Dye-sensitized Nanocrystalline Solar Cells Research Articles

Effect of 1-Hexyl-3-Methylimidazolium Iodide Ionic Liquid on Ionic Conductivity and Energy Conversion Efficiency of Solid Polymer Electrolyte-Based Nano-Crystalline Dye-Sensitized Solar Cells.

Solid polymer electrolytes (SPEs) were prepared using rice starch as the polymer, sodium iodide (NaI) as the salt and 1-hexyl-3-methylimidazolium iodide (HMII) as the ionic liquid (IL). The solution casting technique was used for preparation of the PEs. The ionic conductivity and temperaturedependent properties of the PEs were measured and all the SPEs were found to follow the Arrhenius thermal activated model. Ionic conductivity increased as the percentage of ILs increased. The SPE containing 20% (wt) of HMII IL showed the highest ionic conductivity of 1.83×10-3 S/cm. Spectral and structural characterization of the PEs were performed by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), respectively. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicate that the decomposition temperature (Tdc), glass transition temperatures (Tg) and melting points (Tm) shifted when complexation with HMII occurred. The PEs were used to fabricate dye-sensitized solar cells (DSSCs) and the DSSCs were analyzed under a 1-sun simulator. The SPE with the highest ionic conductivity displayed a short circuit current density (Jsc) of 9.07 (mA cm-2), open circuit voltage (Voc) of 0.58 (V), a fill factor (FF) of 0.65 and had the highest energy conversion efficiency of 3.42%.

Lateral Intermolecular Electronic Interactions of Diketopyrrolopyrrole D−π–A Solar Dye Sensitizers Adsorbed on Mesoporous Alumina

The development of push–pull organic dyes utilizing the donor–(π-conjugated bridge)–acceptor (D−π–A) motif has induced a paradigm shift in the design of efficient nanocrystalline dye-sensitized solar cells (DSSCs), offering control over the aesthetic properties and performance. Because of the large transient dipole moment characterizing this type of dye upon photoexcitation, these molecules are intrinsically subjected to significant lateral electronic interactions once adsorbed on a solid surface, which can greatly affect the efficiency of the electron injection in DSSCs. Here, we investigated the detailed intermolecular interactions upon photoexcitation of D−π–A diketopyrrolopyrrole (DPP)-based dye molecules, denoted (E)-3-(5-(4-(4-(5-(4-(bis(2′,4′-dibutoxy-[1,1′-biphenyl]-4-yl)amino)phenyl)thiophen-2-yl)-2,5-bis(2-ethylhexyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)phenyl)furan-2-yl)-2-cyanoacrylic acid (DPP_A) and commercially available under the name “Dyenamo Blue”, using ultrafast trans...

Preparation of titanium dioxide nanorods/nanoparticles via one-step hydrothermal method and their influence as a photoanode material in nanocrystalline dye-sensitized solar cell

Titanium dioxide (TiO2) nanostructures composed of nanorods and nanoparticles (NRs/NPs) were prepared via a one-step hydrothermal method. The structural and phase purity of the synthesized products was characterized by powder X-ray diffraction (PXRD) analysis and the result showed anatase phase with good crystalline nature. The surface morphology of the nanostructures has been identified using transmission electron microscopy (TEM) analysis and the results showed nanorods and nanoparticles morphology. The elemental states of TiO2 NRs/NPs were identified using X-ray photoelectron spectroscopy (XPS). In order to quantify the surface area of the synthesized products, nitrogen adsorption and desorption isotherm analysis was used and the surface area of 93.08 m2/g was obtained from the Brunauer–Emmett–Teller (BET) approach. Dye-sensitized solar cell has been fabricated using prepared NRs/NPs. The influence of NRs/NPs in the fabricated device has been tested under the illumination of 1 sun and the performance was compared with commercial P25 nanoparticles. A power conversion efficiency of ∼9% has been found with NRs/NPs employed solar cell. The electrochemical process of the fabricated device was studied under the illumination with the help of electrochemical impedance spectroscopy analysis (EIS) which showed longer lifetime (26·9 ms) and reduced charge recombination at the interface of NRs/NPs and redox couples.

Low-cost synthesized organic compounds in solvent free quasi-solid state polyethyleneimine, polyethylene glycol based polymer electrolyte for dye-sensitized solar cells with high photovoltaic conversion efficiencies

The present work reports on solvent free quasi-solid state polymer electrolyte comprising of polyethyleneimine, polyethylene glycol, KI, I2 with newly synthesized N,O,S based organic compounds and application for nanocrystalline dye-sensitized solar cell (DSSC). The synthesized compounds was confirmed by NMR and mass spectra the conductivity and the surface study were analysed by FTIR spectra, impedance spectra, CV, microscope image, UV and XRD. The performance of the fabricated solar cell and conductivity of polymer electrolyte was enhanced by the electron donicity of hetero atom in the synthesized organic compound such as tetraethylene glycol and OCCO units. Among all synthesized organic compound, the (4,4′-((((oxybis(ethane-2,1-diyl))bis(oxy))bis(ethane-2,1diyl))bis(sulfanediyl))dipyridine) dopant (I) showed a strong interaction with nano TiO2 electrode, redox couple and the electrolyte resulted with short circuit current (Jsc), open-circuit voltage (Voc), fill factor (ff) and energy conversion (ŋ) values of about 12.9, 890, 0.56 and 9.2% under the sunlight irradiation of 70 mW/cm2.

Dependence of solar cell performance on the nature of alkaline counterion in gel polymer electrolytes containing binary iodides

Performance of dye-sensitized nano-crystalline TiO2 thin film-based photo-electrochemical solar cells (PECSCs) containing gel polymer electrolytes is largely governed by the nature of the cation in the electrolyte. Dependence of the photovoltaic performance in these quasi-solid state PECSCs on the alkaline cation size has already been investigated for single cation iodide salt-based electrolytes. The present study reports the ionic conductivity dependence on the nature of alkaline cations (counterion) in a gel polymer electrolyte based on binary iodides. Polyacrylonitrile-based gel polymer electrolyte series containing binary iodide salts is prepared using one of the alkaline iodides (LiI, NaI, KI, RbI, and CsI) and tetrapropylammonium iodide (Pr4NI). All the electrolytes based on binary salts have shown conductivity enhancement compared to their single cation counterparts. When combined with Pr4NI, each of the Li+, Na+, K+, Rb+, and Cs+ cation containing iodide salts incorporated in the gel electrolytes has shown a room temperature conductivity enhancement of 85.59, 12.03, 12.71, 20.77, and 15.36%, respectively. The conductivities of gel electrolytes containing binary iodide systems with Pr4NI and KI/RbI/CsI are higher and have shown values of 3.28, 3.43, and 3.23 mS cm−1, respectively at room temperature. The influence of the nature of counterions on the performance of quasi-solid state dye-sensitized solar cells is investigated by assembling two series of cells. All the binary cationic solar cells have shown more or less enhancements of open circuit voltage, short circuit current density, fill factor, and efficiency compared to their single cation counterparts. This work highlights the importance of employing binary cations (a large and a small) in electrolytes intended for quasi-solid state solar cells. The percentage of energy conversion efficiency enhancement shown for the PECSCs made with electrolytes containing Pr4NI along with Li+, Na+, K+, Rb+, and Cs+ iodides is 260.27, 133.65, 65.27, 25.32, and 8.36%, respectively. The highest efficiency of 4.93% is shown by the solar cell containing KI and Pr4NI. However, the highest enhancements of ionic conductivity as well as the energy conversion efficiency were exhibited by the PECSC made with Li+-containing binary cationic electrolyte.

A poly (ethylene oxide), poly (vinylidene fluoride) and polycapro lactone polymer blend doped with an indigenous nitrogen–sulfur based organic compound as a novel electrolyte system for dye-sensitized solar cell applications

The present study reports, for the first time, the strategy of blending three different polymers followed by the doping of an organic nitrogenous compound to develop a solvent-free novel doped multi-polymer blend electrolyte system for dye-sensitized solar cell (DSSC) applications. Precisely, this novel electrolyte consists of poly (ethylene oxide) (PEO) blended with poly (vinylidene fluoride) (PVdF) and poly (capro lactone) (PCL) that is incorporated into the synthesized 2,6-bis (2-thio pyridyl) pyridine (BTPP) along with KI and I2. The current–voltage (I–V) characteristics of the nanocrystalline DSSC fabricated using the present electrolyte generates a photocurrent of 15.5mA/cm2, a photo-voltage of 905mV, a fill factor of 0.53 and yields an overall energy conversion efficiency of 9.3% under a simulated sunlight radiation of 80mW/cm2. The impressive photoelectric performance of the fabricated solar cell is mainly attributed to the synergic effects of the electrolyte composed of the unique blending of three polymers and the electron donicity of BTPP that leads to strongly influence the interaction between the nanocrystalline TiO2 electrode and I−/I3− electrolyte, thereby leading to high conversion efficiency.

Efficiency Enhancement of ZnO Nanocrystalline Dye-Sensitized Solar Cells by Post-Treatment

In this paper, ZnO nanocrystalline photoanodes were treated by zinc acetate aqueous solution. The effect of surface chemical modification processing on the photovoltaic performance and electrochemical properties of ZnO nanocrystalline dye-sensitized solar cells (DSSCs) were studied systematically. The SEM results revealed that the surface of the ZnO photoanode films were rough and some aggregations were formed after the surface chemical modification processing. The number of aggregations increased with increasing processing time, and showed wide grain size distribution simultaneously, which effectively increased the light scattering and decreased the grain boundaries to suppress the electron recombination. Moreover, the surface of these photoanode films were filled with micropores, which was benefit to the infiltration of electrolyte solution. The short circuit current density increased from 7.20 mA•cm-2 to 8.61 mA • cm-2 when post-treatment 20 min, and the maximum energy conversion efficiency reached 3.61%, which enhanced 43% compared with that without post-treatment.

Effect of the alkaline cation size on the conductivity in gel polymer electrolytes and their influence on photo electrochemical solar cells.

The nature and concentration of cationic species in the electrolyte exert a profound influence on the efficiency of nanocrystalline dye-sensitized solar cells (DSSCs). A series of DSSCs based on gel electrolytes containing five alkali iodide salts (LiI, NaI, KI, RbI and CsI) and polyacrylonitrile with plasticizers were fabricated and studied, in order to investigate the dependence of solar cell performance on the cation size. The ionic conductivity of electrolytes with relatively large cations, K(+), Rb(+) and Cs(+), was higher and essentially constant, while for the electrolytes containing the two smaller cations, Na(+) and Li(+), the conductivity values were lower. The temperature dependence of conductivity in this series appears to follow the Vogel-Tamman-Fulcher equation. The sample containing the smallest cation shows the lowest conductivity and the highest activation energy of ∼36.5 meV, while K(+), Rb(+) and Cs(+) containing samples show an activation energy of ∼30.5 meV. DSSCs based on the gel electrolyte and a TiO2 double layer with the N719 dye exhibited an enhancement in the open circuit voltage with increasing cation size. This can be attributed to the decrease in the recombination rate of electrons and to the conduction band shift resulting from cation adsorption by TiO2. The maximum efficiency value, 3.48%, was obtained for the CsI containing cell. The efficiencies shown in this study are lower compared to values reported in the literature, and this can be attributed to the use of a single salt and the absence of other additives, since the focus of the present study was to analyze the cation effect. The highest short circuit current density of 9.43 mA cm(-2) was shown by the RbI containing cell. The enhancement of the solar cell performance with increasing size of the cation is discussed in terms of the effect of the cations on the TiO2 anode and ion transport in the electrolyte. In liquid electrolyte based DSSCs, the short circuit current density has been reported to decrease with the increasing size of the cation. However, in this work, it follows an opposite trend highlighting a major difference between liquid and quasi-solid electrolytes on the solar cell performance.

Enhanced performance of a nanocrystalline dye-sensitized solar cell based on polyurethane dendrimers

The photovoltaic parameters of dye sensitized solar cells (DSSCs) fabricated with and without fourth generation polyurethane dendrimers have been discussed.

Properties of transition metal doped-titania electrodes: Impact on efficiency of amorphous and nanocrystalline dye-sensitized solar cells

In this work, we present the doping by transition metal cations (M: Mn2+, Co2+, Cu2+) effect on TiO2-electrode used in dye sensitized solar cells. The pure and metal transition (Mn, Co, Cu)-doped TiO2 powders, with 0.6% as atomic ratio of M to Ti, were prepared using sol–gel protocol to obtain single phase powders with high chemical purity. The synthesized nanopowders have been systematically characterized as made and after heat treatment at 400°C. The obtained transition metal cations doped TiO2 powders were characterized by X-ray diffraction, Raman, FT-infrared, UV–vis spectroscopies and I–V measurements. In comparison with undoped and doped TiO2 nanopowders after heat treatment, we demonstrate that the addition of Mn in TiO2 improves considerably the crystallinity, reduces the indirect band gap and increases the power conversion efficiency for the dye sensitized solar cell assembled.

Modifying Oxide Single Crystal Surfaces to Study Photoinduced Electron Transfer

Single crystal oxide semiconductor electrodes provide an ideal experimental system for the elucidation of the models and parameters that control light absorption, charge separation, and transport at semiconductor/liquid interfaces. Such fundamental investigations can prove very valuable in the understanding of dye sensitized nanocrystalline solar cells. The single crystal experimental system is much less complex than its nanocrystalline counterpart and the study of well-defined crystallographic surfaces allows for more definitive conclusions to be made concerning the relation between sensitizer attachment and surface structure and the sensitizer’s performance. I will report recent work on the sensitization of low index faces of both anatase and rutile forms of TiO2 and ZnO single crystals with dyes, quantum dots and polymers. We employ atomic force microscopy (AFM) to verify that atomically flat terraced oxide surfaces are prepared and to elucidate the structure of the sensitizers adsorbed on these surfaces. Photocurrent spectroscopy and attenuated reflection spectroscopy are used to correlate the photocurrent response with the optical absorption of the sensitizing species and the relative electron injection efficiencies of for instance dye monomers and aggregates. We have also recently begun to grow homoepitaxial layers on both anatase and rutile using atomic layer deposition (ALD). These layers can have superior electronic properties compared to the substrate crystal and allows us to control the doping density in the near surface region. The primary focus of this talk will be on CdSe and PbS quantum dots as sensitizers. PbS quantum dots adsorbed on anatase (001) surfaces irradiated with light of >2.5 times their band gap have been shown to produce more than one injected electron per incident photon (1), a process known as carrier multiplication or multiple exciton generation (MEG). Harnessing MEG may result in more efficient solar conversion devices.1. Justin B. Sambur, Thomas Novet and B. A. Parkinson, “Multiple Exciton Collection in a Sensitized Photovoltaic System”, Science, 330, 63-66, (2010)

A Ru(II) molecular antenna bearing a novel bipyridine–acrylonitrile ligand: Synthesis and application in dye solar cells

A new molecular photosensitizer (DK108) was synthesized from the reaction of cis-[Ru(H2dcbpy)2Cl2] with the novel bipyridine-acrylonitrile ligand 5. DK108 was completely characterized by a variety of spectroscopic techniques (one- and two-dimensional NMR, UV–Vis, FTIR, HRMS, Raman, and cyclic voltammetry), its photo-electrochemical properties were thoroughly investigated, and was utilized in nanocrystalline dye-sensitized solar cells. Liquid electrolyte dye solar cells incorporating DK108-sensitized TiO2 photoelectrodes afford overall power conversion efficiencies of 1.3%. Despite the relatively low power conversion efficiencies of DK108-sensitized TiO2 films, their fully transparent nature above 600nm render DK108 suitable for building integration applications and the investigation of fundamental issues related to the sensitization mechanism.

Aggregated TiO<SUB>2</SUB>-Based Nanotubes for Dye Sensitized Solar Cells

One-dimensional (1D) semiconducting oxides have attracted great attention for dye sensitized solar cells (DSCs), but the overall performance is still quite limited as compared to TiO2 nanocrystalline DSCs. Here, we report the synthesis of aggregated TiO2 based nanotubes with controlled morphologies and crystalline structures to obtain an overall power conversion efficiency of 9.9% using conventional dye without any additional chemical treatment steps. The high efficiency is attributed to the unique aggregate structure for light harvesting, optimized high surface area, and good crystallinity of the nanotube aggregates obtained through proper thermal annealing. This study demonstrates that high efficiency DSCs can be obtained with 1D nanomaterials, and provides lessons on the importance of optimizing both the nanocrystalline structure and the overall microscale morphology.

Performance Characteristics of Pyrazole as an Effective Dopant in a Blended Polymer Electrolyte for Nanocrystalline Dye-Sensitized Solar Cell Applications

Thin films of nanocomposite blended solid polymer electrolyte consisting of polymethyl methacrylate (PMMA)/polyvinylidene fluoride (PVDF), potassium iodide (KI) and iodine (I 2) as redox couple and pyrazole (PYR) as dopant were prepared using solution casting technique. The consequences of inclusion of PYR within PMMA/PVDF/KI/I 2 were investigated in terms of photovoltaic performance of the cell whereas the PYR impregnated polymer electrolyte solution when introduced into dye-sensitized solar cells (DSSCs) exhibited an overall energy-conversion efficiency of 5.5% at room temperature under AM1.5 illumination.

Synthesis and characterization of Y-shape electron donor–acceptor type organic dyes for dye-sensitized solar cells

Three Y-shape organic dyes, (Z)-3-(5-(3,5-bis(4-(9H-carbazol-9-yl)styryl)-4-methoxyphenyl)thiophen-2-yl)-2-cyanoacrylic acid (OD-1), (Z)-3-(5′-(3,5-bis(4-(9H-carbazol-9-yl)styryl)-4-methoxyphenyl)-2,2′-bithiophen-5-yl)-2-cyanoacrylic acid (OD-2) and (Z)-3-(5′-(3,5-bis(4-(9H-carbazol-9-yl)styryl)-4-methoxyphenyl)-3,4′-4″-trithiophenyl-5-yl)-2-cyanoacrylic acid (OD-3) were synthesized and used as sensitizers in nanocrystalline dye-sensitized solar cells (DSSCs). The introduction of the bis(carbazolylstyryl) units as an electron donor group and oligothiophene units as a both electron donors and π-spacers increased the conjugation length of the sensitizers and thus improved their molar absorption coefficient and light harvesting efficiency. DSSCs with the configuration of SnO2:F/TiO2/organic dye/liquid electrolyte/Pt devices were fabricated using these OD-1, OD-2 and OD-3 as a sensitizers. Among the devices, the DSSC composed of OD-3 exhibited highest power conversion efficiency of 3.03% under AM1.5G (100 mW cm−2).

Novel Ru(ii) sensitizers bearing an unsymmetrical pyridine-quinoline hybrid ligand with extended π-conjugation: synthesis and application in dye-sensitized solar cells

Heteroleptic ruthenium(II) sensitizers DV42 and DV51, encompassing a novel unsymmetrical pyridine-quinoline hybrid ligand with extended π-conjugation, were synthesized, characterized, and utilized in nanocrystalline dye-sensitized solar cells. Due to the extended conjugation of DV42 and DV51, the absorption of the corresponding sensitized TiO2 films extends into the red spectral range, shifted by 30-40 nm relative to the absorption of TiO2 films sensitized with the standard Z907 ruthenium(II) dye. Contact angle measurements of DV42- and DV51-sensitized TiO2 films suggest that these films are hydrophilic with contact angle values commonly observed upon sensitization with the standard N3 ruthenium(II) dye. Electrochemical studies of the novel ruthenium(II) dyes show that their first oxidation potentials lie well below the I(-)/I3(-) redox potential allowing easy regeneration. The excited-state oxidation potentials of both dyes lie above the TiO2 conduction band, permitting efficient electron injection from the excited dye molecules into the semiconductor conduction band. Liquid electrolyte dye-sensitized solar cells incorporating DV42- or DV51-sensitized TiO2 photoelectrodes afford overall power conversion efficiencies of 3.24 or 4.36% respectively. These efficiencies are up to 56% of the power conversion efficiencies attained by TiO2 photoelectrodes sensitized by the benchmark Z907 ruthenium(II) dye under similar experimental conditions.

A new ruthenium sensitizer containing dipyridylamine ligand for effective nanocrystalline dye-sensitized solar cells

Two series of novel ruthenium bipyridyl sensitizers incorporating conjugated dipyridylamine ligands with general formula [Ru (dcbpy) (L) (NCS)2, where dcbpy is 4,4′-dicarboxylic acid-2,2′-bipyridine and L is N-hexyl-4,4′-di(4-hexylstyryl)-2,2′-dipyridylamine, JJ-95 or N-hexyl-4,4′-di{(5-hexylthiophen-2-yl)vinyl}-2,2′-dipyridylamine, JJ-99] have been synthesized and demonstrated as efficient sensitizers in dye-sensitized solar cells. A mesoporous titania film stained with JJ-99 exhibits a remarkable incident monochromatic photon-to-current conversion efficiency of 84%. Under standard AM 1.5 sunlight, the solar cell using a liquid-based electrolyte exhibits a short-circuit photocurrent density of 18.89mA/cm2, an open-circuit voltage of 0.66V, and a fill factor of 0.69, corresponding to an overall conversion efficiency of 8.76%.

Numerical model for the prediction of interfacial effect of ZnO/TCO on the performance of dye-sensitized solar cells

The dye-sensitized nanocrystalline solar cell (DSC) offers potential opportunities in the area of renewable energy sources mainly due to its simple fabrication procedure and use of low cost materials. A theoretical model based on the thermionic emission theory was developed to determine the interfacial effect of ZnO/TCO on the performance of DSC. It was found that under conditions where thermionic emission is valid, photoelectric outputs are affected by temperature and Schottky barrier height (ϕb). The model can be used to facilitate better selection of suitable TCO material.

Preparation of Jeffamine based quaternary ammonium iodide melt for dye sensitized solar cells

A novel Jeffamine based Quaternary Ammonium Iodide (JQAI) melt which contains ether group in backbone were designed and synthesized as non-volatile iodide resource for fabrication of dye sensitized solar cells. 1H NMR spectroscopy and electrospray mass spectrometry techniques were used to confirm the formation of novel ionic liquid. The apparent diffusion coefficient (Dapp) of triiodide and iodide in novel ionic liquid demonstrated by steady state voltammogram shows linear increase on increasing the concentration of iodine from 0.1 to 0.5M. With 0.5M I2, the value of Dapp for triiodide and iodide was found to be 7.502×10−8cm2s−1 and 15.04×10−8cm2s−1 respectively. JQAI was successfully used as an iodide resource for dye sensitized nanocrystalline solar cells. Using this ionic liquid a maximum of 2.34% efficiency was obtained with the observed photo-voltage of 0.536V and photocurrent of 4.65mA using the electrolyte composition 0.5M I2 in JQAI for fabricated dye sensitized solar cell. Addition of small concentration of LiI (0.1M) to the electrolyte containing 0.5M I2 leads to further increase in the photo‐voltage from 0.536 to 0.686V which results in higher energy conversion efficiency (3.03%). Such substantial increase in efficiency was ascribed to the attraction of Li cation towards the large electronegative oxygen atom reside in the quaternary ammonium ionic liquid.

Reaction Order and Ideality Factor in Dye-Sensitized Nanocrystalline Solar Cells: A Theoretical Investigation

Nonlinear recombination in dye-sensitized solar cells was studied from a fundamental point of view. A model based on Marcus theory was used to describe the recombination from both conduction band and trap states. By combination of this model with the empirical form of nonlinear recombination, dependency of the reaction order (β) on the microscopic parameters of the solar cell was investigated. It was analytically shown that β is always less than unity and also depends on the quasi Fermi-level in semiconductors. By this nonconstant β, the dependency of the ideality factor (m), electron diffusion length (Ln), and the electron lifetime (τn) on the Fermi-level were studied. It was discussed that the nonconstant β can explain the flattening of the Ln at high Fermi-level, as observed in some recent experimental works. For the lifetime, it was shown that only the quantity τn/m is accessible in the common open-circuit voltage decay method. It was also shown that the lifetime and the ideality factor can be obtaine...