Luminescent Down-shifting Research Articles

Ultraviolet-Filtering Luminescent Transparent Coatings for High-Performance PTB7-Th:ITIC–Based Organic Solar Cells

Photovoltaic (PV) devices based on organic heterojunctions have recently achieved remarkable power conversion efficiency (PCE) values. However, photodegradation is often a cause of dramatic drops in device performance. The use of ultraviolet (UV)-absorbing luminescent downshifting (LDS) layers can be a mitigation strategy to simultaneously filter UV radiation reaching the device and reemit it with lower energy in the visible spectral range, matching the maximum spectral response of the PV cells and thus enabling the increase of the photocurrent generated by the cell. In this work, we report the use of a Eu3+-doped siliceous-based organic–inorganic hybrid as a coating on organic solar cells based on the PTB7-Th:ITIC bulk heterojunction with the purpose of increasing their performance. We found that the applied coatings yield a PCE enhancement of ∼22% (from 3.1 to 3.8%) in solar cells with spin-coated layers, compared with the bare solar cells, which is among the highest performance enhancements induced by plastic luminescent coatings.

A Bayesian approach to luminescent down-conversion.

Photon conversion embodies a range of promising possibilities in pushing the theoretical Shockley-Queisser efficiency model of classical solar cells. Luminescent down-conversion, despite its potential, is held back in practical applications due to the difficulty of proper characterization in no small part because of concurrent luminescent downshifting events. Recent advances have demonstrated the opportunity provided by photon correlation measurement for down-conversion characterization. In this methodological work, we present a general method based on Bayesian probabilities for deriving auto-correlation functions analytically. This method is then applied to the five down-conversion mechanisms reported in the literature and successfully tested against numerical simulations. We show that the zero delay auto-correlation function can be the most direct way to demonstrate down-conversion and assess its efficiency. Our analysis offers additional useful tools for the design of characterization experiments and emphasizes some universal behavior valid for all reported conversion mechanisms.

Exploring the development of nanocomposite encapsulation solutions for enhancing the efficiency of PV systems using optical modelling

Plasmon enhanced luminescent down-shifting (PLDS) represents a passive design strategy in which the narrow spectral responsivity of photovoltaics (PVs) is increased through the application of a semi-transparent, fluorescent, polymer nanocomposite encapsulation. However, the additional loss pathways facilitated through the integration of the PLDS layer into the optical system must be overcome for the retrofitted structure to offer an enhancement to the underlying PV-device. In this study, through exploiting the antireflection properties of thin films and PLDS coatings, some of these loss mechanisms were addressed using a transfer matrix model. Two initial designs of this structure enhanced (SE) PLDS architecture were developed for a monocrystalline silicon (mc-Si) PV device using Ag nanoparticles to modify the properties of the poly (methyl-methacrylate) - PMMA encapsulation and antireflection coatings (ARC). Through the careful consideration of the composition and optical thickness of the ARC and the position at which it is integrated within the stratified SE-PLDS architecture, a 52% enhancement of the photocurrent is predicted to be produced, as compared to the conventional PV-device. Reducing the SE-PLDS layer's thickness further extended the improvement up to a 55% total enhancement in the mc-Si cell electrical generating capacity, even in the absence of plasmon assisted photoluminescence.

Microwave-assisted synthesis of multifunctional fluorescent carbon quantum dots from A4/B2 polyamidation monomer sets

Carbon quantum dots (CQDs) are becoming a desirable alternative to metal-based QDs due to their high biocompatibility, low toxicity, ease of preparation, and unique photophysical properties. In the present study, a simple microwave-assisted synthesis using a domestic oven has been adopted to produce multifunctional CQDs from the ethlyenediaminetetraacetic acid (EDTA) and 4, 7, 10-trioxa-1, 13-tridecanediamine (TTDDA) monomers. The molecular surface of the prepared CQDs is composed of hyperbranched polyamides obtained from the polymerization reaction of both EDTA and TTDDA. The controlled functionalities and chemical structures of the molecular surface of CQDs are attained by varying the initial feed ratio of EDTA and TTDDA from 1:1 to 1:2, 1:3, 1:4, 1:5, and 3:1. The T-richCD3 (EDTA: TTDDA = 1:4) with highest mass yield of 25 wt% exhibited five-folds higher photoluminescence quantum yield (PLQY) (53.3%) compared to E-richCD1 (EDTA: TTDDA = 3:1). All synthesized CQDs revealed good sensitivity and selectivity to a Cu2+ ion that is prone to cause different neurodegenerative diseases and obstruct many biological activities, while the sensitivity increased with the decrease in EDTA to TTDDA ratio. The zebrafish model has been used to demonstrate the toxicity, adverse effects, transport, and biocompatibility of CQDs. At higher concentrations (1.0 mg/mL), the T-richCDs exhibited superior cell viability than the E-richCDs for Madin-Darby Canine Kidney (MDCK) and human breast cancer MDA-MB-231 (MDAMB) cells. Because of the excellent down conversion fluorescence ability, T-richCD3 were employed as luminescent down-shifting (LDS) layer in CuInSe2 solar cell to enhance its performance.

Organic luminescent down-shifting liquid beam splitters for hybrid photovoltaic-thermal (PVT) applications

Hybridised photovoltaic-thermal (PVT) systems, obtained by merging photo-voltaic (PV) and photo-thermal (PT) technologies, can lead to enhanced conversion efficiencies. Liquid spectral beam splitters (SBSs) offer control of the ‘thermal’ and ‘electrical’ components of the solar spectrum. Combining PVT systems with liquid SBSs facilitates enhanced control of the thermal and electrical outputs, further improving the PVT systems efficiency and making them economically viable. Traditionally, liquid SBSs contain nanostructures suspended in a base-fluid to capitalise on the enhanced heat transfer capabilities offered by the nanostructures' surface morphology. These nanofluids have certain disadvantages, such as stability problems, environmental hazards and synthetic cost concerns, which preclude them from becoming a viable substitute for commercial (single-phase) fluids. This study offers an alternative strategy by employing a set of newly developed fluids containing organic and organometallic imidazo[4,5-f][1,10]phenanthroline derivatives for SBS-PVT systems. These new working fluids were designed to mimic the behaviour of luminescent down-shifting (LDS) molecules while offering enhanced thermophysical characteristics over the host base-fluid. Their optical, fluorescent and thermophysical properties enabled an increased heating rate within the working fluid. Their integration as working fluids in an SBS-PVT system lead to optical efficiencies of ~63% i.e. an 18%–20% improvement over the standalone PV technology. The fluid properties displayed a 61% increase in the economic value of the energy captured when compared to the host base-fluid alone for the same PVT system. Consequently, these novel fluids and the organic molecules they contain can be effectively designed as high performance spectrally selective fluids for PVT applications.

Enhancing the Photovoltaic Performance of Solid-State Dye-Sensitized Solar Cells with Composite Materials and Luminescent Down-Shifting

Dye-sensitized solar cells produce saturation of electrons and holes when exposed to high-intensity UV photons. These photon energies do not match the bandgap of the semiconductor materials, which not only degrades the dye and electrolyte but also disrupts the electron kinetics. In this work, graphene oxide (GO) was incorporated into TiO2 to form a composite photoanode structure. The results indicated that a composite photoanode based on GO/TiO2 enhanced the power conversion efficiency of a solid-state dye-sensitized solar cell (ss-DSSC) by 62% compared to that of pure TiO2. This enhancement is attributed to the high conductivity of graphene oxide. Further improvement in device performance was obtained by plasmonic luminescent down-shifting (LDS), where the UV region of the solar spectrum is shifted hundreds of nanometers. The multifunctional LDS coating layer was fabricated with a composite of ZnSe quantum dots and Ag nanoparticles. The experimental results demonstrated the ability of LDS to absorb photons at wavelengths below 400 nm and re-emit them at longer wavelengths (above 400 nm), where the cell has better photovoltaic response. When compared to a bare ss-DSSC, the power conversion efficiency (PCE) is enhanced by 37.62% for cells with a Ag/ZnSe coating layer. Moreover, the LDS-coated device exhibits 16.45% increased photon-to-current conversion efficiency compared to the LDS-free device for wavelengths lower than 500 nm. The 240-h aging tests confirmed that the LDS-coated ss-DSSC retained ∼ 83% of its original PCE value. This potential LDS coating layer not only leads to excellent device stability but also improves the cell performance, which increases the market value of the ss-DSSCs.

Improvement of the current generation in silicon solar cells by utilizing graphene quantum dot as spectral converter

This paper deals with a luminescent layer applied on a commercial Silicon (Si) solar cell by spin coating of an aqueous solution of graphene quantum dots (GQDs), synthesized by the hydrothermal method at 200 °C for 24 h. The GQDs layer, acted as a luminescent down-shifting (LDS) layer, causes a relative enhancement in the short circuit current density (JSC) of mc-Si and c-Si solar cells up to 5.14% and 6.82%, respectively. Remarkable relative enhancements in JSC under UV illumination showed that the LDS layer increases the JSC by downshifting effect; Diffuse reflectance spectroscopy (DRS) of the solar cells with and without the LDS layers showed that the GQD filled LDS layers do not have a considerable effect on the light reflection from the Si solar cell to affect the JSC.

Enhancing luminescent down-shifting of Eu-doped phosphors by incorporating plasmonic silver nanoparticles for silicon solar cells

This study experimentally demonstrated enhanced fluorescence emissions from luminescent down-shifting (LDS) Eu-doped phosphors under the effects of localized surface plasmon resonance (LPSR) from silver nanoparticles (Ag NPs). The plasmonic effects of the Ag NPs was examined in terms of plasmon-enhanced Raman scattering and plasmonic absorption. The fluorescence emission of the Eu-doped phosphors was examined in terms of photoluminescence (PL). Overlap between the plasmonic absorption band of Ag NPs and the PL emission band of Eu-doped phosphors increased fluorescence emissions by enhancing excitation. This study also developed an optical process model describing LSPR (Ag NPs), LDS (Eu-doped phosphors), and plasmon-enhanced fluorescence (PEF; Eu-doped phosphors with Ag NPs) on silicon solar cells. PEF was experimentally confirmed in terms of PL, external quantum efficiency (EQE), and photovoltaic current–voltage measurements. Compared to the cell with only an anti-reflection layer of SiO2/SOG, the inclusion of Ag NPs with the Eu-doped phosphors enhanced the PL emission intensity by 1.1243 times at a wavelength of 514 nm and also improved the EQE response by 8.3% (from 57.28% to 62.05%) and conversion efficiency by 7.1% (from 12.04% to 12.89%).

Colorful opaque photovoltaic modules with down-converting InP/ZnSexS1-x quantum dot layers

Abstract The luminescent down-shifting (LDS) layer, which transforms incoming high energy solar photons to visible ones, promises augmentation of both photoelectric performance and aesthetic appeals of photovoltaic (PV) modules. For efficient, colored PVs with LDS layer, luminophores with high photoluminescence quantum yield (PL QY), small overlap between absorption and emission spectra, and proven photostability are prerequisites. Here, we demonstrate colorful, opaque PV modules with LDS layers of minimized photon sacrifice enabled by structurally-engineered, eco-friendly InP/ZnSexS1-x quantum dots (QDs). Specifically, composition-controlled, thick shells allow enhanced absorption in the UV region and improved PL QY of QDs. Additionally, the ligand-engineering guarantees the stability of LDS layers after the damp heat test. Benefited from QD-LDS layers, commercially available CIGS and c-Si PV modules are awarded with 40% EQE enhancement in the ultraviolet region and wide-ranging color tunability over the entire visible region by QD-LDS layers. Hence, this integrated approach for desirable luminophores will contribute to the realization of highly-efficient, aesthetically-appealing opaque PV modules.

Luminescent down-shifting film based on optimized mixture of organic dyes for improving the performance of P3HT:PC61BM photovoltaic devices

During the last few years, great interest has been given to research in organic solar cells. Apart from the low cost techniques needed for the production of the active layers, the plasticity of these types of materials offers an additional benefit compared to traditional silicon-based solar cells. However, the commercialization of organic photovoltaic technologies is limited by rapid degradation and low efficiency. Recently, the use of luminescent down-shifting (LDS) films has been explored as a tool for increasing the external quantum efficiency of organic-based devices. A previously observed superposition in the emission–absorption spectra of Kremer blue (Kb) and Coumarin 7 (C7) dyes suggests that an energy transfer process can take place among these molecules. Decay time photoluminescence measurements in Kb100−xC7x samples were carried out to confirm a Föster resonance energy transfer process. An optimization process following the design of experiments methodology was carried out to adjust the optical properties of Kb100−xC7x films for applications in the P3HT:PC61BM organic photovoltaic device. An increment of 18.6% in the short circuit current density (Jsc) of P3HT:PC61BM devices coated with a Kb92.5C77.5 LDS film was observed. A degradation test shows a rapid drop in the electric current density of devices without the LDS film, which we attribute to the so-called burn-in, widely reported in the literature. For devices coated with the Kb92.5C77.5 LDS film, no rapid drop in the electric current density was observed, suggesting that the use of the luminescent layer mitigates the photoinduced burn-in loss.

Luminescent down-shifting natural dyes to enhance photovoltaic efficiency of multicrystalline silicon solar module

The short wavelength photons (below 500 nm) of the solar spectrum are under-utilized in multicrystalline silicon (mc-Si) solar modules because of their high surface recombination losses. The application of luminescent down-shifting (LDS) materials is an effective way to utilize the short wavelength photons to enhance the efficiency of a mc-Si solar module. This study utilized four ‘natural’ dyes extracted from the wheat husk, rice husk, turmeric rhizomes (Curcuma longa L.), and Moringa Oleifera leaves for LDS application. These natural dyes showed absorption in the UV and blue range, and emission in the visible range which is effectively utilized by the silicon solar cell. Optimum concentrations of the natural dyes were incorporated in the front ethylene vinyl acetate (EVA) layers which were used to encapsulate bare Si cells into photovoltaic (PV) modules. The mc-Si PV modules which had the front encapsulation of EVA films containing the turmeric and moringa dyes showed relative enhancement of ~ 6.8% (±3.6) and ~ 9% (±4) respectively, in their efficiencies with respect to that of the corresponding bare silicon cells. The gains in the photovoltaic efficiency obtained with the turmeric and moringa dyes were found to be comparable to (or slightly greater than) the values reported in the literature using various Eu3+ based lanthanide complexes as LDS materials. Finally, the inclusion of natural LDS dyes in the encapsulating EVA layer would offer an economical and pro-environmental solution at high volume manufacturing to improve the utilization of short-wavelength photons.

Bandgap-Tuned CuInS2/ZnS Core/Shell Quantum Dots for a Luminescent Downshifting Layer in a Crystalline Silicon Solar Module

CuInS2 (CIS) quantum dots (QDs) were investigated as a luminescent downshifting (LDS) material that converts near-ultraviolet (UV) light to visible light and were applied to a single crystalline si...

Eu(III) complex-polymer composite luminescence down-shifting layers for reducing the blue-losses in thin film solar cells

In this work a luminescence down-shifting (LDS) layer, which can reduce significantly the blue-loss due to absorption in the n-type layer of popular thin-film solar cells such as CIGS, CdTe and CZTS is demonstrated. The potential benefits of the developed LDS layer is demonstrated in a prototype CdTe/CdS solar cell. The blue response of the devices coated with Eu(TTA)3Phen-based LDS layer exhibit an improvement by a factor of two to three times, reaching almost 6% relative enhancement in the short-circuit photocurrent density, compared with the reference device without LDS. The spectral characteristics of the Eu-complex were studied by dissolving in different organic solvents and polymer matrices. The microstructure of the polymer matrix plays a key role on the size, shape and spatial distribution of Eu-complex microparticles, which enables a control of photoluminescence properties at optimal conditions of agglomeration, isotropic luminescence and reduced quenching. The results indicate that the solvents affect differently the spectral characteristics of the emission spectra of the Eu-complex, which show a hypsochromic band shift as the solvent polarity increases. The analysis of the relative intensity ratio (R) of 5D0 → 7F2 to 5D0 → 7F1 transition indicated the deterioration of local symmetry around europium ions with the reduction of solvent polarity. These results provide a means to improve the emission efficiency of fluorophores embedded in porous matrices and also bring new insights into LDS materials for photovoltaic devices. The developed LDS layer will have applications in devices which use a high band gap heterojunction partner.

Improving the efficiency of silicon solar cells using in situ fabricated perovskite quantum dots as luminescence downshifting materials

Abstract Luminescence downshifting (LDS) layer integration has been proven to be an efficient way to ameliorate the poor UV-blue spectral response and improve the power conversion efficiency (PCE) for solar cells (SCs). By employing an in situ fabricated CH3NH3PbBr3 (CH3NH3 = methylammonium, MAPbBr3) quantum dot/polyacrylonitrile (PAN) composite film as the LDS layer, we observed a clear enhancement in the external quantum efficiency (EQE) for silicon SCs, predominantly in the UV-blue region. With a theoretically calculated intrinsic LDS efficiency (η LDS) of up to 72%, silicon SCs with the LDS layer exhibited an absolute value of 1% for PCE improvement in comparison to those without the LDS layer. The combination of easy fabrication and low cost makes it a practical way to achieve photovoltaic enhancement of Si-based SCs.

Enhance short-wavelength response of CIGS solar cell by CdSe quantum disks as luminescent down-shifting material

As the luminescent down-shifting (LDS) material, Cadmium selenide (CdSe) quantum disks (QDs) have been synthesized for improving the short-wavelength response of Cu(In, Ga)Se2 (CIGS) solar cells. The peak of the photoluminescence spectra of the as-prepared QDs is coinciding with the peak of the external quantum efficiency (EQE) of CIGS solar cell. The absorption and photoluminescence spectra of the as-prepared CdSe QDs show that the photons of wavelength below 460 nm, which could not be converted into electricity by CIGS solar cell, would be absorbed by the QDs and generating longer wavelength photons that could contribute to charge carrier generation by the cell. The QDs were embedded into the polymethylmethacrylate (PMMA) forming the colloidal fluorescent mixture. Subsequently, the mixture was applied to the surface of the solar cell as the LDS layer. It is found that the EQE of CIGS devices increases up to about 25% in the range of 300–460 nm due to LDS. The placement of the LDS layer upon the CIGS solar cell improved the electrical power output of the bare cell to 114%.

Enhancement of solar cell efficiency via luminescent downshifting by an optimized coverglass

A novel approach to enhance the solar cell efficiency via employing a luminescent downshifting mechanism is presented in this work. Gold metal ions were diffused into a commercially available sodalime silicate glass using a versatile field-assisted solid-state ion diffusion technique under different experimental conditions. Some of these samples were irradiated with ns-laser to segregate the diffused ions into dimers and trimers to enhance their luminescence characteristics. The consequent structural modifications in the glass matrix were examined using Fourier transform infrared spectroscopy. Optical absorption and luminescence measurements were performed to check the presence of resonant plasmonic absorption of nanoclusters and suitability of the samples as luminescent downshifters, respectively. At UV excitation wavelengths (260 and 340 nm), the doped samples downshifted the solar spectrum compared to their undoped counterparts. Furthermore, ns-laser irradiation of the doped samples significantly enhanced the luminescence intensity in comparison to the unirradiated samples. Real-time performance of these samples was tested by measuring the output power of a Si solar cell covered with the treated coverglass when illuminated with a solar simulator. Finally, the Vicker's micro-indentation was applied to conclude that ionic diffusion increased the glass hardness as well.

Photovoltaic efficiency enhancement for crystalline silicon solar cells via a Bi-functional layer based on europium complex@nanozeolite@SiO2

Eu3+ complexes are the prime candidates for luminescent down-shifting (LDS) converters of solar cells due to their high luminescent quantum efficiencies (LQE), large Stoke shifts and tunable excitation. However, their instability towards heat will shorten their life in solar cells, especially for outdoor use. Besides, the optical loss of the front glass and encapsulants will trade off the enhanced efficiency by photo-conversion. In this paper, highly emissive hybrid material Eu(PPO)n-C4Si@NZ (HY) was obtained by assembling europium complex into three different sizes of stable zeolite L functionalized with a water-soluble stopper. Then a bi-functional layer by incorporating HY (LDS) with anti-reflective SiO2 was developed. Benefitting from the dual functions, the as-prepared cell with HY@SiO2 film substrate manifests an increased external quantum efficiency (EQE) in both UV and the longer wavelength regions, compared with pure glass based c-Si solar cell. In the best case, the conversion efficiency of the c-Si solar cell is increased by a relative 3.30% (from 16.386% to 16.926%).

Study of the Effect of Luminescence Down-Shifting on Silicon Solar Cells with SiC Based Composite as Optical Windows Layer

Study of the Effect of Luminescence Down-Shifting on Silicon Solar Cells with SiC Based Composite as Optical Windows Layer

Optimizing the optical properties of a dye-based luminescent down-shifter to improve the performance of organic photovoltaic devices

Through luminescence downshifting (LDS) effect, high energy solar radiation is converted to a wavelength region where the response of the photovoltaic devices is better. Additionally, LDS layers deposited on organic materials-based devices could provide a protective feature for the atmospheric agents, like ultraviolet photons, oxygen and moisture, that cause material degradation. This work reports an optimization procedure for the optical properties of a LDS layer composed by the organic dye commercially called Kremer Blue dispersed on poly-methyl methacrylate (PMMA) inert matrix. With optimized values for photoluminescence quantum yield (PLQY) and absorbance parameters, this LDS layer became an efficient, low cost UV filter for solar cells based on poly (3-hexylthiophene):[6,6]‐phenyl C61‐butyric acid methyl ester (P3HT:PC61BM) blend, at the same time that provoked a significant increasing (around 6%) in the device's photocurrent production. Such optimization procedure can be applied to other materials that could be candidates as luminescence down-shifters for the various photovoltaic technologies currently available.

Enhanced spectral response of CIGS solar cells with anti-reflective subwavelength structures and quantum dots

A cover glass integrated with subwavelength structures (SWSs) and quantum dots (QDs) was realized to enhance the spectral response of Cu(In1-xGax)Se2 (CIGS) thin film solar cells. The nanoscale SWSs was produced on the front and backside of cover glass using the self-masked etching method. The fabricated SWSs-integrated glass (SIG) exhibited superior anti-reflective properties over a broad wavelength range and a broad range of incident angle. The average transmittance of the single and double-sided SIG was increased from 92.4% to 95.2% and 97.8% in the wavelength range between 300 and 1200 nm, as compared to that of a flat surface glass. QDs were formed between the fabricated SIG and ZnO layer to act as a luminescent down-shifting (LDS) layer. A large amount of light can pass through the SIG, enhancing the efficiency of the LDS by improving light absorption and lowering reflection. After successful integration of the SIG with QDs (QD/SIG) on top of the CIGS devices, photovoltaic performance was significantly improved. The power conversion efficiency of the CIGS devices integrated with QD/double-sided SIG was improved by 7.41%, compared with that of a reference device (without QD/cover glass). The efficiency improvement is attributed to the enhanced solar energy harvesting by the efficient LDS and the minimized surface reflection loss.