Luminescent Down-shifting Layer Research Articles

Improving efficiency of silicon solar cells using europium-doped silicate-phosphor layer by spin-on film coating

This paper reports impressive enhancements in the efficiency of crystalline silicon solar cells through the application of a Eu-doped silicate phosphor luminescent downshifting (LDS) layer controlled by spin-on film technique. Surface morphology was examined using scanning electron microscope (SEM), chemical composition was analyzed using energy dispersive spectroscopy (EDS), and fluorescence emission was characterized using photoluminescence (PL) measurements at room temperature. The optical reflectance, absorbance, and external quantum efficiency (EQE) response of SiO2-coated cells with and without Eu-doped silicate phosphor were measured and compared. An 18.77% improvement in efficiency was achieved, as determined by photovoltaic current–voltage measurement under one-sun AM 1.5G illuminations.

External Quantum Efficiency Improvement with Luminescent Downshifting Layers: Experimental and Modelling

Core-shell quantum dots CdSe/ZnS and lumogen yellow organic dye are characterized by their inclusion in luminescent downshifting (LDS) layers. Layers were deposited on top of crystalline silicon cell (c-Si), dye synthesized solar cell (DSSC), and cadmium telluride (CdTe) minimodules. External quantum efficiency measurements for the solar cell/LDS devices are discussed. Experimental results were compared with an optical model developed by Rothemund, 2014.

Ligand exchange as a tool to improve quantum dot miscibility in polymer composite layers used as luminescent down-shifting layers for photovoltaic applications

UV cured luminescent CuInS2/ZnS quantum dot–polymer composites are prepared, their ligands are exchanged with oligomeric ligands and these composites are evaluated as down-shifting layers.

Eu3+-Mn2+-doped bi-functional glasses with solar photon downshifting: Application to CdS/CdTe solar cells

Luminescent downshifting is a viable way for enhancing the short-wavelength spectral-response of photovoltaic device, especially for CdS/CdTe thin-film solar cells. Phosphate glasses codoped with rare earth Mn2+-Eu3+ ions were prepared by high temperature melting method, and the absorption, excitation, and emission spectra of the glasses were investigated in detail. Under the illumination of sunlight (<520 nm excitation), the emission of the glasses can vary from ultraviolet to visible with emitting strong red emission, which just matched the spectral-response of CdS/CdTe cells, result in harvesting short wavelength photons and transferring them into the photocurrent output towards the photoelectric conversion efficiency improvement. In this work, such rare earth ions codoped phosphate glasses are investigated for their potential as bi-functional superstrate glass for CdS/CdTe solar cells and experimental performances of Luminescent downshifting layers fabricated with actual CdS/CdTe cells obtained. As a result, prepared Mn2+-Eu3+ glasses could effectively improve the photoelectric conversion efficiency by 7.140% compared to pure CdS/CdTe solar cells.

Optical Model for Simulation and Optimization of Luminescent down-shifting Layers in Photovoltaics

We present an optical model that was developed for the purpose of simulation and optimization of luminescent down-shifting layers based on phosphor particles. The model combines three-dimensional ray tracing with a novel effective scattering approach based on the Mie scattering theory. Verification of the model with experimental results shows that the model accurately takes various layer parameters into account, such as the layer thickness, the phosphor volume concentration, and the phosphor particle size distribution. Finally, using the verified model, we investigate the concept of luminescent down-shifting in organic solar cells and discuss the optimal layer parameters. Preliminary simulation results show that in the case of the studied solar cell, an improvement in the short-circuit current density of more than 6% can be obtained.

Printable luminescent down shifter for enhancing efficiency and stability of organic photovoltaics

The proof of concept of using luminescent down shifting (LDS) layers as alternative UV filters for P3HT:PCBM OPVs is demonstrated using a lanthanide-based metal complex. The results are verified using a combination of indoor light soaking, with single cell devices, and outdoor performance monitoring, using a 16-cell monolithically connected OPV module. By applying the LDS layer, a ~5% relative enhancement in photocurrent is observed for both sets of devices. More significantly, indoor light soaking tests on single cell devices without encapsulation showed an 850% enhancement in the measured half-life (T50%). The OPV modules were encapsulated and tested for outdoor stability over a 70 day period in the Negev desert, Israel. The modules made with the LDS filter are shown to match the stability of those made with a commercial UV filter and outperform the modules with no filter applied, with a 51% enhancement in the measured stability (T75%). Significantly, the work provides clear experimental evidence that the LDS layer can act as a UV filter in OPVs without compromising the efficiency of the solar cell, thus providing an added benefit over commercial UV filters.

Highly transmissive luminescent down-shifting layers filled with phosphor particles for photovoltaics: publisher’s note

This publisher’s note amends the author list and Acknowledgments of [Opt. Mater. Express5, 1295 (2015]. The author names were corrected online as of June 24, 2015: https://www.osapublishing.org/ome/abstract.cfm?uri=ome-5-6-1296.

Optical model for simulation and optimization of luminescent down-shifting layers filled with phosphor particles for photovoltaics

We developed an optical model for simulation and optimization of luminescent down-shifting (LDS) layers for photovoltaics. These layers consist of micron-sized phosphor particles embedded in a polymer binder. The model is based on ray tracing and employs an effective approach to scattering and photoluminescence modelling. Experimental verification of the model shows that the model accurately takes all the structural parameters and material properties of the LDS layers into account, including the layer thickness, phosphor particle volume concentration, and phosphor particle size distribution. Finally, using the verified model, complete organic solar cells on glass substrate covered with the LDS layers are simulated. Simulations reveal that an optimized LDS layer can result in more than 6% larger short-circuit current of the solar cell.

Experimental validation of adding-doubling modeling of solar cells including luminescent down-shifting layers

Luminescent down-shifting (LDS) layers applied on top of solar cells can potentially increase solar cell performance due to the better match of the incident irradiance spectrum reaching the cell to its spectral response. In this study, the adding-doubling tool is presented, which allows fast predictions of the influence of LDS sheets on solar cell performance. The model is validated by comparing its predictions to experimental data. Four LDS sheets including different conversion materials were investigated. The modeling tool was able to predict the external quantum efficiency with an average deviation of 0.02.

Highly transmissive luminescent down-shifting layers filled with phosphor particles for photovoltaics

We study the optical properties of polymer layers filled with phosphor particles in two aspects. First, we used two different polymer binders with refractive indices n = 1.46 and n = 1.61 (λ = 600 nm) to study the influence of Δn with the phosphor particles (n = 1.81). Second, we prepared two particle size distributions D50 = 12 µm and D50 = 19 µm. The particles were dispersed in both polymer binders in several volume concentrations and coated with thicknesses of 150-600 µm onto glass substrates. Experimental results and numerical simulations show that the layers of the higher refractive index binder with larger particles result in the highest optical transmittance in the visible light spectrum. Finally, we used numerical simulations to determine optimal layer composition for application in realistic photovoltaic devices.

Novel Non‐radiative Exciton Harvesting Scheme Yields a 15% Efficiency Improvement in High‐Efficiency III–V Solar Cells

High‐efficiency III–V solar cells typically incorporate an indirect wide‐bandgap semiconductor as a passivation layer to limit surface recombination at higher photon energies. The poor extraction efficiency of the carriers photogenerated in this window layer limits the performance of the devices in the high‐energy region of the spectrum. To address this problem, a resonance energy transfer (RET)‐mediated luminescent down‐shifting (LDS) layer is engineered by depositing an epilayer of colloidal quantum dots (QDs) on an InGaP solar cell. In this configuration, while the QDs act as a standard LDS layer, excitons are also funneled from the window layer to the QD epilayer using near‐field RET. The luminescence energy of the QDs is tuned below the bandgap of the window layer and the emitted light is absorbed in the p–n junction, where carriers are generated and efficiently extracted. The overall performance of the solar cell is found to be significantly improved after hybridization, with a large 14.6% relative and 2% absolute enhancement of the photon conversion efficiency.

A simple strategy for synthesizing highly luminescent carbon nanodots and application as effective down-shifting layers

We propose a novel strategy to prepare highly luminescent carbon nanodots (C-dots) by employing a hydrothermal method with citric acid as the carbon source and ethylenediamine as the nitrogen source, together with adding moderate ammonia water (AW) to achieve both appropriate inner structure and excellent N passivation. The effect of pH value and AW amount on the luminescence properties has been thoroughly investigated. The photoluminescence quantum yield of the resultant C-dots reaches as high as 84.8%, which is of 10.56% higher than that of the C-dots synthesized in the absence of AW in the reaction precursors. We have further combined the highest luminescent C-dots with polyvinyl alcohol to form luminescent down-shifting layers on silicon nanowire solar cells. An effective enhancement of short-circuit current density has been realized and the contribution of the down-shifting has been extracted quantitatively from the deterioration of surface reflectance and the gain of the optical absorption redistribution by means of a theoretical model on external quantum efficiency analysis.

External Thermalization of Carriers With Luminescent Down Shifting for Lower Operating Solar Cell Temperature

Luminescent down shifting (LDS) is a light management technique that can be used to exploit more efficiently the short-wavelength photons of the solar spectrum, to which most solar cell technologies exhibit relatively poor response. In practice, LDS is a thermalization process of carriers that takes place outside the solar cell itself and, therefore, has the potential of reducing its operating temperature, and thus increasing its electrical power output in field applications. In this study, we use ray-tracing and an electric-like thermal circuit to calculate the temperature variation of both multicrystalline silicon (mc-Si) and cadmium telluride (CdTe) photovoltaic modules containing LDS layers. We find that the dominant factors for the final operating cell temperature under the modified spectrum are reduced light reflection and parasitic absorption in the encapsulants. LDS, in practice, results in only a small variation compared with standard non-LDS modules, of up to +0.1 °C for the case of mc-Si and -0.6 °C for the CdTe. Although lowering operating cell temperature by means of LDS does not constitute in itself a strong reason for adopting the technology, this study paves the way for using optically active encapsulation layers with this purpose in mind.

Efficiency Enhancement of GaAs Solar Cell Using Luminescent Down-Shifting Layer Consisting of (CdSe)ZnS Quantum Dots With Calculation and Experiment

In this work, we report the efficiency enhancement of a GaAs solar cell by using a luminescent down-shifting (LDS) layer consisting of (CdSe)ZnS quantum dots (QDs). The calculated conversion efficiency shows strong dependence on the luminescence quantum efficiency (LQE) and concentration of QDs in the LDS layer as well as the difference in external quantum efficiency (EQE) of the solar cell in the absorption and emission regions of the QD. Although the irradiance of the modified spectrum by the LDS layer was reduced with increases in QD concentration, the emission range of QDs in the spectrum was intensified. So the optimum parameters need to be calculated carefully. When we measured the GaAs solar cell with the LDS layer, it showed increased current density and consequently improved efficiency. The highest performance difference between the GaAs solar cell efficiencies with and without the LDS layer was over 2.8%, although a crystalline silicon solar cell below the LDS layer showed negative change in efficiency owing to its small EQE difference.

Multifunctional Luminescent Down‐Shifting Fluoropolymer Coatings: A Straightforward Strategy to Improve the UV‐Light Harvesting Ability and Long‐Term Outdoor Stability of Organic Dye‐Sensitized Solar Cells

A new multifunctional coating for photovoltaic cells incorporating light‐management, UV‐protection, and easy‐cleaning capabilities is presented. Such coating consists of a new photocurable fluorinated polymer embedding a luminescent europium complex that acts as luminescent down‐shifting (LDS) material converting UV photons into visible light. The combination of this system with ruthenium‐free organic dye‐sensitized solar cells (DSSCs) gives a 70% relative increase in power conversion efficiency as compared with control uncoated devices, which is the highest efficiency enhancement reported to date on organic DSSC systems by means of a polymeric LDS layer. Long‐term (&gt;2000 h) weathering tests in real outdoor conditions reveal the excellent stabilizing effect of the new coating on DSSC devices, which fully preserve their initial performance. This excellent outdoor stability is attributed to the combined action of the luminescent material that acts as UV‐screen and the highly photostable, hydrophobic fluoropolymeric carrier that further prevents photochemical and physical degradation of the solar cell components. The straightforward approach presented to simultaneously improve performance and outdoor stability of DSSC devices may be readily extended to a large variety of sensitizer/luminophore combinations, thus enabling the fabrication of highly efficient and extremely stable DSSCs in an easy and versatile fashion.

Assessment of luminescent downshifting layers for the improvement of light-harvesting efficiency in dye-sensitized solar cells.

Luminescence downshifting (LDS) of light can be a practical photon management technique to compensate the narrow absorption band of high-extinction-coefficient dyes in dye-sensitized solar cells (DSSCs). Herein, an optical analysis on the loss mechanisms in a reflective LDS (R-LDS)/DSSC configuration is reported. For squaraine dye (550-700 nm absorption band) and CaAlSiN3 :Eu(2+) LDS material (550-700 nm emission band), the major loss channels are found to be non-unity luminescence quantum efficiency (QE) and electrolyte absorption. By using an ideal LDS layer (QE=100 %), a less absorbing electrolyte (Co-based), and antireflection coatings, approximately 20 % better light harvesting is obtained. If the absorption/emission band of dye/LDS is shifted to 800 nm, a maximal short-circuit current density (Jsc ) of 22.1 mA cm(-2) can be achieved. By putting the LDS layer in front of the DSSC (transmissive mode), more significant loss channels are observed, and hence a lower overall efficiency than the R-LDS configuration.

Improved efficiency of ZnSe QDs—Si hybrid solar cell system by down shifting process

Traditional Si solar cells have a narrow active absorption cross section among the short wavelength range (200–400 nm). The down-shifting process can efficiently improve the spectral response of Si solar cells by converting shorter wavelengths (i.e., ultraviolet, UV) to longer wavelengths (i.e., the visible range). Here, ZnSe quantum dots (QDs), prepared by an aqueous solution method and employed as a luminescent down-shifting layer, were spin coated onto the upper surface of manufactured Si solar cells. Measurements under standard test conditions (AM1.5, 100 mW/cm2) show that the efficiency of the ZnSe QDs–Si hybrid solar cell is increased from 11.48% to12%. The improvement of the ZnSe QDs–Si hybrid solar cell is ascribed to the efficient down-shifting process of ZnSe QDs, which enhances spectra response in the UV region for Si solar cells. The mechanism of this optical coupling and efficiency enhancement is investigated in detail. These results support the case that low-cost ZnSe QDs can be employed as efficient down-shifting material on large-area solar cells.

Improvement of the solar cell efficiency by the ZnO nanoparticle layer via the down-shifting effect

A down-shifting material can generate one low-energy photon for every one incident high-energy photon. When such a material is placed on the front side of a photovoltaic solar cell, it has the potential to enhance the overall efficiency of the PV device by emitting photons in the spectral range where the solar cell efficiency is higher. This paper examines the application of ZnO nanoparticles as a luminescent down-shifting layer (LDSL) on the Si-based, CIGS and CdTe photovoltaic devices. The experimental results measured on a Si-based photovoltaic cell with a top luminescent down-shifting layer are analyzed.Theoretical solar cells performances were simulated using the SCAPS program. The elaborated electrical and optical models take into account the photoluminescence of the ZnO nanoparticle top layer. The obtained external quantum efficiency (EQE) and I–V characteristics were analyzed in order to estimate the impact of the photoluminescent down-shifting layer on the final efficiency of the Si, CIGS and CdTe solar cells. Contrary to the EQE curves, the I–V characteristics of the CIGS and CdTe solar cells are strongly affected by the presence of the photoluminescent down-shifting layer on their top.

Semiconductor Nanocrystals as Luminescent Down-Shifting Layers To Enhance the Efficiency of Thin-Film CdTe/CdS and Crystalline Si Solar Cells

A simple optical model is presented to describe the influence of a planar luminescent down-shifting layer (LDSL) on the external quantum efficiencies of photovoltaic solar cells. By employing various visible light-emitting LDSLs based on CdTe quantum dots or CdSe/CdS core–shell quantum dots and tetrapods, we show enhancement in the quantum efficiencies of thin-film CdTe/CdS solar cells predominantly in the ultraviolet regime, the extent of which depends on the photoluminescence quantum yield (PLQY) of the quantum dots. Similarly, a broad enhancement in the quantum efficiencies of crystalline Si solar cells, from ultraviolet to visible regime, can be expected for an infrared emitting LDSL based on PbS quantum dots. A PLQY of 80% or higher is generally required to achieve a maximum possible short-circuit current increase of 16 and 50% for the CdTe/CdS and crystalline Si solar cells, respectively. As also demonstrated in this work, the model can be conveniently extended to incorporate LDSLs based on organic dyes or upconverting materials.

Integration of a silk fibroin based film as a luminescent down-shifting layer in ITO-free organic solar cells

A bio-derived silk-fibroin film doped with a luminescent dye and its application as luminescent down-shifting layer in organic solar cells.