Reconsidering figures of merit for performance and stability of perovskite photovoltaics

The development of hybrid organic-inorganic halide perovskite solar cells (PSCs) that combine high performance and operational stability is vital for implementing this technology. Recently, reversible improvement and degradation of PSC efficiency have been reported under illumination-darkness cycling. Quantifying the performance and stability of cells exhibiting significant diurnal performance variations is challenging. We report the outdoor stability measurements of two types of devices showing either reversible photo-degradation or reversible efficiency improvement under sunlight. Instead of the initial (or stabilized) efficiency and T as the figures of merit for the performance and stability of such devices, we propose using the value of the energy output generated during the first day of exposure and the time needed to reach its 20% drop, respectively. The latter accounts for both the long-term irreversible degradation and the reversible diurnal efficiency variation and does not depend on the type of process prevailing in a given perovskite cell

COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study

Background: The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods: International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results: ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P < 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation: This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men

Preorganisation in bistriazolyl anion receptors

A series of 4,6-bis-(1,2,3-triazolyl)-pyrimidine and 4,6-bis-(1,2,3-triazolyl)-pyridine anion receptors were synthesized and the effect of the pyrimidine and pyridine moieties on their binding properties was examined. We found that intramolecular interactions preorganize the 4,6 bis (1,2,3-triazolyl)-pyridine receptors resulting in higher anion binding constants in comparison with the non-preorganized 4,6-bis-(1,2,3-triazolyl)-pyrimidine receptor.status: publishe

Outdoor Measurement and Modeling of Perovskite Module Temperatures

Photovoltaic cells and modules are exposed to partially rapid changing environmental parameters that influence the device temperature. The evolution of the device temperature of a perovskite module of 225 cm2 area is presented during a period of 25 days under central European conditions. The temperature of the glass-glass packaged perovskite solar module is directly measured at the back contact by a thermocouple. The device is exposed to ambient temperatures from 3 to 34 °C up to solar irradiation levels exceeding 1300 W m-2. The highest recorded module temperature is 61 °C under constant high irradiation levels. Under strong fluctuations of the global solar irradiance, temperature gradients of more than 3 K min-1 with total changes of more than 20 K are measured. Based on the experimental data, a dynamic iterative model is developed for the module temperature evolution in dependence on ambient temperature and solar irradiation. Furthermore, specific thermal device properties that enable an extrapolation of the module response beyond the measured parameter space can be determined. With this set of parameters, it can be predicted that the temperature of the perovskite layer in thin-film photovoltaic devices is exceeding 70 °C under realistic outdoor conditions. Additionally, perovskite module temperatures can be calculated in final applications.status: publishe

An Interdiffusion Method for Highly Performing Cesium/Formamidinium Double Cation Perovskites

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The fabrication of high-quality cesium (Cs)/formamidinium (FA) double-cation perovskite films through a two-step interdiffusion method is reported. CsxFA1-xPbI3-y(1-x)Bry(1-x) films with different compositions are achieved by controlling the amount of CsI and formamidinium bromide (FABr) in the respective precursor solutions. The effects of incorporating Cs+ and Br− on the properties of the resulting perovskite films and on the performance of the corresponding perovskite solar cells are systematically studied. Small area perovskite solar cells with a power conversion efficiency (PCE) of 19.3% and a perovskite module (4 cm2) with an aperture PCE of 16.4%, using the Cs/FA double cation perovskite made with 10 mol% CsI and 15 mol% FABr (Cs0.1FA0.9PbI2.865Br0.135) are achieved. The Cs/FA double cation perovskites show negligible degradation after annealing at 85 °C for 336 h, outperforming the perovskite materials containing methylammonium (MA).status: publishe

A study of quenching approaches to optimize ultrasonic spray coated perovskite layers scalable for PV

Perovskite materials have gathered increased interest over the last decade. Their rapidly rising efficiency, coupled with the compatibility with solution processing and thin film technology has put perovskite solar cells (PSC) on the spotlight of photovoltaic research. On top of that, band gap tunability via composition changes makes them a perfect candidate for tandem applications, allowing for further harvest of the solar irradiation spectrum and improved power conversion efficiency (PCE). In order to convert all these advantages into large scale production and have increased dissemination in the energy generation market, perovskite fabrication must be adapted and optimized with the use of high throughput, continuous processes, such as ultrasonic spray coating (USSC). In this paper we investigate the ultrasonically spray coated perovskite layers for photovoltaic applications, with particular focus on the quenching-assisted crystallization step. Different quenching techniques are introduced to the process and compared in terms of final layer morphology and cell performance. Finally, gas quenching is used with the large-scale-compatible deposition and allows the production of perovskite solar cells with PCE >15%

Optical Analysis of Planar Multicrystalline Perovskite Solar Cells

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Optical analysis of planar multicrystalline perovskite solar cells

© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Organometal halide perovskites are attracting strong interest as light-harvesting absorber materials in single- and multijunction solar cells. In order to advance the technology, careful optical design of the device architecture and elaborate analysis of optical losses are essential. In this work, a detailed optical analysis of semitransparent and opaque planar CH3NH3PbI3 solar cells is reported. Using a combination of variable-angle spectroscopic ellipsometry and spectrophotometry data, the complex refractive indices of all involved materials in the device architecture are accurately determined, taking the underlying layer stack explicitly into account. The optical properties of partial and complete layer stacks of solar cells, comprising CH3NH3PbI3 films with different CH3NH3PbI3 surface topography roughnesses, are simulated using the transfer-matrix method. Very good agreement between simulated and experimental data is demonstrated. Sub-bandgap absorption is observed in CH3NH3PbI3 layer stacks, which is by means of a ray-tracing model shown to be related to diffuse scattering at the multicrystalline CH3NH3PbI3/air interface. Finally, the optical losses of all layers are discriminated for opaque and semitransparent CH3NH3PbI3 solar cells and four-terminal perovskite/Si tandem solar cells.status: publishe

Non-hazardous solvent systems for processing perovskite photovoltaics

© 2016 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Replacing toxic solvents with nonhazardous solvents is one of the key challenges for industrial scale commercialization of thin film perovskite photovoltaics. Here, nonhazardous solvent/alcohol/acid systems are presented for the single-step deposition of pinhole-free perovskite layers with combined lead halide precursors of Pb(CH3CO2)2·3H2O, PbCl2, and CH3NH3I. Comparable performance to standard hazardous inks is achieved: devices with 15.1% power conversion efficiency are demonstrated and maintain 13.5% tracked for 5 min at maximum power point. Blade coated 4 cm2 solar modules fabricated with highest performing device ink attain 11.9% in power conversion efficiency.status: publishe

Anion binding and transport properties of cyclic 2,6-bis(1,2,3-triazol-1-yl)pyridines

A series of cyclic 2,6-bis-(1,2,3-triazolyl)-pyridine anion receptors with thiourea functionalities were synthesized by click reaction of 2,6-diazidopyridine with protected propargylamine followed by condensation of a bisthiocyanate derivative with a series of diamines. Their chloride binding affinities as well as their transport properties in POPC bilayers were examined. These receptors were found to function as anion carriers, which can mediate both Cl?/NO3? antiport and H+/Cl? symport, and the transport activity of these hosts were dominated by their lipophilicity