Non-stoichiometry and ion transport in halide perovskites: Equilibrium situation and light effects

In recent years, hybrid halide perovskites have been attracting great attention due to their exceptional photo-electrochemical properties.[1-2] When used as light-harvesters in solar cells, device efficiencies exceeding 22% can be realized. We showed that a deeper understanding of (i) functionality, (ii) stability, as well as (iii) the possibility to improve the performance require a thorough insight into non-stoichiometry and ion transport.[3-5] In this contribution, we study the nature of the ionic conductivity in methylammonium lead iodide (MAPbI3), the archetypal halide perovskite, by means of a great number of electrochemical and nuclear magnetic techniques.[4] To aid the experimental investigation, we include detailed defect chemical modelling describing the effects of iodine partial pressure (Fig. 1a), doping and interaction with oxygen.[5] We also discuss results that show the significance of ion redistribution phenomena for relevant interfaces. By extending this study to the situation under illumination, we observe a striking enhancement of ionic conductivity by more than 2 orders of magnitude in MAPbI3, alongside the expected increase in electronic conductivity.[6] We provide a mechanistic explanation of this astonishing phenomenon and discuss its relevance for future light-triggered ionic devices (“opto-ionics”, see Fig. 1b). Please click Additional Files below to see the full abstract

Prognosis Prediction for Class III Malocclusion Treatment by Feature Wrapping Method

Objective: To use the feature wrapping (FW) method to identify which cephalometric markers show the highest classification accuracy in prognosis prediction for Class III malocclusion and to compare the prediction accuracy between the FW method and conventional statistical methods such as discriminant analysis (DA). Materials and Methods: The sample set consisted of 38 patients (15 boys and 23 girls, mean age 8.53 ± 1.36 years) who were diagnosed with Class III malocclusion and received both first-phase (orthopedic) and second-phase (fixed orthodontic) treatments. Lateral cephalograms were taken before (T0) and after first-phase treatment (T1) and after second-phase treatment and retention (T2). Based on the measurements taken at the T2 stage, the patients were allocated into good (n = 20) or poor (n = 18) prognosis groups. Forty-six cephalometric variables on T0 lateral cephalograms were analyzed by the FW method to identify key determinants for discriminating between the two groups. Sequential forward search (SFS) algorism and support vector machine (SVM) were used in conjunction with the FW method to improve classification accuracy. To compare the prediction accuracy of the FW method with conventional statistical methods, DA was performed for the same data set. Results: AB to mandibular plane angle (°) and A to N-perpendicular (mm) were selected as the most accurate cephalometric predictors by both the FW and DA methods. However, classification accuracy was higher with the FW method (97.2%) compared with DA (92.1%), because the FW method with SFS and SVM has a more precise classification algorithm. Conclusions: The FW method, which uses a learning algorithm, might be an effective alternative to DA for prognosis prediction

Composition variations in Cu2ZnSnSe4 thin films analyzed by X-ray diffraction, energy dispersive X-ray spectroscopy, particle induced X-ray emission, photoluminescence, and Raman spectroscopy

Compositional and structural studies of Cu2ZnSnSe4 (CZTSe) thin films were carried out by X-ray diffraction, energy dispersive X-ray spectroscopy (EDS), particle induced X-ray emission (PIXE), photoluminescence, and Raman spectroscopy. CZTSe thin films with different compositions were deposited on sodalime glass by coevaporation. The composition of the filmsmeasured by two differentmethods, EDS and PIXE, showed significant differences. Generally, the Zn/Sn ratio measured by EDS is larger than that measured by PIXE. Both the micro- PIXE and the micro-Raman imaging results indicated the compositional and structural inhomogeneity of the sample. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/37033This researchwas supported by the International Research&Development Program of the National Research Foundation of Korea funded by theMinistry of Science, ICT and Future Planning of Korea (Grant number: 2011-0019204) and by the New & Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning grant funded by the Korea government’s Ministry of Trade, Industry and Energy (No. 20123010010130)

Composition variations in Cu2ZnSnSe4 thin films analyzed by X-ray diffraction, energy dispersive X-ray spectroscopy, particle induced X-ray emission, photoluminescence, and Raman spectroscopy

Compositional and structural studies of Cu2ZnSnSe4 (CZTSe) thin films were carried out by X-ray diffraction, energy dispersive X-ray spectroscopy (EDS), particle induced X-ray emission (PIXE), photoluminescence, and Raman spectroscopy. CZTSe thin films with different compositions were deposited on sodalime glass by coevaporation. The composition of the filmsmeasured by two differentmethods, EDS and PIXE, showed significant differences. Generally, the Zn/Sn ratio measured by EDS is larger than that measured by PIXE. Both the micro- PIXE and the micro-Raman imaging results indicated the compositional and structural inhomogeneity of the sample. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/37033This researchwas supported by the International Research&Development Program of the National Research Foundation of Korea funded by theMinistry of Science, ICT and Future Planning of Korea (Grant number: 2011-0019204) and by the New & Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning grant funded by the Korea government’s Ministry of Trade, Industry and Energy (No. 20123010010130)

An Ontology-based Bayesian Network Approach for Representing Uncertainty in Clinical Practice Guidelines

Abstract. Clinical Practice Guidelines (CPGs) play an important role in improving the quality of care and patient outcomes. Although several machine-readable representations of practice guidelines implemented with semantic web technologies have been presented, there is no implementation to represent uncertainty with respect to activity graphs in clinical practice guidelines. In this paper, we are exploring a Bayesian Network(BN) approach for representing the uncertainty in CPGs based on ontologies. Based on the representation of uncertainty in CPGs, when an activity occurs, we can evaluate its effect on the whole clinical process, which, in turn, can help doctors judge the risk of uncertainty for other activities, and make a decision. A variable elimination algorithm is applied to implement the BN inference and a validation of an aspirin therapy scenario for diabetic patients is proposed.

Thermochemical Stability of Hybrid Halide Perovskites

This contribution discusses the chemical stability of methylammonium (MA) halide perovskites (MAPbI(3), MAPbBr(3), and MAPbCl(3)); it considers degradation processes relevant for devices (vs T, O-2, H2O, voltage, illumination) by outlining their thermodynamic constraints and linking them to experimental observations. Thermodynamic considerations indicate that degradation under O-2 is highly favored, albeit in principle preventable by encapsulation. The same is true for H2O exposure. Intrinsic degradation is unavoidable in devices, and under real conditions, it can be thermodynamically favored, as is the case for photodecomposition. The Gibbs energies of the decomposition reactions show strong dependences on the A-cation (decomposition vs T), on the halide (vs illumination), or on both (vs O-2, H2O). The stability trends vs composition change with degradation pathway, but MAPbI(3) often appears as the most unstable. These serious stability issues appear to have no master solution, though some approaches (e.g., encapsulation, exploiting lower dimensionality, and alternative contact phases) have so far shown promise

Weather Effect and Response of Promoted Rice Varieties on Fusarium Infection in Paddy Field

Fusarium infection rate of the paddy rice grain after harvest seemed to be influenced by the average temperature from late July (before heading) to the end of September (during ripening). In case of 2010 and 2013 in which average temperature of the same period was similar, Fusarium infection was related to cumulative precipitation, cumulative precipitation days, and precipitation durations over two days. The distribution ratio of Fusarium species complex isolated from paddy rice grains after harvest was 57% in 2010 and 45% in 2013 for Fusarium graminearum species complex (FGSC), 35% and 50% for Fusarium incarnatum-equiseti species complex, and 8% and 5% for Fusarium fujikuroi species complex (FFSC). The distribution ratios of FGSC and FFSC were higher in 2010 than 2013. Among the total 26 promoted rice varieties, the ‘Mihyang’ showed resistant response against the natural infection with Fusarium species belonging to FGSC and the varieties of ‘Nampyeong’, ‘Hi-ami’and ‘Younghojinmi’ showed resistant response against the natural infection with overall Fusarium pathogens. Majority of the promoted rice varieties could not be classified for resistance or susceptibility. These results are valuable as basic data to determine the resistance and susceptibility of rice variety against Fusarium spp. infection in the field

Macroscopic and microscopic electrical properties of Cu(In,Ga)Se-2 thin-film solar cells with various Ga/(In plus Ga) contents

CuIn<inf>1-x</inf>Ga<inf>x</inf>Se<inf>2</inf> (CIGS) thin-films were deposited by a three-stage co-evaporation process. We obtained an optimum value for the Ga/(In + Ga) ratio of CIGS solar cells of 0.29, which exhibits a band-gap of 1.14 eV and has the highest conversion efficiency. The Ga/(In + Ga) ratio in CIGS solar cells is one of main characteristics that can improve efficiency, but the optimum value is still uncertain. In this study, we investigated the local electrical properties, which are closely related to the device properties, of CIGS according to the Ga/(In + Ga) ratio. We measured the local current of the films using conductive atomic force microscopy. The local current indicates relatively small values for the current ratio and the average current on the film surface, which has a high shunt resistance and a low series resistance in high-efficiency CIGS thin-films. However, low efficiency CIGS exhibits the opposite electrical behavior. Thus, the macroscopic and microscopic electrical behaviors are closely correlated with the conversion efficiency and with the device factors of CIGS thin-film solar cells with a varying Ga/(In + Ga) ratio. These results suggest that the control of carrier transport over the grains will improve the conversion efficiency of CIGS thin-film solar cells. © 2015 Elsevier B.V. All rights reserved.1

Nanoscale investigation of surface potential distribution of Cu2ZnSn(S,Se)4 thin films grown with additional NaF layers

CZTS precursors [SLG/Mo (300 nm)/ZnS (460 nm)/SnS (480 nm)/Cu (240 nm)] were deposited by RF/DC sputtering, and then NaF layers (0, 15, and 30 nm) were grown by electron beam evaporation. The precursors were annealed in a furnace with Se metals at 590°C for 20 minutes. The final composition of the CZTSSe thin-films was of Cu/(Zn + Sn) ~ 0.88 and Zn/Sn ~ 1.05, with a metal S/Se ratio estimated at ~0.05. The CZTSSe thin-films have different NaF layer thicknesses in the range from 0 to 30 nm, achieving a ~3% conversion efficiency, and the CZTSSe thin-films contain ~3% of Na. Kelvin probe force microscopy was used to identify the local potential difference that varied according to the thickness of the NaF layer on the CZTSSe thin-films. The potential values at the grain boundaries were observed to increase as the NaF thickness increased. Moreover, the ratio of the positively charged GBs in the CZTSSe thin-films with an NaF layer was higher than that of pure CZTSSe thin-films. A positively charged potential was observed around the grain boundaries of the CZTSSe thin-films, which is a beneficial characteristic that can improve the performance of a device. © 2014, Kim et al.; licensee Springer.TRU