Microstructure, chemical composition, and dielectric response of CaCu3Ti4O12 ceramics doped with F, Al, and Mg ions

Ceramics with nominal chemical composition CaCu3Ti4O12 (CCTO), CaCu3Ti3.96Al0.04O11.96F0.04 (CCTOAF), and Ca0.98Mg0.08Cu2.94Ti3.96Al0.04O11.96F0.04 (CCTOMAF) were prepared by the solid-state reactions technique. Using SEM, EDX, XPS, EPR, NMR, and complex impedance spectroscopy, the microstructure, elements distribution, chemical composition of grains and grain boundaries, and the dielectric response of ceramics were investigated. In the ССТО, CCTOAF, and CCTOMAF series, the average grain size increases, the degree of copper segregation at the grain boundaries is inversely related to grain size, and the dielectric loss decreases from 0.071 to 0.047 and 0.030, respectively, while dielectric permittivity ε′ at 1 kHz is 5.6 × 104, 7.1 × 104, and 4.3 × 104, respectively. Additives of Al, Mg, F and milled particles (ZrO2, Al2O3, and SiO2) can either partially introduce into the perovskite structure or form low-melting eutectics at the grain boundaries, causing abnormal grain growth. The presence of copper ions in various oxidation states, as well as evidence of exchange spin interactions between them, was confirmed in all samples

Morphological, optical and photovoltaic characteristics of MoSe2/SiOx/Si heterojunctions

This work reports the effect of different processing parameters on the structural and morphological characteristics of MoSe2 layers grown by chemical vapour deposition (CVD), using MoO3 and Se powders as solid precursors. It shows the strong dependence of the size, shape and thickness of the MoSe2 layers on the processing parameters. The morphology of the samples was investigated by field emission scanning electron microscopy (FESEM) and the thickness of the deposited layers was determined by atomic force microscopy (AFM). Raman and photoluminescence (PL) spectroscopies were used to confirm the high quality of the MoSe2 layers. Surface composition was examined by photoelectron spectroscopy (XPS). Moreover, the MoSe2/SiOx/Si heterojunctions exhibit diode behaviour, with a rectification ratio of 10, measured at ±2.0 V, which is due to the p-i-n heterojunctions formed at the p-Si/SiOx/MoSe2 interface. A photovoltaic effect was observed with a short circuit current density (Jsc), open circuit voltage (VOC) and efficiency of -0.80 mA/cm2, 1.55 V and 0.5%, respectively. These results provide a guide for the preparation of p-i-n heterojunctions based on few-layer MoSe2 with improved photovoltaic response.Tis work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contracts UID/CTM/04540/2019 and UID/FIS/04650/2019. Part of this work was supported by the COST Action MP1406 “Multiscale in modeling and validation for solar photovoltaics (MultiscaleSolar)”. Te authors acknowledge the CERIC-ERIC Consortium for access to experimental facilities and fnancial support under proposal 20182042

All-Oxide p-n Junction Thermoelectric Generator Based on SnOx and ZnO Thin Films.

Achieving thermoelectric devices with high performance based on low-cost and nontoxic materials is extremely challenging. Moreover, as we move toward an Internet-of-Things society, a miniaturized local power source such as a thermoelectric generator (TEG) is desired to power increasing numbers of wireless sensors. Therefore, in this work, an all-oxide p-n junction TEG composed of low-cost, abundant, and nontoxic materials, such as n-type ZnO and p-type SnOx thin films, deposited on borosilicate glass substrate is proposed. A type II heterojunction between SnOx and ZnO films was predicted by density functional theory (DFT) calculations and confirmed experimentally by X-ray photoelectron spectroscopy (XPS). Moreover, scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDS) show a sharp interface between the SnOx and ZnO layers, confirming the high quality of the p-n junction even after annealing at 523 K. ZnO and SnOx thin films exhibit Seebeck coefficients (α) of ∼121 and ∼258 μV/K, respectively, at 298 K, resulting in power factors (PF) of 180 μW/m K2 (for ZnO) and 37 μW/m K2 (for SnOx). Moreover, the thermal conductivities of ZnO and SnOx films are 8.7 and 1.24 W/m K, respectively, at 298 K, with no significant changes until 575 K. The four pairs all-oxide TEG generated a maximum power output (Pout) of 1.8 nW (≈126 μW/cm2) at a temperature difference of 160 K. The output voltage (Vout) and output current (Iout) at the maximum power output of the TEG are 124 mV and 0.0146 μA, respectively. This work paves the way for achieving a high-performance TEG device based on oxide thin films. This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Materials and Interfaces, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acsami.1c09748

Perovskite ferroelectric thin film as an efficient interface to enhance the photovoltaic characteristics of Si/SnOx heterojunctions

The photovoltaic (PV) response of SnOx/Si heterojunctions (HJs) through the change of the SnO and SnO2 ratio in the samples that allows us to obtain p- or n-type SnOx films is investigated in this work. The values of short-circuit photocurrent density (Jsc), open-circuit voltage (VOC), fill factor (FF) and power conversion efficiency (PCE) are found to be 12.6 mA cm−2, 0.23 V, 27% and 8.3%, for the p-SnOx/n-Si HJ and 10.3 mA cm−2, 0.20 V, 20% and 4.5% for the n-SnOx/p-Si HJ. The enhanced PV effect observed in the p-SnOx/n-Si HJs can be attributed to a small band offset between SnOx and Si, which lowers the diffusion length that can contribute to higher recombination rate and smaller series resistance. Furthermore, the values of Jsc, VOC, FF and PCE were enhanced up to 30.9 mA cm−2, −2.0 V, 19% and 10.9%, respectively, through the insertion of a 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BCZT) ferroelectric layer between n-Si and p-SnOx. The built-in field developed at the Si/BCZT/SiOx/SnOx interfaces together with the depolarizing field, provides a favorable electric potential for the separation and further transport of photo generated electron–hole (e–h) pairs. This work provides a viable approach by combining ferroelectrics with p-SnOx/n-Si HJs for building efficient ferroelectric-based solar cells.This work was supported by: (i) the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contracts UIDB/04650/2020 and the Scientific and Technological Cooperation Program between Portugal (FCT) and Morocco (CNRST) - 2019/2020; (ii) the reference project UID/EEA/04436/2013, by FEDER funds through the COMPETE 2020 – Programa Operacional Competitividade e Internacionalização (POCI) with the reference project POCI-01-0145- FEDER-006941; (iii) CMEMS-UMinho Strategic Project UIDB/ 04436/2020 and UIDP/04436/2020; (iv) the Programa Operacional Regional do Norte (NORTE2020), through Fundo Europeu de Desenvolvimento Regional (FEDER), Project NORTE-01-0145-FEDER-000032, NextSea; (v) DST-SERB, Govt. of India through Grant No. ECR/2017/00006; (vi) the statutory grant (No. 8201003902) of Department of Quantum Technologies of Wroclaw University of Science and Technology an (vii) the project CICECO-Aveiro Institute of Materials, UIDB/50011/ 2020 & UIDP/50011/2020, financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. The authors acknowledge the CERIC-ERIC Consortium for access to experimental facilities and financial support under proposal 20192056