Incident Monochromatic Photon-to-current Conversion Efficiency Research Articles

Influence of 2-naphthoic acid anchoring groups to the photovoltaic performance of zinc phthalocyanine-based photosensitizers in dye-sensitized solar cell

Two different zinc phthalocyanines bearing different numbers of 2-naphthoic acid anchoring groups at the peripheral positions were synthesized and characterized with UV–Vis, proton nuclear magnetic resonance (1H NMR), fouirer transform infrared (FT-IR), and matrix-assisted laser desorption/ionization mass (MALDI-TOF MS) spectroscopy. Then their electrochemical, and spectroelectrochemical performances were investigated to predict their suitability of them as photosensitizers in dye-sensitized solar cells (DSSC). In the voltammetric analysis results, [2,9,16-Tri-(4-carboxyethylphenoxy)-23-(4-[6-carboxy-2-naphtoxy]) substituted zinc(II) phthalocyanine (ZnPc(3)) and [2,9,16,23-tetra-(4-(6-carboxy-2-naphthoxy) substituted zinc(II) phthalocyanine (ZnPc(4)) illustrate similar electron transfer processes. The substituent environments of the complexes slightly influenced the position and reversibility of the redox couples. Redox processes of ZnPc(3) bearing unsymmetrical carboxyethylphenoxy and 2-naphthoic acid anchoring groups slightly shift towards the positive potentials concerning ZnPc(4) bearing symmetrical 2-naphthoic acid substituents. Peak positions of both complexes reflecting the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) positions indicate the suitability of the complexes for the efficient charge carrier transferring from these photosensitizers to the semiconductor and redox mediator in the DSSC. Pc-based spectroelectrochemical responses of the complexes supported the HOMO and LUMO positions for both neutral and electrogenerated ZnPc species. DSSC responses indicated that ZnPc(3), which has the asymmetric carboxyethylphenoxy and 2-naphthoic acid substituents, gave higher DSSC efficiency withshort-circuit photocurrent density (JSC) (9.54 mA cm−2), open circuit potential (VOC) (697 mV), fill factor (FF) (51%), incident monochromatic photon-to-current conversion efficiency (IPCE) (51%), and power conversion efficiency (ƞ) (3.4%) parameters concerning ZnPc(4) bearing symmetric 2-naphthoic acid anchoring groups.

Fabrication of 3D Bi2O3-BiOI heterojunction by a simple dipping method: Highly enhanced visible-light photoelectrocatalytic activity

Three-dimensional (3D) Bi2O3-BiOI heterojunction was fabricated on the basis of Bi2O3 film by a simple dipping method at room temperature. The as-prepared film samples were characterized by scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–Vis DRS spectra. Results indicated that BiOI nanosheets with cross-flake arrays were formed via in situ etching and exchanging of Bi2O3 layer by I− in KI aqueous solution, which grow around the residual Bi2O3 particles to form 3D Bi2O3-BiOI heterojunction. Liner sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) Nyquist plots and incident monochromatic photon-to-current conversion efficiency (IPCE) indicated that easier generation, separation and transfer of photogenerated charges were achieved on the special 3D heterojunction. The photocurrent density of the 3D Bi2O3-BiOI composite increased by 8.4 times relative to pure Bi2O3 at 0.35V vs. Ag/AgCl in 0.2M Na2SO4 aqueous solution under visible light irradiation. For the PEC degradation of phenol, the composite film also exhibited greatly enhanced activity. The calculated rate constant was 3.8 times that on pure Bi2O3. Furthermore, good stability in long-time photocurrent and cyclic degradation of phenol can both be observed, indicating that the 3D Bi2O3-BiOI film can be potentially applied in water oxidation and environmental remediation.

Enhanced Photovoltaic Performances of Dye-Sensitized Solar Cells by Co-Sensitization of Benzothiadiazole and Squaraine-Based Dyes.

Dye-sensitized solar cells (DSSCs) based on a donor-acceptor-donor oligothienylene dye containing benzothiadiazole (T4BTD-A) were cosensitized with dyes containing cis-configured squaraine rings (HSQ3 and HSQ4). The cosensitized dyes showed incident monochromatic photon-to-current conversion efficiency (IPCE) greater than 70% in the 300-850 nm wavelength region. The individual overall conversion efficiencies of the sensitizers T4BTD-A, HSQ3, and HSQ4 were 6.4%, 4.8%, and 5.8%, respectively. Improved power conversion efficiencies of 7.0% and 7.7% were observed when T4BTD-A was cosensitized with HSQ3 and HSQ4, respectively, thanks to a significant increase in current density (JSC) for the cosensitized DSSCs. Intensity-modulated photovoltage spectroscopy results showed a longer lifetime for cosensitized T4BTD-A+HSQ3 and T4BTD-A+HSQ4 compared to that of HSQ3 and HSQ4, respectively.

A Novel Alkoxysilyl Azobenzene Dye Photosensitizer with Alkylamino Group for Dye-Sensitized Solar Cells

A newly designed alkoxysilyl azobenzene dye with alkylamino group, 4-diethoxyphenylsilyl-4′-dimethylaminoazobenzene, was synthesized and examined as the photosensitizer for a dye-sensitized solar cell (DSSC). The novel azobenzene dye exhibited a strong absorption band in the visible region, and the solar cell using the dye as the sensitizer showed an incident monochromatic photon-to-current conversion efficiency (IPCE) value of 66 % at 440 nm and a light-to-electric energy conversion efficiency of 2.2 % under simulated sunlight irradiation of AM-1.5G one sun condition. The energy conversion efficiency obtained here is the highest value among those reported so far for azobenzene-sensitized solar cells, indicating the potential of alkoxysilyl dyes as photosensitizers for DSSCs.

Synthesis and Characterization of 2D‐D‐π‐A‐Type Organic Dyes Bearing Bis(3,6‐di‐tert‐butylcarbazol‐9‐ylphenyl)aniline as Donor Moiety for Dye‐Sensitized Solar Cells

AbstractA series of novel 2D‐D‐π‐A‐type organic dyes, namely CCTTnA (n = 1–3), bearing bis(3,6‐di‐tert‐butylcarbazol‐9‐ylphenyl)aniline as an electron‐donor moiety (2D‐D), oligothiophene segments with a number of thiophene units from one to three units as π‐conjugated spacers (π), and cyanoacrylic acid as the electron acceptor (A) were synthesized and characterized as dye sensitizers for dye‐sensitized solar cells (DSSCs). These compounds exhibit high thermal and electrochemical stability. Detailed investigations of these dyes reveal that both peripheral carbazole donors (2D) have beneficial influence on the red‐shifted absorption spectrum of the dye in solution and dye adsorbed on TiO2 film, and the broadening of the incident monochromatic photon‐to‐current conversion efficiency (IPCE) spectra of the DSSCs, leading to enhanced energy conversion efficiency (η). Among these dyes, CCTT3A shows the best photovoltaic performance, and a maximal incident monochromatic photon‐to‐current conversion efficiency (IPCE) value of 80 %, a short‐circuit photocurrent density (Jsc) of 9.98 mA cm–2, open‐circuit voltage (Voc) of 0.70 V, and fill factor (FF) of 0.67, corresponding to an overall conversion efficiency η of 4.6 % were achieved. This work suggests that organic dyes based on this type of donor moiety or donor molecular architecture are promising candidates for improved performance DSSCs.

Highly Asymmetric Tribenzonaphtho‐Condensed Porphyrazinatozinc Complex: An Efficient Near‐Infrared Sensitizer for Dye‐Sensitized Solar Cells

AbstractNovel, highly asymmetric zinc phthalocyanine (ZnPc) derivatives (Zn‐tri‐PcNc) containing tribenzonaphtho‐condensed porphyrazine with one carboxyl and three tert‐butyl (tBu) or n‐butoxy (nBuO) peripheral substituents were synthesized by using 6‐carboxymethyl‐2,3‐dicyanonaphthalene and 4‐tBu‐ or nBuO‐phthalonitrile as starting agents. The new, highly asymmetric ZnPc containing tBu groups (Zn‐tri‐PcNc‐2 b) yielded a 3.56 % conversion efficiency in sensitizing TiO2‐based dye‐sensitized solar cells (DSSCs) under simulated AM 1.5G solar irradiation (100 mW cm−2), which is higher than that of the nBuO‐containing analogue Zn‐tri‐PcNc‐3 b (2.20 %). Moreover, Zn‐tri‐PcNc‐2 b displays 60.7 % of the maximum incident monochromatic photon‐to‐current conversion efficiency (IPCE) in the red/near‐IR region, which is much higher than that of Zn‐tri‐PcNc‐3 b (22.9 %), thus highlighting the potential of Zn‐tri‐PcNc‐2 b as a DSSC component.

Synthesis of Organic Dyes with Linkers Between 9,9-Dimethylfluorenyl Terminal and α-Cyanoacrylic Acid Anchor, Effect of the Linkers on UV-Vis Absorption Spectra, and Photovoltaic Properties in Dye-Sensitized Solar Cells

Six metal-free organic dyes having thiophene (1), benzene-thiophene (2), thiophene-benzene (3), thiophene-pyridine (4), thiophene-thiophene (5), and pyridine (6) linkers between 9,9-dimethylfluorenyl terminal group and <TEX>$\alpha$</TEX>-cyanoacrylic acid anchor were synthesized. Among them, organic dye 5 showed the longest <TEX>${\lambda}_{max}$</TEX> value (424 nm) in UV-Vis absorption spectrum, better incident monochromatic photon-to-current conversion efficiency (IPCE), highest short circuit photocurrent density (<TEX>$J_{SC},\;9.33\;mA^2/cm^2$</TEX>), and highest overall conversion efficiency (<TEX>$\eta$</TEX>, 3.91%).

Structure–Function Relationships in Unsymmetrical Zinc Phthalocyanines for Dye‐Sensitized Solar Cells

A series of unsymmetrical zinc phthalocyanines bearing an anchoring carboxylic function linked to the phthalocyanine ring through different spacers were designed for dye-sensitised solar cells (DSSC). The modification of the spacer group allows not only a variable distance between the dye and the nanocrystalline TiO(2), but also a distinct orientation of the phthalocyanine on the semiconductor surface. The photovoltaic data show that the nature of the spacer group plays a significant role in the electron injection from the photo-excited dye into the nanocrystalline TiO(2) semiconductor, the recombination rates and the efficiency of the cells. The incident monochromatic photon-to-current conversion efficiency (IPCE) for phthalocyanines bearing an insulating spacer is as low as 9%, whereas for those with a conducting spacer an outstanding IPCE 80% was obtained.

Carboxy-1,4-phenylenevinylene- and carboxy-2, 6-naphthylene-vinylene unsymmetrical substituted zinc phthalocyanines for dye-sensitized solar cells

Two unsymmetrical Zn (II) phthalocyanines 1 and 2 bearing an anchoring carboxylic function linked to the phthalocyanine ring through different rigid arylenevinylene bridges have been designed for dye-sensitized solar cell (DSSC) applications. The phthalocyanines 1 and 2, when anchored onto nanocrystalline TiO 2 films, yielded 30% incident monochromatic photon-to-current conversion efficiency (IPCE) and 2% power conversion efficiencies under AM1.5 sun.

Co-sensitization of Organic Dyes for Efficient Ionic Liquid Electrolyte-Based Dye-Sensitized Solar Cells

The co-sensitization of two organic dyes (SQ1 and JK2), which are complementary in their spectral responses, shows enhanced photovoltaic performance compared with that of an individual organic dye-sensitized solar cell. The power conversion efficiency of the co-sensitized organic dye solar cell based on the newly developed binary ionic liquid (solvent-free) electrolyte gives 6.4% under AM 1.5 sunlight at 100 mW/cm2 irradiation, which is higher than that of individual dye-sensitized solar cells. The incident monochromatic photon-to-current conversion efficiency (IPCE) of the co-sensitized solar cell shows typical absorption peaks at 530 and 650 nm corresponding to the two dyes and displays a broad spectral response over the entire visible spectrum with IPCE of >40% in the 400-700 nm wavelength domain.

Molecular engineering of organic dyes containing N-aryl carbazole moiety for solar cell

Organic dyes containing N-aryl carbazole moiety are designed and synthesized. Under standard global AM 1.5 solar condition, the JK-25 sensitized cell gave a short circuit photocurrent density ( J sc) of 11.50 mA cm −2, an open circuit voltage ( V oc) of 0.68 V, a fill factor of 0.66, corresponding to an overall conversion efficiency η of 5.15%, and the maximum incident monochromatic photon-to-current conversion efficiency (IPCE) of 77% at 430 nm.

Photovoltaic Cells Based on Sequentially Adsorbed Multilayers of Conjugated Poly(p-phenylene ethynylene)s and a Water-Soluble Fullerene Derivative

We describe the layer-by-layer (LBL) fabrication of multilayer films and photovoltaic cells using poly(phenylene ethynylene)-based anionic conjugated polyelectrolytes as electron donors and water-soluble cationic fullerene C60 derivatives as acceptors. LBL film deposition was found to be linearly related to the number of bilayers as monitored by UV-vis absorption. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) of the multilayer films revealed an aggregated but relatively uniform morphology devoid of any long-range phase separation. The maximum incident monochromatic photon to current conversion efficiency (IPCE) of the photovoltaic cells was 5.5%, the highest efficiency reported to date for cells fabricated by using the LBL fabrication technique, and since the thin film cells do not provide complete absorption of the incident light, the current generation per photon absorbed may be as much as 10%. The cells exhibited open circuit voltages of 200-250 mV with highest measured short circuit currents up to 0.5 mA/cm2 and fill factors around 30%. The power conversion efficiencies measured at AM 1.5 solar conditions (100 mW/cm2) varied between 0.01 and 0.04%, and similar to the IPCE results, the efficiency is a function of the thickness of the PV active layer.

Comparative studies of substituted ruthenium(II)–pyrazoyl–pyridine complexes with classical N3 photosensitizer: the influence of NCS dye ligands on the efficiency of solid-state nanocrystalline solar cells

New dyes of the type [Ru(II)(bdmpp)(dcbpy)X](PF 6) (where bdmpp is 2,6-bis(3,5-dimethyl- N-pyrazoyl)pyridine, dcbpy is 2,2′-bipyridine-4,4′-dicarboxylic acid and X=Cl − (RuCl) or NCS − (RuNCS)) have been tested with success as molecular antennas in titania nanocrystalline photoelectrochemical cells (DSSCs) and compared with the Grätzel’s N3 photosensitizer, in modules fabricated using a composite polymer solid-state electrolyte The solar cells made using the complex with the NCS ligand have a significantly better performance than those fabricated with the dye containing the Cl − ligand. The comparison of their action spectra has revealed that the RuNCS dye presents higher incident monochromatic photon-to-current conversion efficiency (IPCE) values. The RuNCS cells produced a short-circuit photocurrent as high as 4.3 mA cm −2 and an open-circuit photovoltage of 584 mV, which led to an overall energy conversion cell efficiency ( η) as high as 1.64%, about three times higher than the corresponding efficiency obtained with RuCl dye. On the basis of the obtained results the energetic diagrams of the corresponding DSSCs were constructed. The observed differences are attributed to the contribution of the isothiocyanato group on the light absorption, on the redox properties and on the increase of the charge injection efficiency. A gain in photovoltaic performance of the NCS containing dyes is also proposed through a reduction of the dark current of the corresponding solid-state solar cells.

A swift dye uptake procedure for dye sensitized solar cells.

Solar cells based on swift self-assembled sensitizer bis(tetrabutylammonium)-cis-di(thiocyanato)-N,N'-bis(4-carboxylato-4'-carboxylic acid-2,2'-bipyridine)ruthenium(II) (N719) on double layers of 12 + 4 microm thick nanocrystalline TiO2 films exhibit the incident monochromatic photon-to-current conversion efficiency (IPCE) 90% and show a short circuit current density of 17 mA cm(-2), 750 mV open circuit potential and 0.72 fill factor yielding power conversion efficiencies over 9.18% under AM 1.5 sun. For the first time highest power conversion efficiencies are obtained for dye sensitized solar cells using a swift self-assembled procedure.

Synthesis and spectroscopic properties of a new bipyridine-bipyrazoyl(pyridine)-thiocyanato-ruthenium(II) complex

The complex [Ru(II)(dcbpyH 2)(bdmpp)NCS](PF 6) ( 1) (where dcbpyH 2 is 2,2′-bipyridine-4,4′-dicarboxylic acid, bdmpp is 2,6-bis(3,5-dimethyl- N-pyrazoyl)pyridine,) is synthesized and characterized extensively by 1H NMR and 13C NMR 1D and 2D, mass spectroscopy, cyclic voltammetry, electronic absorption spectroscopy and IR. The half-wave potential of the Ru(II)/Ru(III) redox couple was measured at E 1/2=+0.795 V versus Ag/AgCl in CH 3CN. The complex presents three intense metal-to-ligand charge transfer (MLCT) (d M→π L*) absorption bands centered at 383 ( ε=21 300 M −1 cm −1), 432 ( ε=22 400 M −1 cm −1) and 475 nm ( ε=23 400 M −1 cm −1), respectively. The absorbance is extremely strong between 400 and 500 nm and even at 620 nm, the extinction coefficient is still high ( ε=3768 M −1 cm −1). The strong π-acceptor property of the trans-isothiocyanate ligand compared with the Cl − ligand is probably the cause of the blue-shift observed in complex 1. These properties make the complex potentially promising for the photosensitization process. The incorporation of TiO 2 photoelectrodes derivatized with this complex into a solar cell using a composite polymer/inorganic oxide solid-state electrolyte confirmed its sensitizing ability. Incident monochromatic photon-to-current conversion efficiency (IPCE) values of about 30% and overall energy conversion efficiency ( η) of 1.7% were obtained.

Electron injection versus charge recombination in photoelectrochemical solar cells using cis-[(dcbH2)2Ru(CNpy)(H2O)]Cl2 as a nanocrystalline TiO2 sensitizer

A transparent photoanode was prepared by immobilizing cis-[(dcbH2)2Ru(CNpy)(H2O)]2+ (dcbH2: 4,4′-(CO2H)2-2,2′-bipyridine; and CNpy: 4-cyanopyridine) in a TCO substrate coated with nanocrystalline TiO2 film for incident monochromatic photon-to-current conversion efficiency (IPCE) measurements. Time-resolved experiments were carried out and electron injection across the excited dye/semiconductor interface, as well as charge recombination and quenching processes were investigated. Transient absorption difference spectra revealed the formation of the oxidized complex [(dcbH2)2Ru(III)(CNpy)(H2O)] upon light excitation. The recovery is a multiphasic process attributed to a charge recombination of the injected electron across the semiconductor/dye interface in the microsecond time domain. The presence of iodide results in a much faster quenching of the oxidized complex. Thus, an appropriate concentration of donor species in the redox mediator is essential to effectively recover the sensitizer closing the electric circuit so that a dye-sensitized solar cell works in a regenerative regime. Therefore, under proper experimental conditions, the compound performs successfully as the molecular sensitizer in photoelectrochemical solar cells based on dye sensitization of nanocrystalline n-type TiO2. Kinetics data of electron injection obtained by time-resolved experiments for cis-[(dcbH2)2Ru(CNpy)(H2O)]2+ are discussed along with the properties of the sensitizer in photoelectrochemical solar cells.

Synthesis of a new copper(i) complex, [Cu(tmdcbpy)2]+ (tmdcbpy = 4,4′,6,6′-tetramethyl-2,2′-bipyridine-5,5′-dicarboxylic acid), and its application to solar cells

A newly synthesized copper(I) complex, [Cu(tmdcbpy)2]+ (tmdcbpy = 4,4′,6,6′-tetramethyl-2,2′-bipyridine-5,5′-dicarboxylic acid), was applied to a solar cell with TiO2, which provided successful results, a photocurrent of about 4 mA cm−2, photovoltage of 630 mV and an IPCE (incident monochromatic photon-to-current conversion efficiency) value of 30%, under visible light irradiation from a AM 1.5G sunlight simulator (100 mW cm−2).

Photoelectric behavior of nanocrystalline TiO 2 electrode with a novel terpyridyl ruthenium complex

The photoelectric behavior of a black dye, tris (isothiocyanato)-[ N-(2,2′:6′,2″-terpyridine-4′-(4-carboxylic acid) phenyl)] ruthenium (II) complex, was examined under different conditions. The dye was adsorbed on nanocrystalline TiO 2 surface strongly and generated incident monochromatic photon-to-current conversion efficiency (IPCE) of about 90% at maximum absorption wavelength and greater than 20% in the near-IR region. A sandwich-type solar cell fabricated by this dye-sensitized nanocrystalline TiO 2 film generated 6.1 mA cm −2 of short-circuit photocurrent, 0.58 V of open-circuit photovoltage and 2.9% of overall yield under irradiation of white light ( 78.0 mW cm −2 ) from a Xe lamp. Since the title dye shows better photoresponse than the N3 dye in the near-IR region, it would be a promising panchromatic sensitizer after optimization.

Comparison of Dye-Sensitized Rutile- and Anatase-Based TiO2Solar Cells

Crack-free nanocrystalline rutile TiO2 films with thicknesses of up to 12 μm were prepared and characterized in connection with their application to dye-sensitized solar cells. The photoelectrochemical properties of the rutile-based solar cell are compared with those of the anatase-based cell. Scanning electron microscopy (SEM) shows that the rutile films consist of homogeneously distributed rod-shaped particles with an average dimension of 20 × 80 nm. Both the thickness and the morphology of the rutile films have a strong influence on the photoelectrochemical properties of the solar cells. Measurements of the incident monochromatic photon-to-current conversion efficiency (IPCE) as a function of film thickness imply that a significant fraction of light in the spectral region below 600 nm is absorbed in the first few microns of the dye-covered films due to strong light absorption by the dye. At longer wavelengths, where the dye absorbs weakly, the IPCE increases in direct proportion to the film thickness, suggesting that the electron-injection rate throughout the cell approaches homogeneity. The open-circuit photovoltage (Voc) shows only a small change with film thickness, which is attributed to the compensating effect associated with the dependence of the number of dye molecules and recombination centers on the surface area. For the same film thickness, the photocurrent−voltage responses of the dye-sensitized rutile and anatase films at one-sun light intensity are remarkably close. Their Voc is essentially the same, whereas the short-circuit photocurrent of the rutile-based cell is only about 30% lower than that of the anatase-based cell. The lower photocurrent of the rutile film correlates with a lesser amount of adsorbed dye, owing to a smaller surface area per unit volume compared with that of the anatase film. Intensity-modulated photocurrent spectroscopy and SEM studies indicate that electron transport is slower in the rutile layer than in the anatase layer due to differences in the extent of interparticle connectivity associated with the particle packing density.

Photovoltaic cells with a conjugated polyelectrolyte

We describe photovoltaic cells made from a novel conjugated polyelectrolyte, the lithium salt of poly(thiophene-3-acetic acid) (PTAA-Li). The aqueous solubility of this polyelectrolyte allows formation of blend electrodes with a dispersion of the metallic polymer Poly(Ethylene DiOxyThiophene) (PEDOT). The incident monochromatic photon to current conversion efficiency (IPCE) of the cells were improved up to 19% by blending PTAA-Li with PEDOT to modify the ITO electrode, in combination with the low bandgap polymer poly(3-(4-octylphenyl)thiophene) (POPT), and C60 as electron acceptor. We attribute the increase of efficiency to the improved contact area between the conjugated polyelectrolyte and PEDOT.