Luminescent Down-shifting Materials Research Articles

Waste-derived carbon quantum dots for improving the photostability of perovskite solar cells to > 1,000 h

Power conversion efficiency (PCE) of perovskite solar cells (PSCs) has reached 26.1%, but PSC devices are plagued by poor stability when exposed to light (especially ultraviolet (UV) radiation), heat, and moisture. UV stability remains a significant challenge to overcome. Luminescent down-shifting (LDS) filters have shown significant enhancement in photostability and efficiency for PSCs. However, most explored LDS materials are costly, non-biodegradable, and the resulting photostability is limited to ∼100 h. In this report, as-obtained waste filtrate from the polyaniline (PANI) synthesis is used to synthesize fluorescent PANI carbon quantum dots (PANI-CQDs) using a facile hydrothermal method. Here we report, for the first time, the use of waste-derived PANI-CQDs to fabricate UV filters that are low-cost, bio-degradable, and room-temperature processible and, importantly, impart high UV and photostability to the PSCs. PSCs with these filters retained 90% and 100% of their initial performance when exposed to UV light and AM 1.5 solar radiation, respectively, for more than 900 h, while PSCs without filters degraded to 14 and 70% of their initial performance under the same conditions. Hence, we clearly show that using a waste-derived LDS filter improves the UV stability of PSCs by six times and photostability beyond 1,000 h.

Continuously in-situ manufacture of perovskite quantum dots/POE encapsulation adhesive film for silicon solar cell enhancement application

Converting the UV-blue irradiation into longer wavelength can efficiently ameliorate the insufficient solar spectral response and enhance the power conversion efficiency (PCE) of silicon solar cells, whereas there is still no appropriate strategy to make the corresponding luminescence downshifting materials compatible with commercial silicon photovoltaic modules practically. Herein, we first demonstrate an in-situ fabricated CsPbBr3 PQDs/POE encapsulation adhesive film, which can simultaneously achieve continuously large-scale manufacture through melt extrusion and possess well compatibility with the encapsulation technique of silicon photovoltaic modules. According to the separate granulation preparation and technical optimization, the composited adhesive film exhibits an intensive PL emission at 515 nm with a full width at a half-maximum of 20 nm and an ultra high PLQY of 98.2%. Moreover, less than 5% PL intensity decline even after keeping in 50 °C/90 RH aging condition for >2400 h proves its excellent working stability and barrier property. By means of hot pressing operation, the silicon solar cells encapsulated with CsPbBr3 PQDs/POE adhesive film harvest an absolute PCE enhancement of 0.68%. This work provides a way of great potential towards further improving the silicon photovoltaic industry and corresponding optoelectronic applications.

Synthesis of YVO4 Ceramic Doped with Europium using Combustion Synthesis Method as a Down-Shifting Material for Solar Cell Applications

Recently, luminescent down-shifting materials, as promising materials, have attracted much interest to improve the performance of photovoltaic systems. Accordingly, the aim of this study was to synthesize the YVO4:Eu3+ powder by combustion method and characterize their photo luminescent properties as a layer deposited on silicon solar cell. The results of the study revealed that the YVO4:Eu3+ powder with an average particle size of about 80 nm was successfully synthesized. Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy, and photoluminescence spectroscopy (PL) were used to investigate the properties of the synthesized powder, their deposition ability on the silicon solar cell, and their effects on the cell performance. The results indicated that the synthesized powder as a luminescent down-shifting material can absorb the ultraviolet light and convert it to visible light. The findings revealed that the deposition of YVO4:Eu3+ on the silicon solar cells can be considered as a promising and effective method to improve the performance of silicon solar cells in terms of power conversion efficiency and long term stability.

Selection, Preparation and Application of Quantum Dots in Perovskite Solar Cells.

As the third generation of new thin-film solar cells, perovskite solar cells (PSCs) have attracted much attention for their excellent photovoltaic performance. Today, PSCs have reported the highest photovoltaic conversion efficiency (PCE) of 25.5%, which is an encouraging value, very close to the highest PCE of the most widely used silicon-based solar cells. However, scholars have found that PSCs have problems of being easily decomposed under ultraviolet (UV) light, poor stability, energy level mismatch and severe hysteresis, which greatly limit their industrialization. As unique materials, quantum dots (QDs) have many excellent properties and have been widely used in PSCs to address the issues mentioned above. In this article, we describe the application of various QDs as additives in different layers of PSCs, as luminescent down-shifting materials, and directly as electron transport layers (ETL), light-absorbing layers and hole transport layers (HTL). The addition of QDs optimizes the energy level arrangement within the device, expands the range of light utilization, passivates defects on the surface of the perovskite film and promotes electron and hole transport, resulting in significant improvements in both PCE and stability. We summarize in detail the role of QDs in PSCs, analyze the perspective and associated issues of QDs in PSCs, and finally offer our insights into the future direction of development.

Intrinsic luminescence-downshifting effects of Zn-based Mn-doped nanoparticle layers on Si solar cells

Luminescence downshifting (LDS) effects of Zn-based Mn-doped nanoparticles (NPs) on characteristics of Si solar cells are investigated. ZnSe:Mn/ZnS core-doped core/shell NPs and ZnSe/ZnS:Mn/ZnS shell-doped core/shell/shell NPs are deposited on glass plates using layer-by-layer method. It is found that shell-doped NPs are superior as LDS materials by measuring their optical properties. We deposit LDS layers made of shell-doped NPs on Si cells and measure their internal quantum efficiencies (IQEs) to examine LDS effects separately from the effects of reflection on LDS layers. We find that IQEs for 300–400 nm are more enhanced for cells with thicker LDS layers. IQE at 350 nm is calculated for Si cells with LDS layers coated using an analytical model for the transmittance of downshifted photons into Si cells. IQEs for the respective cells are in qualitative agreement with the measurements.

Recent Advances in Colloidal Quantum Dots or Perovskite Quantum Dots as a Luminescent Downshifting Layer Embedded on Solar Cells.

The solar cell has a poor spectral response in the UV region, which affects its power conversion efficiency (PCE). The utilization of a luminescent downshifting (LDS) layer has been suggested to improve the spectral response of the photovoltaics in the short wavelength region through photoluminescence (PL) conversion and antireflection effects, which then enhance the PCE of the solar cell. Recently, colloidal quantum dots (CQDs) or perovskite quantum dots (PQDs) have been gaining prime importance as an LDS material due to their eminent optical characteristics, such as their wide absorption band, adjustable visible emission, short PL lifetime, and near-unity quantum yields. However, the instability of QDs that occurs under certain air, heat, and moisture conditions limits its commercialization. Thus, in this review, we will focus on the physical and optical characteristics of QDs. Further, we will discuss different synthesis approaches and the stability issues of QDs. Different approaches to improve the stability of QDs will be discussed in detail alongside the recent breakthroughs in QD-based solar cells for various applications and their current challenges. We expect that this review will provide an effective gateway for researchers to fabricate LDS-layer-based solar cells.

Carbon quantum dots anchored on the anti-reflection silica layer as solid luminescence down-shifting materials in solar panel encapsulation

Using the ultraviolet (UV) spectrum of light to enhance the output of encapsulated solar panels will promote the wider use of solar power. In this work, fluorescent carbon quantum dots anchored on porous silica film with preferable yellow/orange emission were prepared via solvothermal fabrication, the sol-gel method, and coating onto the top glass of a solar panel in sequence. Structural evolution investigations, optical characterizations, and performance evaluations were carried out to demonstrate the anchoring effects. The film was dual-functional due to its inclusion of anti-reflection (AR) and luminescence down-shifting (LDS) materials. This solid material provided a better means of solar panel encapsulation and achieved electrical gain, as the anchoring effect avoided the dispersion of LDS materials inside the encapsulation. Placing the film on top of the solar panel could guarantee the best UV absorption/conversion for LDS. In conclusion, the inclusion of a new fluorescent material was compatible with the standard AR process of photovoltaic glass with no additional cost.

Synthesis and photophysical properties of tetraphenylethylene derivatives as luminescent downshifting materials for organic photovoltaic applications

Luminescent Down-Shifting (LDS) is an optical approach applied in several photovoltaic (PV) technologies in which high energy solar radiation is converted to a wavelength region where the response of the photovoltaic devices is better. The use of LDS layers on organic photovoltaics (OPV) could serve two purposes: to prevent cell degradation by filtering the incident ultraviolet (UV) radiation and to improve the spectral response of PV cells at short-wavelength. This work reports, the design and synthesis of a series of tetraphenylethylene (TPE) derivatives based on TPE-A or A-π-TPE-π-A molecular structure featuring various electron-acceptor (A) groups. The photophysical properties of the new LDS compounds were systematically studied in 1,4-dioxane solution and film (Zeonex) by UV–visible absorption and fluorescence spectroscopy, and electrochemical properties studied by cyclic voltammetry. Thermal stability of the new LDS compounds was evaluated by Thermogravimetric analysis (TGA). Theoretical computational studies provided evidence of existence of intramolecular charge-transfer (ICT) between frontier orbitals of donor and acceptor moieties. The good photophysical and thermal properties of the synthesized TPE derivatives, associated with high molar absorption coefficients in UV spectrum and emission maximum in the range of 476–531 nm, make them promising candidates for LDS layers in OPV application.

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.

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%.

Tuning solar absorption spectra via carbon quantum dots/VAE composite layer and efficiency enhancement for crystalline Si solar module

AbstractIn this work, fluorescent carbon quantum dots (CQDs) composite transparent film with blue emission was prepared via hydrothermal fabrication, mixing with vinyl acetate‐ethylene (VAE) emulsion, coated and cross‐linked on the glass in sequence. This CQD/VAE film has good sticking ability and compatibility of sealing ethylene‐vinyl acetate (EVA) material and works well as luminescent downshifting (LDS) materials. Based on these features, we did a set of optical characteristics analysis for CQD/VAE film and inserted a CQD/VAE film between glass and EVA encapsulation in a mini metal wrap through (MWT) solar module. This LDS could convert UV part of solar spectra, which are normally blocked by EVA, into the blue range and improve the light absorption by solar cell. Enhancement in the performance of solar modules was proved, especially the improvement of current of short circuit (Isc), external quantum efficiency (EQE) of the UV wavelength and solar module efficiency. This material provides the chance for prompt application, since it simply solves the dispersion problem of LDS material inside encapsulation and keeps the transparency of sealing polymer materials.

Colloidal N-Doped Graphene Quantum Dots with Tailored Luminescent Downshifting and Detection of UVA Radiation with Enhanced Responsivity.

Luminescent downshifting (LDS) materials are in great demand for their applications in light conversion devices. In this work, by an ingenious chemical approach of in situ doping, N-doped graphene quantum dots (N-GQDs) have been synthesized with tailored green photoluminescence (PL) under ultraviolet (UV) light excitation. The incorporation of N atoms in the form of pyridinic and graphitic C–N bonding into the sp2-hybridized graphitic framework of N-GQDs has led to tailored LDS via PL emissions. The LDS property of synthesized N-GQDs has been advantageously utilized to demonstrate enhanced responsivity (R) of a low-cost commercially available photoconductive cell (PC) for detection of UVA radiation through an indigenous technique. The linear optical responses of samples are optimized by varying the concentration and the dispersing medium. Also the N-GQDs are shown to be photostable in poly(vinyl alcohol) (PVA) hydrogel. A 60% enhancement in photocurrent of the PC-based photodetector under UV radiation has been obtained here by using N-GQDs/PVA as LDS material. Thus, detection of UVA radiation with a high specific detectivity (D*) of 9 × 1013 Jones and responsivity (R) of 3 A W–1 has been demonstrated, which might open the opportunity of using this material in future energy conversion devices.

Cr3+-doped Mg4Ga4Ge3O16 near-infrared phosphor membrane for optical information storage and recording

A new near-infrared phosphor Mg4Ga4Ge3O16: Cr3+ with multi-photo-functionalities has been developed. Such phosphors can act as luminescent down-shifting materials converting UV and visible photons into NIR light (600–850 nm). UV irradiation induced strong NIR long persistent luminescence (LPL) can persist for more than 10 h. With the prolonged decay time, the extinguished NIR LPL can be rejuvenated by external photo stimulus including not only 980 nm light but also visible light. Such NIR photostimulated persistent luminescence (PSPL) presents separated write-in and read-out wavelength ranges. Meanwhile, photochromism (PC), that the material surface undergoes reversible change between white/pale green and ronbrown when triggered alternatively by UV and visible irradiation/heating, was also observed. Several recycle measurements demonstrate the robust fatigue resistance of PC property. Owning to the multi-photo-functionalities of Mg4Ga4Ge3O16: Cr3+, the fabrication of flexible phosphor membranes endows their application for optical information storage and repeatable optical recording. The electron motion in traps was studied by thermoluminescence (TL) and the color center formation was verified with electron spin resonance (ESR) spectra, based on which an energy level diagram was proposed for the illustration of the multifunctional mechanism. The revealing of multi-photo-functional mechanism and fabrication of flexible phosphor membranes may promote the development of a universal design principle for further study.

Photo‐Thermo‐Refractive Glasses Doped with Silver Molecular Clusters as Luminescence Downshifting Material for Photovoltaic Applications

AbstractSilver nanostructures, including molecular clusters and plasmonic nanoparticles, attract much attention due to their unique optical properties and potential applications in various fields. Glasses doped with silver molecular clusters are known to possess bright luminescence under UV excitation, which opens up prospects of using the glasses as solar spectral converters to overcome poor spectral response for most of photovoltaic cells in the short‐wavelength region. In this study, silver molecular clusters are formed in photo‐thermo‐refractive glass matrix both by UV irradiation and by Na+↔Ag+ion exchange and optically characterized. Photo‐thermo‐refractive glasses doped with silver molecular clusters, independently on silver introduction method, are shown to demonstrate broad absorption in the UV, intense white emission under excitation at 360 nm, and high photoluminescence quantum yield that meet requirements for luminescence downshifting materials. Despite this, only photo‐thermo‐refractive glass with silver molecular clusters uniformly distributed in the glass volume enhances the output power of a silicon photovoltaic cell, thus showing the potential for future application of photo‐thermo‐refractive glasses in photovoltaics, particularly in case of further experiments.

Perovskite Quantum Dots Embedded Composite Films Enhancing UV Response of Silicon Photodetectors for Broadband and Solar‐Blind Light Detection

AbstractIn this work, the integration of in situ fabricated perovskite quantum dots embedded composite films (PQDCFs) as downshifting materials is first reported for enhancing the ultraviolet (UV) response of silicon (Si) photodetectors toward broadband and solar‐blind light detection. External quantum efficiency measurements show that the UV response of PQDCF coated Si photodiodes greatly improves from near 0% to at most of 50.6% ± 0.5% @ 290 nm. As compared to the calculated maximum value of 87%, the light coupling efficiency of the integrated device is determined to be 80%@395 nm, suggesting an efficient downshifting process. Furthermore, PQDCF is also successfully adapted for electron multiplying charge coupled device (EMCCD) based image sensor. The PQDCF coated EMCCD shows linear response with high‐resolution imaging under illumination at 360, 620, and 960 nm, implying the ability of broadband light detection in the UV, visible (VIS), and near infrared (NIR) region. Furthermore, a solar‐blind UV detection is demonstrated by integrating a solar‐blind UV filter with PQDCF coated EMCCD. In all, the use of PQDCF as luminescent downshifting materials provides an effective and low‐cost way to improve the UV response of Si photodetectors.

Preparation, characterization and application of EVA film containing Eu3+ complex with 1-tridecanecarboxylic acid ligand

In this study, on the basis of complex Eu(DBM)3Phen which was widely applied in polymer matrices, quaternary complex Eu(DBM)2Phen(TA) was synthesized by the introduction of 1-tridecanecarboxylic acid (TA). XRD analyses show that Eu(DBM)2Phen(TA) inclines to amorphization compared with Eu(DBM)3Phen which is crystal. Ethylene-vinyl acetate (EVA) film doped with Eu(DBM)2Phen(TA) was prepared by casting method. SEM and AFM analyses show that the compatibility of Eu(DBM)2Phen(TA) with EVA is better than that of Eu(DBM)3Phen with EVA. Under the same addition amount of Eu3+ complexes, visible light transmittance of Eu(DBM)2Phen(TA)/EVA film is obviously greater than that of Eu(DBM)3Phen/EVA film, and the fluorescence intensity of Eu(DBM)2Phen(TA)/EVA film is only slightly lower than that of Eu(DBM)3Phen/EVA film. With the optimum addition amount of Eu3+ complexes, the energy conversion efficiency of the polycrystalline silicon solar cell coated with Eu(DBM)2Phen(TA)/EVA film is improved to 12.14%, and in comparison, that of the solar cell coated with Eu(DBM)3Phen/EVA film is only 11.98%. Hence Eu(DBM)2Phen(TA)/EVA film has a potential prospect as luminescent down-shifting material.

Efficient Cu+ to Ho3+ Energy Transfer in Highly CuO/SnO Co-doped Phosphate Glass

Glasses activated with Cu+ ions and rare-earths are attractive materials for luminescent down-shifting (LDS) in solar cells. This calls for investigating on fundamental interactions between dopants aiming to understand the factors underpinning resulting optical properties. Accordingly, this Communication reports for the first time on the determination of Cu+ → Ho3+ energy transfer efficiencies in melt-quenched phosphate glass containing holmium(III) together with a high concentration of Cu+ ions obtained through CuO/SnO co-doping. Material characterization was carried out by UV/Vis absorption and photoluminescence spectroscopy including a Cu+ emission decay assessment. The data revealed suppressed Cu+ visible emission and reduced lifetimes in the presence of Ho3+ ions consistent with an efficient Cu+ → Ho3+ energy transfer, most significant for Cu+ emission in resonance with Ho3+ absorption. The findings point to Cu+ ions being efficient energy donors to Ho3+ which may have implications for the development of glasses for LDS and laser materials as well.

Application of luminescence downshifting materials for enhanced stability of CH3NH3PbI3(1-x)Cl3x perovskite photovoltaic devices

The application of luminescent down shifting (LDS) layers as alternative UV filters for CH3NH3PbI3(1-x)Cl3x perovskite solar cell (PSC) devices is reported. A combination of photo-absorption measurements and of device decay measurements during light soaking are used to verify the stability. The application of a UV filter or LDS layer was able to significantly retard photo-induced degradation with ∼18% drop in device power conversion efficiency (PCE) observed over 30 h for non-encapsulated devices, which is compared to ∼97% for an un-filtered device, also without encapsulation. Whilst the PCE of the PSC device decreases with the application of the LDS layer, the drop is not as significant as when a commercial UV filter is used. Considering that UV filters will be essential for the commercialization of PSCs, the work provides evidence that the LDS layer can act as an alternative UV filter in PSCs and can limit the drop in PCE that can be expected from the inclusion of a UV filter, thus providing an added benefit over commercial UV filters.