optical communications. The mechanism behind this fast response was studied, and a relatively long drift length compared to the AgBiS2 film thickness is believed to be the key reason. Similar to NaBiS2 devices, ion migration was also found easy in AgBiS2 devices with an activation energy of 124 meV, which could lead to their increasing noise currents with time. Importantly, these noise currents could be also effectively suppressed when optimising the AgBiS2 film thickness, in which a balance between large shunt resistant and cumulative quantity of defects should be reached. Finally, owing to the small bandgap of AgBiS2 NCs (~1.2 eV), AgBiS2 photodetectors could effectively monitor the heartbeat rates by probing the transmission change of blood vessels illuminated by NIR light, which has been widely used in the medical field owing to its deeper penetration in tissues. These three projects not only uncovered several remarkable optoelectronic characteristics of ABZ2 materials, but also investigated possible methods to further alter these characteristics. Although ABZ2 materials have shown great potential as light harvesters, it can be seen that both cation disorder (or charge-carrier localisation) and ion migration are still limiting the performance. More studies on the root causes of both phenomena, and how to effectively suppress their effects on the materials, would be hence crucial in the future work. With more understandings on this material class, we could expect more efficient, stable, and cleaner optoelectronic devices to be realised in the future.

AbstractMountain treelines are thought to be sensitive to climate change. However, how climate impacts mountain treelines is not yet fully understood as treelines may also be affected by other human activities. Here, we focus on “closed‐loop” mountain treelines (CLMT) that completely encircle a mountain and are less likely to have been influenced by human land‐use change. We detect a total length of ~916,425 km of CLMT across 243 mountain ranges globally and reveal a bimodal latitudinal distribution of treeline elevations with higher treeline elevations occurring at greater distances from the coast. Spatially, we find that temperature is the main climatic driver of treeline elevation in boreal and tropical regions, whereas precipitation drives CLMT position in temperate zones. Temporally, we show that 70% of CLMT have moved upward, with a mean shift rate of 1.2 m/year over the first decade of the 21st century. CLMT are shifting fastest in the tropics (mean of 3.1 m/year), but with greater variability. Our work provides a new mountain treeline database that isolates climate impacts from other anthropogenic pressures, and has important implications for biodiversity, natural resources, and ecosystem adaptation in a changing climate.

Synopsis Climate change is accelerating the increase of temperatures across the planet and resulting in the warming of oceans. Ocean warming threatens the survival of many aquatic species, including squids, and has introduced physiological, behavioral, and developmental changes, as well as physical changes in their biological materials composition, structure, and properties. Here, we characterize and analyze how the structure, morphology, and mechanical properties of European common squid Loligo vulgaris sucker ring teeth (SRT) are affected by temperature. SRT are predatory teethed structures located inside the suction cups of squids that are used to capture prey and are composed of semicrystalline structural proteins with a high modulus (GPa-range). We observed here that this biological material reversibly softens with temperature, undergoing a glass transition at ∼35°C, to a MPa-range modulus. We analyzed the SRT protein nanostructures as a function of temperature, as well as microscale and macroscale morphological changes, to understand their impact in the material properties. The results suggested that even small deviations from their habitat temperatures can result in significant softening of the material (up to 40% in modulus loss). Temperature changes following recent global climate trends and predictions might affect environmental adaptation in squid species and pose emerging survival challenges to adapt to increasing ocean temperatures.

For layered oxide cathodes, aluminum doping has widely been shown to improve performance, particularly at high degrees of delithiation. While this has led to increased interest in Al-doped systems, including $\mathrm{LiNi_{0.8}Co_{0.15}Al_{0.05}O_{2}}$ (NCA), the aluminum surface environment has not been thoroughly investigated. Using hard x-ray photoelectron spectroscopy measurements of the Al 1s core region for NCA electrodes, we examined the evolution of the surface aluminum environment under electrochemical and thermal stress. By correlating the aluminum environment to transition metal reduction and electrolyte decomposition, we provide further insight into the cathode-electrolyte interface layer. A remarkable finding is that Al-O coatings in LiPF$_6$ electrolyte mimic the evolution observed for the aluminum surface environment in doped layered oxides. ECS transactions 80(10), 197 - 206 (2017). doi:10.1149/08010.0197ecst Published by Pennington, NJ

Synopsis The biological structures that fill the environment around us are derived from materials produced by organisms. These biological materials are key to the mechanical function of organisms. The pathways and growth processes that produce biological materials can influence the mechanical properties of the materials, which can in turn shape the higher level function of the system into which the materials are incorporated. Characterizing a biological system requires thorough knowledge of the underlying materials, including their mechanical function, diversity, evolution, and sensitivity to the environment. Anthropogenic activity is driving rapid and widespread changes to the natural environment and global climate, which are influencing organismal growth and physiology in myriad ways. Here, we briefly introduce a collection of articles that focus on the intersection of anthropogenic activity and the mechanical function of biological materials, as part of the “Global Change in a Material World” bundle for Integrative and Comparative Biology. In addition, we provide an analysis of the current scientific literature in this field, highlighting an urgent need to better understand how changes to our world, driven by human activity, are influencing the fundamental architecture and mechanical performance of organisms across the globe.

This paper examines the 2021-2023 energy crisis in Europe exacerbated by the energy consequences of the full-scale Russia – Ukraine war which began in February 2022. We show that this is an historically unprecedented price shock to both gas and electricity prices. We then draw on lessons from UK energy policy in World War Two to inform European energy policy during this crisis. In light of this, we highlight four good and three bad policy responses to observed across Europe. The EU has responsibility for the European single market in electricity and gas (which also formally includes Norway and effectively includes the UK). We examine its attempts to co-ordinate EU-27 responses to the crisis. We conclude with longer-run lessons for energy and climate policy arising from this gas and electricity price shock.

Over the past several years, online disinformation and misinformation concerning climate change have gained substantive attention within the scientific community. However, while the dynamics that drive the circulation of false online information have been analysed extensively, it remains unclear whether (and how) this phenomenon can be counteracted. This research project analyses the emerging role of bottom-up mobilisations as a form of noise-reduction, thereby examining how social movements may deploy peer-produced communication narra- tives to counteract the circulation of online disinformation and misinformation relating to climate change. To investigate this communication dynamic, this research applies techniques from computational social sciences to an original dataset of ≈ 250k Facebook posts produced by two movements that best embody this novel and innovative generation of radical envi- ronmental activism: Extinction Rebellion and Fridays for Future. The central thesis of this project forwards two original contributions to the fields of climate change communication and social movement studies. First, it analyses the emergence of a new generation of radical climate change movements and the significance of this new development in climate activism (Chapter II). Second, it offers interdisciplinary empirical evidence on how radical climate movements can act as a bottom-up force for what I term ‘epistemic activism’. It presents a theoretical framework where activist-led, peer-produced communication can provide a coun- tering force to both vertical disinformation and horizontal misinformation. It quantitatively analyses two channels through which these forms of false information can be opposed. For reducing vertical disinformation, this work assesses the use of naming and shaming against information polluters (Chapter III), while for horizontal misinformation, it evaluates the dissemination of scientific counter-narratives (Chapter IV). Ultimately, this thesis shows that the two movements under analysis engage extensively in epistemic activism, with great potential to influence the online climate change debate positively.