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Plasmon Enhanced Upconversion Luminescence near Gold Nanoparticles–Simulation and Analysis of the Interactions (Optics Express)

One-dimensional SIC photonic structures to enhance the efficiency of systems with silicon solar cells and upconverters (26th EUPVSEC Hamburg)

Investigation on the intensity dependence of upconversion systems (26th EUPVSEC Hamburg)

Photonic Structures for a Solar Cell-Upconversion-System (FuturePV)

Characterization and Simulation of Upconversion Processes (Quantsol 2011)

Experimental analysis of upconversion with both coherent monochromatic irradiation and broad spectrum illumination (Solar Energy Materials and Solar Cells)

Origin of the High Upconversion Green Luminescence Efficiency in beta-NaYF(4):2%Er(3+),20%Yb(3+) (Chemistry of Materials)

Anomalous Independence of Multiple Exciton Generation on Different Group IV-VI Quantum Dot Architectures (Nano Letters)

Two-Fold Emission From the S-Shell of PbSe/CdSe Core/Shell Quantum Dots (Small)

 

Plasmon enhanced upconversion luminescence near gold nanoparticles–simulation and analysis of the interactions

Stefan Fischer,1 Florian Hallermann,2 Toni Eichelkraut,3 Gero von Plessen,2 Karl W. Krämer,4 Daniel Biner,4 Heiko Steinkemper,1 Martin Hermle,1 and Jan C. Goldschmidt1 [top]

1Fraunhofer Institute for Solar Energy Systems, Heidenhofstr. 2, 79110 Freiburg, Germany
2Institute of Physics (1A), RWTH Aachen University, 52056 Aachen, Germany
3Institute of Condensed Matter Theory and Solid State Optics, Abbe Center of Photonics, Friedrich-Schiller-Universität, 07743 Jena, Germany
4Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland

We investigate plasmon resonances in gold nanoparticles to enhance the quantum yield of upconverting materials. For this purpose, we use a rate equation model that describes the upconversion of trivalent erbium based upconverters. Changes of the optical field acting on the upconverter and the changes to the transition probabilities of the upconverter in the proximity of a gold nanoparticle are calculated using Mie theory and exact electrodynamic theory respectively. With this data, the influence on the luminescence of the upconverter is determined using the rate equation model. The results show that upconversion luminescence can be increased in the proximity of a spherical gold nanoparticle due to the change in the optical field and the modification of the transition rates. [top]

doi:10.1364/OE.20.000271

 

One-dimensional SIC photonic structures to enhance the efficiency of systems with silicon solar cells and upconverters

B. Herter, M. Peters, S.Janz, M. Hermle, J. C. Goldschmidt [top]
Fraunhofer Institute for Solar Energy Systems, Heidenhofstr. 2, 79110 Freiburg, Germany

In silicon solar cells, photons with energies lower than the fixed bandgap of 1.12 eV are transmitted through the semiconductor material and do not contribute to current generation. This limitation can be overcome using an upconverting material below the solar cell, which transforms two or more low-energy photons into one highenergy photon, which can be utilized in the solar cell. Available efficient upconverters like NaYF4:Er, however, typically only work efficiently over a narrow wavelength range. The used spectral range can be enlarged with a second luminescent material, which absorbs over a wider spectral range and emits in the absorption range of the upconverter, a concept known as spectral concentration. In this paper, we investigate photonic structures for a special system applying both spectral and spatial concentration using fluorescent concentrators. The photonic structures ensure that all photons reach the part of the system where they can be used the most efficiently. We show that the required photonic structures can be realized with a one-dimensional stack of alternating layers of silicon carbides with different silicon to carbon ratios. We present results of the simulation and optimization of these photonic structures, as well as characterization of such structures produced in a PECVD process. [top]

doi:10.4229/26thEUPVSEC2011-1DV.1.2

 

Investigation on the intensity dependence of upconversion systems

H. Steinkemper*, S. Fischer*, K. W. Krämer+, D. Biner+, M. Hermle*, J. C. Goldschmidt* [top]
*  Fraunhofer Institute for Solar Energy Systems, Heidenhofstr. 2, 79110 Freiburg, Germany
+ Department of Chemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland

Silicon solar cells lose about 20% of the energy of the solar spectrum due to sub-band-gap losses. Upconversion (UC) materials, which generate one high-energy photon out of two or more low-energy photons, can be used to minimize these losses and to significantly enhance the solar cell efficiency. Since UC is a non-linear process, the quantum yield of an upconverter increases with increasing irradiance. In this paper, we investigate the intensity dependence of the upconverter β-NaY0.8Er0.2F4 under broad-band excitation. An UC quantum yield of ηUC,lamp = 2.5% was achieved for broad-band excitation with a photon flux of 56·1020 s-1m-2 for the considered excitation spectrum which corresponds to an irradiance of 730 Wm-2 under monochromatic illumination at 1523 nm. The results are compared to monochromatic laser illumination and simulations with a rate equation model. The observed intensity dependences for broad-band and monochromatic excitation show the same curve shape and the values are approximately equivalent. These results suggest that UC is efficient under broad-band excitation as well. [top]

doi:10.4229/26thEUPVSEC2011-1DV.1.39

 

Photonic Structures for a Solar Cell-Upconversion-System

B. Herter, M. Peters, S.Janz, M. Hermle, J. C. Goldschmidt [top]

Fraunhofer Institute for Solar Energy Systems, Heidenhofstr. 2, 79110 Freiburg, Germany

Upconversion can reduce the sub-bandgap losses of solar cells. For a better utilization of the full solar spectrum, the upconverter needs to be combined with a second luminescent material. Such complex systems require photonic structures to ensure efficient photon distribution. Optimized designs for such structures were generated by transfer matrix calculations. The characteristics of realized one-dimensional stacks of a-SiC-layers show good agreement to the calculations. [top]

FuturePV

 

Characterization and Simulation of Upconversion Processes

S. Fischer1, H. Steinkemper1, F. Hallermann2, G. von Plessen2, K. W. Krämer3, D. Biner3, M. Hermle1, J. C. Goldschmidt1 [top]

1 Fraunhofer Institute for Solar Energy Systems, Heidenhofstr. 2, 79110 Freiburg, Germany
2 Institute of Physics (1A), RWTH Aachen University, 52056 Aachen, Germany
3 Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland

About 20% of the solar energy is not utilized in silicon solar cells because the photons with energies below the band-gap of silicon are transmitted through the device. Upconversion (UC) of these low energy photons is a promising approach to enhance the efficiency of solar cells. Hexagonal sodium yttrium fluoride (β-NaYF4) doped with trivalent erbium (Er3+), especially with a doping ratio of one erbium ion to four ytterbium ions (β-NaEr0.2Y0.8F4), is known for its very high quantum yield for UC of near infrared (NIR) photons at wavelength around 1523nm. An UC quantum yield of 4.3% at an irradiance of 1370Wm-2 was measured by photoluminescence measurements [1]. Due to the non-linearity of the UC processes the UC quantum yield increases with increasing irradiance. For a better understanding of the UC we developed a rate equation model. With experimentally determined parameters of β-NaEr0.2Y0.8F4 we found a very good agreement between the simulations and the corresponding experiments. In addition, we connected the rate equation model with a simulation of noble metal nanoparticles. The influence of a metal nanoparticle on the upconverter was determined and spatially resolved in three dimensions. [top]

Quantsol2011

 

Experimental analysis of upconversion with both coherent monochromatic irradiation and broad spectrum illumination

J.C. Goldschmidta, S. Fischera, P. Löpera, K.W. Krämerb, D. Binerb, M. Hermlea and S.W. Glunza [top]

a Fraunhofer Institute for Solar Energy Systems, Heidenhofstr. 2, 79110 Freiburg, Germany

b Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland

Upconversion of sub-band-gap photons promises to increase solar cell efficiencies by making these photons useful. In this paper, we investigate the application of β-NaYF4:20% Er3+ to silicon solar cells. We determine the external quantum efficiency of an upconverter silicon solar cell, both under monochromatic excitation and, for the first time in the context of silicon solar cells, under broad spectrum illumination as it is relevant for the application to harvest solar energy. The investigated upconverter silicon solar cell responds under broad spectrum illumination with an average upconversion efficiency of 1.07±0.13% in the spectral range from 1460 to 1600 nm. The resulting efficiency increase for the used solar cell with an overall efficiency of 16.7% is calculated to be 0.014% relative. [top]

doi:10.1016/j.solmat.2011.01.019

 

Origin of the High Upconversion Green Luminescence Efficiency in beta-NaYF(4):2%Er(3+),20%Yb(3+)

Renero-Lecuna, C.1,2; Martin-Rodriguez, R.1,2; Valiente, R.1,2; Gonzalez, J.3; Rodriguez, F.3; Kramer, K.W. 4; Gudel, H.U.4 [top]

1. Univ Cantabria, Dept Fis Aplicada, MALTA CONSOLIDER Team, E-39005 Santander, Spain
2. ICMA CSIC, Ctr Asociado Cond Extremas, Santander 39005, Spain
3. Univ Cantabria, Fac Ciencias, DCITIMAC, MALTA CONSOLIDER Team, E-39005 Santander, Spain
4. Univ Bern, Dept Chem & Biochem, CH-3012 Bern, Switzerland

Site-selective spectroscopy in hexagonal beta-NaYF(4):Er(3+),Yb(3+) has revealed different environments for Er(3+) ions (multisite formation). The low-temperature (4)S(3/2) -> (4)I(15/2)Er(3+) green emission depends on the excitation wavelength associated with the (4)F(7/2) Er(3+) level. We have studied the effect of hydrostatic pressure on the green, red, and blue Er(3+) emission upon NIR excitation at similar to 980 nm, in order to establish the role played by energy resonance conditions and the multiple Er(3+) sites due to the disordered structure for the upconversion (UC) process (energy tuning). The variation of photoluminescence spectra and lifetimes as a function of pressure and temperature reveals that the origin of the high green UC efficiency of the beta-NaYF(4):Er(3+),Yb(3+) compound is mainly due to the multisite distribution, and the low phonon energy of the host lattice. [top]

doi:10.1021/cm2004227

 

Anomalous Independence of Multiple Exciton Generation on Different Group IV-VI Quantum Dot Architectures

M. Tuan Trinh, Leo Polak, Juleon M. Schins, Arjan J. Houtepen, Roman Vaxenburg, Georgy I. Maikov, Gal Grinbom, Aaron G. Midgett§, Joseph M. Luther§, Matthew C. Beard§, Arthur J. Nozik§, Mischa Bonn, Efrat Lifshitz, and Laurens D. A. Siebbeles*[top]

Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands

Department of Chemistry and Solid State Institute, Technion, Haifa 3200, Israel

§ National Renewable Energy Laboratory, 1617 Cole Boulevard., Golden, Colorado 80401, United States

FOM Institute for Atomic and Molecular Physics, Science Park 104, 1098 XG Amsterdam, The Netherlands

Multiple exciton generation (MEG) in PbSe quantum dots (QDs), PbSe(x)S(1-x) alloy QDs, PbSe/PbS core/shell QDs, and PbSe/ PbSe(y)S(1-y) core/alloy-shell QDs was studied with time-resolved optical pump and probe spectroscopy. The optical absorption exhibits a red-shift upon the introduction of a shell around a PbSe core, which increases with the thickness of the shell. According to electronic structure calculations this can be attributed to charge delocalization into the shell. Remarkably, the measured quantum yield of MEG, the hot exciton cooling rate, and the Auger recombination rate of biexcitons are similar for pure PbSe QDs and core/shell QDs with the same core size and varying shell thickness. The higher density of states in the alloy and core/shell QDs provide a faster exciton cooling channel that likely competes with the fast MEG process due to a higher biexciton density of states. Calculations reveal only a minor asymmetric delocalization of holes and electrons over the entire core/shell volume, which may partially explain why the Auger recombination rate does not depend on the presence of a shell. [top]

doi:10.1021/nl200014g


Two-Fold Emission From the S-Shell of PbSe/CdSe Core/Shell Quantum Dots

Grodzińska D, Evers WH, Dorland R, van Rijssel J, van Huis MA, Meijerink A, de Mello Donegá C, Vanmaekelbergh D. [top]

Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science, Utrecht University, P.O. Box 80000, 3508 TA Utrecht, Netherlands.

The optical properties of PbSe/CdSe core/shell quantum dots with core sizes smaller than 4 nm in the 5-300 K range are reported. The photoluminescence spectra show two peaks, which become increasingly separated in energy as the core diameter is reduced below 4 nm. It is shown that these peaks are due to intrinsic exciton transitions in each quantum dot, rather than emission from different quantum dot sub-ensembles. Most likely, the energy separation between the peaks is due to inter-valley coupling between the L-points of PbSe. The temperature dependence of the relative intensities of the peaks implies that the two emitting states are not in thermal equilibrium and that dark exciton states must play an important role. [top]

doi:10.1002/smll.201101819

Funding

The Nanospec Project is funded by the European Community's Seventh Framework Program (FP7/2007-2013) under grant agreement no. [246200].

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