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Role of Urbach Energy in Photovoltaics
Vlk, Aleš ; Abelová, Lucie ; Hájková, Zdeňka ; Remeš, Zdeněk ; Holovský, Jakub ; Ledinský, Martin
Organic-inorganic halide perovskites provide new opportunities for improvement of optoelectronic device performance, especially the efficiency of solar cells. To evaluate the quality of a new material many parameters has to be taken into account. Here, we discuss one of the often overlooked semiconductor’s parameters, Urbach energy, which is an easily accessible measure of material disorder. Moreover, we present its importance on the example of organic-inorganic halide perovskites.
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Mass production of hydrogenated ZnO nanorods
Chang, Yu-Ying ; Remeš, Zdeněk ; Míčová, J.
We have developed an inexpensive and efficient technology of hydrothermal growth of ZnO nanorods from zinc nitrate hexahydrate (Zn(NO3)2·6H2O), as a precursor and hexamethylenetetramine (HMTA) (C6H12N4), as a surfactant followed by plasma hydrogenation in a novel inductively coupled plasma (ICP) quartz reactor and equipped with the rotary sample holder to stir powder during plasma treatment. We have optimized the photoluminescence spectroscopy for measuring optical scattering samples with the high sensitivity, precise sample positioning and very low influence of the scattered excitation light. Here we present the latest results on the enhancement of the UV photoluminescence of the ZnO nanorods after plasma hydrogenation. The exciton-related photoluminescence has been significantly enhanced whereas the deep defect related yellow photoluminescence has been significantly decreased.\n
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Comparison of microbial interactions of zinc oxide nanomaterials in various size and shape
Rutherford, D. ; Jíra, J. ; Mičová, J. ; Remeš, Zdeněk ; Hsu, H.S. ; Rezek, B.
Zinc oxide nanoparticles (ZnO NP) have shown great potential as a novel antibacterial material at a time when resistance towards conventional antibiotics is becoming more prevalent. We report bacteria inactivation by ZnO NP with novel hedgehog-like morphology using model gram-negative (E. coli) and gram-positive (S. aureus) bacteria. E. coli exposed to the novel ZnO hedgehog NP during growth resulted in 4 orders of magnitude reduction in viable cell concentration after 24 h, which is more than 2 orders higher reduction compared to commercially available ZnO NPs with nominal sizes from 50 nm to 20 um. There was a positive correlation between hedgehog NP concentration and bacteria cell concentration reduction within the range tested 0.1 – 1.0 mg/mL. S. aureus was less sensitive to ZnO NP exposure and inactivation effect of various ZnO NP, was comparable. The effect can be thus attributed to direct mechanical damage of the bacterial mebrane that is the most effective for the novel hedgehog ZnO NP. This conclusion was corroborated also by disk diffusion assays.\n
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Characterization of hydrogenated silicon thin films and diode structures with integrated silicon and germanium nanoparticles
Stuchlík, Jiří ; Fajgar, R. ; Remeš, Zdeněk ; Kupčík, Jaroslav ; Stuchlíková, Hana
P-I-N diode structures based on the thin films of amorphous hydrogenated silicon (a-Si:H) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique were prepared with embedded Si and Ge nanoparticles. The Reactive Laser Ablation (RLA) of germanium target was used to cover the intrinsic a-Si:H layer by Ge NPs under a low pressure of the silane. The RLA was performed using focused excimer ArF laser beam under SiH4 background atmosphere. Reaction between ablated Ge NPs and SiH4 led to formation of Ge NPs covered by thin GeSi:H layer. The deposited NPs were covered and stabilized by a-Si:H layer by PECVD. Those two deposition processes were alternated repeatedly. Volt-ampere characteristics of final diode structures were measured in dark and under illumination as well as their electroluminescence spectra.
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Germanium and tin nanoparticles encapsulated in amorphous silicon matrix for optoelectronic application
Stuchlíková, The-Ha ; Remeš, Zdeněk ; Stuchlík, Jiří
The plasma enhanced chemical vapour deposition was combined with in situ deposition of Ge and Sn thin film by evaporation technique at surface temperature about 220 °C to form nanoparticles on the surface of hydrogenated silicon thin films to prepare diodes. Formation of nanoparticles was additionally stimulated by plasma treatment through a low pressure hydrogen glow discharge. The diodes based on PIN diode structures with and without the embedded Ge or Sn nanoparticles were characterized by temperature dependence of electrical conductivity, activation energy of conductivity, measurement of volt-ampere characteristics in dark and under solar illumination\n
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The photoluminescence and optical absorptance of plasma hydrogenated nanocrystalline ZnO thin films
Remeš, Zdeněk ; Chang, Yu-Ying ; Stuchlík, Jiří ; Mičová, J.
We have developed the technology of the deposition of the nominally undoped ZnO nanocrystalline thin films by DC reactive magnetron sputtering of Zn target in the gas mixture of argon and oxygen plasma. We have optimized the photoluminescence spectroscopy for measuring optically scattering thin layers with the high sensitivity, precise sample positioning and very low influence of the scattered excitation light. Here we present the latest results on the enhancement of the photoluminescence of the nanocrystalline ZnO thin films after plasma hydrogenation. The photoluminescence in near UV region has been enhanced whereas the deep defect related photoluminescence has been significantly decreased. We found good room temperature stability of the plasma hydrogenated ZnO nanocrystals in air, but fast degradation at elevated temperature\n
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Characterization of hydrogenated silicon thin films and diode structures with integrated germanium nanoparticles
Stuchlík, Jiří ; Fajgar, Radek ; Kupčík, Jaroslav ; Remeš, Zdeněk ; Stuchlíková, The-Ha
Substrates with ZnO (or ITO) conductive layers were covered by thin film of a-Si:H deposited by PECVD technique. Under a turbo-molecular vacuum (10-4 Pa) the reactive laser ablation (RLA) was used to cover this a-Si:H thin film by germanium NPs. The RLA was performed using focused excimer ArF laser beam (193 nm, 100 mJ/pulse) under SiH4 background atmosphere (0.5 Pa). As a target the elemental germanium was used. Reaction between ablated Ge and silane led to formation of Ge NPs covered by thin SiGe layer. Then the deposited NPs were covered and stabilized by a-Si:H layer by PECVD. Those two deposition processes was alternated and applied a few times. The Si:H thin films with integrated Ge NPs were characterized by microscopic, spectroscopic and diffraction techniques. I-V characteristics of final diode structures without and under illumination were measured as well as their electroluminescence behaviour.
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The hydrogen plasma doping of ZnO thin films and nanoparticles
Remeš, Zdeněk ; Neykova, Neda ; Potocký, Štěpán ; Chang, Yu-Ying ; Hsu, H.S.
The optical absorptance and photoluminescence studies has been applied on the hydrogen and oxygen plasma treated, nominally undoped ZnO thin films and aligned nanocolumns grown on the nucleated glass substrate by the hydrothermal process in an oil bath containing a flask with ZnO nutrient solution. The localized defect states at 2.3 eV below the optical absorption edge were detected by photothermal deflection spectroscopy (PDS) in a broad spectral range from near UV to near IR. The optical absorptance spectroscopy shows that hydrogen doping increases free electron concentration changing ZnO to be electrically conductive (hydrogen doping).\n
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