Role of refractive index in highly efficient laminated luminescent solar concentrators

doi:10.1016/j.nanoen.2020.104470

Nano Energy

Volume 70, April 2020, 104470

https://doi.org/10.1016/j.nanoen.2020.104470 Get rights and content

Highlights

•
We report refractive index-engineered laminated LSCs based on CdSe/CdS QDs.
•
The optical efficiency strongly depends on the refractive index configuration.
•
The laminated LSCs exhibits an optimal external optical efficiency of ~3.44%.

Abstract

As a large-area solar radiation collector, luminescent solar concentrators (LSCs) can be used as power generation units in semitransparent solar windows, modernized agricultural greenhouses and building facades. However, the external optical efficiency and long-term stability of the LSCs limit their practical applications due to the sensitivity of the emitters to the light and environmental conditions. Here, we used the concept of “laminated glass” to prepare LSCs, which consist of two waveguide layers and the quantum dots (QDs)/polymer interlayer, and we tune the refractive index of the different parts of the system to improve the external optical efficiency and stability of the LSCs, simultaneously. The waveguide layer can be glass, quartz, polymethyl methacrylate (PMMA) and other transparent materials. The CdSe/CdS core/shell QDs were used as fluorophores to prepare the interlayer of the LSCs. The external optical efficiency of the laminated LSCs is associated with the refractive index of the three layers: the closer the refractive index, the higher the η_opt. The highest external optical efficiency of 3.4% has been achieved for the laminated PMMA/QDs-polymer/PMMA LSCs, which improved ~92% compared to the single-layered CdSe/CdS based LSCs. To the best of our knowledge, this is the highest efficiency for the LSCs based on CdSe/CdS QDs. These results pave the way to realize high efficiency laminated windows as power generation units by suitably tuning the structure of the LSC, and provide the theoretical guidance for the LSCs utilized in building integrated photovoltaics.

Graphical abstract

External optical efficiency of the laminated LSCs with different refractive index configuration. Inset is the photograph of the laminated LSCs based on CdSe/CdS QDs.

Introduction

Luminescent solar concentrators (LSCs) have attracted great attention as large-area sunlight collectors for photovoltaics (PVs) because of their light-weight, simple architecture and cost-effective fabrication [[1], [2], [3], [4], [5]]. A typical luminescent solar concentrator (LSC) consists of optical waveguide materials embedded or covered with highly emissive fluorophores (e.g. down-shifting or up-converting materials). Upon sun radiating onto the surface of an LSC, the fluorophores re-emit photons and these photons are guided to the device edges by total internal reflection (TIR) [4,6]. Usually, the LSCs coupled with photovoltaic (PV) cells can decrease the usage of expensive PV cells. If the power conversion efficiency (PCE) of the LSCs is high enough (>6%), the combination of PV cells with LSCs can reduce the cost of solar electricity [7].

The optical properties of the fluorophores are the most important factors that affect the PCE of the LSCs. They determine the absorption spectral region, the emission wavelength and the reabsorption losses of the LSCs. Colloidal semiconductor quantum dots (QDs) are very attractive fluorophores, which have been recently used as light converter in LSCs due to their tunable absorption and emission properties, high fluorescent quantum yield (QY) and easy preparation [[8], [9], [10]]. Various types of QDs, such as carbon QDs, silicon QDs, core/shell CdSe/CdS QDs, and PbS/CdS QDs are incorporated in polymer slabs for the fabrication of LSCs [[11], [12], [13], [14], [15]]. Compared with the bare QDs, the heterostructured QDs have higher QY, better spectra separation between emission and absorption spectra and improved stability [13,16,17]. The application of these QDs has achieved an improvement of the external optical efficiency (η_opt, defined as the ratio of the output power from the edges and the input power through the top surface of the LSC) of LSCs. For example, the LSC based on core/shell CdSe/CdS QDs exhibits an enhancement in quantum efficiency (48%) with respect to that of the LSC based on bare CdSe QDs [13]. PbS/CdS QDs based LSCs have the η_opt of 6.1% with a geometrical factor (G, defined as the ratio of the top surface area and the lateral area of the LSC) of 10 [14].

Another important factor affecting the performance of the LSCs is their geometric structure. In previous reports about the QDs based LSCs, QDs are embedded in an optical waveguide or coated on the surface of the waveguide, which may limit the efficiency of the device due to the restriction of absorption and emission spectra, and may decrease the long-term stability because of the exposure of some QDs to the environmental atmosphere [18,19]. Recent studies have improved the performance of LSCs by proposing alternative architectures, for instance, the tandem or sandwich structure, or adding an additional reflection layer (e.g. diffuse mirrors) [[20], [21], [22], [23], [24], [25]]. In the tandem structure, one layer of LSC based on QDs was stacked on the top of another one and every layer has different emitters with different absorption ranges. The η_opt of these LSCs was improved compared to the single-layered structure due to the enhancement of absorption efficiency [23]. Compared with single-layered LSC, the tandem LSCs increase the cost of final electricity due to the increase of the PV material usage and complexity of the fabrication processes. In addition, because the two layers of the LSCs are in direct contact with the surrounding environment, the QDs are easily degraded when the LSCs are exposed to high humidity environment [18]. Last but not least, some QDs contain toxic elements (e.g. Pb and Cd), which may result in health issues if dispersed in the environment. Based on these considerations, we proposed the sandwich structure in our previous work: QDs thin film layer sandwiched between two glass layers to isolate the QDs from surrounding environment (air and water), which improved the η_opt, stability and safety, simultaneously [24]. However, obtaining high η_opt in large-area LSCs is still a big challenge as (i) the high concentration QDs in the thin film make it difficult to prepare a flat and uniform film, leading to the decrease of η_opt because of scattering; (2) the as-prepared sandwich structure is not so mechanical stable as the thin film polymer (in micrometer range) usually cannot cohere the glass very well. Using the concept of “laminated glass”, the LSCs can be prepared by replacing the intermediate thin-film layer with thick QDs/polymer layer (up to millimetre) to realize building integrated PVs (BIPVs). Compared to thin film interlayer, the “laminated glass” could offer improved mechanical stability of the LSC and large-scale production using industrial approach; Bergren et al. reported the use of this structure for preparation of LSCs based on CuInS₂/ZnS QDs [1]; while there is no report for using such structure for CdSe/CdS QDs based LSCs. In addition, in the multilayered structure, there is still less investigation of the relationship between the match of the refractive index (n) between layers and the efficiency of the LSCs. Thus, it is of great significance to understand the relationship between n and efficiency in laminated LSC for selecting suitable materials to obtain highly efficient LSC. In this work, we prepared laminated LSCs based on CdSe/CdS core/shell QDs by “laminated glass” technology. The QDs/polymer solution was injected into the gap between two waveguide layers, forming an LSC by in-situ polymerization under ultraviolet (UV) light. Through changing the top and bottom layer materials [e.g. glass, quartz and polymethyl methacrylate (PMMA)], the relationship between η_opt and the match of refractive indexes of different layers in the LSCs has been investigated. The closer the n between interlayer and top/bottom layer, the higher the η_opt of the LSC. We demonstrate that the combined use of luminophores with large Stokes shift and matrices with matched refractive indexes boosts the overall efficiency of the LSCs. This result could broaden the field of application of LSCs not only to BIPVs, but also to other flexible polymer power roofs.

Section snippets

The structure of the QDs

CdSe/CdS core/shell QDs were synthesized via a hot injection method followed by a successive ionic layer adsorption and reaction (SILAR) process at 240 °C, as described in detail in the experimental section. The structure of the QDs was characterized by transmission electron microscopy (TEM), as shown in Fig. 1a. From the bright field TEM image, it can be seen that the QDs exhibit a uniform spherical morphology and good dispersion without aggregation. The selected-area electron diffraction

Conclusion and perspectives

In summary, CdSe/CdS core/shell QDs were used to prepare laminated LSCs, in which QDs/PLMA layer was laminated between two identical waveguides (glass, quartz or PMMA). Compared to the thin-film geometry, the laminated structure offers the benefit of optimization of the best matches between the QDs interlayer and the out-layer in order to obtain highest efficiency of the LSCs. The laminated LSCs exhibit better η_opt than single-layered LSCs, due to the reduction of reabsorption loss and the

Materials

Selenium pellet (Se, ≥99.999%), lauryl methacrylate monomer (LMA), ethylene glycol dimethacrylate (EGDM), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), hexane, toluene, methanol, and ethanol were purchased from Sinopharm Chemical Reagent Co. Ltd. Sulphur (S, 100%), oleylamine (OLA), oleic acid (OA), and octadecene (ODE), Cadmium oxide (CdO, 99%), trioctyl phosphine oxide (TOPO) and trioctyl phosphine (TOP, 97%) were purchased from Sigma-Aldrich. All chemicals were used as purchased.

Synthesis of CdSe/CdS core/shell QDs

The

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

H. Zhao acknowledges the start funding support from Qingdao University and the funding from the Natural Science Foundation of Shandong Province (ZR2018MB001). Y. Q. Wang would like to thank the financial support from Shandong Province “Double-Hundred Talent Plan” (Grant No.: WST2018006), Shandong Province High-end Foreign Experts Recruitment Program, and Qingdao International Center for Semiconductor Photoelectric Nanomaterials, and Shandong Provincial University Key Laboratory of

Guiju Liu received her Bachelor degree in Materials Physics from Qingdao University (China) in 2014. She obtained Master degree at Qingdao University (China) in 2017. Currently, she is a Ph.D. student majoring in Materials Physics and Chemistry at Qingdao University. Her research mainly focuses on the synthesis and structural characterization of quantum dots and their applications in luminescent solar concentrators and hydrogen generation.

References (30)

C. Corrado et al.
Optimization of gain and energy conversion efficiency using front-facing photovoltaic cell luminescent solar concentrator design
Sol. Energy Mater. Sol. Cells
(2013)
Z. Wang et al.
Carbon dots based nanocomposite thin film for highly efficient luminescent solar concentrators
Org. Electron.
(2018)
H. Zhao et al.
Quality factor of luminescent solar concentrators and practical concentration limits attainable with semiconductor quantum dots
Nano Energy
(2018)
G. Liu et al.
High efficiency sandwich structure luminescent solar concentrators based on colloidal quantum dots
Nano Energy
(2019)
M. Zhu et al.
Deep-red emitting zinc and aluminium co-doped copper indium sulfide quantum dots for luminescent solar concentrators
J. Colloid Interface Sci.
(2019)
M.R. Bergren et al.
High-performance CuInS₂ quantum dot laminated glass luminescent solar concentrators for windows
ACS Energy Lett
(2018)
L.J. Brennan et al.
Large area quantum dot luminescent solar concentrators for use with dye-sensitised solar cells
J. Mater. Chem. A
(2018)
D. Cambie et al.
A leaf-inspired luminescent solar concentrator for energy-efficient continuous-flow photochemistry
Angew. Chem. Int. Ed.
(2017)
M.J. Currie et al.
High-efficiency organic solar concentrators for photovoltaics
Science
(2008)
F. Meinardi et al.
Doped halide perovskite nanocrystals for reabsorption-free luminescent solar concentrators
ACS Energy Lett
(2017)

F. Meinardi et al.

Highly efficient large-area colourless luminescent solar concentrators using heavy-metal-free colloidal quantum dots

Nat. Nanotechnol.

(2015)

C.S. Erickson et al.

Zero-reabsorption doped-nanocrystal luminescent solar concentrators

ACS Nano

(2014)

W. Chen et al.

Heavy metal free nanocrystals with near infrared emission applying in luminescent solar concentrator

Solar RRL

(2017)

R. Mazzaro et al.

The renaissance of luminescent solar concentrators: the role of inorganic nanomaterials

Adv. Energy Mater.

(2018)

F. Meinardi et al.

Highly efficient luminescent solar concentrators based on earth-abundant indirect-bandgap silicon quantum dots

Nat. Photonics

(2017)

Cited by (23)

Color-tunable multilayered laminated luminescent solar concentrators based on colloidal quantum dots
2023, Nano Energy
Luminescent solar concentrators (LSC) are a promising technology for building integrated photovoltaics (BIPV). Besides obtaining satisfactory efficiencies and aesthetic appeal, a simple and low-cost fabrication process is required to deploy large-scale LSCs. Herein, we introduced a facile and cost-effective fabrication method to obtain laminated LSC (L-LSC) devices. By optimizing the fabrication parameters, L-LSC based on polymer substrates exhibited higher efficiency (power conversion efficiency, PCE=0.24%, external photon efficiency, η_ext=4.14% and optical efficiency, η_opt=3.46%) compared to glass-based L-LSC (PCE=0.09%, η_ext=1.59%, $η_{opt}$ =1.76%) due to their excellent optical properties and good compatibility with the laminated emissive layer. Using the optimized L-LSC device, a color-tunable multilayered L-LSC structure is then proposed. By embedding different QDs into two interlayers, the color appearance of the device can be tuned, simultaneously improving the overall efficiency. This study presents a notable advancement towards a practical application of L-LSCs with a satisfactory efficiency and color aesthetics for sustainable BIPVs.
Modification of CaS:Eu phosphor under mild conditions toward an extreme stability at harsh environment over 1.5 months
2023, Materials Letters: X
The chemical instability of CaS:Eu phosphors is a curial problem that hinders its practical application, especially under high temperature and humid environment. In this work, CaS:Eu capped by methacrylate-functionalized Si compound are successfully prepared under a mild condition, without seriously sacrificing the photoluminescence capability. The stability of the as-prepared samples is subsequently tested in stirred hot water (90 °C) for over a month, the outstanding hydrophobicity and chemical stability of the as-prepared samples sufficiently reserve the optical and chemical properties. Systematic characterizations are conducted to reveal the chemical features of the modified CaS:Eu phosphor.
Luminescence solar concentrators: A technology update
2023, Nano Energy
In this paper, we present a technology summary and update on the latest research advances in luminescent solar concentrators (LSCs). LSCs are optoelectronic devices based on a sun irradiation collector made of fluorophores that, after the solar radiation absorption, re-emit visible light propagating via a waveguide towards smaller area photovoltaic (PV) cells, which convert radiant energy into electricity. Here we review their basic principles, their performance analysis, and measurements, the various types of fluorophores so far employed, and the design and architectures proposed. We also include a brief review of the use of the energy transfer process and photonics to reduce their optical losses and improve their photons trapping efficiency. While their main application today is building integrated PV to meet future energy and emission targets, other envisaged alternative applications are also briefly summarised. The final performances in terms of electrical power conversion are linked to various fluorophores and device designs, while current limitations of scalability and stability are impeding their wider use.
High-efficiency luminescent solar concentrators based on Composition-tunable Eco-friendly Core/shell quantum dots
2023, Chemical Engineering Journal
Citation Excerpt :
Luminescent solar concentrators (LSCs) are large-scale sunlight collection/concentration devices comprised of an optical waveguide slab with embedded luminescent species and integrated PV cells, which have been applied to optimize the traditional PV systems since 1976 [10]. In a typical device operation process, the embedded luminophores in the waveguide can absorb the incident sunlight and re-emit the photons that are guided to the smaller edges of LSCs by total internal reflection, where the attached PV cells can generate photocurrent under concentrated light illumination [11–13]. In this case, once the power conversion efficiency (PCE) of the LSC is over 6 % [14], they are able to reduce the cost of PV systems via replacing the solar cells and hold great promise in building-integrated PV (BIPV) due to flexible design of their device parameters including the color, weight, geometry and transparency etc [15].
Luminescent solar concentrators (LSCs) fabricated using colloidal quantum dots (QDs) are considered as promising cost-effective solar collectors for future building-integrated photovoltaics (BIPV). Nevertheless, the solar-to-electricity conversion efficiency of the LSCs is commonly low due to limited quantum efficiency and large reabsorption loss of QDs. In addition, most of the efficient LSCs contain heavy metal-based QDs, limiting their potential commercial applications. Herein, we demonstrate a novel type of eco-friendly CuGaAlS/ZnS (CGAS/ZnS) core/shell QDs with efficient surface passivation and manipulated their optical properties by varying the copper contents, which effectively regulates the intrinsic band structure and radiative recombination dynamics. As a result, the optimal Cu-deficient CGAS/ZnS core/shell QDs exhibit the highest photoluminescence quantum yield (PLQY) of ∼ 91 % and large Stokes shift (∼0.81 eV). The prepared QDs were applied as emitters and integrated in polymer matrix to fabricate LSCs (10 × 10 × 0.15 cm³), delivering an unprecedented power conversion efficiency (PCE) of 4.29 % under standard one sun AM 1.5G illumination (100 mW cm⁻²). Our results imply that tuning the components of multinary environment-friendly core/shell QDs endows the feasibility to realize low-cost and high-efficiency BIPV applications.
Recent progress in organic luminescent solar concentrators for agrivoltaics: Opportunities for rare-earth complexes
2022, Solar Energy
Citation Excerpt :
Implementation of sustainable energy in net-zero energy buildings is being experimented with in less dense areas in contrast to overpopulated cities where limited space prohibits the installation of PV modules to satisfy the electricity needs of more significant structures. Over the last decade, LSCs have emerged as a favourable application for integrating solar energy harvesting and semi-transparent photovoltaics into building facades (Liu et al., 2020; Meinardi et al., 2017). The most conventional LSC configuration comprises a host polymer blended into luminescent materials, (Mateen et al., 2018) such as plastic sheets or thin films doped with fluorophores (Debije et al., 2021; Mazzaro and Vomiero, 2018; Papakonstantinou et al., 2021; Papucci et al., 2021a,b; Yang et al., 2022).
Agri-photovoltaics technology combines agriculture and photovoltaics to develop efficient plants and crops. Luminescent solar concentrators (LSCs), a type of solar photovoltaics (Agri-PV), could potentially revolutionize agricultural methods and electricity generation. We introduce the new notation Agri-LSC, which combines greenhouse agriculture with luminescent solar concentrators. In this context, many studies have previously focused on LSC devices based on organic dyes showing high photophysical performances used for Agri-PV. However, their vulnerabilities are exposed by issues such as reabsorption, photostability, and short Stokes-shift. Rare-earth complexes could overcome these limitations as an alternative to organic materials since they possess high photoluminescence quantum yields with a broad Stokes-shift. Furthermore, when mixed with host polymers, the high level of transparency of lanthanide complex-based LSCs permits the necessary light to pass unhindered through the device. Lanthanide complexes are also considered luminescent down-shifters (LDS), thus implying their ability to clear out UV light below 400 nm, known to be harmful to crops, and transform it into a proper visible light where the photosynthesis of plants is much higher.
Renewable energy for a green future: Electricity produced from efficient luminescent solar concentrators
2022, Solar Energy Advances
This article proposes an overarching review of the technologies engaged in world wide energy demand which uses from non-renewable to renewable energies. The electricity generated from renewable systems is largely reducing CO₂ emissions, one of the greenhouse gasses realesed from non-renewable energy sources that contribute to the global warming. The photovoltaic (PV) system is the technology with stronger potential to produce affordable electricity using solar energy. Therefore, we are focusing on the PVs regarding i) how they are assembled, ii) the energy losses from spectral mismatches, and iii) the improvements of their efficiencies by several ways, which include the connection of PVs with new techologies, e.g. the luminescent solar concentrator (LSC). Recent studies have reported advantages of applying LSCs connected to PVs’ cells, as well as some strategies for minimizing or eliminating self-absorption losses. Moreover, some efficiency meters evaluate LSCs’ operation. Guided by mainly recent researches, this article approaches flexibility, low cost, easy fabrication, and great efficiency of LSCs, the main goal for the PVs’ productions upon power electricity demand.

View all citing articles on Scopus

Raffaello Mazzaro received his Ph.D. in Chemistry in 2016, in collaboration between the CNR-IMM institute in Bologna and the chemistry department G. Ciamician of the University of Bologna, Italy. After working as a research fellow at Luleå University of Technology, Sweden, he is currently a postdoctoral fellow at CNR-IMM institute in Bologna.. His interests and past activities are mainly focused on energy conversion processes performed by optically active nanomaterials, such as quantum dots and metal oxides nanostructures.

Changchun Sun received his Bachelor Degree in Textile Engineering from Changchun University of Technology, China. He is currently a postgraduate student at Qingdao University, and his research direction focus on the flexible fiber catalytic electrode for hydrogen generation and supercritical carbon dioxide anhydrous dyeing.

Yuanming Zhang is an Associate Professor of College of Textiles & Clothing and State Key Laboratory of Bio-Fibers and Eco-Textiles, Qingdao University. He received Ph.D. degree (2018) from Donghua University. His research interests focus on the structure and performance of textile fiber materials, new textile materials, new processes and equipment, comprehensive development and utilization of environmentally friendly polymer materials.

Yiqian Wang received his Ph.D. degree in condensed matter physics from Institute of Physics, Chinese Academy of Sciences, China in 2001. Then he worked as a research fellow at INRS-EMT, Canada and Imperial College London, UK. He is currently a Professor at Qingdao University. His research interest includes the fabrication and characterization of nanomaterials, as well as exploitation of their potential applications.

Haiguang Zhao is a Professor of College of Physics & State Key Laboratory, Qingdao University, China. He received M.Sc. degree (2007) from Zhejiang University and Ph.D. degree (2012) from Institut National de la Recherche Scientifique (INRS), Quebec University. His research interests focus on the synthesis of low-dimensional semiconductor materials (including metal oxide, quantum dots, nanoplatelets and inorganic perovskite) for solar energy applications, such as solar cell, luminescent solar concentrator and solar-driven water splitting.

Guangting Han is a Professor of College of Textiles & Clothing and director of State Key Laboratory of Bio-Fibers and Eco-Textiles, Qingdao University. He received Master degree (1988) from China Textile University and Ph.D. degree (2006) from Donghua University. His research interests focus on the structure and performance of textile fiber materials, new textile materials, new processes and equipment, comprehensive development and utilization of environmentally friendly polymer materials.

Alberto Vomiero is a chair professor in Experimental Physics at the Department of Engineering Sciences and Mathematics, Luleå University of Technology, Sweden and a professor in Industrial Engineering at the Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Italy. He is leading a multidisciplinary group focusing on the development of advanced nanomaterials for energy and environmental applications, including solar cells, water splitting and photocatalysis. He is a former Marie Curie International Outgoing Fellow of the European Commission, Fellow of the Swedish Foundations, of the Royal Society of Chemistry, and several other Societies.

View full text

Full paperRole of refractive index in highly efficient laminated luminescent solar concentrators

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

The structure of the QDs

Conclusion and perspectives

Materials

Synthesis of CdSe/CdS core/shell QDs

Declaration of competing interest

Acknowledgements

Sol. Energy Mater. Sol. Cells

Org. Electron.

Nano Energy

Nano Energy

J. Colloid Interface Sci.

High-performance CuInS2 quantum dot laminated glass luminescent solar concentrators for windows

ACS Energy Lett

Large area quantum dot luminescent solar concentrators for use with dye-sensitised solar cells

J. Mater. Chem. A

A leaf-inspired luminescent solar concentrator for energy-efficient continuous-flow photochemistry

Angew. Chem. Int. Ed.

High-efficiency organic solar concentrators for photovoltaics

Science

Doped halide perovskite nanocrystals for reabsorption-free luminescent solar concentrators

ACS Energy Lett

Highly efficient large-area colourless luminescent solar concentrators using heavy-metal-free colloidal quantum dots

Nat. Nanotechnol.

Zero-reabsorption doped-nanocrystal luminescent solar concentrators

ACS Nano

Heavy metal free nanocrystals with near infrared emission applying in luminescent solar concentrator

Solar RRL

The renaissance of luminescent solar concentrators: the role of inorganic nanomaterials

Adv. Energy Mater.

Highly efficient luminescent solar concentrators based on earth-abundant indirect-bandgap silicon quantum dots

Nat. Photonics

Full paper
Role of refractive index in highly efficient laminated luminescent solar concentrators

High-performance CuInS₂ quantum dot laminated glass luminescent solar concentrators for windows