29 research outputs found
Ergebnisse der konservativen und operativen Therapie bei Tibia vara Blount an 12 Kniegelenken
Light trapping in a-Si:H thin film solar cells using silver nanostructures
Plasmonic thin film solar cells (modified with metallic nanostructures) often display enhanced light absorption due to surface plasmon resonance (SPR). However, the plasmonic field localization may not be significantly beneficial to improved photocurrent conversion efficiency for all types of cell configurations. For instance, the integration of random metallic nanoparticles (NPs) into thin film solar cells often introduces additional texturing. This texturing might also contribute to enhanced photon-current efficiency. An experimental systematic investigation to decouple both the plasmonic and the texturing contributions is hard to realize for cells modified with randomly deposited metallic nanoparticles. This work presents an experimental and computational investigation of well-defined plasmonic (Ag) nanoparticles, fabricated by nanosphere lithography, integrated to the back contact of hydrogenated amorphous silicon (a-Si:H) solar cells. The size, shape, periodicity and the vertical position of the Ag nanoparticles were well-controlled. The experimental results suggested that a-Si:H solar cells modified with a periodic arrangement of Ag NPs (700 nm periodicity) fabricated just at the top of the metal contact in the back reflector yields the highest improvement in terms of current density (JSC). Finite-difference time-domain (FDTD) simulations also indicated that Ag nanoparticles located at the top of the metal contact in the back reflector is expected to lead to the most efficient light confinement inside the a-Si:H absorber intrinsic layer (i-layer)
Influence of Coulomb correlations on gain and stimulated emission in (Zn,Cd)Se/Zn(S,Se)/(Zn,Mg)(S,Se) quantum-well lasers
The influence of Coulomb correlations on gain and stimulated emission in (Zn,Cd)Se/Zn(S,Se)/(Zn,Mg)(S,Se) quantum-well lasers is studied under stationary conditions. Systematic temperature-dependent measurements under application of different spectroscopic techniques were performed. Optical gain is measured by means of the variable stripe-length method, whereas excitonic bleaching under lasing conditions is analyzed through two-beam photoluminescence excitation (PLE) spectroscopy. Furthermore, complementary low-density single-beam PLE spectra are recorded in order to study the temperature dependence of the heavy-hole exciton peaks. The experimental data as a whole are shown to be inconsistent with any of the usually quoted excitonic models for lasing in II-VI heterostructures. The experiments are more adequately explained by a strongly correlated electron-hole plasma described by Bethe-Salpeter-like equations for the optical response and recombination rates in the excited medium. The nonequilibrium Green’s-function approach used consistently includes, at a microscopic level, band structure, quantum-confinement, and many-body effects
Optical gain characteristics and excitonic nonlinearities in II–VI laser diodes
Gain characteristics and lasing of (Zn, Cd)Se/Zn(S, Se)/(Zn, Mg)(S, Se) separate confinement heterostructures are investigated by optical-gain spectroscopy and by high-excitation spectroscopy under quasi-stationary conditions. The optical gain is measured by means of the stripe-length method whereas excitonic bleaching under lasing conditions is analyzed through two-beam photoluminescence excitation (PLE) spectroscopy. At low lattice temperature, we find a rather low threshold density of 15–20 kW/cm2 for both laser structures and the excitonic enhancement is still preserved at the onset of lasing. The red shift of the gain maximum with respect to the low-density PLE exciton peak increases with temperature. The results indicate a considerable influence of Coulomb correlations even at the high densities necessary for stimulated emission and are more adequately explained by a strongly correlated electron-hole plasma model that goes beyond the simple “excitonic lasing” concept
Plasmonic Light-Trapping Concept for Nanoabsorber Photovoltaics
Plasmonic nanoparticles were once sought to harness enormous potential for light-trapping in inorganic thin-film photovoltaics. However, the incorporation of such metallic nanostructures near solar cell absorbing layers without inducing overall harm to performance has proven to be a major obstacle. Herein, we demonstrate a solar cell design which integrates a periodic array of plasmonic Ag nanoparticles within the p-i-n structure of a-Ge:H ultrathin optical cavity solar cells. The plasmonic solar cells showed a 33% short-circuit current density increase relative to geometrically identical cells where the Ag nanoparticles were replaced by SiO2. We experimentally mapped the localized surface plasmon excitations on the surface of Ag nanoparticles embedded in the optoelectronic device using electron energy loss spectroscopy and correlated the results to the device performance. Using three-dimensional optical simulations, we further explored the light-trapping mechanisms responsible for the observed performance enhancements. The nanostructured cells produced localized and tunable charge carrier generation enhancements while maintaining the planar geometry of the ultrathin absorbing layer. Therefore, this design concept provides a direct and useful avenue for initial light-trapping efforts in next-generation photovoltaics based on ultrathin nanoabsorbers, such as few layer transition metal dichalcogenides
Das Zentrum fĂĽr Lehre in Regensburg - Vernetzung medizindidaktischer Expertise zur Verbesserung der medizinischen Ausbildung
Rational design of highly efficient flexible and transparent p-type composite electrode based on single-walled carbon nanotubes
Transparent electrodes are of great importance in electronics and energy technologies. At present, transparent conductive oxides are mainly n-type conductors dominating the market and have restricted the technological advancements. Single-walled carbon nanotubes (SWCNTs) have recently emerged as promising p-type transparent conductor owing to their superior hole mobility, conductivity, transparency, flexibility and possibility to tune the work function. Here, we develop a novel rational design of p-type flexible transparent conductive film (TCF) based on SWCNTs combined with poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), molybdenum oxide and SWCNT fibers. In a configuration of SWCNTs-MoO3-PEDOT:PSS/SWCNT fibers, we achieved a record equivalent sheet resistance of 17 Ω/sq with a transmittance of 90% at 550 nm and a high degree of flexibility. We demonstrate that our solar cells developed on the basis of the proposed electrode and hydrogenated amorphous silicon (a-Si:H) yield an outstanding short-circuit current density of Jsc = 15.03 mA/cm2 and a record power conversion efficiency of PCE = 8.8% for SWCNTs/a-Si:H hybrid solar cells. We anticipate that this novel rationally designed p-type TCF opens a new avenue in widespread energy technologies, where high hole conductivity and transparency of the material are prerequisites for their successful implementation.Peer reviewe