Improved power conversion efficiency of bulk heterojunction poly(3-hexylthiophene):PCBM photovoltaic devices using small molecule additive

We report that the power conversion efficiency (PCE) of the bulk heterojunction organic photovoltaic device based on poly(3-hexylthiophene):[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) blend was improved by incorporating a small molecule SM having absorption band in the longer wavelength region. SM is a small molecule containing thienothiadiazole central unit with terminal cyanovinylene 4-nitrophenyl at both sides, which were connected to the central unit via a thiophene ring. The combination of SM with P3HT and PCBM allows not only a broad band absorption up to longer wavelength, but also tuning the inter-energy level leading to a higher short circuit current (J_sc) and open circuit voltage (V_oc). The device based on the as cast P3HT:PCBM:SM exhibits a PCE of 3.69%, which is higher than the device based on P3HT:PCBM and SM:PCBM blends. The overall PCE of the device based on thermally annealed blend is further improved up to 4.1%. The improvement of the PCE has been attributed to a better charge transport in the device, due to the increased crystallinity of the blend through thermal annealing.     

Synthesis and photovoltaic properties of an alternating phenylenevinylene copolymer with substituted-triphenylamine units along the backbone for bulk heterojunction and dye-sensitized solar cells

We have fabricated bulk heterojunction (BHJ) photovoltaic devices based on the as cast and thermally annealed P:[6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) blends and found that these devices gave power conversion efficiency (PCE) of about 1.15 and 1.60% respectively. P is a novel alternating phenylenevinylene copolymer which contains 2-cyano-3-(4-(diphenylamino)phenyl)acrylic acid units along the backbone and was synthesized by Heck coupling. This copolymer was soluble in common organic solvents and showed long-wavelength absorption maximum at 390-420 nm with optical band gap of 1.94 eV. The improvement of PCE after thermal annealing of the device based on the P:PCBM blend was attributed to the increase in hole mobility due to the enhanced crystallinity of P induced by thermal treatment. In addition, we have fabricated BHJ photovoltaic devices based on the as cast and thermally annealed PB:P:PCBM ternary blend. PB is a low band gap alternating phenylenevinylene copolymer with BF₂-azopyrrole complex units, which has been previously synthesized in our laboratory. We found that the device based on this ternary blend exhibited higher PCE (2.56%) as compared to either P:PCBM (1.15%) or PB:PCBM (1.57%) blend. This feature was associated with the well energy level alignment of P, PB and PCBM, the higher donor-acceptor interfaces for the exciton dissociation and the improved light harvesting property of the ternary blend. The further increase in the PCE with thermally annealed ternary blend (3.48%) has been correlated with the increase in the crystallinity of both P and PB. Finally, we used copolymer P as sensitizer for quasi solid state dye-sensitized solar cell and we achieved PCE of approximately 3.78%.     

Triphenylamine-substituted methanofullerene derivatives for enhanced open-circuit voltages and efficiencies in polymer solar cells

A new class of triphenylamine substituted methanofullerene derivatives, bis(4'-(diphenylamino)biphenyl-4-yl)methanofullerene (1) and the bisadduct (2), were synthesized. The incident photon to current efficiency (IPCE) studies revealed that the diphenylamino components have contribution to the photocurrent that expands the light harvesting window around 400 nm. When being blended with poly (3-hexylthiophene) (P3HT) to fabricate the solar cell, the device of P3HT:1 (1:0.7) shows high open circuit voltage (V_oc) of 0.69 V under the illumination of AM 1.5, 100 mW/cm² with high power conversion efficiency (PCE) of 3.16%, which is about 0.1 V higher than that of the corresponding [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) devices. This indicates that the arylamine substituents on 1 have played some special roles on the high V_oc performance. Similar effects are also observed for 2. The device of P3HT:2 (1:1) shows even higher V_oc of 0.87 V with the PCE of 1.83%. These results indicate that 1 and 2 are alternative high performance acceptors.     

Effects of a perfluorinated compound as an additive on the power conversion efficiencies of polymer solar cells

A perfluorinated compound, 4-amino-2-(trifluoromethyl)benzonitrile (ATMB), was applied as an additive to polymer solar cells (PSCs) with P3HT [poly(3-hexylthiophene)]:PCBM [[6,6]-phenyl-C₆₁-butyric acid methyl ester] blend films. The addition of 6 wt% ATMB to a P3HT:PCBM layer led to an increased power conversion efficiency of 5.03% due to the enhanced short circuit current and fill factor when compared with that of the reference cell without an additive. On the other hand, the devices with 4-aminobenzonitrile as an additive, not containing fluorine atoms in the molecule, displayed lower PCEs than that of the reference cell. The UV-visible absorption spectra, X-ray measurements and carrier mobility studies revealed that ATMB facilitated ordering of the P3HT chains, resulting in higher absorbance, larger crystal size of P3HT and enhanced hole mobility. XPS depth profiling measurements also showed that the additive molecules were predominantly positioned in the range of 25 nm under the surface of the P3HT:PCBM film, leading to improved fill factor.     

Synthesis, photophysical and photovoltaic properties of star-shaped molecules with triphenylamine as core and phenylethenylthiophene or dithienylethylene as arms

Two solution-processable star-shaped compounds, P and T ,that contain triphenylamine as core and phenylethenylthiophene or dithienylethylene, respectively, as arms were synthesized. They carry also a cyano group on the vinylene bond in the arms. These compounds showed an excellent thermal stability and relatively low (66-72 °C) glass transition temperatures. Their UV-vis spectra showed maximum at 431-459 nm with optical band gaps of 2.22-2.41 eV. They behaved as yellow-orange light emitters with photoluminescence (PL) maximum at 521-610 nm. The PL maximum of T was red shifted relative to P. Photovoltaic devices with active layers based on P (or T) and PCBM were prepared and the thin film composition and the thermal annealing treatment were screened in order to optimize the performance of the devices. The morphology of the blend films and the hole mobilities of P and T were also investigated. Photovoltaic performances of the devices with blend film containing 50 wt%/PCBM in P and T showed highest power conversion efficiencies (PCEs) 0.29% and 0.41%, respectively.     

Two-dimensional regioregular polythiophenes with conjugated side chains for use in organic solar cells

We have prepared two two-dimensional polythiophenes (2D-PTs; P1 and P2) possessing alkyl-thiophene side chains by Stille coupling reactions. Optical measurements indicate that the bandgaps of P1 and P2 being 1.98 and 1.77 eV, respectively. P2 displayed a red-shift in its absorption spectrum because of the longer length of its conjugated side chains. Desirable highest occupied molecular orbital (HUMO) and lowest unoccupied molecular orbital (LUMO) energy levels were obtained from electrochemical studies, which suggested that these systems would exhibit high open-circuit voltages when blended with fullerene as electron acceptors. The hole mobility (thin film transistor (TFT) measurement) of P1 and P2 are 3.5×10⁻⁴ and 4.6×10⁻³ cm² V⁻¹ s⁻¹, respectively. A power conversion efficiency of 2.5% is obtained under simulated solar illumination (AM 1.5G, 100 mW cm⁻²) from a polymer solar cell comprising an active layer containing 25 wt% P1 and 75 wt% [6,6]-phenyl-C₇₁ butyric acid methyl ester (PC₇₁BM).     

Synthesis and organic photovoltaic (OPV) properties of triphenylamine derivatives based on a hexafluorocyclopentene “core”

A series of new “D-A-D” chromophores containing hexafluorocyclopentene thiophene as an acceptor and a triphenylamine unit as a donor, called TP-G1, TP-G2, TPB-G1 and TPB-G2, were designed and synthesized. Heterojunction organic photovoltaic (OPV) cells containing these chromophores were fabricated, and device 1, with the structure of ITO/PEDOT:PSS/TP-G1:P3HT/LiF/Al, displayed an open-circuit voltage (V_oc), short-circuit current (J_sc) and power-conversion efficiency (η) of 0.74 V, 1.178 mA/cm² and 0.22%, respectively. The triphenylamine group could effectively induce the open-ring isomer to close because the 4- and 4′- positions of the benzene rings were substituted by an electron-donating group and the value of the quantum yields of the closed-ring isomers increased. As a result, the closed-ring isomer facilitated intramolecular π-electron delocalization and exhibited a broad absorption band ranging from 200 to 850 nm. Due to the fluorine substitution of hexafluorocylopentene at the molecular center and the hole-transport characteristics of the triphenylamine moiety on the periphery, our chromophores showed obvious dual semiconductor properties, i.e., n- and p-type, which demonstrated a potential application for OPV devices.     

Preparation and photocatalytic activities of two new Zn-doped SrTiO3 and BaTiO3 photocatalysts for hydrogen production from water without cocatalysts loading

Sr_2/3Zn_1/3TiO₃ (1) and Ba_5/6Zn_1/6TiO₃ (2) with perovskite structure have been prepared by a facile sol–gel method, among which the A sites (Sr and Ba for 1 and 2, respectively) were partially replaced by zinc ions. The photocatalysts were characterized by powder X-ray diffraction, UV–vis diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The results of photocatalysis experiment showed that both 1 and 2 exhibited good activity for water reduction to form H₂ without cocatalysts loading under ultraviolet light irradiation. Compared with pure SrTiO₃ and BaTiO₃, 1 and 2 showed remarkable improvement in H₂ production efficiency, respectively. And the photocatalytic mechanisms of them were investigated by the theoretical method. This study demonstrated that the substitutional doping of appropriate ions could change the crystal and band structures and significantly promote electron transport in catalysts, which result in their good photocatalytic activities.     

New compounds in the potassium-aluminium-hydrogen system observed during release and uptake of hydrogen

Three new compounds are observed in the potassium-aluminium-hydrogen system, which are characterised using in-situ synchrotron radiation powder X-ray diffraction (SR-PXD), thermal analysis (TG and DSC) and Siverts measurements (PCT). All three new compounds (denoted 1, 2 and 3) are observed during release and uptake of hydrogen in the potassium-aluminium-hydrogen system and may be new intermediates. All three compounds were indexed and the following unit cells were found, 1: cubic, a = 17.0248(9) Å, 2: cubic, a = 14.2746(4) Å and 3: orthorhombic, a = 10.46(1), b = 6.661(6) and c = 6.173(5) Å. Formation and observation of 1, 2 and 3 depends on the mechano-chemical sample preparation (ball milling), temperature, (heating rate), and hydrogen pressure (and temperature for pressure change). Compound 1 is often observed in the temperature range 55-150 °C for a medium ball-milled sample heated under a constant hydrogen pressure of 50 bar 1 is clearly an intermediate for formation of KAlH₄ and may have the composition K_yAlH_x with 1 ≤ y ≤ 3 and 4 ≤ x ≤ 6. Applying hydrogen pressure abruptly at elevated temperatures leads to faster hydrogenation, which can then be performed at lower hydrogen pressures. In the latter case, 1 is only observed shortly in a few PXD patterns. Compounds 2 and 3 are mainly observed during dehydrogenation of KAlH₄ in the temperature ranges of ca. 200 to 350 °C and 200 to 390 °C respectively, as relatively weak Bragg diffraction peaks.     

Gas and vapor adsorption in octacyanometallate-based frameworks Mn2[M(CN)8] (M = W,Mo) with exposed Mn sites

Dehydration of the isostructural three-dimensional (3D) octacyanometallate-based materials Mn₂M(CN)₈·7H₂O (M = Mo, 1·7H₂O; W, 2·7H₂O) generates robust porous frameworks (1 and 2). In the structure, the [M(CN)₈]⁴⁻ units are linked via octahedral Mn²⁺ centers to form an open 3D framework with 1D channels, in which the non-coordinated and coordinated water molecules are involved. The permanent porosities have been confirmed by thermogravimetric analysis, variable-temperature X-ray diffraction and Raman spectra, and adsorption (H₂O, N₂ and H₂) measurements. H₂ adsorption at 1.1 bar and 77 K was 0.60 wt% for 1 and 0.49 wt% for 2. At initial loading ΔH_ads has the value of ca. 10.0 kJ mol⁻¹ for both materials, which represents the highest value reported for any cyanide-based assemblies. The high enthalpy can be attributed to the presence of coordinatively-unsaturated Mn²⁺ sites left exposed by the removal of coordinated water molecules in the structure.     

Synthesis and characterization of trivalent metal porphyrin with NCS ligand for application in dye-sensitized solar cells

Two novel trivalent metal porphyrin dyes, P_Mn-HT-SCN and P_Ga-HT-SCN, were designed, synthesized and firstly applied in dye-sensitized solar cells (DSSCs). These two dyes possess porphyrin donor modified with manganese (III) and gallium (III) as coordination metal and NCS as the second ligand, cyanoacrylic acid as electron-accepting moiety and 4-hexylthiophene as π-spacers. Each of the porphyrin showed different adsorption behavior and saturated coverage on the TiO₂ surface. Between the two dyes, the P_Mn-HT-SCN-based DSSCs afforded the best photovoltaic performance: a short-circuit photocurrent density (J_sc) of 4.32 mA/cm², an open-circuit photovoltage (V_oc) of 0.61 V and a fill factor (FF) of 0.58, corresponding to a solar-to-electricity conversion efficiency of 1.53% under 100 mW/cm² irradiation.     

Silane-based hydrogen storage materials for fuel cell application: Hydrogen release via methanolysis and regeneration by hydride reduction from organosilanes

A series of cyclic- and linear organosilanes, 1-5, was prepared and examined as potential hydrogen storage materials. When a stoichiometric amount of methanol was added to a mixture of cyclic organosilane, (CH₂SiH₂)₃ (1) or (CH₂SiH₂CHSiH₃)₂ (2), and 5 mol% NaOMe, rapid hydrogen release was observed at room temperature within 10-15 s. The hydrogen storage capacities of compounds 1 and 2 were estimated to be 3.70 and 4.04 wt.-% H₂, respectively. However, to ensure the complete methanolysis from organosilanes including methanol evaporation at exothermic dehydrogenation condition, two equivs of methanol were used. The resulting methoxysilanes, (CH₂Si(OMe)₂)₃ (6) and (CH₂Si(OMe)₂CHSi(OMe)₃)₂ (7), were regenerated to the starting organosilanes in high yields by LiAlH₄ reduction. Linear organosilanes, SiH₃CH₂SiH₂CH₂SiH₃ (3), SiH₃CH₂CH(SiH₃)₂ (4), and SiH₃CH₂CH(SiH₃)CH₂SiH₃ (5) also showed fast hydrogen release kinetics at room temperature with hydrogen storage capacities of 4.26, 4.55, and 4.27 wt.% H₂, respectively; the corresponding methoxysilanes were successfully regenerated by LiAlH₄. Compound 1 was further tested as hydrogen source for fuel cell operation.     

Syntheses and photovoltaic properties of polymeric sensitizers using thiophene-based copolymer derivatives for dye-sensitized solar cells

We synthesized the thiophene-based copolymers (P(3TAF-co-3TAa)-A-n and P(3TAF-co-3TAa)-B-n) using two different kinds of thiophene monomers, (N-(3-thienylmethylene)-2-aminofluorene and 3-thiophene acetic acid), as sensitizers on the DSSCs. P(3TAF-co-3TAa)-A-n (n=1, 2, 3) was synthesized with different molar ratios (3TAF:3TAa=1:5, 1:10, 1:20) of monomers at room temperature, respectively. Also, P(3TAF-co-3TAa)-B-n (n=1, 2, 3) was synthesized with above molar ratios of monomers at 0 °C, respectively. The DSSCs devices were fabricated using the thiophene-based copolymers as sensitizers and their photovoltaic performances were measured by using a solar simulator under AM 1.5. In the DSSCs devices using polymeric sensitizers, V_oc is 0.53-0.60 V, J_sc is 1.9-4.5 mA/cm², FF is 0.51-0.63 and the power conversion efficiency is 0.63-1.53%, respectively.     

Understanding the performance and loss-mechanisms in donor-acceptor polymer based solar cells: Photocurrent generation, charge separation and carrier transport

Advances in bandgap and molecular spectral engineering have led to color-tunable donor-acceptor (DA) polymers for use in esthetically colored bulk-heterojunction (BHJ) photovoltaic devices where control and optimization of the physical processes governing their operation is necessary to realize high efficiency. We detail a study of the processes of photogeneration of charge carriers, their separation at the DA heterojunctions and their transport in solar cells fabricated from a series of dioxythiophene-benzothiadiazole (DOT-BTD) copolymers (PG1-PG3) as the electron donor and methanofullerene (PCBM) derivatives as the electron acceptor. We also examine the effect of the blend composition on carrier transport and photoresponse. The photogeneration of carriers and their dissociation increases with increase in concentration of the acceptor and peaks at ∼88% of PCBM. Measurements on single-carrier devices show that hole mobility in the polymer phase of the blends is enhanced by up to two orders at compositions having >80% of PCBM by weight. However, even at the optimized composition, the electron mobility in the blend is two orders of magnitude higher than the hole mobility. This largely imbalanced carrier transport results in the build-up of space-charges, limiting the efficiency of charge separation at short-circuit (∼53%) and the fill factor (<45%). To highlight the importance of attaining charge balance in BHJ DA blends for photovoltaics, we further investigate and compare solar cells from two model polymers, a low bandgap DA polymer (PSBTBT) and poly-3-hexylthiophene (P3HT), blended with PCBM. Our findings indicate that, in contrast to the DOT-BTD copolymers, carrier transport is significantly more balanced in these model systems, preventing space-charge build-up and reducing recombination, which results in a markedly improved charge separation efficiency and fill factor.     

The structural characterization of (NH4)2B10H10 and thermal decomposition studies of (NH4)2B10H10 and (NH4)2B12H12

The structure of (NH₄)₂B₁₀H₁₀ (1) was determined through powder XRD analysis. The thermal decomposition of 1 and (NH₄)₂B₁₂H₁₂ (2) was examined between 20 and 1000 °C using STMBMS methods. Between 200 and 400 °C a mixture of NH₃ and H₂ evolves from both compounds; above 400 °C only H₂ evolves. The dihydrogen bonding interaction in 1 is much stronger than that in 2. The stronger dihydrogen bond in 1 resulted in a significant reduction by up to 60 °C, but with a corresponding 25% decrease in the yield of H₂ in the lower temperature region and a doubling of the yield of NH₃. The decomposition of 1 follows a lower temperature exothermic reaction pathway that yields substantially more NH₃ than the higher temperature endothermic pathway of 2. Heating of 1 at 250 °C resulted in partial conversion of B₁₀H₁₀²⁻ to B₁₂H₁₂²⁻. Both 1 and 2 form an insoluble polymeric material after decomposition. The elements of the reaction network that control the release of H₂ from the B₁₀H₁₀²⁻ can be altered by conducting the experiment under conditions in which pressures of NH₃ and H₂ are either near, or away from, their equilibrium values.     

Local measurements of the time-dependent heat release rate and equivalence ratio using chemiluminescent emission from a flame

Chemiluminescent emissions from OH^⋅, CH^⋅, and C^⋅₂ and continuous emissions from CO^⋅₂ have been measured in natural-gas-fuelled, premixed, counterflow flames operating with an equivalence ratio between 0.7 and 1.3 and strain rates between 80 and 400 s⁻¹, achieved by varying the exit velocity of the jet between 1 and 5 m s⁻¹. Cassegrain receiving optics coupled to a high-performance spectroscopic unit allowed local, temporally resolved measurements of intensity of chemiluminescence in flat flames, which were compared with measurements along a line of sight obtained from flame spectra. This study allowed independent evaluation of the effects of strain rate and equivalence ratio on intensity of chemiluminescence and the ability of intensity of chemiluminescence to indicate heat release rate. Results suggest that intensities of chemiluminescence from OH^⋅ and CH^⋅ and background intensity from CO^⋅₂ are good indicators of heat release rate, whereas that from C^⋅₂ is not. The study also evaluated the ability to measure equivalence ratio of the reacting mixture using intensity of chemiluminescence and found that the intensity ratio OH^⋅/CH^⋅ has a monotonic decrease with equivalence ratio for lean and stoichiometric mixtures, while remaining independent of flame strain rate. The results indicate that the intensity ratio OH^⋅/CH^⋅ can measure with uncertainties of 5% the equivalence ratio up to values of 1.1 and with uncertainties of 20% for richer mixtures due to the low sensitivity of the intensity ratio OH^⋅/CH^⋅ for rich mixtures. The intensity ratios of C^⋅₂/OH^⋅ and C^⋅₂/CH^⋅ have a non-monotonic dependence on equivalence ratio and a dependence on strain rate and are thus not suitable for measurements of equivalence ratio. An approach to measuring the time-dependent equivalence ratio of the reacting mixture is suggested and data processing methods and associated uncertainties are presented. The potential of the technique for local measurements in practical burners is discussed and further evaluation of the spatial resolution is required in such flames. However, suggestions have been provided on how the spatial resolution can be improved in practical flames.     

A copper based metal-organic framework as single source for the synthesis of electrode materials for high-performance supercapacitors and glucose sensing applications

The article describes the conversion of MOF-199 to Cu–Cu₂O–CuO/C 700 (1) and Cu–Cu₂O–CuO/C 800 (2) nanostructures by simple pyrolysis at 700 and 800 °C under inert atmosphere. The X-ray photoelectron spectroscopy analysis reveals that the nanostructures Cu–Cu₂O–CuO/C consist of graphitic carbon functionalized with carboxylic, carbonyl and hydroxyl functional groups with copper/copper oxide particles on surfaces. The electrochemical properties of 1 and 2 are evaluated as electrode material for supercapacitors using cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The results for the capacitive performance from cyclic voltammetry and galvanostatic charge/discharge reveal that both the samples have gravimetric capacitance greater than 750 F g⁻¹ at a scan rate of 2 mV s⁻¹ and current density of 2 mA cm⁻². The samples retain about 43% of their initial capacitance even at high scan rate of 75 mV s⁻¹. The cycling performance of the nanostructures illustrate that there is 5.5% capacitance loss after 3000 cycles. The sample 1 and 2 are washed with 1 mol L⁻¹ HCl solution to obtain copper oxide free materials Cu/C 700 (3) and Cu/C 800 (4). Samples 3 and 4 are tested as electrocatalysts for glucose sensing and the cyclic voltammetry measurement shows enhanced current densities compared to the literature values.     

A nickel-complex sensitiser for dye-sensitised solar cells

We report the first example of a Ni(II) complex that demonstrates sensitiser function in a Dye-Sensitised Solar Cell (DSSC). Complexes [Ni(dcbpy)(qdt)] (1), [Ni(decbpy)(qdt)] (2) and [Ni(decbpy)Cl₂] (3) (where dcbpy = 4,4′-dicarboxy-2,2′-bipyridine; decbpy = 4,4′-di(CO₂Et)-2,2′-bipyridine; and qdt = quinoxaline-2,3-dithiolate) have been prepared. Characterisation was carried out using electrochemical, spectroscopic and computational techniques. Intensive visible transitions of 1 and 2 have been assigned predominantly to Ligand-to-Ligand Charge Transfer (LLCT) from the qdt to the diimine ligand, suggesting appropriate charge separation for application in a photoelectrochemical device. TiO₂ sensitised with 2, following charge injection, processes a recombination time significantly long for photovoltaic function. In a DSSC, using redox electrolyte, photocurrents and photovoltages of 0.293 mA and 521 mV were observed, with optimum values requiring TiCl₄ post-treatment of TiO₂ and co-adsorption of Chenodeoxycholic acid (Cheno). Although photovoltaic function was observed, the low photocurrent is attributed to a short-lived excited state lifetime resulting in poor charge injection from the Ni(II) sensitiser.     

Novel iminocoumarin dyes as photosensitizers for dye-sensitized solar cell

Novel iminocoumarin dyes (2a-c and 3a-c) having carboxyl and hydroxyl anchoring groups onto the dyes skeletons have been designed and synthesized for the application of dye-sensitized nanocrystalline TiO₂ solar cells (DSSCs). The photophysical and electrochemical studies showed that these iminocoumarin dyes are suitable as light harvesting sensitizers in DSSC application. The dyes having carboxyl and hydroxyl anchoring groups (2a-c) showed better efficiency when compared to the dyes having carboxyl group (3a-c) alone. The cell consisted of dye 2a generated the highest solar-to-electricity conversion efficiency (η) of 0.767% (open circuit voltage (V_oc) = 0.491 V, short circuit photocurrent density (J_sc) = 2.461 mA cm⁻², fill factor (ff) = 0.635) under simulated AM 1.5 irradiation (1000 W m⁻²) with a total semiconductor area of 0.25 cm². The corresponding incident photon-to-current conversion efficiency (IPCE) of the above cell was 21.38%. The overall low efficiency of the dyes is ascribed to the lack of light harvesting ability at longer wavelength region.