A Theoretical Exploration of Emerging Solar Absorber Materials

Renewable energy sources are the only sustainable solutions that can address the increasing worldwide demand for energy without significantly furthering anthropogenic climate change and damage to our environment. Photovoltaics are able to harness the massive amount of solar radiation onto the earth each day through direct conversion to electricity, however have historically been expensive to produce and deploy on a large scale. In this thesis, we examine some of the challenges facing current photovoltaic technologies and how recently-developed materials, such as the inorganic-organic lead halide perovskites, have inspired the search for materials that may be used to provide highly-efficient, yet also cheap, mass-producible and flexible solar cells. Through ab initio density functional theory, we examine three families of compounds and, through the calculation of their electronic, optical and defect properties, are able to assess their suitability and potential as absorbers within photovoltaic devices. The caesium silver bismuth halides are lead-free analogues of the lead halide perovskites, however our calculations demonstrate that they are limited in comparison to their lead counterparts due to a mismatch in orbital angular momentum in their electronic structure, weakening their absorption. The silver copper sulfides have also shown recent promise as solar absorber materials, although we show that consideration of the optical properties is essential in successfully predicting the potential of such emergent materials. Finally, our survey of the lead bismuth sulfides predicts a promising compound for solar absorption, including the cell architecture that would be necessary to produce high device efficiencies. Through this study, we can accurately calculate properties of these materials but also hope to provide guidance in the future search for new photovoltaic technologies at the atomic scale

Understanding the electronic structure of Y2Ti2O5S2 for green hydrogen production: a hybrid- DFT and GW study

Combined hybDFT and GW study reveals surface properties and optoelectronic behaviour of Y2Ti2O5S2 for green hydrogen production

Spatial Electron-hole Separation in a One Dimensional Hybrid Organic-Inorganic Lead Iodide.

The increasing efficiency of the inorganic-organic hybrid halides has revolutionised photovoltaic research. Despite this rapid progress, the significant issues of poor stability and toxicity have yet to be suitably overcome. In this article, we use Density Functional Theory to examine (Pb2I6) · (H2DPNDI) · (H2O) · (NMP), an alternative lead-based hybrid inorganic-organic solar absorber based on a photoactive organic cation. Our results demonstrate that optical properties suitable for photovoltaic applications, in addition to spatial electron-hole separation, are possible but efficient charge transport may be a limiting factor

Understanding the Photocatalytic Activity of La₅Ti₂AgS₅O₇ and La₅Ti₂CuS₅O₇ for Green Hydrogen Production:Computational Insights

[Image: see text] Green production of hydrogen is possible with photocatalytic water splitting, where hydrogen is produced while water is reduced by using energy derived from light. In this study, density functional theory (DFT) is employed to gain insights into the photocatalytic performance of La(5)Ti(2)AgS(5)O(7) and La(5)Ti(2)CuS(5)O(7)—two emerging candidate materials for water splitting. The electronic structure of both bulk materials was calculated by using hybrid DFT, which indicated the band gaps and charge carrier effective masses are suitable for photocatalytic water splitting. Notably, the unique one-dimensional octahedral TiO(x)S(6–x) and tetragonal MS(4) channels formed provide a structural separation for photoexcited charge carriers which should inhibit charge recombination. Band alignments of surfaces that appear on the Wulff constructions of 12 nonpolar symmetric surface slabs were calculated by using hybrid DFT for each of the materials. All surfaces of La(5)Ti(2)AgS(5)O(7) have band edge positions suitable for hydrogen evolution; however, the small overpotentials on the largest facets likely decrease the photocatalytic activity. In La(5)Ti(2)CuS(5)O(7), 72% of the surface area can support oxygen evolution thermodynamically and kinetically. Based on their similar electronic structures, La(5)Ti(2)AgS(5)O(7) and La(5)Ti(2)CuS(5)O(7) could be effectively employed in Z-scheme photocatalytic water splitting

The Availability of Prior ECGs Improves Paramedic Accuracy in Recognizing ST-Segment Elevation Myocardial Infarction

Introduction Early and accurate identification of ST-elevation myocardial infarction (STEMI) by prehospital providers has been shown to significantly improve door to balloon times and improve patient outcomes. Previous studies have shown that paramedic accuracy in reading 12 lead ECGs can range from 86% to 94%. However, recent studies have demonstrated that accuracy diminishes for the more uncommon STEMI presentations (e.g. lateral). Unlike hospital physicians, paramedics rarely have the ability to review previous ECGs for comparison. Whether or not a prior ECG can improve paramedic accuracy is not known. Study hypothesis The availability of prior ECGs improves paramedic accuracy in ECG interpretation. Methods 130 paramedics were given a single clinical scenario. Then they were randomly assigned 12 computerized prehospital ECGs, 6 with and 6 without an accompanying prior ECG. All ECGs were obtained from a local STEMI registry. For each ECG paramedics were asked to determine whether or not there was a STEMI and to rate their confidence in their interpretation. To determine if the old ECGs improved accuracy we used a mixed effects logistic regression model to calculate p-values between the control and intervention. Results The addition of a previous ECG improved the accuracy of identifying STEMIs from 75.5% to 80.5% (p = 0.015). A previous ECG also increased paramedic confidence in their interpretation (p = 0.011). Conclusions The availability of previous ECGs improves paramedic accuracy and enhances their confidence in interpreting STEMIs. Further studies are needed to evaluate this impact in a clinical setting

Descriptors for Electron and Hole Charge Carriers in Metal Oxides

Metal oxides can act as insulators, semiconductors, or metals depending on their chemical composition and crystal structure. Metal oxide semiconductors, which support equilibrium populations of electron and hole charge carriers, have widespread applications including batteries, solar cells, and display technologies. It is often difficult to predict in advance whether these materials will exhibit localized or delocalized charge carriers upon oxidation or reduction. We combine data from first-principles calculations of the electronic structure and dielectric response of 214 metal oxides to predict the energetic driving force for carrier localization and transport. We assess descriptors based on the carrier effective mass, static polaron binding energy, and Fröhlich electron–phonon coupling. Numerical analysis allows us to assign p- and n-type transport of a metal oxide to three classes: (i) band transport with high mobility; (ii) small polaron transport with low mobility; and (iii) intermediate behavior. The results of this classification agree with observations regarding carrier dynamics and lifetimes and are used to predict 10 candidate p-type oxides

Cu₂SiSe₃ as a promising solar absorber: harnessing cation dissimilarity to avoid killer antisites

Copper-chalcogenides are promising candidates for thin film photovoltaics due to their ideal electronic structure and potential for defect tolerance. To this end, we have theoretically investigated the optoelectronic properties of Cu₂SiSe₃, due to its simple ternary composition, and the favourable difference in charge and size between the cation species, limiting antisite defects and cation disorder. We find it to have an ideal, direct bandgap of 1.52 eV and a maximum efficiency of 30% for a 1.5 μm-thick film at the radiative limit. Using hybrid density functional theory, the formation energies of all intrinsic defects are calculated, revealing the p-type copper vacancy as the dominant defect species, which forms a perturbed host state. Overall, defect concentrations are predicted to be low and have limited impact on non-radiative recombination, as a consequence of the p–d coupling and antibonding character at the valence band maxima. Therefore, we propose that Cu₂SiSe₃ should be investigated further as a potential defect-tolerant photovoltaic absorber