Autor Mario Kotlár

Combined in Situ Photoluminescence and X-ray Scattering Reveals Defect Formation in Lead-Halide Perovskite Films

Nada Mrkyvkova*, Vladimír Held, Peter Nádaždy, Riyas Subair, Eva Majkova, Matej Jergel, Aleš Vlk, Martin Ledinsky, Mário Kotlár, Jianjun Tian, Peter Siffalovic

J. Phys. Chem. Lett. 2021, 12, 41, 10156–10162

https://doi.org/10.1021/acs.jpclett.1c02869

Abstract

Lead-halide perovskites have established a firm foothold in photovoltaics and optoelectronics due to their steadily increasing power conversion efficiencies approaching conventional inorganic single-crystal semiconductors. However, further performance improvement requires reducing defect-assisted, nonradiative recombination of charge carriers in the perovskite layers. A deeper understanding of perovskite formation and associated process control is a prerequisite for effective defect reduction. In this study, we analyze the crystallization kinetics of the lead-halide perovskite MAPbI3–xClx during thermal annealing, employing in situ photoluminescence (PL) spectroscopy complemented by lab-based grazing-incidence wide-angle X-ray scattering (GIWAXS). In situ GIWAXS measurements are used to quantify the transition from a crystalline precursor to the perovskite structure. We show that the nonmonotonous character of PL intensity development reflects the perovskite phase volume, as well as the occurrence of the defects states at the perovskite layer surface and grain boundaries. The combined characterization approach enables easy determination of defect kinetics during perovskite formation in real-time.

Formation of CuCrCoFeNiO high entropy alloy thin films by rapid thermal processing of Cu/CrNiO/FeCo multilayers

Formation of CuCrCoFeNiO high entropy alloy thin films by rapid thermal processing of Cu/CrNiO/FeCo multilayers

AnniWanga, Manuel OlivaRamireza, MariaCaplovicovab,ViliamVretenarb, JuliusBoettchera, MarcusHopfelda, ThomasKupsa, DominikFlocka, PeterSchaafa

Surface and coatings technology, ISSN 0257-8972, 405 (2021), 126563

doi.org/10.1016/j.surfcoat.2020.126563

Abstract

This study presents the synthesis of High Entropy Alloy (HEA) films starting from elemental Cu and binary alloy CoFe and CrNiO multilayers, followed by rapid thermal processing (RTP). By that, the HEA films (HEAFs) were formed by phase formation via short-range and fast diffusion processes. Multilayers with a total thickness of 760 nm consisting of 16 repetitions of a Cu (11 nm)/CrNiO (16.5 nm)/CoFe (20 nm) sequence were annealed at temperatures from 600 °C to 1000 °C for 5 min. The reaction products were then analyzed by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM) combined with electron energy loss spectroscopy (EELS), in order to identify the phase transformations and elemental distributions. A duplex FCC structure containing CrCoFeNiO HEA and pure Cu phase was successfully synthesized at 600 °C and 800 °C by the solid-state reaction. CuCrCoFeNiO HEA formed within in a Cu nanocrystalline matrix. As the annealing temperature increased, the oxygen content in the films decreased, Both HEA and Cu possess significant 〈111〉 preferred orientation. The HEA phase demonstrated a typical microstructure of alloys with intensive nano-twins. Moreover, the grain growth kinetics of the HEA phase was evaluated, and the activation energy was found to be 185(10) kJ/mol. This is comparable to that of conventional stainless steel (~150 kJ/mol) and less than half of the value for CrCoFeNi bulk (434 kJ/mol). A surface energy-driven grain growth mechanism of the HEAFs via multilayer alloy formation is proposed in this study. The mechanical properties, hardness and Young’s modulus, were measured via nanoindentation, and the strengthening mechanism was proposed and compared with current literature.

Prestavba suterénu Nanocentra

V rámci projektu Accord bude zakúpený nový FIB-SEM mikroskop, ktorý bude inštalovaný v priestoroch Centra pre Nanodiagnostiku materiálov.

S nákupom je úzko spojená rozsiahla rekonštrukcia suterénu Centra pre Nanodiagnostiku materiálov, ktorá začala v Marci 2022.

Úprava priestorov sa začala odstránením priečok

Práce začali odstránením starých podláh, priečok a prácami na novej podlahe. Pre samotný mikroskop bude vytvorený samostatný betónový blok, ktorí bude oddelený od zvyšku miestnosti. Po zhotovení nových podláh, budú mať nové laboratóriá vyššiu svetlú výšku.

Miesto pre samostatný betónový blok pod FIB-SEM mikroskop.
Realizácia hydroizolácie
Miesto pre FIB-SEM mikroskop
Nové podlahy

Po ukončení rekonštrukcie vznikli z pôvodne zanedbaných priestorov nové atraktívne laboratóriá. Po inštalácii nového prístrojového vybavenia zlepšia tieto laboratóriá možnosti výskumných aktivít Slovenskej Technickej Univerzity. Týmto bola univerzita obohatená o nové reprezentatívne priestory.

Vstupná hala
Servisná miestnosť
Miesto pre inštaláciu nového FIB-SEM mikroskopu