Down-shifting Layer Research Articles

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.

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.

Efficiency enhancement of silicon solar cells through a downshifting and antireflective oxysulfide phosphor layer

A simple, rapid, and low-cost anti-reflection coating (ARC) for polycrystalline silicon (pc-Si) solar cells has been developed by spin coating a solution of submicron spherical Gd2O2S:Eu3+ phosphor impregnated in a polyvinylpyrrolidone (PVP) matrix on the textured surface of the solar cell. Under a simulated one-sun illumination, this predesigned device achieved an enhancement of 6.74mA/cm2 in short-circuit current density and 2.76% in power conversion efficiency relative to those for a pristine cell. Based on photoluminescence, reflectance, and optical spectral studies, the underlying mechanism for these improvements can be attributed to the luminescent down-shifting (LDS) capability in the ultraviolet range and additional promotion of light absorption within the measured spectral region. Our results indicate that a suitable inorganic phosphor impregnated in a polymer matrix may potentially serve as a feasible solution to compensate for the spectral mismatch and Fresnel reflection loss of silicon solar cells.

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.

Reduced ultraviolet light induced degradation and enhanced light harvesting using YVO4:Eu3+ down-shifting nano-phosphor layer in organometal halide perovskite solar cells

We report a simple method to mitigate ultra-violet (UV) degradation in TiO2 based perovskite solar cells (PSC) using a transparent luminescent down-shifting (DS) YVO4:Eu3+ nano-phosphor layer. The PSC coated with DS phosphor showed an improvement in stability under prolonged illumination retaining more than 50% of its initial efficiency, whereas PSC without the phosphor layer degraded to ∼35% of its initial value. The phosphor layer also provided ∼8.5% enhancement in photocurrent due to DS of incident UV photons into additional red photons. YVO4:Eu3+ layer thus served a bi-functional role in PSC by reducing photo-degradation as well as enhancing energy conversion efficiency.

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.

Oxyfluoride glass (SiO_2-PbF_2) co-doped with Ag nanoclusters and Tm^3+ ions for UV-driven, Hg-free, white light generation with a tuneable tint

Bulk SiO2-PbF2 oxyfluoride glasses co-doped with dispersed luminescent Ag nanoclusters and Tm3+ ions have been prepared by conventional melt-quenching method. Luminescence from 400 to 900 nm has been excited in this glass by UV light from 340 to 400 nm. The prepared glass has potential for application as a low cost glass phosphor in Hg-free white light generation in UV-driven devices, flexible monitors and as down-shifting layers for enhanced solar cells. Co-doping with Tm3+, which has an absorption band 3H6→1D2, affects the tint of the total Ag-Tm3+ white emission band of this glass by changing the excitation wavelength to about 365 nm, which is almost the same wavelength as that of a commercial LED.

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.

Lead silicate glass SiO2–PbF2 doped with luminescent Ag nanoclusters of a fixed site

Bulk SiO2–PbF2 glass doped homogeneously with luminescent Ag nanoclusters has been synthesized using a melt-quenching technique. A broad range of luminescence from 400 nm to 900 nm can be excited with a broad range of UV and some visible excitation wavelengths. The luminescence spectra have been found to be invariant with excitation wavelength at room temperature, indicating a negligible distribution of Ag cluster sites. The UV excitation efficiency of Ag nanoclusters has been determined by shifting the absorption edge further into the UV using an Al2O3 glass-network modifier. The prepared glass is proposed as a low-cost glass phosphor for Hg-free environmentally-friendly white light generation in UV/blue-driven light emitting diodes, in flexible monitors and as down-shifting layers for enhanced solar cells.

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.

Optical modelling of the external quantum efficiency of solar cells with luminescent down-shifting layers

Luminescent down-shifting (LDS) is an elegant, purely optical method to improve the short-wavelength response of photovoltaic (PV) modules by red-shifting the incident solar spectrum. This paper in a first step develops a simple optical model to investigate the effect of LDS layers on top of PV modules on their external quantum efficiency. A meaningful figure of merit is the LDS efficiency ηLDS which quantifies the efficiency of the LDS layer to down-shift absorbed photons and send them towards the underlying solar cell. The simplified optical model developed here, extracts LDS efficiencies from experimental quantum efficiency spectra, and thereby enables assessing the current status and future potential of LDS for various solar cell technologies. Our simplified LDS model is fast, easy-to-use and universally applicable to analyze experimental LDS results. Moreover, it is especially useful for screening candidate LDS materials.

Dual-band ultraviolet-short-wavelength infrared imaging via luminescent downshifting with colloidal quantum dots

The performance of short-wavelength infrared (SWIR) cameras in the visible and ultraviolet (UV) regions is limited by the absorption of high-energy photons in inactive regions of the imaging array. Dual-band UV-SWIR imaging can be achieved by using PbS colloidal quantum dots (CQD) to downshift incident UV light to the SWIR band. The CQD downshifting layer has minimal impact on the SWIR imaging performance and greatly increases the UV sensitivity of an InGaAs camera. A dual-lens design in which the QDs are incorporated on a removable substrate is demonstrated, which provides UV sensitivity without modification of the InGaAs camera focal plane array. A single-lens design in which the QDs are deposited directly on the focal plane array is demonstrated using both a standard InGaAs focal plane and a substrate-thinned focal plane. Higher UV resolution for the substrate-thinned focal plane is observed.

Increased conversion efficiency in cadmium telluride photovoltaics by luminescent downshifting with quantum dot/poly(methyl methacrylate) films

AbstractCommercially available quantum dots have been encapsulated in a poly(methyl methacrylate) film and used as a luminescent downshifting layer on cadmium sulfide/cadmium telluride photovoltaic devices. Application of these films has resulted in a relative improvement to the short‐circuit current of over 4% by I–V measurement, with a significant increase in the contribution of short‐wavelength light resulting in 25% of the current available in this part of the spectrum being captured. The films have been shown to be highly scattering and the associated difficulties this provides to external quantum efficiency measurements have been discussed. A range of optical characterisation techniques, particularly laser beam induced current, have been used to probe the effect the films have on a cadmium sulfide/cadmium telluride device. An alternate methodology for performing external quantum efficiency measurements with the quantum dot films has been proposed. Copyright © 2013 John Wiley & Sons, Ltd.

Enhancement in solar cell efficiency by luminescent down-shifting layers

In this paper, core-shell semiconductor quantum dots (QDs) CdSeS/ZnS with emission at 490 nm and 450 nm were investigated for their use in luminescent down-shifting (LDS) layers. Luminescent quantum yield (LQY) of the QDs measurements in solution proposed that they were suitable candidates for inclusion in LDS layers. QDs were encapsulated in poly(methyl,methacrylate) (PMMA) polymer matrix and films were fabricated of 134 ± 0.05 microns. Selections of organic dyes from BASF Lumogen F range were also investigated for their use as LDS layers; Violet 570 and Yellow 083. The addition of LDS layers containing Violet 570 dye demonstrated a unity LQY when encapsulated within a PMMA matrix. A PV device of an LDS layer of Lumogen Violet 570 deposited on top of a crystalline silicon cell was fabricated where it was demonstrated to increase the efficiency of the cell by 34.5% relative.

Enhanced Light Harvesting with a Reflective Luminescent Down-Shifting Layer for Dye-Sensitized Solar Cells

For a dye-sensitized solar cell with a near-infrared squaraine (SQ1) sensitizer, the photovoltaic performance was enhanced remarkably with a reflective luminescent down-shifting (R-LDS) layer to increase the light-harvesting efficiency at the wavelength region 400-550 nm where the SQ1 dye has weak absorption. Relative enhancements greater than 200% in IPCE near 500 nm and 40-54% in JSC were achieved with red phosphor CaAlSiN3:Eu(2+) as the LDS material, attaining 5.0 and 4.8% overall efficiencies of power conversion for the R-LDS layer coated on the counter electrode (front illumination) and working electrode (back illumination), respectively.

ZnO nanoparticles as a luminescent down-shifting layer for photosensitive devices

The optical properties of ZnO nanoparticles (NPs) fabricated by three different methods were studied by the UV-excited continuous wave photoluminescence in order to estimate their down-shifting (DS) efficiency. Such a luminescent layer modifies the incident solar radiation via emitting wavelengths better matching the spectral response of the underlying photosensitive device (photodiode), thereby increasing its efficiency. Some of the studied ZnO NPs were subsequently deposited on the front side of commercial silicon photodiodes and the external quantum efficiency (EQE) characteristics of the final devices were measured. Through comparison of the photodiode's EQE characteristics before and after the deposition of the ZnO NPs layer, it was concluded that for the photodiode with a low UV sensitivity (about 8%), the ZnO luminescent layer produces a down-shifting effect and the EQE in the UV and blue range improves by 16.6%, while for the photodiodes with a higher initial UV sensitivity (about 50%), the EQE in this range decreases with the ZnO layer thickness, due to the effects competing with DS, like the diminution of the ZnO layer transmittance and an increasing diffusion.

Zinc oxide nanoparticles as luminescent down-shifting layer for solar cells

Zinc oxide nanoparticles as luminescent down-shifting layer for solar cells

CdSe/ZnSe/ZnS量子点在单晶太阳能电池中的应用

The luminescent down-shifting characteristics of CdSe /ZnSe /ZnS core /shell /shell quantum dots( QDs) were studied by incorporating the QDs as the down-shifting luminescent material into polymethyl-methacrylate( PMMA). Firstly,the optical high-pass filter with threshold 420 nm was used to cover the solar cell,so as to make the spectral response of the cell almost zero in the waveband range of 300 ~ 420 nm. Then the luminescent down-shifting( LD) layer of QDs was prepared on the external surface of the optical filters,we found the external quantum efficiency( EQE) of solar cell improved. This indicates that LD layer can realize the down-shifting of frequency spectra at300 ~ 420 nm,which is out of the spectral response region of the normal cell. Finally,in order to analyze the possibility of applying quantum dots to solar cells,the minimum fluorescence quantum efficiency( FQE) of the quantum dots was calculated to be 87. 8% according to the measured EQE of solar cell.

EFFICIENT ULTRAVIOLET LIGHT FREQUENCY DOWN-SHIFTING BY A THIN FILM OF ZnO NANOPARTICLES

The maximal efficiency of a single junction solar cell (SC) is defined as the Shockley–Queisser limit, which determines the maximal output power which can be furnished by a SC as a function of the bandgap of the semiconductor constituting the cell. The short wavelength spectral response of a SC can be improved if a luminescent down-converting layer is added to the SC structure. We propose the use of a layer containing ZnO nanoparticles (NPs) as a luminescent down-shifter. ZnO is able to absorb efficiently the ultraviolet light (λ < 400 nm), where the SC spectral response is low and to re-emit lower energy photons (longer wavelength photons) for which the SC spectral response is enhanced, thus increasing the total photocurrent. The stoichiometry and crystallinity of ZnO NPs can be controlled and adjusted to obtain the highest visible photoluminescent emission, indicator of an efficient down-shifting. The ratio between the ZnO UV absorption and visible emission is also estimated and from these results we expect the increase of the SC efficiency using ZnO NPs as a down-shifting layer placed on the front side of the SC.