Nitride MOVPE tops the bill

AbstractThe predominance of activity in the nitrides field and the emergence of in situ monitoring into mainstream metal organic vapour phase epitaxy were among the themes of the 8th European Workshop on MOVPE. The location of Prague close to the geographical centre of the united Europe did much to encourage participation from all corners of the continent, with over 200 delegates from 21 countries attending the workshop, held from 8–11 June 1999

A combined Na and Cl treatment to promote grain growth in MOCVD grown CdTe thin films

The role of sodium (Na) in cadmium telluride (CdTe) thin film photovoltaic absorbers deposited on a metal-coated substrate is investigated. Introducing Na during the growth of the structure influences the morphological and crystallographic properties of the CdTe layer grown by metal-organic chemical vapour deposition (MOCVD). It is observed that the introduction of Na between the metal and CdTe layers induces a slight randomisation via promotion of (400) and (220) orientations. It is shown that the inclusion of Na between the substrate and the Mo back metal contact enlarges the CdTe grains following a CdCl2 treatment by 50% but weakens the adhesion to the substrate. The introduction of Na between the Mo back contact and CdTe layer promotes the formation of large faceted grains for the as-grown films with an average grain size ten times larger than in the case of Na free deposition while maintaining good adhesion to the substrate. There is no further grain growth following CdCl2 treatment however the CdTe grain size is still double that of the Na-free samples

Whole-genome sequencing reveals host factors underlying critical COVID-19

Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease

Potential for further reduction in the embodied carbon in PV solar energy systems

In this study the potential for further reduction in Greenhouse Gas Emissions (GHG) of c-Si, mc-Si and CdTe PV systems are assessed to inform climate change mitigation in the UK. The amount of CO2 equivalent released in grams for each kWh of electricity over the lifetime of the PV system (gCO2-e/kWh) has been assessed using a model to predict the change in GHG as a result of engineering improvements in the PV module and system operation. The scenarios modelled here are for two different locations in the UK (Midlands and South West England) to give a typical range. Similarly a range of carbon intensity in manufacture is considered by taking manufacture in China and the UK. This study considers the impact of; system and inverter lifetimes, continuing trends of increases in module conversion efficiencies and reduction in carbon intensity during manufacture. For most of the scenarios considered the extension of the PV system lifetime to 40 years makes the largest impact while extending inverter lifetime for deployment of thin film PV modules becomes more significant and cannot be ignored. All of the four interventions considered in this paper can significantly contribute to a reduction in the carbon footprint of PV by the near term target of 2020. For all three module systems considered the model shows the potential for the carbon footprint to be reduced to one third of the 2012 values giving a range of 11-38 gCO2-e/kWh, which is within the range of current wind generation in the UK

Lightweight and low-cost thin film photovoltaics for large area extra-terrestrial applications

This work describes progress towards achieving a flexible, high specific power and low-cost photovoltaic (PV) for emerging large area space applications. The study reports the highest conversion efficiency of 15.3% AM1.5G for a CdTe device on ultra-thin cerium-doped cover glass, the standard protective material for extra-terrestrial PVs. The deposition technique used for all of the semiconductor layers comprising the device structure was atmospheric pressure metal organic chemical vapour deposition. Improvements to the device structure over those previously reported led to a Voc of 788 mV and a relatively low series resistance of 3.3 Ω·cm2. These were largely achieved by the introduction of a post-growth air anneal and a refinement of the front contact bus bars, respectively. The aluminium-doped zinc oxide transparent conductive oxide, being the first layer applied to the cover glass, was subject to thermal shock cycling +80 to (-) 196°C to test the adhesion under the extreme conditions likely to be encountered for space application. Scotch Tape testing and sheet resistance measurements before and after the thermal shock testing demonstrated that the aluminium-doped zinc oxide remained well adhered to the cover glass and its electrical performance unchanged