Modelling of TiO2-Perovskite Interface

Treball Final de Màster Universitari en Física Aplicada. Codi: SIN019. Curs acadèmic: 2016/2017Perovskite-TiO2 interface has become crucial for the operation of perovskite solar cell devices. In this work, we show an equivalent circuit for the impedance spectroscopy response of these devices that has been calculated for a previous model that was developed for explaining the accumulation in the perovskite-TiO2 interface. This circuit explains unique behaviors such as the inductive loop and the negative capacitance. To get more insight, we show the results from the modelling of this interface by solving the Poisson equations on both sides for the case of accumulation

Reduction of the formaldehyde content in leathers treated with formaldehyde resins by means of plant polyphenols

Formaldehyde has applications in many industrial processes, including synthesis of resins and syntans to be used in the retanning process of leather. When resins are employed, they can hydrolyse, releasing formaldehyde. Due to the carcinogenicity of formaldehyde, its presence in leather should be avoided or kept below allowable limits. The aim of this study is to determine the effect of polyphenols contained in vegetable compounds (mimosa, quebracho and tara) in the reduction of the formaldehyde content in leathers treated with resins synthesized with formaldehyde (melamine-formaldehyde and dicyandiamide-formaldehyde). The formaldehyde content in leathers treated only with resin increases with time while the formaldehyde content in leathers treated additionally with vegetable compounds is reduced. The lower the formaldehyde content in the leather, the higher the ability of vegetable compounds to reduce such content. Mimosa shows the strongest ability to reduce the formaldehyde content, and this capacity increases with ageing. The addition of 4% (on shaved wet-blue weight) of mimosa gives rise to an 85% reduction in the formaldehyde content 140 days after leather processing of split hides treated with a formaldehyde resin of low formaldehyde content. However, this reduction is 68% in splits hides treated with a resin of high formaldehyde content. This is of great importance in baby’s leather articles, in which the formaldehyde content is low; therefore, the addition of a small amount (3%) of vegetable compounds (especially mimosa) guarantees that the formaldehyde content is below the allowed limits (16 mg/kg in the most restrictive regulation). Reducing the formaldehyde content using the polyphenols contained in vegetable compounds constitutes a good alternative not only in the leather sector but also in other industrial sectors (wood, textile, etc.) that use formaldehyde resins.Peer ReviewedPostprint (published version

On the Internationalization of CAD Learning Through an English Glossary

Comunicació presentada al XXIX Congreso International INGEGRAF 2019 "La transformación Digital en la Ingeniería Gráfica” (20-21 Junio 2019, Logroño - La Rioja)The internationalization of higher education is an essential factor to improve the quality and efficiency of Spanish universities, providing students with the main skills, and knowledge to interact effectively in an international and multicultural work context as professionals. The internationalization of universities must be a transversal process, not exclusive of its territorial dimension, aimed at advancing towards a society and a knowledge economy that propitiate a solid and stable model of development and growth. To this end, professors in the area of Graphic Expression for Engineering at the Universitat Jaume I (UJI) have developed an online glossary of specific terms in English related to the 3D modelling CAD tools used in Graphic Engineering subjects. This new online tool seeks to train students to increase their technical vocabulary in English and improve their learning and communication skills to face possible collaborations in future European projects. The glossary is introduced weekly to the students during the course. Subsequently, a survey is conducted to the students to verify the effectiveness of the training. This work collects the results and conclusions of this analysis

Beyond Impedance Spectroscopy of Perovskite Solar Cells: Insights from the Spectral Correlation of the Electrooptical Frequency Techniques

Small perturbation techniques have proven to be useful tools for the investigation of perovskite solar cells. A correct interpretation of the spectra given by impedance spectroscopy (IS), intensity-modulated photocurrent spectroscopy (IMPS), and intensity-modulated photovoltage spectroscopy (IMVS) is key for the understanding of device operation. The utilization of a correct equivalent circuit to extract real parameters is essential to make this good interpretation. In this work, we present an equivalent circuit, which is able to reproduce the general and the exotic behaviors found in impedance spectra. From the measurements, we demonstrate that the midfrequency features that may appear to depend on the active layer thickness, and we also prove the spectral correlation of the three techniques that has been suggested theoretically

Analysis of the Influence of Selective Contact Heterojunctions on the Performance of Perovskite Solar Cells

Knowledge of the mechanisms that take place at the selective contacts, located at the charge-transport-layer (CTL)/perovskite heterojunctions, is crucial for the optimization of perovskite solar cells. Anomalous high values of the low-frequency capacitance at open-circuit and short-circuit indicate a high accumulation of charge at the interfaces, which could hinder the extraction of charge and increase hysteresis in current-voltage curve. To investigate this issue, we develop a simulation model based on the drift diffusion differential equations with specific boundary conditions at the interfaces. We have simulated the CTL/perovskite structures as part of the entire perovskite solar cell, in order to establish the realistic energy profile across the interface. The energy profile allows to detect in which situations free charge accumulation at the interfaces exists, and to quantify this accumulation as a function of the device and material parameters. We discuss the role and the importance of each CTL/perovskite interface at open-circuit and short-circuit. We conclude that the accumulation of charge at the interfaces is strongly affected by the specific contact materials, and critically depends on a compromise between the presence of ions, the values of the carrier mobility, and the interfacial and bulk recombination parameters

Limited information of impedance spectroscopy about electronic diffusion transport: The case of perovskite solar cells

Impedance Spectroscopy (IS) has proven to be a powerful tool for the extraction of significant electronic parameters in a wide variety of electrochemical systems, such as solar cells or electrochemical cells. However, this has not been the case with perovskite solar cells, which have the particular ionic-electronic combined transport that complicates the interpretation of experimental results due to an overlapping of different phenomena with similar characteristic frequencies. Therefore, the diffusion of electrons is indistinguishable on IS, and there appears the need to use other small perturbation experimental techniques. Here, we show that voltage-modulated measurements do not provide the same information as light-modulated techniques. We investigate the responses of perovskite solar cells to IS, Intensity-Modulated Photocurrent Spectroscopy (IMPS) and Intensity-Modulated Photovoltage Spectroscopy (IMVS). We find that the perturbations by light instead of voltage can uncover the electronic transport from other phenomena, resulting in a loop in the high-frequency region of the complex planes of the IMPS and IMVS spectra. The calculated responses are endorsed by the experimental data that reproduce the expected high frequency loops. Finally, we discuss the requirement to use a combination of small perturbation techniques for successful estimation of diffusion parameters of perovskite solar cells

Intensity-Modulated Photocurrent Spectroscopy for Solar Energy Conversion Devices: What Does a Negative Value Mean?

Small perturbation techniques constitute a wide family of tools for the characterization of solar energy conversion devices such as photovoltaic cells and photoelectrochemical (PEC) cells for solar fuel production. Two main small perturbation methods frequently used in the area of solar energy conversion materials are impedance spectroscopy (IS) and intensity-modulated photocurrent spectroscopy (IMPS). The first one consists of applying a small voltage perturbation and measuring modulated extracted current. The second one consists of applying the perturbation to the illumination and measuring the modulated extracted current

Extracting in Situ Charge Carrier Diffusion Parameters in Perovskite Solar Cells with Light Modulated Techniques.

Frequency resolved methods are widely used to determine device properties of perovskite solar cells. However, obtaining the electronic parameters for diffusion and recombination by impedance spectroscopy has been so far elusive, since the measured spectra do not present the diffusion of electrons. Here we show that intensity modulated photocurrent spectroscopy (IMPS) displays a high frequency spiraling feature determined by the diffusion-recombination constants, under conditions of generation of carriers far from the collecting contact. We present models and experiments in two different configurations: the standard sandwich-contacts solar cell device and the quasi-interdigitated back-contact (QIBC) device for lateral long-range diffusion. The results of the measurements produce the hole diffusion coefficient of D p = 0.029 cm2/s and lifetime of τ p = 16 μs for one cell and D p = 0.76 cm2/s and τ p = 1.6 μs for the other. The analysis in the frequency domain is effective to separate the carrier diffusion (at high frequency) from the ionic contact phenomena at a low frequency. This result opens the way for a systematic determination of transport and recombination features in a variety of operando conditions

Priming of plant resistance by natural compounds. Hexanoic acid as a model

Some alternative control strategies of currently emerging plant diseases are based on the use of resistance inducers. This review highlights the recent advances made in the characterization of natural compounds that induce resistance by a priming mechanism. These include vitamins, chitosans, oligogalacturonides, volatile organic compounds, azelaic and pipecolic acid, among others. Overall, other than providing novel disease control strategies that meet environmental regulations, natural priming agents are valuable tools to help unravel the complex mechanisms underlying the induced resistance (IR) phenomenon. The data presented in this review reflect the novel contributions made from studying these natural plant inducers, with special emphasis placed on hexanoic acid (Hx), proposed herein as a model tool for this research field. Hx is a potent natural priming agent of proven efficiency in a wide range of host plants and pathogens. It can early activate broad-spectrum defenses by inducing callose deposition and the salicylic acid (SA) and jasmonic acid (JA) pathways. Later it can prime pathogen-specific responses according to the pathogen’s lifestyle. Interestingly, Hx primes redox-related genes to produce an anti-oxidant protective effect, which might be critical for limiting the infection of necrotrophs. Our Hx-IR findings also strongly suggest that it is an attractive tool for the molecular characterization of the plant alarmed state, with the added advantage of it being a natural compound.This work was supported by grants from the Spanish Ministry of Science and Innovation (AGL2010-22300-C03-01-02-03) co-funded by European Regional Development Fund (ERDF) and Generalitat Valenciana Grupos de Excelencia (PROMETEO/2012/066). Maria de la O Leyva and Ivan Finiti were recipients of a research contract from AGL2010-22300-C03-01. We thank the SCIE Greenhouse section at the University of Valencia and the SCIC at the Universitat Jaume I for technical support

Radiative Recombination Processes in Halide Perovskites Observed by Light Emission Voltage Modulated Spectroscopy

The kinetics of light emission in halide perovskite light-emitting diodes (LEDs) and solar cells is composed of a radiative recombination of voltage-injected carriers mediated by additional steps such as carrier trapping, redistribution of injected carriers, and photon recycling that affect the observed luminescence decays. These processes are investigated in high-performance halide perovskite LEDs, with external quantum efficiency (EQE) and luminance values higher than 20% and 80 000 Cd m−2, by measuring the frequency-resolved emitted light with respect to modulated voltage through a new methodology termed light emission voltage modulated spectroscopy (LEVS). The spectra are shown to provide detailed information on at least three different characteristic times. Essentially, new information is obtained with respect to the electrical method of impedance spectroscopy (IS), and overall, LEVS shows promise to capture internal kinetics that are difficult to be discerned by other techniques.Funding for open access charge: CRUE-Universitat Jaume IThe authors thank the financial support by the Ministerio de Ciencia e Innovación of Spain (MICINN) and Agencia Estatal de Investigación AEI/10.13039/501100011033 by projects PID2019-107348GB-100 and STABLE PID2019-107314RB-I00, and by the Generalitat Valenciana with Prometeo Q-Solutions project CIPROM/2021/078