Dr.-Ing. Niels Jon Benson

Technology for Nanostructures
University of Duisburg-Essen

Contact

Hub
  • 3D Printed Al2O3 for Terahertz Technology
    Ornik, J. and Sakaki, M. and Koch, M. and Balzer, J.C. and Benson, N.
    IEEE Access (2020)
    In this work we demonstrate that 3D printed Al2O3 is a promising material for prototyping and precise fabrication of quasi-optical devices in the terahertz frequency range. The 3D printed Al2O3 exhibits a low absorption coefficient (α < 2 cm-1 at 1 THz) and a high refractive index (n > 3). The printing resolution in the sub 50 μm range allows for the implementation of structures in the 0.3-3.0 THz range on the subwavelength scale. Furthermore, the printing process enables the realization of crystalline solids, which allows the use of the Al2O3 birefringence effect. Here, a Δn ≈ 0.05 was achieved and used for the implementation of λ/2-wave plates working at ~1 THz. The material properties and wave plates were characterized using a terahertz time-domain spectrometer. CCBY
    view abstract10.1109/ACCESS.2020.3047514
  • A Stochastic Large-Signal Model for Printed High-Frequency Rectifiers Used for Efficient Generation of Higher Harmonics
    Neumann, K. and Kuhnel, L. and Langer, F. and Rennings, A. and Benson, N. and Schmechel, R. and Erni, D.
    IEEE Transactions on Microwave Theory and Techniques 68 (2020)
    This article investigates the stochastic Schottky barrier variations of printed distributed Schottky diodes consisting of a self-assembled arrangement of crystalline silicon microcones onto a metal layer. The microcone formation emerges from an inkjet printed Si nanoparticle film after laser sintering, yielding a Schottky diode when a corresponding top metallization is applied. The I - V characteristic and the voltage-dependent impedance of such diode is measured. By using the simulation software Advanced Design System (ADS), we develop a new scalable circuit model consisting of many different elementary diodes, which can explain the measured behavior. The elementary microcone diodes differ electrically in their barrier height, which is modeled as a stochastic process with a Gaussian distribution. A comparison between this model and a single diode model based on the thermionic field emission theory is conducted. We show that the distributed model outperforms the single-diode model in every regard and allows a prediction of the power levels of the harmonic frequency generation. Through more in-depth research, we find that a distributed barrier height leads to a smoother I - V curve, which in turn can lead to higher second and third harmonic power levels. By adjusting the barrier height distribution, the desired harmonics can be increased. © 1963-2012 IEEE.
    view abstract10.1109/TMTT.2020.2990561
  • Fine structure of the optical absorption resonance in Cs2AgBiBr6 double perovskite thin films
    Schmitz, A. and Leander Schaberg, L. and Sirotinskaya, S. and Pantaler, M. and Lupascu, D.C. and Benson, N. and Bacher, G.
    ACS Energy Letters 5 (2020)
    The lead-free double perovskite Cs2AgBiX6 (X = Br, Cl) has recently demonstrated great potential for applications in solar cells, photodetectors, and X-ray detectors. This material is characterized by a dominant resonant absorption feature in the UV-blue spectral region, which is still under controversial discussion regarding its origin. Here, we uncover an electronic fine structure of this optical feature in Cs2AgBiBr6 thin films. A detailed temperature-resolved study combining photoluminescence (PL), photoluminescence excitation (PLE), and absorption spectroscopy reveals the existence of three optical transitions, situated approximately 100 meV around the resonance at 2.83 eV. PL measurements under pulsed excitation uncover a short-lived blue emission at the absorption resonance energy that persists up to room temperature and indicates the competition of direct emission from the resonant state and fast relaxation into the red emissive ground state. We derive a comprehensive energy scheme and suggest possible mechanisms leading to the observed fine structure splitting. © 2020 American Chemical Society
    view abstract10.1021/acsenergylett.9b02781
  • Frequency-Coded mm-Wave Tags for Self-Localization System Using Dielectric Resonators
    Jiménez-Sáez, A. and Alhaj-Abbas, A. and Schüßler, M. and Abuelhaija, A. and El-Absi, M. and Sakaki, M. and Samfaß, L. and Benson, N. and Hoffmann, M. and Jakoby, R. and Kaiser, T. and Solbach, K.
    Journal of Infrared, Millimeter, and Terahertz Waves 41 (2020)
    The paper describes the development of passive, chipless tags for a novel indoor self-localization system operating at high mm-wave frequencies. One tag concept is based on the low-Q fundamental mode of dielectric resonators (DR) which exhibits peak scattering at its resonance frequency. As the radar cross-section (RCS) of DRs at mm-wave frequencies is far too low for the intended application, arrays of DRs and combinations with dielectric lens and corner reflectors are investigated to boost the RCS while keeping the scattering retro-directive over wide-angle incidence. Satisfactory results are demonstrated experimentally in W-band with metal corner reflectors combined with planar arrays of DRs; the tags produce a high RCS level over a moderately broad angular range and a wide frequency range where they exhibit a notch at the resonance frequency of the dielectric resonators. These designs suffer from low coding range of 3 to 6 bit, degradations of RCS in angular range, and a difficult separation of the tag response from strong clutter. Both the suppression of large clutter interference by using time gating of the tag response and a larger coding range are promised by a chipless tag concept based on multiple high-Q resonators in photonic crystal (PhC) technology. Experimental samples are characterized as transmission resonators and as retro-directive tags at the 230 GHz band. As a concept to boost the retro-directive RCS with a truly wide-angle response, the integration of PhC resonators with a Luneburg lens is discussed. © 2020, The Author(s).
    view abstract10.1007/s10762-020-00707-0
  • Influence of the cathode microstructure on the stability of inverted planar perovskite solar cells
    Sirotinskaya, S. and Schmechel, R. and Benson, N.
    RSC Advances 10 (2020)
    One of the main challenges for perovskite solar cells (PSC) is their environmental stability, as oxygen and water induced aging may result in mobile decomposition compounds, which can enhance the recombination rate and react with charge carrier extraction layers or the contact metallization. In this contribution the importance of the microstructure of the contact metallization on the environmental cell stability is investigated. For this purpose, the storage stability of inverted planar methylammonium lead iodide (MAPI)-based perovskite solar cells without encapsulation is tested, using the metals aluminum (Al), silver (Ag), gold (Au) and nickel (Ni) as representative cathode materials. For this study, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analysis of the different electrodes as well as the perovskite is correlated with PSC device current-voltage (J-V) and impedance measurements. Our findings substantiate that the metal microstructure has a significant influence on the PSC aging properties. While a strong perovskite decomposition and iodide diffusion to the contacts were detected for devices using Al, Ag or Au cathodes with a polycrystalline microstructure, these effects were strongly reduced when Ni metallization was employed, where a nanocrystalline microstructure was exhibited under the chosen process conditions. This journal is © The Royal Society of Chemistry.
    view abstract10.1039/d0ra00195c
  • Temperature Characterization of High-Q Resonators of Different Materials for mm-Wave Indoor Localization Tag Landmarks
    Jimenez-Saez, A. and Schusler, M. and Pandel, D. and Krause, C. and Zhao, Y. and Bogel, G.V. and Benson, N. and Jakoby, R.
    14th European Conference on Antennas and Propagation, EuCAP 2020 (2020)
    This paper discusses a temperature-dependent characterization of deep reactive ion-etched 10 k\Omega cm high-resistive silicon (DRIE HR-Si), 3D printed alumina (Al-{2}O-{3}) and milled Rogers RT/Duroid® 6010.2LM. The characterization is performed by measuring high-Q photonic crystal resonator samples in W-band and the measurements are taken from 30C to 115C. HR-Si is the material with the lowest losses at room temperature. However, its losses increase with temperature and become higher than 3D printed alumina at 75°C, reducing the radar cross-section and maximum readout range of chipless wireless RFID tags integrating several of these resonators. These results demonstrate that, while HR-Si performance is higher for the usual temperatures achieved in an indoor localization scenario, 3D printed alumina is more suitable if a temperature-stable response is needed or if the tags need to operate at high temperatures, such as in case of fire. © 2020 EurAAP.
    view abstract10.23919/EuCAP48036.2020.9135861
  • Ultra-fast measurement circuit for transient space charge limited current in organic semiconductor thin films
    Rojek, K. and Schmechel, R. and Benson, N.
    Measurement Science and Technology 31 (2020)
    The charge carrier mobility is a crucial parameter determining the device performance for numerous different semiconductor applications. Consequently, an accurate measurement of this quantity is crucial. For this purpose, the transient space charge limited current (SCLC) method is commonly applied and is preferable over, for example, Hall or field effect measurements, as the analyzed current direction is in line with typical device architectures. For the transient SCLC method, a voltage step is applied and the transit time of injected charge carriers is determined using displacement currents. Consequently, the difficulty of this method is the use of an adequate RC time constant for the sample charging, as it needs to be much shorter than the transit time. This parameter generally limits the application of transient SCLC strongly, in terms of obtainable charge carrier mobility or minimum required film thickness. Here, we demonstrate a measurement circuit with a low RC time constant, which works in a wide current range (1 ϵA-0.5 A) and thus allows for significant flexibility in terms of minimum film thickness or detectable charge carrier mobility. The circuit is fast enough to measure, for example, charge carrier mobilities of up to 10-4 cm2 Vs-1 for a 76 nm thick 4,4',4"-Tris[phenyl(m-tolyl)amino]triphenylamine (MTDATA) layer, without using limited bridge circuitry. For this purpose, a capacitor coupled fast transistor switch generates a voltage step to avoid voltage oscillations and a fast operational amplifier is used for amplification of the voltage over a variable measurement resistor. We demonstrate the circuit working principle by measuring benchmarked MTDATA diodes and discuss its range of application. © 2019 IOP Publishing Ltd.
    view abstract10.1088/1361-6501/ab3b2d
  • 3D Printed 90 GHz Frequency-Coded Chipless Wireless RFID Tag
    Jimenez-Saez, A. and Schusler, M. and Pandel, D. and Benson, N. and Jakoby, R.
    IMWS-AMP 2019 - 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (2019)
    This paper presents the design and measurement results of a 4-bit chipless 3D printed ceramic wireless RFID tag in alumina. It is shown how the accuracy and material quality of the recently presented manufacturing method for millimeterwave components can be used to implement photonic crystal high-Q resonators. Wireless measurements of a four-resonator RFID tag show a loaded quality factor of 902 and a radar cross section equal to -43.3 dBsqm at 90.4 GHz. © 2019 IEEE.
    view abstract10.1109/IMWS-AMP.2019.8880140
  • 3D printed alumina for low-loss millimeter wave components
    Jimenez-Saez, A. and Schubler, M. and Krause, C. and Pandel, D. and Rezer, K. and Bogel, G.V. and Benson, N. and Jakoby, R.
    IEEE Access 7 (2019)
    This paper compares the performance of three different materials and processing techniques suitable for low-loss mm-Wave components. The comparison is made by fabricating the same 2D photonic crystal structure in the W-band. Rogers RT/duroid® 6010.2LM and high resistive silicon are milled and etched, respectively. In addition, a novel technique consisting of 3D printed alumina is tested and its performance is compared with the technologies and materials above, which all have similar relative permittivities of around ten. The material characterization is carried out by means of high-Q resonator samples integrated into 2D photonic crystal structures. The results of these samples prove the high material purity and low loss of the 3D printed alumina structures, which opens up the use of this technology for high-permittivity low-loss mm-Wave components. © 2013 IEEE.
    view abstract10.1109/ACCESS.2019.2906034
  • Analysis of stochastic Schottky barrier variations within printed high frequency rectifiers for harmonics generation
    Neumann, K. and Kuehnel, L. and Langer, F. and Rennings, A. and Benson, N. and Schmechel, R. and Erni, D.
    IMWS-AMP 2019 - 2019 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (2019)
    In this paper we investigate the stochastic Schottky barrier variations of printed distributed Schottky diodes consisting of a self-assembled arrangement of crystalline silicon microcones onto a metal layer. The microcone formation emerges from an inkjet printed Si nanoparticle film after laser sintering yielding a Schottky diode when a corresponding top metallization is applied. The elementary microcone diodes differ electrically in their barrier height, which is modelled as a gaussian distribution. The circuit simulation software Advanced Design System (ADS) is used to analyze the rectification abilities of the overall structure. The results show that a distributed barrier height leads to a smoother IV-characteristic, which can also be interpreted as an aggregated diode with a smaller turn on voltage. A Fourier analysis of the rectified time-domain signal shows an amplification of the frequency components up to the third harmonic in comparison to a non distributed single diode. © 2019 IEEE.
    view abstract10.1109/IMWS-AMP.2019.8880082
  • MIS-TSC: A combination of the thermally stimulated current method and a metal-insulator-semiconductor device for unipolar trap spectroscopy
    Rojek, K. and Schmechel, R. and Benson, N.
    Applied Physics Letters 114 (2019)
    To determine the density of states distribution of traps within a semiconductor, the thermally stimulated current (TSC) method is often applied. However, the bipolar nature of the typical device structure does not allow for strict unipolar operation, and therefore the method does not allow for the separate evaluation of electron and hole traps. The recombination between electrons and holes makes the interpretation of the data difficult, which becomes an essential drawback of this method. To address these issues, we propose the use of a metal insulator semiconductor (MIS) device structure for TSC measurements, which can be operated strictly unipolar by the sign of the applied voltage during the charging process. Thus, the problem of recombination and bipolar contribution to the measurement signal is avoided. As an additional benefit, the MIS device structure typically results in very low leakage currents, and thus a low noise level for the measurement. This permits precise measurements even below 1 pA, and consequently increases the resolution of the method. This aspect is especially important for fractional TSC, as the measurement time is long and the current low when compared to the envelope measurement. Here, we demonstrate the basic principle of this TSC approach, which we name MIS-TSC, using the well-studied organic semiconductor P3HT as a benchmark. © 2019 Author(s).
    view abstract10.1063/1.5090947
  • Printing "smart" Inks of Redox-Responsive Organometallic Polymers on Microelectrode Arrays for Molecular Sensing
    Cirelli, M. and Hao, J. and Bor, T.C. and Duvigneau, J. and Benson, N. and Akkerman, R. and Hempenius, M.A. and Vancso, G.J.
    ACS Applied Materials and Interfaces 11 (2019)
    Printing arrays of responsive spots for multiplexed sensing with electrochemical readout requires new molecules and precise, high-throughput deposition of active compounds on microelectrodes with spatial control. We have designed and developed new redox-responsive polymers, featuring a poly(ferrocenylsilane) (PFS) backbone and side groups with disulfide units, which allow an efficient and stable bonding to Au substrates, using sulfur-gold coupling chemistry in a "grafting-to" approach. The polymer molecules can be employed for area selective molecular sensing following their deposition by high-precision inkjet printing. The new PFS derivatives, which serve as "molecular inks", were characterized by 1H NMR, 13C NMR, and FTIR spectroscopies and by gel permeation chromatography. The viscosity and surface tension of the inks were assessed by rheology and pendant drop contact angle measurements, respectively. Commercial microelectrode arrays were modified with the new PFS ink by using inkjet printing in the "drop-on-demand" mode. FTIR spectroscopy, AFM, and EDX-SEM confirmed a successful, spatially localized PFS modification of the individual electrodes within the sensing cells of the microelectrode arrays. The potential application of these devices to act as an electrochemical sensor array was demonstrated with a model analyte, ascorbic acid, by using cyclic voltammetry and amperometric measurements. © 2019 American Chemical Society.
    view abstract10.1021/acsami.9b11927
  • Spatially resolved investigation of the defect states in methylammonium lead iodide perovskite bicrystals
    Sirotinskaya, S. and Fettkenhauer, C. and Okada, D. and Yamamoto, Y. and Lupascu, D.C. and Schmechel, R. and Benson, N.
    Journal of Materials Chemistry C 7 (2019)
    Organic-inorganic halide perovskites are one of the most promising novel materials for photovoltaic applications. One of the most common and well-researched compounds in this material class is methylammonium lead iodide (MAPI). However, the formation of different kinds of defects in the polycrystalline MAPI thin films and their influence on the electrical performance of solar cells is still a matter of debate. In this work, we use single MAPI crystals grown by inverse temperature crystallization as a model system for the systematic experimental evaluation of defects as suggested by current theoretical work on MAPI thin films. The macroscopic nature of these crystallites enables an experimental approach that allows the separate evaluation of the grain boundary and crystallite bulk. For this purpose, we have employed a combination of μ-PL and μ-XPS measurements to probe the defect types suggested by the literature to determine the most likely defect types in the MAPI crystallites/thin film areas. © The Royal Society of Chemistry 2019.
    view abstract10.1039/c8tc06622a
  • Film forming properties of silicon nanoparticles on SixNy coated substrates during excimer laser annealing
    Caninenberg, M. and Kiesler, D. and Benson, N. and Schmechel, R.
    Optics and Laser Technology 90 (2017)
    In this article we investigate the film forming properties of excimer laser annealed silicon nanoparticles on non-silicon substrates. In contrast to their film forming properties on oxide free silicon substrates, the nanoparticle thin film tends to dewet and form a porous µ-structure on the silicon nitrite covered glass model substrates considered for our investigation. This is quantified using a SEM study in conjunction with image processing software, in order to evaluate the µ-structure size and inter µ-structure distance in dependence of the laser energy density. To generalize our results, the film forming process is described using a COMSOL Multiphysics ® fluid dynamics model, which solves the Navier Stokes equation for incompressible Newtonian fluids. To account for the porous nanoparticle thin film structure in the simulation, an effective medium approach is used by applying a conservative level set one phase method to our mesh. This effort allows us to predict the Si melt film formation ranging from a porous Si µ-structure to a compact 100% density Si thin film in dependence of the substrate / thin film interaction, as well as the laser energy used for the nanoparticle processing. © 2016 Elsevier Ltd
    view abstract10.1016/j.optlastec.2016.11.010
  • Soluble metal oxo alkoxide inks with advanced rheological properties for inkjet-printed thin-film transistors
    Meyer, S. and Pham, D.V. and Merkulov, S. and Weber, D. and Merkulov, A. and Benson, N. and Schmechel, R.
    ACS Applied Materials and Interfaces 9 (2017)
    Semiconductor inks containing an indium-based oxo alkoxide precursor material were optimized regarding rheology requirements for a commercial 10 pL inkjet printhead. The rheological stability is evaluated by measuring the dynamic viscosity of the formulations for 12 h with a constant shear rate stress under ambient conditions. It is believed that the observed superior stability of the inks is the result of effectively suppressing the hydrolysis and condensation reaction between the metal oxo alkoxide precursor complex and atmospheric water. This can be attributed to a strong precursor coordination and the resulting reduction in ligand exchange dynamics of the solvent tetrahydrofurfuryl alcohol which is used as the main solvent in the formulations. It is also shown that with a proper selection of cosolvents, having high polar Hansen solubility parameter values, the inks drop formation properties and wettability can be finetuned by maintaining the inks rheological stability. Good drop jetting performance without satellite formation and high drop velocities of 8.25 m/s were found with the support of dimensionless numbers and printability windows. By printing single 10 pL ink dots onto short channel indium-tin-oxide electrodes, In2O3 calcination at 350 °C and a solution-processed back-channel protection, high average saturation mobility of approximately 10 cm2/(V s) are demonstrated in a bottom-contact coplanar thinfilm transistor device structure. © 2017 American Chemical Society.
    view abstract10.1021/acsami.6b12586
  • Modelling of electron beam induced nanowire attraction
    Bitzer, L.A. and Speich, C. and Schäfer, D. and Erni, D. and Prost, W. and Tegude, F.J. and Benson, N. and Schmechel, R.
    Journal of Applied Physics 119 (2016)
    Scanning electron microscope (SEM) induced nanowire (NW) attraction or bundling is a well known effect, which is mainly ascribed to structural or material dependent properties. However, there have also been recent reports of electron beam induced nanowire bending by SEM imaging, which is not fully explained by the current models, especially when considering the electro-dynamic interaction between NWs. In this article, we contribute to the understanding of this phenomenon, by introducing an electro-dynamic model based on capacitor and Lorentz force interaction, where the active NW bending is stimulated by an electromagnetic force between individual wires. The model includes geometrical, electrical, and mechanical NW parameters, as well as the influence of the electron beam source parameters and is validated using in-situ observations of electron beam induced GaAs nanowire (NW) bending by SEM imaging. © 2016 AIP Publishing LLC.
    view abstract10.1063/1.4945674
  • Super-resolution for scanning light stimulation systems
    Bitzer, L.A. and Neumann, K. and Benson, N. and Schmechel, R.
    Review of Scientific Instruments 87 (2016)
    Super-resolution (SR) is a technique used in digital image processing to overcome the resolution limitation of imaging systems. In this process, a single high resolution image is reconstructed from multiple low resolution images. SR is commonly used for CCD and CMOS (Complementary Metal-Oxide-Semiconductor) sensor images, as well as for medical applications, e.g., magnetic resonance imaging. Here, we demonstrate that super-resolution can be applied with scanning light stimulation (LS) systems, which are common to obtain space-resolved electro-optical parameters of a sample. For our purposes, the Projection Onto Convex Sets (POCS) was chosen and modified to suit the needs of LS systems. To demonstrate the SR adaption, an Optical Beam Induced Current (OBIC) LS system was used. The POCS algorithm was optimized by means of OBIC short circuit current measurements on a multicrystalline solar cell, resulting in a mean square error reduction of up to 61% and improved image quality. © 2016 Author(s).
    view abstract10.1063/1.4961748
  • Sample temperature profile during the excimer laser annealing of silicon nanoparticles
    Caninenberg, M. and Verheyen, E. and Kiesler, D. and Stoib, B. and Brandt, M.S. and Benson, N. and Schmechel, R.
    Optics and Laser Technology 74 (2015)
    Based on the heat diffusion equation we describe the temperature profile of a silicon nanoparticle thin film on silicon during excimer laser annealing using COMSOL Multiphysics. For this purpose system specific material parameters are determined such as the silicon nanoparticle melting point at 1683 K, the surface reflectivity at 248 nm of 20% and the nanoparticle thermal conductivity between 0.3 and 1.2 W/m K. To validate our model, the simulation results are compared to experimental data obtained by Raman spectroscopy, SEM microscopy and electrochemical capacitance-voltage measurements (ECV). The experimental data are in good agreement with our theoretical findings and support the validity of the model. © 2015, Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.optlastec.2015.05.020
  • Scanning light stimulation system with active focus correction at μm resolution for PV applications
    Bitzer, L.A. and Elagin, M. and Semtsiv, M.P. and Masselink, W.T. and Benson, N. and Schmechel, R.
    IEEE Journal of Photovoltaics 5 (2015)
    Recently, we introduced a scanning light stimulation system with an automated focus correction. The method is however resolution limited by a CMOS sensor used to focus the light beam. Here, to achieve a higher resolution, we enhanced the light beam focusing process by combining it with an edge detection technique. By this modification, the system resolution is improved down to a 1/e2 -diameter of 4.3 μm as demonstrated using an example measurement on a multicrystalline solar cell. Furthermore, it is shown that the obtained resolution is mainly limited by height variations of the positioning system, and methods to compensate these limitations are discussed using example measurements on a quantum well solar cell. © 2011-2012 IEEE.
    view abstract10.1109/JPHOTOV.2015.2392933
  • High temperature thermoelectric device concept using large area PN junctions
    Chavez, R. and Angst, S. and Hall, J. and Stoetzel, J. and Kessler, V. and Bitzer, L. and Maculewicz, F. and Benson, N. and Wiggers, H. and Wolf, D. and Schierning, G. and Schmechel, R.
    Journal of Electronic Materials 43 (2014)
    A new high temperature thermoelectric device concept using large area nanostructured silicon p-type and n-type (PN) junctions is presented. In contrast to conventional thermoelectric generators, where the n-type and p-type semiconductors are connected electrically in series and thermally in parallel, we experimentally demonstrate a device concept in which a large area PN junction made from highly doped densified silicon nanoparticles is subject to a temperature gradient parallel to the PN interface. In the proposed device concept, the electrical contacts are made at the cold side eliminating the hot side substrate and difficulties that go along with high temperature electrical contacts. This concept allows temperature gradients greater than 300 K to be experimentally applied with hot side temperatures larger than 800 K. Electronic properties of the PN junctions and power output characterizations are presented. A fundamental working principle is discussed using a particle network model with temperature and electric fields as variables, and which considers electrical conductivity and thermal conductivity according to Fourier's law, as well as Peltier and Seebeck effects. © 2014 TMS.
    view abstract10.1007/s11664-014-3073-x
  • Note: Automated optical focusing on encapsulated devices for scanning light stimulation systems
    Bitzer, L.A. and Benson, N. and Schmechel, R.
    Review of Scientific Instruments 85 (2014)
    Recently, a scanning light stimulation system with an automated, adaptive focus correction during the measurement was introduced. Here, its application on encapsulated devices is discussed. This includes the changes an encapsulating optical medium introduces to the focusing process as well as to the subsequent light stimulation measurement. Further, the focusing method is modified to compensate for the influence of refraction and to maintain a minimum beam diameter on the sample surface. © 2014 AIP Publishing LLC.
    view abstract10.1063/1.4892379
  • A new adaptive light beam focusing principle for scanning light stimulation systems
    Bitzer, L.A. and Meseth, M. and Benson, N. and Schmechel, R.
    Review of Scientific Instruments 84 (2013)
    In this article a novel principle to achieve optimal focusing conditions or rather the smallest possible beam diameter for scanning light stimulation systems is presented. It is based on the following methodology: First, a reference point on a camera sensor is introduced where optimal focusing conditions are adjusted and the distance between the light focusing optic and the reference point is determined using a laser displacement sensor. In a second step, this displacement sensor is used to map the topography of the sample under investigation. Finally, the actual measurement is conducted, using optimal focusing conditions in each measurement point at the sample surface, that are determined by the height difference between camera sensor and the sample topography. This principle is independent of the measurement values, the optical or electrical properties of the sample, the used light source, or the selected wavelength. Furthermore, the samples can be tilted, rough, bent, or of different surface materials. In the following the principle is implemented using an optical beam induced current system, but basically it can be applied to any other scanning light stimulation system. Measurements to demonstrate its operation are shown, using a polycrystalline silicon solar cell. © 2013 American Institute of Physics.
    view abstract10.1063/1.4791795
  • A novel adaptive focusing principle for scanning light stimulation systems down to 2μm resolution
    Bitzer, L.A. and Benson, N. and Schmechel, R.
    Conference Record of the IEEE Photovoltaic Specialists Conference (2013)
    A new principle to achieve optimal focusing conditions or rather the smallest possible beam diameter for scanning light stimulation systems is presented. It is based on the following three steps: First, a reference point is introduced on a CMOS sensor to adjust the beam diameter. The distance between the light focusing optic and the reference point is then determined using a laser displacement sensor. In a second step, this displacement sensor is used to obtain the topography of the sample under investigation. Finally, the actual measurement is conducted, using optimal focusing conditions in each measurement point on the sample surface. They are determined by the height difference between the CMOS sensor and the sample topography. This principle is independent of optical or electrical sample properties, the used light source or the selected wavelength. Furthermore, the samples can be tilted, rough, bent or of different surface materials. The described focusing principle can be applied to any scanning light stimulation system. Here, it is implemented using an optical beam induced current (OBIC) setup with a laser light source. © 2013 IEEE.
    view abstract10.1109/PVSC.2013.6744233
  • Excimer laser doping using highly doped silicon nanoparticles
    Meseth, M. and Kunert, B.C. and Bitzer, L. and Kunze, F. and Meyer, S. and Kiefer, F. and Dehnen, M. and Orthner, H. and Petermann, N. and Kummer, M. and Wiggers, H. and Harder, N.-P. and Benson, N. and Schmechel, R.
    Physica Status Solidi (A) Applications and Materials Science 210 (2013)
    Laser doping of crystalline Si (c-Si) using highly doped Si nanoparticles (NPs) as the dopant source is investigated. For this purpose Si NPs are deposited onto c-Si substrates from dispersion using a spin coater and subsequently laser annealed by scanning over the sample with a 248 nm line profile excimer laser. Scanning electron microscope (SEM) investigations demonstrate that the laser intensity as well as the oxide concentration in the NP thin film strongly influence the film forming properties of the annealed NPs. Substrate doping is substantiated using electrochemical capacitance voltage (ECV) measurements on realized pn-junctions. In dependence of the laser fluencies ranging from 0.81 to 2.54 J cm-2, the effective doping depth is determined to be in the range of 50 to 250 nm. The rectifying behaviour of the pn- or np-junctions is verified by current voltage measurements. A homogeneous in-plane doping distribution realized by the laser doping process is demonstrated on the μm scale by light beam induced current measurements. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/pssa.201329012
  • Laser-doping of crystalline silicon substrates using doped silicon nanoparticles
    Meseth, M. and Lamine, K. and Dehnen, M. and Kayser, S. and Brock, W. and Behrenberg, D. and Orthner, H. and Elsukova, A. and Hartmann, N. and Wiggers, H. and Hülser, T. and Nienhaus, H. and Benson, N. and Schmechel, R.
    Thin Solid Films 548 (2013)
    Crystalline Si substrates are doped by laser annealing of solution processed Si. For this experiment, dispersions of highly B-doped Si nanoparticles are deposited onto intrinsic Si and laser processed using an 807.5 nm continuous wave laser. During laser processing the particles as well as a surface-near substrate layer are melted to subsequently crystallize in the same orientation as the substrate. The doping profile is investigated by secondary ion mass spectroscopy revealing a constant B concentration of 2 × 10 18 cm- 3 throughout the entire analyzed depth of 5 μm. Four-point probe measurements demonstrate that the effective conductivity of the doped sample is increased by almost two orders of magnitude. The absolute doping depth is estimated to be in between 8 μm and 100 μm. Further, a pn-diode is created by laser doping an n-type c-Si substrate using the Si NPs. © 2013 Published by Elsevier B.V.
    view abstract10.1016/j.tsf.2013.09.056
  • Reduced Coulomb interaction in organic solar cells by the introduction of high-k SrTiO3 nanoparticles
    Benson, N. and Engel, M. and Schaefer, D. and Erni, D. and Kern, J. and Deibel, C. and Herzig, E.M. and Muller-Buschbaum, P. and Schmechel, R.
    Conference Record of the IEEE Photovoltaic Specialists Conference (2013)
    A concept is introduced which allows for reduced Coulomb interaction in organic solar cells and as such for enhanced power conversion efficiencies. The concept is based on the introduction of electrically insulating, nanostructured high-k materials into the organic matrix, which do not contribute to the charge carrier transport, however, enhance the effective permittivity of the organic active layer. Using an analytical model, it is demonstrated that even at a distance of 20 nm to the organic/inorganic interface of the nanostructure, the Coulomb interaction in the organic semiconductor can be reduced by more than 15 %. The concept is substantiated experimentally by realizing P3HT:PCBM solar cells with integrated SrTiO3 nanoparticles. It could be demonstrated that in comparison to a reference cells without nanoparticles, the power conversion efficiency is improved by ∼17 %. This effect is interpreted to be the result of an organic active layer effective permittivity enhancement, which is supported by the result of transient absorption as well as grazing incidence wide angle x-ray scattering measurements. © 2013 IEEE.
    view abstract10.1109/PVSC.2013.6745113
  • Reduced Coulomb interaction in organic solar cells by the introduction of inorganic high-k nanostructured materials
    Engel, M. and Schaefer, D. and Erni, D. and Benson, N. and Schmechel, R.
    Physica Status Solidi (A) Applications and Materials Science 210 (2013)
    In this paper a concept is introduced, which allows for reduced Coulomb interaction in organic solar cells and as such for enhanced power conversion efficiencies. The concept is based on the introduction of electrically insulating, nanostructured high-k materials into the organic matrix, which do not contribute to the charge transport; however, enhance the effective permittivity of the organic active layer and thereby reduce the Coulomb interaction. Using an analytical model, it is demonstrated that even at a distance of 20 nm to the organic/inorganic interface of the nanostructure, the Coulomb interaction in the organic semiconductor can be reduced by more than 15%. The concept is implemented using P3HT:PCBM solar cells with integrated high-k nanoparticles (strontium titanate). It could be demonstrated that in comparison to a reference cell without integrated nanoparticles, the power conversion efficiencies is improved by ∼17%. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/pssa.201228771
  • A sintered nanoparticle p-n junction observed by a Seebeck microscan
    Becker, A. and Schierning, G. and Theissmann, R. and Meseth, M. and Benson, N. and Schmechel, R. and Schwesig, D. and Petermann, N. and Wiggers, H. and Ziolkowski, P.
    Journal of Applied Physics 111 (2012)
    A nanoparticular p-n junction was realized by a field-assisted sintering process, using p-type and n-type doped silicon nanoparticles. A spatially resolved Seebeck microscan showed a broad transition from the positively doped to the negatively doped range. Overshoots on both sides are characteristic for the transition. Despite the tip size being much larger than the mean particle size, information about the dopant distribution between the particles is deduced from modeling the measured data under different assumptions, including the limited spatial resolution of the tip. The best match between measured and modeled data is achieved by the idea of doping compensation, due to the sintering process. Due to a short time at high temperature during the field-assisted sintering process, solid state diffusion is too slow to be solely responsible for the observed compensation of donors and acceptors over a wide range. Therefore, these measurements support a densification mechanism based on (partial) melting and recrystallization. © 2012 American Institute of Physics.
    view abstract10.1063/1.3693609
  • Reduced exciton binding energy in organic semiconductors: Tailoring the Coulomb interaction
    Engel, M. and Kunze, F. and Lupascu, D.C. and Benson, N. and Schmechel, R.
    Physica Status Solidi - Rapid Research Letters 6 (2012)
    For organic photovoltaics (OPV) the maximum in obtainable power conversion efficiency is limited by a low semiconductor permittivity and the resulting enhanced Coulomb interaction (CI). This, however, is an aspect rarely addressed in the OPV development. Here, a concept is introduced which allows a reduced CI in organic semiconductors. This is the result of a device structure, which upon exciton formation forces part of the electric field between complementary charges through a high-k material, resulting in partial field screening and as such a reduced CI. The feasibility of this concept is substantiated by an investigation on the exciton separation efficiency in pentacene devices. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    view abstract10.1002/pssr.201105488
  • The realization of a pn-diode using only silicon nanoparticles
    Meseth, M. and Ziolkowski, P. and Schierning, G. and Theissmann, R. and Petermann, N. and Wiggers, H. and Benson, N. and Schmechel, R.
    Scripta Materialia 67 (2012)
    Si nanoparticles (Si-NPs) are a non-toxic and low-cost material resource that can be processed from dispersion for electrical thin film or from powder for bulk application using various sintering techniques. So far research on electronic applications using Si-NPs is limited. Few reports exist on thermoelectric research, or hybrid photovoltaic applications. In the following we demonstrate the realization of the first Si pn-diode using only Si-NPs in combination with field-assisted sintering. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    view abstract10.1016/j.scriptamat.2012.04.039
  • electronics

  • interfaces

  • laser annealing

  • photovoltaics

  • printable electronics

  • solar cells

  • thin films

« back