Intensity-modulated Photovoltage Research Articles

Efficiency enhancement of PbS quantum dots-sensitized nanocrystalline SnO2 thin film prepared by two-phase method

A novel two-phase method was employed to directly deposit PbS quantum dots (QDs) on nanocrystalline SnO2 thin films. In the two-phase method, the nanocrystalline SnO2 thin film with adsorption of Pb2+ ions was placed in an aqueous solution, and S2- ions were dissolved in an oil solution. As two solutions were contacted, S2- ions prefer to transfer to the aqueous solution and diffuse to the thin film surface with the adsorbed Pb2+ ions to homogeneously form monodispersed PbS QDs on the nanocrystalline thin film. The homogeneous monodispersed QDs-sensitized thin film was used as a photoelectrode to fabricate QDs-sensitized solar cell. The loaded amount of PbS QDs and the thickness of ZnS passivation layer were optimized to obtain the highest light-to-electric conversion efficiency of 1.01 % under the simulated AM 1.5 illumination, which is increased by 61 % compared with that of the PbS QDs-sensitized solar cell employing the successive ionic layer adsorption and reaction (SILAR). The solar cell with homogeneous sensitization of QDs generates a photocurrent density of 11.09 mA center dot cm(-2), which is 2.4 times higher than that of the unhomogeneous one prepared by SILAR. The conversion efficiency enhancement mechanism due to the two-phase method was discussed in detail through the measurements of intensity-modulated photovoltage spectrum and electrochemical impedance spectroscopy.

Correlating Changes in Electron Lifetime and Mobility on Photocatalytic Activity at Network-Modified TiO2 Aerogels

We use intensity-modulated photovoltage spectroscopy (IMVS) and intensity-modulated photocurrent spectroscopy (IMPS) to characterize carrier dynamics in titania (TiO2) aerogels under photocatalytic conditions. By systematically increasing the weight fraction of the sol–gel precursor during TiO2 sol–gel synthesis, we are able to impart drastic changes in carrier transport/trapping and improve the photocatalytic activity of TiO2 aerogels for two mechanistically divergent photochemical reactions: reductive water splitting (H2 generation) and oxidative degradation of dichloroacetate (DCA). The lifetimes of photogenerated electrons increase in going from lowest-to-highest precursor concentrations, as measured by IMVS, indicating increasing site density for electron traps—a trend that correlates with an 8× improvement for photocatalytic H2 generation. Electron mobility in the aerogel films, as measured by IMPS, decreases with increasing trap density, further implicating the trapping sites as reactive sites. In ...

Efficient thieno[3,2-a]carbazole-based organic dyes for dye-sensitized solar cells

A new series of donor-π-acceptor organic dyes based on thieno[3,2-a]carbazole as a new donor moiety, designated as JH-dyes, has been synthesized for dye-sensitized solar cells (DSCs). The photophysical properties and DSC performances of JH-dyes have been characterized. Among the three JH-dyes, a high power conversion efficiency (η) of 8.04% with a short-circuit current (Jsc) of 14.08 mA cm−2 and an open-circuit voltage (Voc) of 0.78 V has been achieved for DSC based on JH03 bearing hexyl chains on the terthiophene π-linker. The electrochemical impedance spectra (EIS) and intensity-modulated photovoltage spectroscopy (IMVS) of JH-cells were measured to understand the effect of molecular structure on charge transfer process and electron life time.

Enhancing the Efficiency and Charge Transport Characteristics of Dye-Sensitized Solar Cells by Adding Graphene Nanosheets to TiO2 Working Electrodes

In this study, TiO2-GN nanocomposite working electrodes were fabricated by adding graphene nanosheets (GNs) to TiO2 thin-film working electrodes. The influence of the thickness of the TiO2 thin-film working electrodes on the efficiency and charge transport characteristics of the corresponding dye-sensitized solar cells (DSSCs) was investigated. A GN solution was spin-coated onto the TiO2 thin films, which were then sintered at 100°C in order to fabricate TiO2-GN working electrodes. The characteristics of various working electrodes were analyzed via scanning electron microscopy, atomic force microscopy, surface profilometry, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy. Moreover, the DSSCs fabricated from these working electrodes were characterized via current density-voltage, incident photo-to-current conversion efficiency, electrochemical impedance spectroscopy, intensity-modulated photocurrent spectroscopy, and intensity-modulated photovoltage spectroscopy measurements. The results indicate that adding GNs to TiO2 thin films can enhance the electron transport rate and charge collection efficiency in TiO2-GN working electrodes, and thereby increase the power conversion efficiency of DSSCs. As such, DSSCs containing the TiO2-GN working electrodes exhibited an efficiency of 8.07%, which is 24.3% higher than that (6.49%) of the DSSCs containing conventional TiO2 working electrodes.

Performance enhancement of dye-sensitized solar cell with a TiCl4-treated TiO2 compact layer

We here show that an effective blocking layer for dye-sensitized solar cells (DSSCs) can be formed by spin coating a commercial TiO2 paste onto a conducting glass substrate. The spin-coated TiO2 layer was made more compact than the main absorption layer by TiCl4 treatment. DSSCs employing a compact layer exhibited an average current density and an efficiency of 19.09 mA/cm2 and 9.10%, respectively, while 16.91 mA/cm2 and 8.33% were obtained from unblocked reference cells. The enhanced DSSC performance is attributed to the increased electron lifetime. Intensity-modulated photovoltage spectroscopy and open-circuit voltage decay analysis showed that a TiCl4-treated compact layer substantially suppresses the charge recombination at the TiO2/substrate interface, thereby increasing the electron lifetime.

Characterization of Planar Lead Halide Perovskite Solar Cells by Impedance Spectroscopy, Open-Circuit Photovoltage Decay, and Intensity-Modulated Photovoltage/Photocurrent Spectroscopy

Thin film lead halide perovskite cells, where the perovskite layer is deposited directly onto a flat titania blocking layer, have reached AM 1.5 efficiencies of over 15%,1 showing that the mesoporous scaffold used in early types of perovskite solar cells is not essential. We used a variety of techniques to gain a better understanding of thin film perovskite cells prepared by a solution-based method. Twelve cells were studied, which showed AM 1.5 efficiencies of ∼11%. The properties of the cells were investigated using impedance spectroscopy, intensity-modulated photovoltage spectroscopy (IMVS), intensity-modulated photocurrent spectroscopy (IMPS), and open-circuit photovoltage decay (OCVD). Despite the fact that all 12 cells were prepared at the same time under nominally identical conditions, their behavior fell into two distinct groups. One half of the cells exhibited ideality factors of m ≈ 2.5, and the other half showed ideality factors of m ≈ 5. Impedance spectroscopy carried out under illumination at open circuit for a range of intensities showed that the cell capacitance was dominated by the geometric capacitance of the perovskite layer rather than the chemical or diffusion capacitance due to photogenerated carriers. The voltage dependence of the recombination resistance gave ideality factors similar to those derived from the intensity dependence of the open-circuit voltage. The IMVS time constant was determined by the product of the geometric capacitance and the recombination resistance. The two types of cells gave very different OCVD responses. The cells with m ≈ 2.5 showed a persistent photovoltage effect that was absent in the case of the cells with higher ideality factors. The IMPS responses provide evidence of minor efficiency losses by recombination under short-circuit conditions.

An insight into the role of oxygen vacancy in hydrogenated TiO₂ nanocrystals in the performance of dye-sensitized solar cells.

Hydrogenated titanium dioxide (H-TiO2) nanocrystals were successfully prepared via annealing TiO2 in H2/N2 mixed gas flow at elevated temperatures ranging from 300 to 600 °C. Electron paramagnetic resonance (EPR) spectra were used to determine the produced oxygen vacancy in H-TiO2. Variations in temperature were studied to investigate the concentration change of oxygen vacancy in H-TiO2. The H-TiO2 nanocrystals prepared at different temperatures were employed into photoanodes sensitized by N719 dye and found to have exceptional effect on the solar-to-electric energy conversion efficiency (η). Photoanodes with H-TiO2 nanocrystals hydrogenated at 300 °C show the highest short-circuit current density (Jsc) of 18.92 mA cm(-2) and photoelectrical conversion efficiency of 7.76% under standard AM 1.5 global solar irradiation, indicating a 27 and 28% enhancement in Jsc and η, respectively, in comparison to those with TiO2. The enhancement is attributed to high donor density, narrow band gap and positive shift of flat band energy (Vfb) of H-TiO2 that promote the driving force for electron injection. Intensity-modulated photocurrent spectroscopy (IMPS) accompanied by intensity-modulated photovoltage spectroscopy (IMVS) and other analyses were applied to shed more light on the fundamental mechanisms inside the charge transfer and transport in these systems.

Comparative Study on Pyrido[3,4-b]pyrazine-Based Sensitizers by Tuning Bulky Donors for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) with cobalt electrolytes have gained increasing attention. In this Research Article, two new pyrido[3,4-b]pyrazine-based sensitizers with different cores of bulky donors (indoline for DT-1 and triphenylamine for DT-2) were designed and synthesized for a comparative study of their photophysical and electrochemical properties and device performance and were also analyzed through density functional theory calculations. The results of density function theory calculations reveal the limited electronic communication between the biphenyl branch at the cis-position of N-phenylindoline and the indoline core, which could act as an insulating blocking group and inhibit the dye aggregation and charge recombination at the interface of TiO2/dye/electrolyte. As expected, DSSCs based on DT-1 with cobalt redox electrolyte gained a higher photoelectric conversion efficiency of 8.57% under standard AM 1.5 G simulated sunlight, with Jsc = 16.08 mA cm(-2), Voc = 802 mV, and FF = 0.66. Both electrochemical impedance spectroscopy (EIS) and intensity-modulated photovoltage spectroscopy (IMVS) suggest that charge recombination in DSSCs based on DT-1 is much less than that in their counterparts of DT-2, owing to the bigger donor size and the insulating blocking branch in the donor of DT-1.

Tuning of spectral response by co-sensitization in black-dye based dye-sensitized solar cell

We have systematically tuned the spectral response of black dye using the co-sensitization technique. In this study we have selected two co-sensitizers coded as AK-01 and U01. The individual overall conversion efficiencies (η) of these co-sensitizers AK-01 and U01 are 6.20% and 6.01%, respectively. A better power conversion efficiency of 10.21% and 10.56% of DSSC was observed when black dye was co-sensitized with AK-01 and U01, respectively, compare to individual single black dye (9.18%). Both AK-01 and U01 co-sensitizers effectively overcome the light absorption of redox electrolyte and improved the dip in the incident-photon-to-current conversion efficiency spectra at 350–420 nm region compared with single black dye. Intensity-modulated photovoltage spectroscopy result shows the longer lifetime of black dye+U01 compared to the black dye which suggest the robust U01 dye sufficiently suppressed the recombination of electrons in the TiO2 with redox electrolyte without any interaction with black dye when co-adsorbed on TiO2.

Comparison of Solid-State Quantum-Dot-Sensitized Solar Cells with ex Situ and in Situ Grown PbS Quantum Dots

Differences in the solar cell performance of solid-state PbS quantum-dot-sensitized solar cells fabricated with ex situ and in situ grown PbS quantum dots were investigated. The PbS quantum dots were either anchored on mesoporous TiO2 via l-glutathione (GSH) linker exchange or prepared in situ by the successive ionic layer adsorption/reaction (SILAR) method to create quantum-dot-sensitized solar cells. Spiro-OMeTAD was used as the organic p-type hole transporting material (HTM). The performance of the cells was evaluated with current–voltage, external quantum efficiency, and impedance spectroscopy (IS) measurements, and electron lifetimes were measured with open-circuit voltage decay (OCVD), intensity-modulated photovoltage spectroscopy (IMVS) techniques as well as with IS measurements. Analysis of the experimental data indicates that the SILAR route provides more intimate contacts at both TiO2/PbS and PbS/HTM interfaces, which results in more efficient charge injection and separation and thus higher photocurrents. However, the results of the OCVD, IMVS, and IS measurements demonstrate that the cells sensitized with PbS quantum dots prepared ex situ have longer electron lifetimes, indicating that back-transfer of electrons to the HTM is slower, probably as a consequence of passivation of surface states by the GSH ligands.

Elucidating Transport-Recombination Mechanisms in Perovskite Solar Cells by Small-Perturbation Techniques

Solar cells using perovskite as semiconducting pigment have recently attracted a surge of interest owing to their remarkable solar-to-electric conversion efficiencies and ease of processing. In this direction various device architectures and materials have been employed, and attempts were made to elucidate the underlying working principles. However, factors governing the performance of perovskite devices are still obscure. For instance, the interpretation of electrochemical impedance spectroscopy (EIS) is not straightforward, and the complexity of the equivalent circuits hinders the identification of transport and recombination mechanisms in devices, especially those that determine the performance of the device. Here in we carried out a comprehensive and complementary characterization of perovskite solar cells by using an array of small-perturbation techniques: EIS and intensity-modulated photocurrent and photovoltage spectroscopy (IMPS/IMVS). The employment of IMPS allowed us to identify two transport times separated by 2 orders of magnitude and with opposite voltage dependences. For recombination, well agreement was found between lifetimes obtained by IMVS and EIS. The feature associated with recombination and charge accumulation in an impedance spectrum through correlation to the IMVS response was experimentally identified. This correlation paves the way to reconstruct the current–voltage curve using a continuity equation model for transport and recombination in the working device. The adopted methodology demonstrates that complementary techniques facilitate the interpretation of EIS results in perovskite solar cells, allowing us for the identification of the transport-recombination mechanisms and providing new insights into the efficiency-determining steps.

An investigation on the photoelectrochemical properties of dye-sensitized solar cells based on graphene–TiO2 composite photoanodes

The graphene–TiO2 nanocomposite has been prepared by mixing graphene oxide (GO) and tetra-n-butyl titanate (TBT) followed by the facile hydrothermal process when the reduction of GO to reduced graphene oxide (RGO) and the hydrolysis of TBT to TiO2 happen. Characterization of the graphene–TiO2 nanostructures is investigated in detail by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. A dye-sensitized solar cell (DSSC) based on graphene–TiO2 composite photoelectrode exhibits a high energy conversion efficiency of 4.28%, compared with a DSSC based on pure TiO2 photoelectrode (3.11%), accompanied by an increment in both short-circuit photocurrent density and open-circuit voltage. The significant enhancement in performance of DSSC is investigated through intensity-modulated photovoltage spectroscopy, intensity-modulated photocurrent spectroscopy, and electrochemical impedance spectroscopy. It is found that the incorporation of two-dimensional graphene nanosheets in the TiO2 electrodes is the key factor leading to the improved photogenerated electron transfer ability and reduced charge recombination.

Novel π-Conjugated Porphyrin Sensitizers for Dye-Sensitized Solar Cells

Inspired by the efficient energy transfer in naturally occurring photosynthetic reaction centers, numerous porphyrins have been designed and synthesized for dye-sensitized solar cell (DSSC) applications. The intrinsic advantages of porphyrin-based dyes are their rigid molecular structures with large absorption coefficients in the visible region and their many reaction sites, i.e., four meso and eight β positions, available for functionalization. However, porphyrins are known to suffer from dye aggregation due to their planar structural nature. In addition to the molecular design for potential porphyrin sensitizers, we have shown that co-sensitization of a zinc porphyrin with a well designed organic dye is a good strategy to change the aggregation morphology of the porphyrin adsorbed on TiO2 film to further improve its device performance. In this lecture, I will present our recent results based on a series of novel porphyrin sensitizers together with the approach of co-sensitization of porphyrins with organic dyes and/or porphyrin dimers. Extension of π-conjugation can be achieved by attaching various cyclic aromatic hydrocarbon substituents, such as anthracene, tetracene, pyrene, fluorene, and amino-substituted electron-donating groups opposite to the anchoring group of the target porphyrin. We will demonstrate that devices made of such porphyrins have reached the power conversion efficiency above 10 % using iodine-based electrolyte under one-sun irradiation. For the co-sensitization approach, combination of a porphyrin dye co-sensitized with an organic dye and a porphyrin dimer on a TiO2 film in a device according to a either a stepwise or a cocktail approach resulted in significant enhancement on both J SC and V OC relative to their individual single-dye sensitized devices. For characterizations, two different approaches based on time-resolved and frequency-domain techniques will be introduced. For the time-resolved approach, transient photocurrent and photovoltage decays were obtained based on several CW bias light irradiations of varied intensities at short-circuit and open-circuit conditions, respectively. A small-intensity LED pulse (~50 ms duration) at 630 nm was used as a perturbation probe to monitor the electron-transport kinetics at short-circuit condition or the charge-recombination kinetics at open-circuit condition. For the frequency-domain approach, electrochemical impedance spectroscopy (EIS), intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS) measurements were also carried out. Both time-resolved and frequency-domain techniques were applied to various highly efficient DSSC systems based on porphyrin and porphyrin + organic dye systems to rationalize their photovoltaic performances.

The Redox Pair Chemical Environment Influence on the Recombination Loss in Dye-Sensitized Solar Cells

Reduction of recombination losses in dye-sensitized solar cells (DSC) is vital to fabricate efficient devices. The electron recombination lifetime depends on the relative energetics of the semiconductor and the redox pair and on the chemical nature of the electrolyte (hole conductor). In this work, the behavior of the electron lifetime in DSC devices prepared with various solvents (acetonitrile, valeronitrile, ethylene carbonate, pure ionic liquids), additives (lithium ions, TBP), and redox pairs (iodide/iodine, Co(II)/Co(III)) is thoroughly studied using high-extinction dyes. Lifetimes were extracted by means of small-perturbation electrochemical techniques (impedance spectroscopy, intensity-modulated photovoltage spectroscopy) and open-circuit voltage decays. To ensure a safe inner comparison and a proper interpretation, all devices were constructed using the same type of TiO2 electrode and the same dyes (C101 and Z907 for iodide/iodine and cobalt-based electrolytes, respectively). Furthermore, small-pe...

Control of the recombination rate by changing the polarity of the electrolyte in dye-sensitized solar cells.

Recombination in Dye-sensitized Solar Cells (DSCs) is an electron transfer process critical for high efficiency. The chemical nature of the electron acceptor is known to have an important impact on recombination and, hence, limits the choice of hole conductors in DSCs and related solar cells. In this respect, Room Temperature Ionic liquids (RTILs) have been recognized as an alternative to volatile organic solvents due to their negligible vapor pressure, which offers the chance for long-term stability. However, RTIL-based electrolytes lead to lower performance, a feature that has been attributed to the high viscosity of ionic liquids and the mass-transport limitation associated with it. In this work we show that the origin of the lower performance is also related to an increase in the recombination loss due to the polar nature of the RTIL and the influence of the reorganization energy of the electron acceptor in a polar environment. To investigate this chemical effect, different mixing ratios of RTILs and an organic solvent (acetonitrile) have been considered. The fabricated devices have been characterized by small-perturbation techniques (Impedance Electrochemical Spectroscopy and Intensity-Modulated Photovoltage and Photocurrent Spectroscopies) and Open-Circuit Voltage Decay measurements, which have been used to extract electron lifetimes at different applied voltages. Two different ruthenium dyes (hydrophilic N719 and hydrophobic Z907) and two different cations in the RTIL (imidazolium- and pyrrolidinium-based) have been considered. The results obtained show that for pure ionic liquids the lifetime-voltage curve is exponential, which is a signature of large reorganization energies for electron transfer. In contrast, pure acetonitrile exhibits a non-exponential behavior, which is consistent with relatively low reorganization energy. Interestingly, and as a general rule, we find that recombination is faster in systems with higher reorganization energies. This is interpreted as a consequence of the availability of more acceptor states for electron transfer. In addition, it is found that mixing RTILs and acetonitrile is an interesting strategy to increase the stability of DSCs without significant recombination losses, provided that the right dye and RTIL, in particular, a pyrrolidinium component, are used.

Electrochemical properties of TiO2 nanoparticle/nanorod composite photoanode for dye-sensitized solar cells

A unique composite of TiO2 nanoparticles (NPs) and nanorods (NRs) has been used to fabricate a photoelectrode for developing dye-sensitized solar cells (DSSCs) with higher sensitivity. The TiO2 nanorods were synthesized using a mechanical process, in which electrospun TiO2 nanofibers was grinded in a controlled way to obtain uniform size distribution. The characteristics of electron transport, recombination lifetime and charge collection were investigated by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). Photoelectrodes prepared with the composites of NRs and NPs showed significant improvements in electron transportation compared to only NP photoelectrodes, which would enhance the photovoltaic performance of DSSCs. IMPS and IMVS measurements show that fast electron transport and slightly decreased recombination lifetime resulted in the improvement of efficiency. The highest energy conversion efficiency obtained from the photoelectrodes fabricated with the as-prepared rutile TiO2 nanofibers at 5 wt% NR content was up to 6.1% under AM1.5G solar illumination. The results demonstrate that the composite nanostructure can take advantage of both the fast electron transport of the nanorods and the high surface area of the nanoparticles.

Synthesis and formation mechanism of mesoporous TiO2 microspheres for scattering layer in dye-sensitized solar cells

Abstract This report describes a facile method for preparing mesoporous TiO 2 microspheres (TMs) for scattering layer in DSSCs. In this method, TMs can be synthesized by direct hydrolysis of TiCl 4 in ethanol aqueous solution at 40 °C, and the microspheres size could be easily controlled by varying the adding amount of CTAB. The TMs were characterized by scanning electron microcopy (SEM), X-ray diffraction (XRD), and nitrogen sorption analysis. A possible formation mechanism of the TMs was proposed on the basis of time-dependent measurements by TEM. Photoanodes consisting of the TMs as scattering layers were then fabricated. The use of TMs largely enhances the dye loading and gives highly effective light scattering. Using TMs with a diameter of 400 nm (TM400), a high photon to electricity conversion of 9.33% has been achieved, indicating a 24% increase in the conversion efficiency compared to the photoanode without scattering layer (7.54%). The charge transport behavior of the cells was investigated by intensity-modulated photocurrent and photovoltage spectroscopic analysis (IMPS and IMVS), and the results indicates that the DSSCs with TM400 as a scattering layer has a higher η cc (80.2%) value than the DSSCs without a scattering layer (71%). This method provides a feasible way for fabricating low-cost scattering layers in DSSCs.

Adsorption and electrochemical properties of photoelectrodes depending on TiO2 film thickness for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) consist of a photoelectrode, electrolytes, and a counter electrode. In this work, we prepared the photo electrode using a commercial paste coated on F-doped SnO2 (FTO) glass substrates by the screen printing method; the thicknesses of the coated layers were 5, 9, and 14μm. We developed an adsorption apparatus to understand the adsorption mechanism of dye molecules depending on TiO2 thin film thickness and to obtain precise adsorption amounts without involving a desorption step. Commercial N719 dye was employed to measure the adsorption data, which were then analyzed using the pseudo-first-order and pseudo-second-order models. The diffusion coefficient of the electrolyte containing the iodide/triiodide redox couple was determined by polarization measurements. Electrochemical properties in terms of electron harvesting and electron transport depending on film thickness were evaluated based on incident photon to current conversion efficiency, intensity-modulated photocurrent spectroscopy, and intensity-modulated photovoltage spectroscopy.

Cyclometalated Ruthenium Sensitizers Bearing a Triphenylamino Group for p-Type NiO Dye-Sensitized Solar Cells

We report the synthesis, photophysical, and electrochemical studies of a series of cyclometalated ruthenium sensitizers carrying triphenylamino linkers for p-type NiO dye-sensitized solar cells (DSSCs). The general structure of these ruthenium sensitizers is Ru[N∧N]2[N∧C], where [N∧N] is a diimine ligand and [N∧C] is a cyclometalated ligand. The triphenylamino group is attached to the -para position of the ruthenium-carbon bond of the [N∧)] ligand as a linker to bridge the ruthenium chromophore and the NiO surface and to enhance the electronic coupling for hole injection. As a result, cells made with these sensitizers generate higher short-circuit currents (Jsc) than cells sensitized with our prior sensitizers with phenylene linkers. Morever the N∧N ligands are systematically tuned from 2,2'-bipyridine (O3), to 1,10-phenanthroline (O13), and to bathophenanthroline (O17). Following the series, the conjugation of the N∧N ligand is increased, which results in the enhancement of extinction coefficient and the red shift of light absorption. However the solar cell sensitized with O3 still gives the largest Jsc of 3.04 mA/cm2. The large Jsc highlights the promising potential of using these cyclometalated ruthenium sensitizers for NiO DSSCs. In addition, the carrier dynamics of these solar cells has been systematically studied by intensity-modulated photovoltage spectroscopy (IMVS) and intensity-modulated photocurrent spectroscopy (IMPS). The results suggest that the O3 solar cell giving the largest Jsc is likely caused by the slow geminate charge recombination and efficient dye regeneration.

One‐step Synthesis of Vertically Aligned Anatase Thornbush‐like TiO2 Nanowire Arrays on Transparent Conducting Oxides for Solid‐State Dye‐Sensitized Solar Cells

Herein, we report a facile synthesis of high-density anatase-phase vertically aligned thornbush-like TiO2 nanowires (TBWs) on transparent conducting oxide glasses. Morphologically controllable TBW arrays of 9 μm in length are generated through a one-step hydrothermal reaction at 200 °C over 11 h using potassium titanium oxide oxalate dehydrate, diethylene glycol (DEG), and water. The TBWs consist of a large number of nanoplates or nanorods, as confirmed by SEM and TEM imaging. The morphologies of TBWs are controllable by adjusting DEG/water ratios. TBW diameters gradually decrease from 600 (TBW600) to 400 (TBW400) to 200 nm (TBW200) and morphologies change from nanoplates to nanorods with an increase in DEG content. TBWs are utilized as photoanodes for quasi-solid-state dye-sensitized solar cells (qssDSSCs) and solid-state DSSCs (ssDSSCs). The energy-conversion efficiency of qssDSSCs is in the order: TBW200 (5.2%)>TBW400 (4.5%)>TBW600 (3.4%). These results can be attributed to the different surface areas, light-scattering effects, and charge transport rates, as confirmed by dye-loading measurements, reflectance spectroscopy, and incident photon-to-electron conversion efficiency and intensity-modulated photovoltage spectroscopy/intensity-modulated photocurrent spectroscopy analyses. TBW200 is further treated with a graft-copolymer-directed organized mesoporous TiO2 to increase the surface area and interconnectivity of TBWs. As a result, the energy-conversion efficiency of the ssDSSC increases to 6.7% at 100 mW cm(-2) , which is among the highest values for N719-dye-based ssDSSCs.