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Special Issue "Advanced Dye-Sensitized Solar Cells"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "B1: Solar Energy and Photovoltaic Systems".

Deadline for manuscript submissions: closed (31 March 2020) | Viewed by 11791

Special Issue Editor

Prof. Dr. Jun-ichi Fujisawa
E-Mail Website
Guest Editor
Graduate School of Science and Technology, Gunma University, Kiryu, Gunma, Japan
Interests: physical chemistry; materials science; organic-inorganic hybrid material; solar cell; electron transfer; interfacial electron transfer transition

Special Issue Information

Dear Colleagues,

Dye-sensitized solar cells have attracted much attention as a next-generation solar cell and, recently, as an indoor power source for IoT devices, because of the characteristic feature of the stable output of the photovoltage and energy conversion efficiency even under weak light illumination. Moreover, it is noteworthy that dye-sensitized solar cells have already been put to practical use, showing the commercial viability. The highest energy conversion efficiency of dye-sensitized solar cells is reported to be ca. 14%, and there is still plenty of room to further improve the energy conversion efficiency. For this purpose, sustained fundamental research is required not only for the development of high performance dyes, photoanode (TiO2, etc.), and redox species, but also for the exploration of a new mechanism to overcome the energy loss in dye-sensitized solar cells such as a direct photocarrier injection mechanism.

This Special Issue aims to contribute to advanced dye-sensitized solar cells through enhanced scientific and multi-disciplinary knowledge to improve the cell performance and stability. We therefore invite papers and reviews on fundamental research and innovative technical developments from different disciplines to pave the way to advanced dye-sensitized solar cells.

Prof. Dr. Jun-ichi Fujisawa
Guest Editor

Manuscript Submission Information

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Keywords

  • dye-sensitized solar cells
  • dye design
  • metal-oxide semiconductors
  • redox species
  • direct photocarrier injection
  • interfacial charge-transfer transitions
  • computational analysis
  • indoor applications

Published Papers (10 papers)

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Research

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Article
Annealing-Temperature Dependent Carrier-Transportation in ZnO/PbS Quantum Dot Solar Cells Fabricated Using Liquid-Phase Ligand Exchange Methods
Energies 2020, 13(19), 5037; https://doi.org/10.3390/en13195037 - 24 Sep 2020
Viewed by 997
Abstract
We constructed ZnO/PbS quantum dot (QD) heterojunction solar cells using liquid-phase ligand exchange methods. Colloidal QD solutions deposited on ZnO-dense layers were treated at different temperatures to systematically study how thermal annealing temperature affected carrier transport properties. The surface of the layers became [...] Read more.
We constructed ZnO/PbS quantum dot (QD) heterojunction solar cells using liquid-phase ligand exchange methods. Colloidal QD solutions deposited on ZnO-dense layers were treated at different temperatures to systematically study how thermal annealing temperature affected carrier transport properties. The surface of the layers became dense and smooth as the temperature approached approximately 80 °C. The morphology of layers became rough for higher temperatures, causing large grain-forming PbS QD aggregation. The number of defect states in the layers indicated a valley-shaped profile with a minimum of 80 °C. This temperature dependence was closely related to the amount of residual n-butylamine complexes in the PbS QD layers and the active layer morphology. The resulting carrier diffusion length obtained on the active layers treated at 80 °C reached approximately 430 nm. The solar cells with a 430-nm-thick active layer produced a power conversion efficiency (PCE) of 11.3%. An even higher PCE is expected in solar cells fabricated under optimal annealing conditions. Full article
(This article belongs to the Special Issue Advanced Dye-Sensitized Solar Cells)
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Article
Density Functional Theory-Based Molecular Modeling: Verification of Decisive Roles of Van der Waals Aggregation of Triiodide Ions for Effective Electron Transfer in Wet-Type N3-Dye-Sensitized Solar Cells
Energies 2020, 13(11), 3027; https://doi.org/10.3390/en13113027 - 11 Jun 2020
Cited by 5 | Viewed by 1270
Abstract
Density functional theory-based molecular modeling (DFT/MM) validates that KI and I2 undergo exothermic van der Waals (vdW) aggregation in acetonitrile (AN) or in the presence of 4-tert-butylpyridine (TBP), forming potassium triiodide (KI3) and, further mutual vdW aggregation leads to the [...] Read more.
Density functional theory-based molecular modeling (DFT/MM) validates that KI and I2 undergo exothermic van der Waals (vdW) aggregation in acetonitrile (AN) or in the presence of 4-tert-butylpyridine (TBP), forming potassium triiodide (KI3) and, further mutual vdW aggregation leads to the formation of (KI3)2 and AN, (KI3)2 and (AN)2 and (KI3)2 and TBP in the AN-based Dye sensitized solar cells (DSSC) electrolytes. All KI3 aggregates have a very low energy gap, 0.17 eV, 0.14 eV and 0.05 eV of lowest unoccupied molecular orbital (LUMO) + 1 and LUMO, respectively, verifying efficient electron diffusion in μm-thick DSSC electrolytes. Hydrogen-bonding aggregation of anatase TiO2 model, Ti9O18H and OH, with N3 (proton) dye is also validated by DFT/MM, and the energy structure verifies unidirectional electron flow from highest occupied molecular orbital (HOMO) on thiocyanide (SCN) groups of N3 dye to LUMO on the TiO2 model at the aggregates. Further, DFT/MM for the aggregation of K+I3 with N3 verifies the most exothermic formation of the aggregate of N3 (proton) and K+I3. The UV-Vis spectra of N3 (proton) and K+I3 is consistent with reported incident photocurrent efficiency (IPCE) action spectra (λ = 450–800 nm) of N3-sensitized DSSC, verifying that the N3 dye of N3 (proton) and K+I3 becomes an effective sensitizer in the anode / TiO2 / N3 (proton) / KI/I2 / acetonitrile (AN) / cathode structured DSSC. The energy structure of LUMO and LUMO + 1 of the aggregates, Ti9O18H and OH and N3 (proton), N3 and K+I3, (KI3)2 and AN and (KI3)2 and TBP verifies high IPCE photocurrent and effective electron diffusion via KI3-aggregates in the DSSC of Ti9O18H and OH and N3 (proton) and K+I3. Full article
(This article belongs to the Special Issue Advanced Dye-Sensitized Solar Cells)
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Article
Magnetron Sputtered Electron Blocking Layer as an Efficient Method to Improve Dye-Sensitized Solar Cell Performance
Energies 2020, 13(11), 2690; https://doi.org/10.3390/en13112690 - 27 May 2020
Cited by 1 | Viewed by 906
Abstract
The main efficiency loss is caused by an intensive recombination process at the interface of fluorine-doped tin oxide (FTO) and electrolyte in dye-sensitized solar cells. Electrons from the photoanode can be injected back to the redox electrolyte and, thus, can reduce the short [...] Read more.
The main efficiency loss is caused by an intensive recombination process at the interface of fluorine-doped tin oxide (FTO) and electrolyte in dye-sensitized solar cells. Electrons from the photoanode can be injected back to the redox electrolyte and, thus, can reduce the short circuit current. To avoid this, the effect of the electron blocking layer (EBL) was studied. An additional thin film of magnetron sputtered TiO2 was deposited directly onto the FTO glass. The obtained EBL was characterized by atomic force microscopy, scanning electron microscopy, optical profilometry, energy dispersive spectroscopy, Raman spectroscopy and UV-VIS-NIR spectrophotometry. The results of the current–voltage characteristics showed that both the short circuit current (Isc) and fill factor (FF) increased. Compared to traditional dye-sensitized solar cell (DSSC) architecture, the power conversion efficiency (η) increased from 4.67% to 6.07% for samples with a 7 × 7 mm2 active area and from 2.62% to 3.06% for those with an area of 7 × 80 mm2. Full article
(This article belongs to the Special Issue Advanced Dye-Sensitized Solar Cells)
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Article
3D Structural Optimization of Zinc Phthalocyanine-Based Sensitizers for Enhancement of Open-Circuit Voltage of Dye-Sensitized Solar Cells
Energies 2020, 13(9), 2288; https://doi.org/10.3390/en13092288 - 05 May 2020
Cited by 1 | Viewed by 750
Abstract
We designed and synthesized two zinc phthalocyanine sensitizers (PcS27 and PcS28), substituted with branched or cyclic alkoxy chains, to investigate the structural effect of peripheral alkyl chains on the performance of dye-sensitized TiO2 solar cells. The bulky cyclic alkyl chains [...] Read more.
We designed and synthesized two zinc phthalocyanine sensitizers (PcS27 and PcS28), substituted with branched or cyclic alkoxy chains, to investigate the structural effect of peripheral alkyl chains on the performance of dye-sensitized TiO2 solar cells. The bulky cyclic alkyl chains of PcS28 decreased the adsorption density of PcS28 on the TiO2 electrode, while the terminal branches of alkoxy chains of PcS27 did not influence the adsorption density in comparison to the previously published PcS20 with linear alkoxy chains. Under one sun conditions, PcS27 cells exhibited higher open-circuit voltage but a slightly lower energy conversion efficiency, 6.0% less than PcS20. These results suggest that the small alternation of alkoxy chains resulted in decreasing electron pushing ability of peripheral phenoxy units, giving lower short-circuit current. Full article
(This article belongs to the Special Issue Advanced Dye-Sensitized Solar Cells)
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Article
Study of How Photoelectrodes Modified by TiO2/Ag Nanofibers in Various Structures Enhance the Efficiency of Dye-Sensitized Solar Cells under Low Illumination
Energies 2020, 13(9), 2248; https://doi.org/10.3390/en13092248 - 04 May 2020
Cited by 10 | Viewed by 997
Abstract
Dye-sensitized solar cells (DSSCs) are low-cost solar cells belonging to the thin-film photovoltaic cell type. In this study, we studied the photovoltaic performances of DSSCs based on titanium dioxide (TiO2) nanofibers (NFs) containing silver (Ag) nanoparticles (NPs) under low illumination. We [...] Read more.
Dye-sensitized solar cells (DSSCs) are low-cost solar cells belonging to the thin-film photovoltaic cell type. In this study, we studied the photovoltaic performances of DSSCs based on titanium dioxide (TiO2) nanofibers (NFs) containing silver (Ag) nanoparticles (NPs) under low illumination. We used the sol-gel method with the electrospinning technique to prepare the TiO2 NFs containing Ag NPs. Herein, we used two ways to add TiO2/Ag NFs to modify the photoelectrode successfully and enhance the performance of DSSCs. One way was that the TiO2/Ag NFs were mixed with pristine TiO2; the other way was that the TiO2/Ag NFs were seeded beside the TiO2 colloid layer as an additional layer on the photoelectrode of the DSSC. According to this experiment, the photovoltaic conversion efficiency of the DSSC which had TiO2/Ag NF seeded as an additional layer on the photoelectrode (5.13%) was increased by 28% compared to the DSSC without the photoelectrode modification (3.99%). This was due to the suppression of electron recombination and the more effective utilization of the light radiation by adding the TiO2/Ag NFs. Because of the good conductivity of Ag, the electrons were quickly transported and electron recombination was reduced. In addition, the photovoltaic conversion efficiency of the DSSC which had TiO2/Ag NF seeded as an additional layer on the photoelectrode increased from 5.13% to 6.23% during the decrease in illumination from 100 mW/cm2 to 30 mW/cm2; however, its photovoltaic conversion efficiency decreased to 5.31% when the illumination was lowered to 10 mW/cm2. Full article
(This article belongs to the Special Issue Advanced Dye-Sensitized Solar Cells)
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Article
Quantification of Dyes Generating Photocurrent and/or Photoluminescence in Dye-Sensitized Solar Cells Using Laser Scanning Microscopy
Energies 2020, 13(8), 1866; https://doi.org/10.3390/en13081866 - 11 Apr 2020
Cited by 3 | Viewed by 1046
Abstract
Photoconversion processes such as electron injection (photooxidation) and dye regeneration (reduction) in dye-sensitized solar cells (DSSCs) occur at considerably inhomogeneous semiconductor/dye/electrolyte interfaces, implying a very high heterogeneity of interfacial photoconversion kinetics. Herein, we present a temporally and spatially resolved investigation of DSSCs comprising [...] Read more.
Photoconversion processes such as electron injection (photooxidation) and dye regeneration (reduction) in dye-sensitized solar cells (DSSCs) occur at considerably inhomogeneous semiconductor/dye/electrolyte interfaces, implying a very high heterogeneity of interfacial photoconversion kinetics. Herein, we present a temporally and spatially resolved investigation of DSSCs comprising a cover glass photoanode with a 100-nm thick TiO2 layer loaded with the metal-free organic dye sensitizer MK-2, which is performed by employing laser scanning microscopy (LSM) for the simultaneous measurement of the photocurrent (PC) and photoluminescence (PL) of DSSCs under short-circuit conditions. Analysis of PL decay curves and the excitation rate dependences of PC and PL obtained for local (or submicrometric) areas of the MK-2-DSSC allows disclosing and quantifying three types of dyes coexisting in the DSSCs: (i) a dye that only generates PC (“PC-dye,” 75% of total dye molecules in the DSSC), (ii) a dye that generates both PC and PL (“PCPL-dye,” 20%), and (iii) a dye that only generates PL (“PL-dye,” 5%). Considering recent theoretical reports on cyanoacrylic dyes, we propose that the PC-dye and the PCPL-dye are covalently bound on a TiO2 surface with different adsorption modes (presumably bidentate and tridentate bridging configurations), whereas the PL-dye is noncovalently trapped within a mesoporous TiO2 film. Full article
(This article belongs to the Special Issue Advanced Dye-Sensitized Solar Cells)
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Article
“Paper Dye-Sensitized Solar Cell” Based on Carbon-Nanotube-Composite Papers
Energies 2020, 13(1), 57; https://doi.org/10.3390/en13010057 - 20 Dec 2019
Cited by 5 | Viewed by 1152
Abstract
We propose a paper solar cell based on carbon nanotube (CNT)-composite papers. To fabricate this cell, we use dye-sensitized solar cells (DSCs) for generating power through the redox reaction of dyes in conjunction with CNT-composite papers, which are composite materials containing CNTs and [...] Read more.
We propose a paper solar cell based on carbon nanotube (CNT)-composite papers. To fabricate this cell, we use dye-sensitized solar cells (DSCs) for generating power through the redox reaction of dyes in conjunction with CNT-composite papers, which are composite materials containing CNTs and pulp (raw paper material) that can be fabricated easily by using a method based on the Japanese washi papermaking technique. The demand for CNT applications is expected to increase due to their high conductivity and metallic or semiconducting characteristics. This CNT-composite paper can also have metallic or semiconducting characteristics based on the contained CNTs in the composite paper. We previously fabricated a DSC that generates electricity by using CNT-composite papers stacked in a typical DSC structure. However, the conversion efficiency of this DSC was just 0.188%, which is not practical. To overcome this low power generation issue, we tried improving the DSC structure by applying electrodes to the CNT-composite papers in grid patterns for efficient current collection and applying an optimally mixed dye for efficient electron excitation. Results showed that the conversion efficiency improved to 0.58%. Moreover, we demonstrated that using a mixed dye can improve the conversion efficiency of the paper DSC. We expect these types of CNT-composite papers to be used as material for new DSCs. Full article
(This article belongs to the Special Issue Advanced Dye-Sensitized Solar Cells)
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Article
Dye-Sensitized Solar Cells Using Aluminum-Doped Zinc Oxide/Titanium Dioxide Photoanodes in Parallel
Energies 2019, 12(18), 3469; https://doi.org/10.3390/en12183469 - 09 Sep 2019
Cited by 4 | Viewed by 1256
Abstract
In this study, both zinc oxide (ZnO) nanorods and aluminum-doped zinc oxide (AZO) nanosheets were deposited by hydrothermal growth on fluorine-doped tin oxide (FTO) glass. After a photoanode was added to ZnO nanorods or AZO nanosheets, the photovoltaic conversion efficiency (PCE) increased due [...] Read more.
In this study, both zinc oxide (ZnO) nanorods and aluminum-doped zinc oxide (AZO) nanosheets were deposited by hydrothermal growth on fluorine-doped tin oxide (FTO) glass. After a photoanode was added to ZnO nanorods or AZO nanosheets, the photovoltaic conversion efficiency (PCE) increased due to improved electron transport and enhanced dye absorption. The improvement in electron transport was verified by electrochemical impedance spectroscopy (EIS), and the increase in dye absorption was verified by ultraviolet-visible spectroscopy. Both of these factors facilitated an increase in PCE. Parameters for dye-sensitized solar cells (DSSCs) using ZnO nanorods/TiO2 and AZO nanosheets/TiO2 photoanodes were tested and the results were recorded using EIS. The results indicated that the addition of the ZnO nanorods increased the short-circuit current density (Jsc) from 9.07 mA/cm2 to 10.91 mA/cm2, the open circuit voltage (Voc) from 0.68 V to 0.70 V, and the PCE from 3.70% to 4.73%, respectively. When the DSSCs were produced in a parallel silver-grid device, the results showed that PCE could be increased from 3.67% to 4.04% due to the reduction in connection resistance. Full article
(This article belongs to the Special Issue Advanced Dye-Sensitized Solar Cells)
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Review

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Review
Interfacial Charge-Transfer Transitions for Direct Charge-Separation Photovoltaics
Energies 2020, 13(10), 2521; https://doi.org/10.3390/en13102521 - 15 May 2020
Cited by 8 | Viewed by 977
Abstract
Photoinduced charge separation (PCS) plays an essential role in various solar energy conversions such as photovoltaic conversion in solar cells. Usually, PCS in solar cells occurs stepwise via solar energy absorption by light absorbers (dyes, inorganic semiconductors, etc.) and the subsequent charge transfer [...] Read more.
Photoinduced charge separation (PCS) plays an essential role in various solar energy conversions such as photovoltaic conversion in solar cells. Usually, PCS in solar cells occurs stepwise via solar energy absorption by light absorbers (dyes, inorganic semiconductors, etc.) and the subsequent charge transfer at heterogeneous interfaces. Unfortunately, this two-step PCS occurs with a relatively large amount of the energy loss (at least ca. 0.3 eV). Hence, the exploration of a new PCS mechanism to minimize the energy loss is a high-priority subject to realize efficient solar energy conversion. Interfacial charge-transfer transitions (ICTTs) enable direct PCS at heterogeneous interfaces without energy loss, in principle. Recently, several progresses have been reported for ICTT at organic-inorganic semiconductor interfaces by our group. First of all, new organic-metal oxide complexes have been developed with various organic and metal-oxide semiconductors for ICTT. Through the vigorous material development and fundamental research of ICTT, we successfully demonstrated efficient photovoltaic conversion due to ICTT for the first time. In addition, we revealed that the efficient photoelectric conversion results from the suppression of charge recombination, providing a theoretical guiding principle to control the charge recombination rate in the ICTT system. These results open up a way to the development of ICTT-based photovoltaic cells. Moreover, we showed the important role of ICTT in the reported efficient dye-sensitized solar cells (DSSCs) with carboxy-anchor dyes, particularly, in the solar energy absorption in the near IR region. This result indicates that the combination of dye sensitization and ICTT would lead to the further enhancement of the power conversion efficiency of DSSC. In this feature article, we review the recent progresses of ICTT and its application in solar cells. Full article
(This article belongs to the Special Issue Advanced Dye-Sensitized Solar Cells)
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Other

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Perspective
Copper Coordination Complexes for Energy-Relevant Applications
Energies 2020, 13(9), 2198; https://doi.org/10.3390/en13092198 - 02 May 2020
Cited by 9 | Viewed by 1796
Abstract
Copper coordination complexes have emerged as a group of transition metal complexes that play important roles in solar energy conversion, utilization and storage, and have the potential to replace the quintessential commonly used transition metals, like Co, Pt, Ir and Ru as light [...] Read more.
Copper coordination complexes have emerged as a group of transition metal complexes that play important roles in solar energy conversion, utilization and storage, and have the potential to replace the quintessential commonly used transition metals, like Co, Pt, Ir and Ru as light sensitizers, redox mediators, electron donors and catalytic centers. The applications of copper coordination compounds in chemistry and energy related technologies are many and demonstrate their rightful place as sustainable, low toxicity and Earth-abundant alternative materials. In this perspective we show the most recent impact made by copper coordination complexes in dye-sensitized solar cells and other energy relevant applications. Full article
(This article belongs to the Special Issue Advanced Dye-Sensitized Solar Cells)
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