@misc{KotHenkelSchmeisser, author = {Kot, Małgorzata and Henkel, Karsten and Schmeißer, Dieter}, title = {Internal chemical potential in mixed covalent-ionic photosensitive systems}, series = {Journal of Vacuum Science \& Technology A}, volume = {43 (2025)}, journal = {Journal of Vacuum Science \& Technology A}, number = {1}, publisher = {American Vacuum Society}, issn = {0734-2101}, doi = {10.1116/6.0004179}, pages = {1 -- 9}, abstract = {The internal chemical potential Γ of mixed covalent-ionic systems represents the potential differences between the covalent and the ionic intrinsic defect states located within the ionic gap. It is the key parameter to control the carrier densities, the stability regimes, and the photosensitive properties of materials. In this work, we describe first the quantitative analysis of the carrier densities in dependence on the internal potential Nπ(Γ) based on the common features of the electronic structure of mixed covalent-ionic materials. Subsequently, this method is applied on two mixed covalent-ionic materials, i.e., formamidinium lead triiodide and gallium oxide, as representatives of the respective families of perovskites (halides) and transparent conducting oxide thin films. Based on this analysis, the carrier densities as well as the photosensitivity mechanisms and the related specific properties of these materials in dependence on their internal chemical potential are discussed.}, language = {en} } @misc{KotGawlińska‐NęcekHenkeletal., author = {Kot, Małgorzata and Gawlińska-Nęcek, Katarzyna and Henkel, Karsten and Flege, Jan Ingo}, title = {Prospects of improving efficiency and stability of hybrid perovskite solar cells by alumina ultrathin films}, series = {Small}, volume = {21}, journal = {Small}, number = {12}, publisher = {Wiley}, issn = {1613-6810}, doi = {10.1002/smll.202408435}, pages = {19}, abstract = {Over the last few years, the influence of low temperature (≤80 °C) and, in particular, of room temperature, atomic layer deposited alumina (ALD-Al2O3) on the properties of the underlying hybrid perovskites of different compositions and on the efficiency and stability of the corresponding perovskite solar cells (PSCs) is extensively investigated. The main conclusion is that most probably thanks to the presence of intrinsic defect states in the ALD-Al2O3 and in the perovskite layers, charge transfer and neutralization are possible and the entire lifetime of the PSCs is thus improved. Moreover, the migration of mobile ions between the layers is blocked by the ALD-Al2O3 layer and thus the occurrence of hysteresis in the current density-voltage characteristics of the PSCs is suppressed. Considering the uniform and nondestructive surface coverage, low thermal budget, small amount of material required, and short duration of the established ALD-Al2O3 deposition on top of hybrid perovskites, this additional, but fully solar cell technology-compatible, process step is most likely the most effective, cheapest, and fastest way to improve the efficiency and long-term stability of PSCs and thus increase their marketability.}, language = {en} } @misc{KotGawlińska‐NęcekPożarowskaetal., author = {Kot, Małgorzata and Gawlińska-Nęcek, Katarzyna and Pożarowska, Emilia and Henkel, Karsten and Schmeißer, Dieter}, title = {Photosensitivity and carrier densities of perovskite solar absorbers}, series = {Advanced science}, volume = {12}, journal = {Advanced science}, number = {16}, publisher = {Wiley}, address = {Hobken, New Jersey}, issn = {2198-3844}, doi = {10.1002/advs.202412711}, pages = {1 -- 8}, abstract = {Dark and light current-voltage characteristics of perovskite solar absorbers are analyzed in terms of their carrier densities. The analysis reveals p-type large polarons as a dominant carrier type in the investigated perovskite solar cells. The mechanism causing photosensitivity is attributed to the dissociation (and pairing) of bipolarons to large polarons (and vice versa) that are controlled by the internal potential Γ. As an example, the polaron concept is tested for a formamidinium lead triiodide perovskite solar cell. The individual steps of the data analysis are demonstrated and determine the ionicity factor of this perovskite film, quantify the density of the large polarons, and predict the gain and loss of photo-induced carriers. It is deduced that a reversible light-on/off operation can only occur when the bias voltage never exceeds a critical value of the internal potential. The results gained in this study suggest that the novel analysis can be successively applied on different hybrid perovskite materials, too.}, language = {en} } @misc{MoralesGertigKotetal., author = {Morales, Carlos and Gertig, Max and Kot, Małgorzata and Alvarado, Carlos and Schubert, Markus Andreas and Zoellner, Marvin Hartwig and Wenger, Christian and Henkel, Karsten and Flege, Jan Ingo}, title = {In situ X-ray photoelectron spectroscopy study of atomic layer deposited cerium oxide on SiO₂ : substrate influence on the reaction mechanism during the early stages of growth}, series = {Advanced materials interfaces}, volume = {12}, journal = {Advanced materials interfaces}, number = {5}, publisher = {Wiley}, address = {Weinheim}, issn = {2196-7350}, doi = {10.1002/admi.202400537}, pages = {1 -- 13}, abstract = {Thermal atomic layer deposition (ALD) of cerium oxide using commercial Ce(thd)4 precursor and O3 on SiO2 substrates is studied employing in-situ X-ray photoelectron spectroscopy (XPS). The system presents a complex growth behavior determined by the change in the reaction mechanism when the precursor interacts with the substrate or the cerium oxide surface. During the first growth stage, non-ALD side reactions promoted by the substrate affect the growth per cycle, the amount of carbon residue on the surface, and the oxidation degree of cerium oxide. On the contrary, the second growth stage is characterized by a constant growth per cycle in good agreement with the literature, low carbon residues, and almost fully oxidized cerium oxide films. This distinction between two growth regimes is not unique to the CeOx/SiO2 system but can be generalized to other metal oxide substrates. Furthermore, the film growth deviates from the ideal layer-by-layer mode, forming micrometric inhomogeneous and defective flakes that eventually coalesce for deposit thicknesses above 10 nm. The ALD-cerium oxide films present less order and a higher density of defects than films grown by physical vapor deposition techniques, likely affecting their reactivity in oxidizing and reducing conditions.}, language = {en} } @misc{KediaDasKotetal., author = {Kedia, Mayank and Das, Chittaranjan and Kot, Malgorzata and Yalcinkaya, Yenal and Zuo, Weiwei and Tabah Tanko, Kenedy and Matvija, Peter and Ezquer, Mikel and Cornago, I{\~n}aki and Hempel, Wolfram and Kauffmann, Florian and Plate, Paul and Lira-Cantu, Monica and Weber, Stefan A.L. and Saliba, Michael}, title = {Mitigating the amorphization of perovskite layers by using atomic layer deposition of alumina}, series = {Energy \& environmental science}, volume = {18}, journal = {Energy \& environmental science}, number = {11}, publisher = {Royal Society of Chemistry (RSC)}, address = {London}, issn = {1754-5692}, doi = {10.1039/D4EE05703A}, pages = {5250 -- 5263}, abstract = {Atomic layer deposition of aluminum oxide (ALD-Al2O3) layers has recently been studied for stabilizing perovskite solar cells (PSCs) against environmental stressors, such as humidity and oxygen. In addition, the ALD-Al2O3 layer acts as a protective barrier, mitigating pernicious halide ion migration from the perovskite towards the hole transport interface. However, its effectiveness in preventing the infiltration of ions and additives from the hole-transport layer into perovskites remains insufficiently understood. Herein, we demonstrate the deposition of a compact ultrathin (∼0.75 nm) ALD-Al2O3 layer that conformally coats the morphology of a triple-cation perovskite layer. This promotes an effective contact of the hole transporter layer on top of the perovskite, thereby improving the charge carrier collection between these two layers. Upon systematically investigating the layer-by-layer structure of the PSC, we discovered that ALD-Al2O3 also acts as a diffusion barrier for the degraded species from the adjacent transport layer into the perovskite. In addition to these protective considerations, ALD-Al2O3 impedes the transition of crystalline perovskites to an undesired amorphous phase. Consequently, the dual functionality (i.e., enhanced contact and diffusion barrier) of the ALD-Al2O3 protection enhanced the device performance from 19.1\% to 20.5\%, while retaining 98\% of its initial performance compared to <10\% for pristine devices after 1500 h of outdoor testing under ambient conditions. Finally, this study deepens our understanding of the mechanism of ALD-Al2O3 as a two-way diffusion barrier, highlighting the multifaceted role of buffer layers in interfacial engineering for the long-term stability of PSCs.}, language = {en} } @misc{WeichbrodtDomaradzkiObstarczyketal., author = {Weichbrodt, Wiktoria and Domaradzki, Jaroslaw and Obstarczyk, Agata and Kot, Malgorzata and Flege, Jan Ingo and Mazur, Michal}, title = {Influence of thermal modification on the gasochromic properties of WO₃ thin films fabricated by electron beam evaporation}, series = {Applied optics}, volume = {65}, journal = {Applied optics}, number = {5}, publisher = {Optica Publishing Group}, address = {Washington, DC}, issn = {1559-128X}, doi = {10.1364/AO.574918}, pages = {A58 -- A67}, abstract = {This paper describes the effect of post-deposition annealing on the structural and gasochromic properties of WO3 thin films deposited by electron beam evaporation and additionally decorated with a Pd catalyst layer of varying thickness. The WO3 layers were annealed at 800°C, which led to a phase transition from an amorphous to a monoclinic crystal structure, accompanied by an increase in surface roughness from 1.3 to 66 nm and the formation of a discontinuous island-like morphology with grain sizes up to 3 µm. The structural changes had a significant effect on the optical response of the layers to hydrogen. For the annealed samples, the absolute change in light transmission reached 20.2-20.9\% for the 1.5 nm thick Pd catalyst and 7.7-9.2\% for the 5 nm thick Pd catalyst at a wavelength of 850 nm. The corresponding optical response was 184-186\% for the thin Pd layer and 353-396\% for the thick Pd layer, depending on the hydrogen concentration (25-1000 ppm). The response time was reduced from 10 min at 25 ppm to < 4 min at 1000 ppm, while the recovery time to the original state in air remained below 66 s under all conditions. XPS studies confirmed the reduction of W6+ to W5+ under the influence of hydrogen and reversible transition PdO - Pd, which correlates with the observed optical changes. The results show that annealing increases crystallinity and modifies porosity, which, in combination with the Pd catalyst directly affects the kinetics and magnitude of the gasochromic response.}, language = {en} } @misc{Gawlińska−NęcekDąbczyńskiNuckowskietal., author = {Gawlińska-Nęcek, Katarzyna and Dąbczyński, Paweł and Nuckowski, Paweł and Starowicz, Zbigniew and Kot, Małgorzata and Panek, Piotr and Flege, Jan Ingo}, title = {Crystallographic changes mediated by copper migration from hole transporting layer into CsPbBr₃ perovskite}, series = {The journal of physical chemistry C}, volume = {129}, journal = {The journal of physical chemistry C}, number = {43}, publisher = {American Chemical Society (ACS)}, address = {Washington, DC}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.5c06144}, pages = {19410 -- 19420}, abstract = {Copper oxides, due to their low cost and high ambient stability, are promising candidates for use as a hole-transporting layer (HTL) in perovskite solar cells. However, it has been found that they can be very unstable in contact with organic-inorganic FAPbI3 perovskite, causing mutual chemical reactions and changing a photoactive to a nonphotoactive perovskite phase. To verify if the copper migration and the occurrence of chemical reactions are a matter of contact with a type of perovskite (organic-inorganic or fully inorganic) or the nature of copper oxides, in this work, the interface between cupric and cuprous oxides and a fully inorganic cesium lead bromide (CsPbBr3) perovskite is investigated. It is found that CsPbBr3 is not robust against copper ion migration from HTL, similarly to organic-inorganic FAPbI3; however, contrary to the previous results, they do not cause chemical reactions. Instead, crystallographic lattice shrinkage of the CsPbBr3 occurred along with the substitution of Pb2+ by copper ions. The work explains the mechanism of this phenomenon and confirms the unreliability of copper(I) oxide and copper(II) oxide as HTLs in p-i-n perovskite solar cells based on both organic-inorganic and fully inorganic lead halide perovskites.}, language = {en} }