Optoelectronic and stability properties of quasi-2D alkylammonium based perovskites

Electronic and stability properties of quasi-2D alkylammonium perovskites are investigated using density functional theory (DFT) calculations and validated experimentally on selected classes of compounds. Our analysis is focused on perovskite structures of formula (A)$_2$(A$'$)$_{n-1}$Pb$_n$X$_{3n+1}$, with large cations A = butyl-, pentyl-, hexylammonium (BA, PA, HXA), small cations A$'$ = methylammonium, formamidinium, ethylammonium, guanidinium (MA,FA,EA,GA) and halogens X = I, Br, Cl. The role of the halogen ions is outlined for the band structure, stability and defect formation energies. Two opposing trends are found for the absorption efficiency versus stability, the latter being assessed with respect to possible degradation mechanisms. Experimental validation is performed on quasi-2D perovskites based on pentylammonium cations, namely: (PA)$_2$PbX$_4$ and (PA)$_2$(MA)Pb$_2$X$_7$, synthesized by antisolvent-assisted vapor crystallization. Structural and optical analysis are inline with the DFT based calculations. In addition, the thermogravimetric analysis shows an enhanced stability of bromide and chloride based compounds, in agreement with the theoretical predictions.Comment: 8 pages, 8 figure

Partial replacement of Pb2+ in MAPbI2.6Cl0.4 perovskite films and their photovoltaic performance

Replacing lead atoms in halide perovskite materials is of significant importance for the development of environmentally friendly perovskite solar cells. In this paper, we investigated the effect of doping the MAPbI2.6Cl0.4 hybrid perovskite (MA-methyl ammonium) with non-toxic elements, such as alkaline earth metal ions (Mg2+) and transition metal ions (Zn2+). The structural, morphological, and optical properties of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis. spectroscopy. Finally, the doped films were used as photoactive layers in solar devices in order to evaluate their photovoltaic performance. Zn proved to be more appropriate to replace partially Pb and films with higher quality were obtained. As a result, the MAPb1-xZnxI2.6Cl0.4 based solar cells have demonstrated a slight improvement of the photovoltaic performances, resulting in a uniform and narrower PCEs (power conversion efficiency) range, compared to pristine MAPbI2.6Cl0.4 based devices

Partial Replacement of Dimethylformamide with Less Toxic Solvents in the Fabrication Process of Mixed-Halide Perovskite Films

The technology of perovskite solar cells (PSC) is getting close to breaching the consumer market. Yet, one of the current challenges is to reduce the toxicity during their fabrication by reducing the use of the toxic solvents involved in the perovskite fabrication process. A good solubilization of lead halides used in hybrid perovskite preparation is required, and it is only possible with polar solvents. A mixture of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is the most popular solvent combination for a perovskite precursor solution. DMF is necessary to ensure a good dissolution of lead iodide, but it is also the most toxic solvent. In this paper, we study the replacement of the dimethylformamide with presumably less toxic alternatives, such as N-methyl-2-Pyrrolidone (NMP) and ethyl acetate (EA), for the preparation of the K0.1FA0.7MA0.2PbI2.8Cl0.2 (KFAMA) hybrid perovskite. The perovskite thin films were investigated by various characterization techniques: X-ray diffraction, atomic force microscopy, scanning electron microscopy, and UV–vis spectroscopy, while the photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. The present study shows that by keeping the same deposition parameters as when only DMF solvent is used, the partial solvent substitution with NMP and EA gives promising results for reducing the toxicity of the fabrication process of KFAMA-based PSCs. Thus, with no specific optimization of the deposition process, and for the maximum possible partial substitution of DMF with NMP and EA solvents, the loss in the power conversion efficiency (PCE) value is only 35% and 18%, respectively, associated with the more structural defects promoted by NMP and EA

Partial Replacement of Dimethylformamide with Less Toxic Solvents in the Fabrication Process of Mixed-Halide Perovskite Films

The technology of perovskite solar cells (PSC) is getting close to breaching the consumer market. Yet, one of the current challenges is to reduce the toxicity during their fabrication by reducing the use of the toxic solvents involved in the perovskite fabrication process. A good solubilization of lead halides used in hybrid perovskite preparation is required, and it is only possible with polar solvents. A mixture of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) is the most popular solvent combination for a perovskite precursor solution. DMF is necessary to ensure a good dissolution of lead iodide, but it is also the most toxic solvent. In this paper, we study the replacement of the dimethylformamide with presumably less toxic alternatives, such as N-methyl-2-Pyrrolidone (NMP) and ethyl acetate (EA), for the preparation of the K0.1FA0.7MA0.2PbI2.8Cl0.2 (KFAMA) hybrid perovskite. The perovskite thin films were investigated by various characterization techniques: X-ray diffraction, atomic force microscopy, scanning electron microscopy, and UV–vis spectroscopy, while the photovoltaic parameters were determined by measuring the IV curves of the corresponding solar cells. The present study shows that by keeping the same deposition parameters as when only DMF solvent is used, the partial solvent substitution with NMP and EA gives promising results for reducing the toxicity of the fabrication process of KFAMA-based PSCs. Thus, with no specific optimization of the deposition process, and for the maximum possible partial substitution of DMF with NMP and EA solvents, the loss in the power conversion efficiency (PCE) value is only 35% and 18%, respectively, associated with the more structural defects promoted by NMP and EA

Worldwide trends in population-based survival for children, adolescents, and young adults diagnosed with leukaemia, by subtype, during 2000–14 (CONCORD-3): analysis of individual data from 258 cancer registries in 61 countries

Background: Leukaemias comprise a heterogenous group of haematological malignancies. In CONCORD-3, we analysed data for children (aged 0–14 years) and adults (aged 15–99 years) diagnosed with a haematological malignancy during 2000–14 in 61 countries. Here, we aimed to examine worldwide trends in survival from leukaemia, by age and morphology, in young patients (aged 0–24 years). Methods: We analysed data from 258 population-based cancer registries in 61 countries participating in CONCORD-3 that submitted data on patients diagnosed with leukaemia. We grouped patients by age as children (0–14 years), adolescents (15–19 years), and young adults (20–24 years). We categorised leukaemia subtypes according to the International Classification of Childhood Cancer (ICCC-3), updated with International Classification of Diseases for Oncology, third edition (ICD-O-3) codes. We estimated 5-year net survival by age and morphology, with 95% CIs, using the non-parametric Pohar-Perme estimator. To control for background mortality, we used life tables by country or region, single year of age, single calendar year and sex, and, where possible, by race or ethnicity. All-age survival estimates were standardised to the marginal distribution of young people with leukaemia included in the analysis. Findings: 164 563 young people were included in this analysis: 121 328 (73·7%) children, 22 963 (14·0%) adolescents, and 20 272 (12·3%) young adults. In 2010–14, the most common subtypes were lymphoid leukaemia (28 205 [68·2%] patients) and acute myeloid leukaemia (7863 [19·0%] patients). Age-standardised 5-year net survival in children, adolescents, and young adults for all leukaemias combined during 2010–14 varied widely, ranging from 46% in Mexico to more than 85% in Canada, Cyprus, Belgium, Denmark, Finland, and Australia. Individuals with lymphoid leukaemia had better age-standardised survival (from 43% in Ecuador to ≥80% in parts of Europe, North America, Oceania, and Asia) than those with acute myeloid leukaemia (from 32% in Peru to ≥70% in most high-income countries in Europe, North America, and Oceania). Throughout 2000–14, survival from all leukaemias combined remained consistently higher for children than adolescents and young adults, and minimal improvement was seen for adolescents and young adults in most countries. Interpretation: This study offers the first worldwide picture of population-based survival from leukaemia in children, adolescents, and young adults. Adolescents and young adults diagnosed with leukaemia continue to have lower survival than children. Trends in survival from leukaemia for adolescents and young adults are important indicators of the quality of cancer management in this age group