Effect In Dye-sensitized Solar Cells Research Articles

Magnetic field modulation effect of photoelectric properties in dye-sensitized solar cells with La0.67(Ca,Ba)0.33MnO3 as counter electrodes.

In recent years, many semiconductor materials with unique band structures have been used as Pt counter electrode (CE) substitutes for dye-sensitized solar cells (DSSCs), which makes the photoelectric properties of DSSCs possible to be modulated by electric field, magnetic field, and light field. In this work, La0.67(Ca Ba)0.33MnO3 (LCBMO) thin film is employed to act as CE in DSSCs. The experimental results indicate that short-circuit current density and photoelectric conversion efficiency present better stability when applying an external magnetic field to the DSSCs. Furthermore, both the exchange current density (J0) and limit diffusion current density (Jlim) are largely enhanced by an external magnetic field. J0 increases from -0.51 mA•cm-2 to -0.65 mA•cm-2, and Jlim increases from 0.2 mA•cm-2 to 0.3 mA•cm-2 when applying a magnetic field of 0.25 T. The fitting results of the impedance test verify that the magnetic field reduces the value of Rct. Both magnetic-field enhancing catalytic activity and CMR effect jointly promote the increase of photocurrent and finally improve the photovoltaic effect in DSSCs.

Investigation of the photovoltaic effect in dye‐sensitized solar cells based on poly(ethylene glycol)‐nanofiber electrolytes

AbstractIn this study, the effectiveness of electrospun poly(ethylene glycol) (PEG) nanofibers as polymer electrolytes for dye‐sensitized solar cells (DSSCs) is evaluated. Regular PEG nanofibers are electrospun at an applied voltage of 15 kV, using a polymer concentration of 13 wt% and tip‐to‐collector distance of 20 cm. Subsequently, the photovoltaic effect in DSSCs containing PEG‐nanofiber electrolytes with different I2 concentrations is analyzed. On reducing the concentration of I2 in the PEG‐nanofiber electrolyte, the short‐circuit photocurrent density (Jsc) of the corresponding DSSC increases significantly. A high power‐conversion efficiency of 5.93% is recorded (by a solar simulator under AM 1.5 illumination) for a PEG‐nanofiber‐based DSSC containing an I2/tetrabuthylammonium iodide (TBAI) molar ratio of 0.25. Additionally, electrochemical impedance spectroscopy is used to analyze the charge‐transfer resistance of the TiO2/PEG‐nanofiber electrolyte interface in the fabricated DSSCs; the electrolyte uptake, ionic conductivity, and charge‐transfer resistance values are investigated as a function of the molar ratio of I2/TBAI.

Enhancement of highly efficient flavone-based organic dyes with different anchoring groups effect in dye-sensitized solar cells using experimental and TD-DFT study

Enhancement of highly efficient flavone-based organic dyes with different anchoring groups effect in dye-sensitized solar cells using experimental and TD-DFT study

Photovoltaics and its magnetic-field promotion effect in dye-sensitized solar cells with BiFeO3 + TiO2 composite photoanodes

In dye-sensitized solar cells (DSSCs), the light absorbance of photoanode is the most important factor in power conversion efficiency (PCE). Here the authors report on an alternative modified TiO2-based photoanode for obtaining enhanced photovoltaic (PV) properties in DSSCs. Multiferroics BiFeO3, which possesses excellent magnetic, electric, and photocatalytic performances, was employed to construct BiFeO3 + TiO2 composite photoanode for DSSCs. In this type of DSSCs with BiFeO3 + TiO2 composite photoanodes, BiFeO3 with suitable bandgap may also act as photoelectric conversion medium, which is generally acted by dye in DSSCs, and increases photogenerated carrier transport channels, which improves the PCE of DSSCs with BiFeO3 + TiO2 composite photoanodes. More importantly, magnetic-field enhanced PV properties in abovementioned DSSCs was firstly obtained, which may result from magnetic-field-suppression the recombination of charge carriers and magnetoresistance effect in BiFeO3. The investigated results offer both an alternative method to improve PV properties in DSSCs, and a referential train of thought to manipulate photoelectric properties of solar cells.

Impact of coupled plasmonic effect with multishaped silver nanoparticles on efficiency of dye sensitized solar cells

Dye sensitized solar cells (DSSCs) have numerous advantages, but in order to use widespread industrial deployment we need to boost the power conversion efficiency. One promising approach to improve DSSC performance is to improve the spectral response of sensitizers with metal nanoparticle-based surface plasmon resonance. Even single shaped nanoparticles (NPs), however, have physical limitations. Thus, in this study a simple synthesis route is used to fabricate multishaped silver (Ag) NPs to create a coupled plasmonic effect in DSSC to cover more of the solar spectrum. The impact of multishaped AgNPs combinations are studied to determine which aspects improve the power conversion efficiency of DSSC. A detailed investigation was made of both the TiO2 (XRD) and AgNPs (UV–Vis spectrometry) to couple the impacts on the DSSC (I-V) with the combination of the morphologies (TEM and FESEM) of AgNPs. Synthesized AgNPs with distinct extinction cross section covers the visible and IR regime from 300 nm to 1100 nm by tuning its plasmonics band. It is inferred that multi-shaped AgNPs predominately enhance the light harvesting, charge separation and carrier transportation. The results show that the increment in short circuit current and open circuit voltage resulted in an increase of 45% overall power conversion efficiency in the standard DSSC device is attributed to the usage of multi-shaped AgNPs. Finally, a mechanism is proposed to support the outcome of the experiment by demonstrating the extinction cross section and the local field of the various shaped AgNPs using Finite-difference time-domain (FDTD) simulation.

Investigation of photovoltaic properties of dye-sensitized solar cells based on azo dyes contain various anchoring groups

Purpose The purpose of this paper is to study the substituent effect in dye-sensitized solar cells’ (DSSCs) performance. For this end, three new metal organic dyes with DPA structure were synthesized. For investigation of the substituent effect, two different anchoring groups, namely, 1,3-dioxo-1Hbenz[de]isoquinolin-2(3H)-yl)benzenesulfonamides and 1,8-naphthalimide, were used. Design/methodology/approach Three organic dyes based on azo were selected, which contain various electron donor groups. Absorption properties of purified dyes were studied in solution and on photoelectrode (TiO2 and ZnO) substrate. DSSCs were prepared to determine the photovoltaic performance of each photosensitizer. Findings The results showed that all organic dyes form J-aggregation on the photoanode substrate. Cyclic voltammetry results for all organic dyes ensured an energetically permissible and thermodynamically favorable charge transfer throughout the continuous cycle of photo-electric conversion. The results illustrate conversion efficiencies of cells based on solution Dyes 1, 2 and 3 and TiO2 as 3.44, 4.71 and 4.82 per cent, respectively. The conversion efficiencies of cells based on solution Dye 1, 2 and 3 and ZnO are 3.21, 4.09 and 4.14 per cent, respectively. Practical implications In this study, the development of effect of assembling materials, offering improved photovoltaic properties. Social implications Organic dye attracts more and more attention because of its low-cost, facile route synthesis and less-hazardous properties. Originality/value To the best of the authors’ knowledge, the effect of anchoring agent and nanostructure on DSSCs performance was investigated for the first time.

Plasmonic and charging effects in dye-sensitized solar cells with Au nanoparticles incorporated into the channels of freestanding TiO2 nanotube arrays by an electrodeposition method

Au nanoparticles (NPs) were incorporated into the channels of freestanding TiO2 nanotube arrays (TNTAs) by an electrodeposition method and then applied to dye-sensitized solar cells (DSSCs) for light harvesting to improve the power conversion efficiency (PCE). The average size of Au NPs incorporated into TNTA channels was approximately 70nm, and the extinction of the Au NPs by UV–vis spectra was approximately 530nm, which is similar to the absorbance of the ruthenium dye (N719) used in DSSCs. The PCE of DSSCs based on TNTAs containing Au NPs increased to 6.80% from a PCE of 5.66% without Au NPs, an enhancement of 20.14% owing to light harvesting from the NP plasmonic and charging effects. However, the PCE of DSSCs based on TNTAs with excess Au NPs decreased from 6.80% to 5.49% due to aggregation of the Au NPs, which led to a decreased open-circuit voltage and fill factor.

Rational design of D-π-A organic dyes to prevent "trade off" effect in dye-sensitized solar cells.

It is an easy task to simulate the spectrum properties for the organic dyes applied in dye-sensitized solar cells (DSSCs) if the suitable method is chosen. However, it is still difficult to quantitatively determine the overall performance for them. In this work, the short-circuit photocurrent density (JSC) and open circuit photovoltage (VOC) are quantitatively calculated by combination of the density functional theory and first principle for DSSCs based on four different organic dyes, 2-((4'-((4-(bis(4-methoxyphenyl)amino)phenyl)diazenyl)biphenyl-4-yl)methylene)but-3-ynoic acid (1), 2-((5-(4-((4-(bis(4-methoxyphenyl)amino)phenyl)diazenyl)phenyl)thiophen-2-yl)methylene)but-3-ynoic acid (2), 3-(7-(4-((4-(bis(4-methoxyphenyl)amino)phenyl)diazenyl)-4H-cyclopenta[2,1-b:3,4-b']-dithiophene)-2-cyanoacrylic acid (3), and 3-(7-(4-((4-(bis(4-methoxyphenyl)amino)phenyl)diazenyl)phenyl)-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2-cyanoacrylic acid (4), in which the triarylamine is donor and the cyanoacrylic acid is acceptor along with variable π group. The 3 and 4 are new theoretically designed organic dyes on the basis of 1 and 2 with different electron-rich group as π group. Both JSC and VOC of 3 and 4 are improved as compared with those of 1 and 2, which breaks the normal "trade-off" rule. As a result, the power conversion efficiency (PCE) of 3 and 4 is improved, especially for 3. The aggregation effect is also considered to evaluate the overall performance, which is favorable to further enhance the reliability of theoretical design.

Aging effect in dye-sensitized solar cells sealed with thermoplastic films

PurposeThe purpose of this paper is to elucidate the aging effect in dye-sensitized solar cells (DSSCs) sealed with thermoplastic film and to compare it with unsealed DSSCs.Design/methodology/approachThe paper presents the steps of the fabrication of standard DSSC, as well as the DSSC-sealing processes, by using thermoplastic film. Current-voltage characterization was performed to observe the changes in efficiency, fill factor, short circuit current density and open circuit voltage for both unsealed and sealed DSSCs for aging time up to 336 h.FindingsThe unsealed DSSC showed significant drop in efficiency from 4.26 to 2.42 per cent within the first 5.5 h of aging time because of the leakage and volatilization of the solvent in the electrolyte. On the other hand, the sealed DSSC exhibited a gradual improvement of efficiency from 4.16 to 4.73 per cent after the first 216 h of aging time. The initial efficiency increment can be ascribed to the improved adsorption of electrolyte into the titanium dioxide film because of the gradual desorption of excess dye from TiO2 with increasing aging time.Originality/valueThis paper demonstrates the importance of the proper sealing process for the long-term operation of DSSC.

Influence of TiO2 Particle Size on Dye-Sensitized Solar Cells Employing an Organic Sensitizer and a Cobalt(III/II) Redox Electrolyte

Dye-sensitized solar cells (DSSCs) are highly efficient and reliable photovoltaic devices that are based on nanostructured semiconductor photoelectrodes. From their inception in 1991, colloidal TiO2 nanoparticles (NPs) with the large surface area have manifested the highest performances and the particle size of around 20 nm is generally regarded as the optimized condition. However, though there have been reports on the influences of particle sizes in conventional DSSCs employing iodide redox electrolyte, the size effects in DSSCs with the state-of-the-art cobalt electrolyte have not been investigated. In this research, systematic analyses on DSSCs with cobalt electrolytes are carried out by using various sizes of NPs (20–30 nm), and the highest performance is obtained in the case of 30 nm sized TiO2 NPs, indicating that there is a reversed power conversion efficiency trend when compared with those with the iodide counterpart. Detailed investigations on various factors—light harvesting, charge injection, d...

Freeze-casted TiO2 photoelectrodes with hierarchical porous structures for efficient light harvesting ability in dye-sensitized solar cells

Hierarchical porous TiO2 photoelectrodes fabricated using freeze-casting method were introduced for efficient light scattering effect in dye-sensitized solar cells (DSSCs). Unique porous microstructures (lamellar or interconnected pore structures) were obtained by controlling the concentrations of slurry and binder. The freeze-casted photoelectrodes exhibited stronger light scattering effects than conventionally screen-printed mesoporous photoelectrode. This is attributed to a great number of scattering sites (interconnected pores with the size range of 50–500nm), which are uniformly distributed throughout the entire freeze-casted photoelectrodes, resulting in an enhancement of the light pathway. As a result, despite a lower dye adsorption and less kinetically efficient charge transport, DSSCs based on freeze-casted photoelectrodes showed significant conversion efficiencies (3.64%) compared with those of DSSCs based on conventionally screen-printed photoelectrodes (2.57%). This study suggests that the hierarchical porous photoelectrodes fabricated using the freeze-casting are promising candidates for highly efficient DSSCs.

Quantitative investigation of local electric field through absorption spectrum in dye‐sensitized solar cells: Atomistic simulations

AbstractThe local transient electric field in dye‐sensitized solar cells (DSSCs), created by heterointerfacial charge transfer on illumination, exerts an important role in the internal photoelectronic processes occurring at dye/semiconductor heterointerface in the time‐resolved measurement, for example, transient absorption spectroscopy. Herein, on the basis of theoretical simulations, we proposed a general strategy to quantitatively examine the nature of local electric field (microscopic nature) through absorption spectra of adsorbed dye molecule (macroscopic observation). A controllably modulated external electric field is imposed on the sensitized system to couple to local electric field, resulting in the absorption spectrum shift of ground‐state dye molecules. By fitting absorption spectrum under applied external electric field with Gauss–Stark equation, the quantitative property of local electric field would be obtained. The Gauss–Stark equation reflects the quantitative relationship between the local electric field and absorption spectrum shift of adsorbed ground‐state dye molecule. Our study not only provides origin and magnitude of Stark effect in DSSCs but also offers a promising route to explore the elementary photoelectronic processes experimentally and theoretically.

Influence of size and shape of sub-micrometer light scattering centers in ZnO-assisted TiO2 photoanode for dye-sensitized solar cells

Sub-micrometer cavities have been incorporated in the TiO2 photoanode of dye-sensitized solar cell to enhance its optical property with light scattering effect. These are large pores of several hundred nanometers in size and scatter incident light due to the difference refraction index between the scattering center and the surrounding materials, according to Mie theory. The pores are created using polystyrene (PS) or zinc oxide (ZnO) templates reported previously which resulted in ellipsoidal and spherical shapes, respectively. The effect of size and shape of scattering center was modeled using a numerical analysis finite-difference time-domain (FDTD). The scattering cross-section was not affected significantly with different shapes if the total displacement volume of the scattering center is comparable. Experiments were carried out to evaluate the optical property with varying size of ZnO templates. Photovoltaic effect of dye-sensitized solar cells made from these ZnO-assisted films were investigated with incident-photon-to-current efficiency to understand the effect of scattering center size on the enhancement of absorption. With 380nm macropores incorporated, the power conversion efficiency has increased by 11% mostly thanks to the improved current density, while 170nm and 500nm macropores samples did not have increment in sufficiently wide range of absorbing wavelengths.

Conjugated or Broken: The Introduction of Isolation Spacer ahead of the Anchoring Moiety and the Improved Device Performance.

Acceptors in traditional dyes are generally designed closed to TiO2 substrate to form a strong electronic coupling with each other (e.g., cyanoacrylic acid) to enhance the electron injection for the high performance of the corresponding solar cells. However, some newly developed dyes with chromophores or main acceptors isolated from anchoring groups also exhibit comparable or even higher performances. To investigate the relatively untouched electronic coupling effect in dye-sensitized solar cells, a relatively precise method is proposed in which the strength is adjusted gradually by changing isolation spacers between main acceptors and anchoring groups to partially control the electronic interaction. After an analysis of 3 different groups of 11 sensitizers, it is inferred that the electronic coupling should be kept at a suitable level to balance the electron injection and recombination. Based on a reference dye LI-81 possessing a cyanoacrylic acid as acceptor and anchoring group, both photocurrent and photovoltage are synergistically improved after the properties of isolation spacers were changed through the adjustment of the length, steric hindrance, and push-pull electronic characteristic. Accordingly, the rationally designed dye LI-87 with an isolation spacer of thiophene ethylene gives an efficiency of 8.54% and further improved to 9.07% in the presence of CDCA, showing a new way to develop efficient sensitizers.

Accessing the charge separation effects in dye-sensitized solar cells based on a vectorial planning of supramolecular ruthenium dyes

Charge recombination has been postulated a critical point in dye sensitized solar cells (DSSC), however the role of the electron-hole separation distance from the TiO2 surface and the oxidized dye has actually never been experimentally demonstrated for this type of device, operating under normal working conditions. In order to elucidate this point, supramolecular ruthenium dyes encompassing vectorial electron transfer properties have been especially devised, consisting of electronically coupled [Ru(dcbH2)2(B)Cl]+ and [Ru(dmb)2(B)Cl]+ complexes acting as acceptor–donor pairs, respectively, where dcbH2=2,2′-bipyridine-4,4′-dicarboxylic acid, and dmb=4,4′-dimethyl-2,2′-bipyridine. In these systems, the two ruthenium complexes are connected by linear bridging ligands (B) of programmed lengths, e.g. 1.85, 2.06 and 2.70nmfor 4,4′-bipyridine (bpy), trans-1,2-bis(4-pyridyl)-ethylene (bpe) or trans-1,4-bis[2-(4-pyridyl)ethenyl]-benzene) (bpeb), respectively, thus allowing a precise control of the interfacial charge-separation distance. By working under similar, reproducible conditions, the overall efficiency of the corresponding DSSCs increased from 2.78 (bpy) to 2.89 (bpe) and 3.25% (bpeb), paralleling the increase of the bridging ligand lengths. Such results were corroborated by impedance measurements, highlighting the important role of the electron-hole separation effect in DSSCs, and also demonstrating how a suitable supramolecular design can improve the overall cell efficiency.

Comparison of p-type sensitizers with different electron-induced effects in dye-sensitized solar cells: A theoretical investigation

Two classical p-type photosensitizers with modified conjugation spacers by the electron-rich unit (thiophene) and electron-deficient unit (pyrimidine) are calculated and investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT). Creatively, regeneration reactions between reduced sensitizers and I3− as well as I2− are explored theoretically, reappearing the regeneration process that electrons are transferred from reduced dyes to I3− or I2− in p-type dye-sensitized solar cells (p-type DSSCs) intuitively, and uncovering the difference of π-spacers with different electron-induced effects in the process of dye regeneration. Besides, calculation also indicates that thiophene-based dye (PS) has better light capture efficiency but unfavorable performance of charge transfer when compared with the pyrimidine-based dye (PN). From another perspective, both sensitizers have efficient driving forces of injection. In addition, dyes absorbing on the (NiO)9 semiconductor are also considered. Our comparison discussion of two sensitizers with different π-spacers provides great assistance for deeply investigating p-type photosensitizes with higher efficiencies and their regeneration processes, contributing to the potential tandem DSSCs.

Magnetic field effects in dye-sensitized solar cells controlled by different cell architecture.

The charge recombination and exciton dissociation are generally recognized as the basic electronic processes limiting the efficiency of photovoltaic devices. In this work, we propose a detailed mechanism of photocurrent generation in dye-sensitized solar cells (DSSCs) examined by magnetic field effect (MFE) technique. Here we demonstrate that the magnitude of the MFE on photocurrent in DSSCs can be controlled by the radius and spin coherence time of electron-hole (e-h) pairs which are experimentally modified by the photoanode morphology (TiO2 nanoparticles or nanotubes) and the electronic orbital structure of various dye molecules (ruthenium N719, dinuclear ruthenium B1 and fully organic squaraine SQ2 dyes). The observed MFE is attributed to magnetic-field-induced spin-mixing of (e-h) pairs according to the Δg mechanism.

Electrochemical grafting of TiO2-based photo-anodes and its effect in dye-sensitized solar cells

We demonstrate that hydroxyl-groups which are located on the surfaces of mesoporous metal oxides (in particular sintered layers of F-doped tin oxide (FTO) and TiO2 on glass plates) are capable of undergoing reactions with 4-nitrobenzene radicals. The highly reactive benzene radicals are generated by the electrochemical reduction of 4-nitrobenzenediazonium tetrafluoroborate in acetonitrile. We found that the grafting surfaces were chemically inert to strong acids and bases. The grafted surfaces were characterized and analyzed by cyclic voltammetry (CV), attenuated total reflectance Fourier transform infrared spectroscopy (ATR–FTIR), X-ray photo electron spectroscopy (XPS), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX). Implementation of electrochemically grafted TiO2 particles as photo-anodes in dye-sensitized solar cells (DSCs) showed that the grafted surface is capable of suppressing the undesired back-electron-transfer processes in dye-sensitized solar cells.

Efficient dye-sensitized solar cells based on CNTs and Zr-doped TiO2 nanoparticles

The light scattering, harvesting and adsorption effects in dye-sensitized solar cells (DSSCs) are studied by preparation of coated carbon nanotubes (CNTs) with TiO2 and Zr-doped TiO2 nanoparticles in the forms of mono- and double-layer cells. X-ray diffraction (XRD) analysis reveals that the phase composition of Zr-doped TiO2 electrode is a mixture of anatase and rutile phases with major rutile content, whereas it is the same mixture with major anatase content for coated CNTs with TiO2. Furthermore, the average crystallite size of Zr-doped TiO2 electrode is slightly decreased with Zr introduction. Field emission scanning electron microscope (FE-SEM) images show that the porosity of Zr-doped TiO2 electrodes is higher than that of undoped electrode, enhancing dye adsorption. UV–visible spectroscopy analysis reveals that the absorption onset of Zr-doped TiO2 electrodes is slightly shifted to longer wavelength (the red-shift) in comparison with that of undoped TiO2 electrode. Moreover, the band gap energy of TiO2 nanoparticles is decreased by Zr introduction, enhancing light absorption. It is found that electron injection of monolayer TiO2 electrode is improved by introduction of 0.025mol% Zr, resulted in enhancement of its power conversion efficiency (PCE) up to 6.81% compared with 6.17% for pure TiO2 electrode. Moreover, electron transport and light scattering are enhanced by incorporation of 0.025 wt% coated CNTs with TiO2 in the over-layer of double layer electrode. Therefore, double layer solar cell composed of 0.025mol% Zr-doped TiO2 nanoparticles as the under-layer and mixtures of these nanoparticles and 0.025wt% coated CNTs with TiO2 as the over-layer shows the highest PCE of 8.19%.

A Drift-Diffusion Study on Charge Unbalancing Effects in Dye-Sensitized Solar Cells

This work describes a modeling investigation of a working Dye-sensitized Solar Cells, including the contribution of ionic drift in the mass transport process of I−3/I− redox couple. We found that the effective built-in electric field profile inside the cell is influenced by the density and distribution of the electronic traps located below the conduction band edge of the TiO2. Although the value of electric field remains low compared to conventional p-n junction solar cells, our results support that the high concentration of ionic species composing the electrolyte prompts a drift current of ionic species, comparable to the related ionic diffusion current, when the device is exposed to light illumination under short-circuit conditions. The simulations carried out for different electrolyte compositions tend to demonstrate that ionic drift is a process which can never been suppressed and therefore should be considered in the description of the mass transport. These results participate in the better understanding of the working principle of the complex and multifaceted chemistry of dye-sensitized solar cells.