Quantifying Infiltration for Quality Control in Printed Mesoscopic Perovskite Solar Cells: A Microscopic Perspective.

Mesoscopic carbon-based perovskite solar cells (CPSCs) are often cited as a potential frontrunner to perovskite commercialization. Infiltration, the extent to which perovskite fills the mesoporous scaffold, is critical for optimum performance and stability. However, infiltration data are usually presented as qualitative photographic comparisons of samples with extreme infiltration variation. This work examines how small infiltration defects impact performance using an optical microscopy examination of the base TiO2 layer to identify issues and develop targeted techniques for infiltration enhancement. Critically, the uninfiltrated area at the base of the stack was found to correlate well with PCE across multiple batches of varied print quality and ZrO2 thickness. Through reduction of mesh mark defects and improvement of print quality in the ZrO2 and carbon layers, a champion PCE of 15.01% is attained. It follows that this facile, multiscaled, nondestructive technique could enable targeted performance enhancement and quality control in future scale-up initiatives.

PEARS: A Web Tool for Fitting Time-Resolved Photoluminescence Decays of Perovskite Materials.

Time-resolved photoluminescence (TRPL) is a powerful tool to investigate charge carrier recombination processes in emissive materials. Perovskite materials are extremely promising for applications in solar cells; however, the interpretation of their TRPL is arduous due to the complicated nature of the recombination processes occurring in these materials. We present here the PErovskite cArrier Recombination Simulator (PEARS) web tool for effortlessly and quickly fitting TRPL of perovskite materials using advanced charge carrier recombination models, allowing for the extraction of recombination rate constants and trap state concentration. PEARS is flexible and can adapt to different situations, by ignoring recombination processes or fixing known parameters (e.g., the doping concentration). The tool is publicly available at https://pears-tool.herokuapp.com.

Ruthenium(II) Polypyridyl Complexes as FRET Donors: Structure- and Sequence-Selective DNA-Binding and Anticancer Properties.

Ruthenium(II) polypyridyl complexes (RPCs) that emit from metal-to-ligand charge transfer (MLCT) states have been developed as DNA probes and are being examined as potential anticancer agents. Here, we report that MLCT-emissive RPCs that bind DNA undergo Förster resonance energy transfer (FRET) with Cy5.5-labeled DNA, forming mega-Stokes shift FRET pairs. Based on this discovery, we developed a simple and rapid FRET binding assay to examine DNA-binding interactions of RPCs with diverse photophysical properties, including non-"light switch" complexes [Ru(dppz)2(5,5'dmb)]2+ and [Ru(PIP)2(5,5'dmb)]2+ (dppz = dipyridophenazine, 5,5'dmb = 5,5'-dimethyl-2,2'-bipyridine, PIP = 2-phenyl-imidazo[4,5-f][1,10]phenanthroline). Binding affinities toward duplex, G-quadruplex, three-way junction, and mismatch DNA were determined, and derived FRET donor-acceptor proximities provide information on potential binding sites. Molecules characterized by this method demonstrate encouraging anticancer properties, including synergy with the PARP inhibitor Olaparib, and mechanistic studies indicate that [Ru(PIP)2(5,5'dmb)]2+ acts to block DNA replication fork progression.

A review of graphene derivative enhancers for perovskite solar cells.

Due to the finite nature, health and environmental hazards currently associated with the use of fossil energy resources, there is a global drive to hasten the development and deployment of renewable energy technologies. One such area encompasses perovskite solar cells (PSCs) that have shown photoconversion efficiencies (PCE) comparable to silicon-based photovoltaics, but their commercialisation has been set back by short-term stability and toxicity issues, among others. A tremendous potential to overcome these drawbacks is presented by the emerging applications of graphene derivative-based materials in PSCs as substitutes or components, composites with other functional materials, and enhancers of charge transport, blocking action, exciton dissociation, substrate coverage, sensitisation and stabilisation. This review aims to illustrate how these highly capable carbon-based materials can advance PSCs by critically outlining and discussing their current applications and strategically identifying prospective research avenues. The reviewed works show that graphene derivatives have great potential in boosting the performance and stability of PSCs through morphological modifications and compositional engineering. This can drive the sustainability and commercial viability aspects of PSCs.

Spectroscopic study of D1-A-D2-A terpolymer films for optoelectronic applications.

Several strategies have been considered in search of more efficient organic materials for charge transfer in photovoltaic devices. Among them, the integration of donor-acceptor (D-A) functional units on a conjugated copolymer has been widely applied. In this framework, we evaluated four terpolymers made up of donor moieties derived from 9,9-dioctylfluorene and 9-(heptadecan-9-yl)-9H-carbazole combined with 2,1,3-benzothiadiazole, the acceptor moiety, in different monomer ratios and polymerization routes (block and random microstructures). The preferred molecular orientation and charge transfer dynamics of the polymeric films were assessed by near edge X-ray absorption fine structure spectroscopy (NEXAFS) and resonant Auger electron spectroscopy (RAES) around the sulfur K-edge. Charge transfer times (τCT) were estimated by the Core-Hole Clock (CHC) method. Films with a high degree of organization were identified for the block terpolymer and random terpolymers with uneven amounts of donor units, showing a preferred orientation of the benzothiadiazole (BT) molecular plane parallel to the substrate surface. The values of τCT measured for all terpolymers were higher than those for typical polymers used in photovoltaic devices, which is not desirable for this type of optoelectronic application, but this may be correlated to the strong acceptor character of BT, the unit probed. To investigate the effect of film formation on the excited state behavior, steady-state and time-resolved photoluminescence measurements were also conducted. X-ray photoelectron spectroscopy (XPS) was employed to characterize the surface chemical composition of the terpolymer films. Based on the spectroscopic data the block copolymer appears to be the most suitable for the desired application.

The Cause and Duration of Emergency Admissions to Hospital in People with Idiopathic Parkinson's Disease, Under the Care of a UK Service, During the First Year of the COVID-19 Pandemic.

BACKGROUND: People with Parkinson's disease (PD) have higher rates of hospitalisation and healthcare utilisation compared to the general population. The COVID-19 pandemic caused significant changes in admissions to hospital and access to healthcare. People with PD are some of the most vulnerable to such changes. There is no pre-existing data on the cause and duration of admission to hospital of people with PD during the COVID-19 pandemic. OBJECTIVE: To determine the cause, duration, and outcome of hospital admissions to Northumbria Healthcare NHS Foundation Trust (NHCFT) for people with idiopathic Parkinson's disease (IPD) in 2020. METHODS: All people with IPD who had an emergency admission to NHCFT between 01/01/2020 and 31/12/2020 were identified. Demographic and disease characteristics, the number, duration, cause of admission and the location prior to admission were collected from an audit of medical notes. RESULTS: 271 people with IPD had one or more emergency admissions to NHCFT between 01/01/2020 and 31/12/2020. There was a total of 453 emergency admissions, with a median duration of 5 (IQR 2-13) days. The most common causes of admission to hospital were PD-related motor dysfunction (includes falls with no other underlying cause or associated injury) and injury (includes falls with fracture), at 78 (17.2%) and 70 (15.5%) respectively. CONCLUSIONS: People with IPD had a short duration but high number of emergency admissions to hospital. Our chronological data on number of admissions shows a peak in admissions during August 2020. As a result of these findings and emerging data we suggest that individuals with PD deconditioned during 2020.

Photocatalytic H2 production and degradation of aqueous 2-chlorophenol over B/N-graphene-coated Cu0/TiO2: A DFT, experimental and mechanistic investigation.

Energy and environmental challenges are global concerns that scientists are interested in alleviating. It is on this premise that we prepared boron/nitrogen graphene-coated Cu0/TiO2 (B/N-graphene-coated Cu/TiO2) photocatalyst of varying B:N ratios with dual functionality of H2 production and 2-Chlorophenol (2-CP) degradation. In-situ coating of Cu0 with B/N-graphene is achieved via solvothermal synthesis and calcination under an inert atmosphere. All B/N-graphene-coated Cu/TiO2 exhibit higher photonic efficiencies (5.68%-7.06% at 300 < λ < 400 nm) towards H2 production than bare TiO2 (0.25% at 300 < λ < 400 nm). Varying the B:N ratio in graphene influences the efficiency of H2 generation. A B:N ratio of 0.08 yields the most active composite exhibiting a photonic efficiency of 7.06% towards H2 evolution and a degradation rate of 4.07 × 10-2 min-1 towards 2-chlorophenol (2-CP). Density functional theory (DFT) investigations determine that B-doping (p-type) enhances graphene stability on Cu0 while N-doping (n-type) increases the reduction potential of Cu0 relative to H+ reduction potential. X-ray photoelectron spectroscopy reveals that increasing the B:N ratio increases p-type BC2O while decreasing n-type pyridinic-N in graphene thus altering the interlayer electron density. Isotopic labelling experiments determine water reduction as the main mechanism by which H2 is produced over B/N-graphene-coated Cu/TiO2. The reactive species involved in the degradation of 2-CP are holes (h+), hydroxyl radical (OH•), and O2•-, of which superoxide (O2•-) plays the major role. This work displays B/N -graphene-coated Cu/TiO2 as a potential photocatalyst for large-scale H2 production and 2-CP degradation.

'Cortical Hand' in the Emergency Department: Two Case Reports.

BACKGROUND: Cortical hand strokes affect the 'hand knob' of the motor cortex, resulting in isolated distal upper limb or hand weakness. They are rare and can be easily misdiagnosed for peripheral lesions. CASE REPORTS: Case 1: A 59-year-old man presented to the Emergency Department (ED) after noticing left hand weakness while driving. There was no sensory deficit noted. A full neurological examination suggested an upper motor neurone rather than a peripheral nerve lesion. This was confirmed by a magnetic resonance imaging scan of his brain. Case 2: An 88-year-old man presented to the ED after developing sudden-onset left hand weakness while completing a newspaper puzzle. Power returned gradually over approximately 4 h, with no sensory symptoms being noted. A transient ischemic attack leading to cortical hand was diagnosed. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Cortical hand strokes are a rare, but important, differential for wrist drop. They are often first strokes and embolic in nature. Therefore, correct diagnosis is vital to enable initiation of secondary prevention.

Factors affecting family medicine programmes in Sub-Saharan Africa: a narrative review of recent literature.

Objective: To identify the factors enabling and limiting family medicine (FM) programmes in Sub-Saharan Africa (SSA). Design: A narrative review was conducted by searching a variety of databases. Papers focusing on the training, deployment, or contribution to healthcare systems of doctors with postgraduate training in FM in SSA, published in peer-reviewed journals from 2015 onwards and in English language were included. Included papers underwent qualitative analysis. Results: Seventy-one papers were included in the review. 38% focussed on South Africa, while papers focussing on FM in a further 15 countries in SSA were identified. Key factors enabling FM programmes are support from key stakeholders, recognition of family practitioners (FP) as specialists, international collaboration, and dedicated FPs. Key factors limiting FM programmes are a lack of sufficient and well-trained faculty, inappropriate training settings, higher rates of trainee attrition, lack of FM in undergraduate curriculums, lack of career pathways, inappropriate deployment, and a lack of a critical mass. Conclusions: Support from national stakeholders, the recognition of FPs as specialists, and sustainable international collaboration promote FM programmes. The absence of a defined role within the healthcare system, low numbers of FM faculty, a poor presence in undergraduate curriculum, high attrition rate of trainees and the lack of a critical mass limit FM programmes. The standardisation of the role of FM and the implementation of undergraduate and postgraduate FM programmes with national and international collaboration could enable FM to reach a critical mass and realise its full potential in strengthening primary healthcare in SSA. Funding: None declared.

Driving and Parkinson's Disease: A Survey of the Patient's Perspective.

BACKGROUND: Parkinson's disease (PD) is a multi-system disorder that can impact on driving ability. Little is known about how these changes in driving ability affect people with PD, making it difficult for clinicians and carers to offer appropriate support. OBJECTIVE: To assess patient views concerning the effect of PD on their driving ability, the impact of these changes and how they manage them. METHOD: An online survey was created by a team of clinicians, people with PD, their carers, and representatives from Parkinson's UK. People with PD throughout the United Kingdom were invited to participate through Parkinson's UK's website, newsletter and Parkinson's Excellence Network email list. RESULTS: 805 people with PD took part in the survey. We found that the loss of a driving licence had an adverse impact on employment, socialisation, travel costs and spontaneous lifestyle choices. Multiple changes in driving ability related to PD were described, including that impulse control disorders can have an adverse impact on driving. Changes in driving ability caused people to change their driving practices including taking shorter journeys and being less likely to drive at night. Participants advised managing changes in driving ability through planning, vehicle adaptions, maintaining skills and self-assessment. CONCLUSION: This study demonstrates the impact that changes in driving ability can have on the lifestyle of people with PD and reveals the strategies that individuals adopt to manage these changes.

Interpreting time-resolved photoluminescence of perovskite materials.

Time-resolved photoluminescence (TRPL) spectroscopy is a powerful technique to investigate excited charge carrier recombinations in semiconductors and molecular systems. The analysis of the TRPL decays of many molecular systems (e.g. molecules and organic materials) is usually fairly straightfoward and can be fitted with an exponential function allowing extraction of the rate constants. Due to the non-excitonic nature of charge carriers in lead halide perovskite materials coupled with the presence of localised trap states in their band-gap, the TRPL of these materials is much more complicated to interpret. Here we discuss two models used in the literature to simulate charge carrier recombinations and TRPL in perovskites. These models consider the bimolecular nature of direct electron-hole recombination but differ in their treatment of trap-mediated recombination with one model describing trapping as a monomolecular process whereas the other as a bimolecular process between free carriers and the available trap states. In comparison, the classical analysis of perovskite TRPL decay curves (using a sum of exponentials) can lead to misinterpretation. Here we offer some recommendations for meaningful measurements of lead halide perovskite thin-films. The fluence dependence as well as charge carrier accumulation due to incomplete depopulation of all photoexcited carriers between consecutive excitation pulses are discussed for both models.

Nitrogen/Carbon-Coated Zero-Valent Copper as Highly Efficient Co-catalysts for TiO2 Applied in Photocatalytic and Photoelectrocatalytic Hydrogen Production.

Zero-valent copper (Cu0) is a promising co-catalyst in semiconductor-based photocatalysis as it is inexpensive and exhibits electronic properties similar to those of Ag and Au. However, its practical application in photocatalytic hydrogen production is limited by its susceptibility to oxidation, forming less active Cu species. Herein, we have carried out in situ encapsulation of Cu0 nanoparticles with N-graphitic carbon layers (14.4% N) to stabilize Cu0 nanoparticles (N/C-coated Cu) and improve the electronic communication with a TiO2 photocatalyst. A facile solvothermal procedure is used to coat the Cu0 nanoparticles at 200 °C, while graphitization is achieved by calcination at 550 °C under an inert atmosphere. The resultant N/C-coated Cu/TiO2 composites outperform the uncoated Cu counterparts, exhibiting a 27-fold enhancement of the hydrogen evolution rate compared to TiO2 and achieving a rate of 19.03 mmol g-1 h-1 under UV-vis irradiation. Likewise, the N/C-coated Cu co-catalyst exhibits a less negative onset potential of -0.05 V toward hydrogen evolution compared to uncoated Cu (ca. -0.30 V). This superior activity is attributed to coating Cu0 with N/C, which enhances the stability, electronic communication with TiO2, conductivity, and interfacial charge transfer processes. The reported synthetic approach is simple and scalable, yielding an efficient and affordable Cu0 co-catalyst for TiO2.

Improving the light harvesting and colour range of methyl ammonium lead tri-bromide (MAPbBr3) perovskite solar cells through co-sensitisation with organic dyes.

Co-sensitisation of methylammonium lead tri-bromide perovskite solar cells with red (D205) and blue (SQ2) organic dyes improves device efficiencies and allows device colour tuning. Sensitising the film after perovskite crystallisation produces higher device efficiencies (2.6% SQ2, 3.1% D205) than perovskite-only devices (2%) and devices sensitised before the perovskite layer deposition (1.5% SQ2, 2.0% D205).

Photoinduced charge transfer: from photography to solar energy.

To celebrate the centenary of Science Progress we offer a short survey of the progress made over the past one hundred years in the research and application of photoinduced charge transfer. After a brief historical overview and introduction to photoinduced charge transfer, we discuss developments in the theory and practice of photography, photovoltaics, photocatalysis, fluorescent probes and chemosensing.

Impact of Aggregation on the Photochemistry of Fullerene Films: Correlating Stability to Triplet Exciton Kinetics.

The photochemistry and stability of fullerene films is found to be strongly dependent upon film nanomorphology. In particular, PC61BM blend films, dispersed with polystyrene, are found to be more susceptible to photobleaching in air than the more aggregated neat films. This enhanced photobleaching correlated with increased oxygen quenching of PC61BM triplet states and the appearance of a carbonyl FTIR absorption band indicative of fullerene oxidation, suggesting PC61BM photo-oxidation is primarily due to triplet-mediated singlet oxygen generation. PC61BM films were observed to undergo photo-oxidation in air for even modest (≤40 min) irradiation times, degrading electron mobility substantially, indicative of electron trap formation. This conclusion is supported by observation of red shifts in photo- and electro-luminescence with photo-oxidation, shown to be in agreement with time-dependent density functional theory calculations of defect generation. These results provide important implications on the environmental stability of PC61BM-based films and devices.

A novel dimethylformamide (DMF) free bar-cast method to deposit organolead perovskite thin films with improved stability.

We report a solvent-free approach to synthesizing organolead perovskites by using solid state reactions to coat perovskite crystals onto Al2O3 or TiO2 nanoparticles followed by addition of terpineol affording perovskite inks. We have bar cast these inks to produce photoactive perovskite thin films which are significantly more stable to humidity than solution-processed films. This new method also avoids the use of toxic DMF solvent.

Facile self-assembly and stabilization of metal oxide nanoparticles.

This paper describes a facile method of self-assembling different metal oxide nanoparticles into nanostructured materials via di-carboxylate linkers (oxalic acid) using TiO2 as an example. In this method, the di-carboxylate linkers react with surface hydroxyls on metal oxide nanoparticles forming covalent, ester-like bonds, which enable the binding of two metal oxide particles, one at either end of the linker and facilitates efficient self-assembly of one group of metal oxide nanoparticles homogeneously distributed onto the surface of another group. The oxalate linkers can then be removed by thermal decomposition. This approach is shown to be effective using differently-sized TiO2 nanoparticles, namely in-house synthesized 3-5nm anatase nanocrystals and Degussa P25 titania particles (mean 21nm particle size). Our data show that the application of a high temperature heat treatment (450°C for 30min), conventionally applied to achieve a stable porous structure by thermal decomposition of the linker molecules and by inducing inter-particle necking, damages the surface area of the nanostructured material. However, here we show that sintering at 300°C for 30min or by flash near infrared radiation sintering for 12s efficiently decomposes the oxalate linkers and stabilizes the nanostructure of the material whilst maintaining its high surface area.

In situ monitoring and optimization of room temperature ultra-fast sensitization for dye-sensitized solar cells.

We describe the fastest dyeing of TiO2 photo-electrodes for dye-sensitized solar cells reported to date (<2 min) at room temperature giving η = 7.5% for an N719-SQ1-CDCA mixture which is significantly higher than devices dyed for >12 h using the same dye mixture (η = 5.5%). Time-lapse photography has been used to monitor the ultra-fast co-sensitization. The data show significantly different dye uptake between passive and pump dyeing reflecting competitive sorption between a Ru complex (N719) and an organic dye (SQ1).

In depth analysis of the quenching of three fluorene-phenylene-based cationic conjugated polyelectrolytes by DNA and DNA bases.

The interaction of three cationic poly {9,9-bis[N,N-(trimethylammonium)hexyl]fluorene-co-1,4-phenylene} polymers with average chain lengths of ∼6, 12, and 100 repeat units (PFP-NR36(I),12(Br),100(Br)) with both double and single stranded, short and long, DNA and DNA bases have been studied by steady state and time-resolved fluorescence techniques. Fluorescence of PFP-NR3 polymers is quenched with high efficiency by DNA (both double and single stranded) and DNA bases. The resulting quenching plots are sigmoidal and are not accurately described by using a Stern-Volmer quenching mechanism. Here, the quenching mechanism is well modeled in terms of an equilibrium in which a PFP-NR3/DNA aggregate complex is formed which brings polymer chains into close enough proximity to allow interchain excitation energy migration and quenching at aggregate or DNA base traps. Such an analysis gives equilibrium constants of 8.4 × 10(6) (±1.2 × 10(6)) M(-1) for short-dsDNA and 8.6 × 10(6) (±1.7 × 10(6)) M(-1) for short-ssDNA with PFP-NR36(I).

A one-step low temperature processing route for organolead halide perovskite solar cells.

Organolead trihalide perovskite solar cells based upon the co-deposition of a combined Al2O3-perovskite layer at T < 110 °C are presented. We report an average PCE = 7.2% on a non-sintered Al2O3 scaffold in devices that have been manufactured from a perovskite precursor containing 5 wt% Al2O3 nanoparticles.