Lidé

prof. Tomáš Markvart, Ph.D.

Všechny publikace

Universal measure of photon collection efficiency of dye luminescent solar concentrators

  • DOI: 10.1016/j.solmat.2022.112101
  • Odkaz: https://doi.org/10.1016/j.solmat.2022.112101
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Luminescent solar concentrators (LSC) are recently getting attention as promising components for use in building integrated photovoltaics (BIPV). Ongoing efforts to reduce their optical losses result in active search for new luminophores with large Stokes shift in order to reduce the reabsorption probability. Here we present a novel figure of merit for a large group of Gaussian dye luminophores that provides an accurate assessment of optical losses. Our approach originates in simplified analytical solution for spectral overlapping integral of absorption/emission bands and results in assessment of average reabsorption probability. The procedure is then generalized for any Gaussian dye LSC, by considering its basic parameters (Stokes shift, absorbance and size), thus resulting in a simple useful tool for designing practical LSC devices. Calculations are correlated with the experimental results of reabsorption probability obtained by measuring edge fluorescence spectra of various LSCs.

A simple and effective methodology for sizing electrical energy storage (EES) systems based on energy balance

  • DOI: 10.1016/j.est.2022.104085
  • Odkaz: https://doi.org/10.1016/j.est.2022.104085
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The use of the electrical energy storage (EES) plays an important role in the transition of energy generation towards renewable energy sources (RESs). An effective sizing of EES systems is very important in order to cope with the volatility of RESs and to ensure a reliable energy supply. The present paper provides a methodology which helps to determine the minimum required EES size for conceiving a fully standalone system. Its approach is based on the evaluation of the energy balance for a given design period, and it can also be applied for sizing the EES system in grid-connected applications. The methodology was validated using measurement data obtained from two different systems corresponding to: a) a near-zero energy building with local generation sources, and b) a large-scale battery energy storage system (BESS) installed in a factory and used for peak-shaving. The obtained results confirmed the effectiveness of the proposed methodology by estimating the required size of the EES system. A good correlation was found between the estimated and the installed BESS size in the considered systems. The deviation between real and estimated BESS capacities was found to be less than 5%.

Observation of energy transfer at optical frequency to an ultrathin silicon waveguide

  • Autoři: Fang, L., Danos, L., prof. Tomáš Markvart, Ph.D., Chen, R.
  • Publikace: Optics Letters. 2020, 45(16), 4618-4621. ISSN 0146-9592.
  • Rok: 2020
  • DOI: 10.1364/OL.396906
  • Odkaz: https://doi.org/10.1364/OL.396906
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Energy transfer from a submonolayer of rhodamine 6G molecules to a 130 nm thick crystalline silicon (Si) waveguide is investigated. The dependence of the fluorescence lifetime of rhodamine on its distance to the Si waveguide is characterized and modeled successfully by a classical dipole model. The energy transfer process could be regarded as photon tunneling into the Si waveguide via the evanescent waves. The experimentally observed tunneling rate is well described by an analytical expression obtained via a complex variable analysis in the complex wavenumber plane.

Silicon photosensitisation using molecular layers

  • DOI: 10.1039/c9fd00095j
  • Odkaz: https://doi.org/10.1039/c9fd00095j
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Silicon photosensitisation via energy transfer from dye molecular layers is a promising area of research for excitonic silicon photovoltaics. We present the synthesis and photophysical characterisation of vinyl and allyl terminated Si(111) surfaces decorated with perylene molecules. The functionalised silicon surfaces together with Langmuir-Blodgett (LB) films based on perylene derivatives were studied using a wide range of steady-state and time resolved spectroscopic techniques. Fluorescence lifetime quenching experiments performed on the perylene modified monolayers revealed energy transfer efficiencies to silicon up to 90 per cent. We present a simple model to account for the near field interaction of a dipole emitter with the silicon surface and distinguish between the ‘true’ FRET region (<5 nm) and a different process, photon tunneling, occurring for distances between 10 nm - 50 nm. The requirements for a future ultra-thin crystalline solar cell paradigm include efficient surface passivation and keeping a close distance between the emitter dipole and surface. These are discussed in the context of existing limitations and questions raised about the finer details of the emitter-silicon interaction.

All UK electricity supplied by wind and photovoltaics – The 30–30 rule

  • DOI: 10.1016/j.energy.2018.11.151
  • Odkaz: https://doi.org/10.1016/j.energy.2018.11.151
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Based on weather and electricity demand data for the period 1984–2013, we develop a system model based on energy balance to determine the size of photovoltaic and wind generation combined with energy storage to provide a firm power supply for Great Britain. A simple graphical methodology is proposed where the required wind and PV generation capacities can be read off from a “system configuration diagram” as a function of the available storage size. We show, by way of illustration, that a reliable supply would be produced by a system based on PV and wind generators generating some 30% more electrical energy (approximately 100 TWh p.a.) than the current electricity supply system if supplemented with 30 days of storage. In terms of generation capacities, the current 82 GW of principally thermal generation would then be replaced by about 150 GW of wind turbines and 35 GW of PV arrays.

Hot photons and open-circuit voltage in molecular absorbers

  • DOI: 10.1088/1361-6641/ab419f
  • Odkaz: https://doi.org/10.1088/1361-6641/ab419f
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Hot carrier solar cells have attracted interest for many years. Although no working exemplars exist today, the challenges to overcome have become clearer and a substantial research effort has been underway with a focus on inorganic semiconductors, including quantum wells. In this paper we propose a novel strategy to potentially exploit hot photons, based on organic absorbers. Our approach, when combined with photon management structures similar to photonic fluorescent collectors, can potentially enhance the efficiency of complete photovoltaic devices. We present a characterisation method of fluorescent collectors by evaluating the chemical potential and temperature of the emitted fluorescence photon flux. We report on observation of temperatures of the emitted photon flux well above the ambient temperature, indicating the presence of hot photons. We propose a theoretical background to describe how excess thermal energy carried by hot photons can be exploited to increase the chemical potential of the photon flux which is closely related to the open-circuit voltage of the solar cell.

Evaluating the Potential of Optical Materials as Solar Cell Absorbers

  • Autoři: RNDr. Branislav Dzurňák, Ph.D., Danos, L., prof. Tomáš Markvart, Ph.D.,
  • Publikace: Proceedings of the International Conference of 35th European Photovoltaic Solar Energy Conference and Exhibition. München: WIP Wirtschaft und Infrastruktur GmbH & Co Planungs KG, 2018. p. 110-113. ISSN 2196-100X. ISBN 978-3-936338-50-8.
  • Rok: 2018
  • DOI: 10.4229/35thEUPVSEC20182018-1CV.4.13
  • Odkaz: https://doi.org/10.4229/35thEUPVSEC20182018-1CV.4.13
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    We have developed a methodology to evaluate materials for potential use as absorbers in solar cells without the need for device fabrication. Using our expertise developed for fluorescence collectors we have fabricated relevant structures and characterised them for reabsorption and absolute fluorescence intensity. The latter then form a basis to deduce the chemical potential of the emitted light, closely related to open-circuit voltage of a solar cell where this material would act as an absorber. Detailed analyses are carried out of the relevant losses focusing on interplay between photon recycling, non-radiative quenching and absorptivity/emissivity. Our results present values of open-circuit voltage that can be achieved using easily available laser dyes.

Impact of Small Phonon Energies on the Charge-Carrier Lifetimes in Metal-Halide Perovskites

  • Autoři: Kirchartz, T., prof. Tomáš Markvart, Ph.D., Rau, U., Egger, D.A.
  • Publikace: Journal of Physical Chemistry Letters. 2018, 9(5), 939-946. ISSN 1948-7185.
  • Rok: 2018
  • DOI: 10.1021/acs.jpclett.7b03414
  • Odkaz: https://doi.org/10.1021/acs.jpclett.7b03414
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    Metal-halide perovskite (MHP) solar cells exhibit long non-radiative lifetimes as a crucial feature enabling high efficiencies. Long non-radiative lifetimes occur if the transfer of electronic into vibrational energy is slow due to, e.g., a low trap density, weak electronphonon coupling or the requirement to release a many phonons in the electronic transition. Here, we combine known material properties of MHPs with basic models for electron-phonon coupling and multiphonon-transition rates in polar semiconductors. We find that the low phonon energies of MAPbI3 lead to a strong dependence of recombination rates on trap position, which we deduce from the underlying physical effects determining non-radiative transitions. This is important for non-radiative recombination in MHPs, as it implies that they are rather insensitive to defects that are not at midgap energy, which can lead to long lifetimes. Therefore, the low phonon energies of MHPs are likely an important factor for their optoelectronic performance.

Reciprocity and Open-Circuit Voltage in Solar Cells

  • DOI: 10.1109/JPHOTOV.2017.2768966
  • Odkaz: https://doi.org/10.1109/JPHOTOV.2017.2768966
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    The equation for open-circuit voltage of a solar cell based on optoelectronic reciprocity is combined with the standard textbook formula to obtain a general result that includes photon recycling as well as losses by carrier transport. It is shown that, in indirect-gap semiconductors, the general expression reduces to the “conventional” and “optoelectronic” expressions in the limits of low and high radiative efficiency.

Light harvesting in silicon(111) surfaces using covalently attached protoporphyrin IX dyes

  • Autoři: Alderman, N., Danos, L., Fang, L., Grossel, M., prof. Tomáš Markvart, Ph.D.,
  • Publikace: Chemical Communications. 2017, 53(89), 12120-12123. ISSN 1359-7345.
  • Rok: 2017
  • DOI: 10.1039/c7cc04767c
  • Odkaz: https://doi.org/10.1039/c7cc04767c
  • Pracoviště: Katedra elektrotechnologie
  • Anotace:
    We report the photosensitization of crystalline silicon via energy transfer using covalently attached protoporphyrin IX (PpIX) derivative molecules at different distances via changing the diol linker to the surface. The diol linker molecule chain length was varied from 2 carbon to 10 carbon lengths in order to change the distance of PpIX to the Si(111) surface between 6 A and 18 A. Fluorescence quenching as a function of the PpIX-Si surface distance showed a decrease in the fluorescence lifetime by almost two orders of magnitude at the closest separation. The experimental fluorescence lifetimes are explained theoretically by a classical Chance-Prock-Silbey model. At a separation below 2 nm, we observe for the first time, a Forster like dipole-dipole energy transfer with a characteristic distance of R-o = 2.7 nm.

Za stránku zodpovídá: Ing. Mgr. Radovan Suk