Understanding mechanisms in DSSCs is fundamental for their improvement; this includes the nanocrystalline semiconducting layer behaviour. Different mesoporous TiO2 layers are fabricated and analyzed for possible use in DSSC solar cells. The preparations included the addition of P123 triblock copolymer as structuring agent to the synthesized anatase sol. This preparation was also mixed with Degussa P25 nanoparticles in one case and polystyrene latex in another. Mesoporous mixed TiO2-SiO2 thin layers were also analyzed. The diverse morphology and features are studied by microscopic techniques and by means of spectral quantum efficiency of a photoelectrochemical cell (PEC) that uses as photoelectrode the unsensitized porous TiO\_2 layer. Contact angle measurements are also performed. We have found that a very high specific area due to very small nanocrystals and small pores can hinder electrolyte penetration in the pores formed by TiO\_2 nanograins, affecting photoelectrodes efficiency.
Novel highly active, optically-transparent electrode catalyst containing Pt, PtOx, graphene oxide and stacked graphene platelet nanofibers is developed for a cathode of Cu(II/I)-mediated dye-sensitized solar cells.
Three Cu(II/I)-phenanthroline and Cu(II/I)-bipyridine redox mediators are studied on various electrodes and in variety of electrolyte solutions using cyclic voltammetry and impedance spectroscopy on symmetrical dummy cells.
In the present work we compare TiO2 nanotube lift-off strategies for the construction of front-side illuminated dye-sensitized solar cells (DSSCs). Anodic nanotube layers were detached from the metallic back contact by using different techniques and transferred onto an FTO substrate. We show that if we use an optimized potential step treatment to fabricate membranes, DSSC cell efficiencies can be significantly increased (>8%). This improved efficiency is ascribed to higher specific dye-loading and enhanced electron transport properties of optimally fabricated TiO2 nanotube membranes.
Dye-sensitized solar cells (DSC), built upon organic/inorganic hybrid materials, are promising third generation solar cells, which attract wide attentions due to their low-cost, flexibility and environment-friendly properties. We review recent progresses in DSC research, focusing on atomic-scale investigations of the interface electronic structures and dynamical processes, including dye adsorption structure onto TiO2, ultrafast electron injection, hot-electron injection, multiple-exciton generation and electron-hole recombination. We briefly summarize advanced experimental techniques and theor…
We use free-standing TiO2 nanotube membranes that are transferred onto FTO slides in front-side illuminated dye-sensitized solar cells (DSSCs). We investigate the key parameters for solar cell arrangement of self-ordered anodic TiO2 nanotube layers on the FTO substrate and namely the influence of the annealing procedure on the DSSC light conversion efficiency. The results show that using an optimal temperature annealing profile can significantly enhance the DSSC efficiency (in our case 9.8 %), as it leads to a markedly lower density of trapping states in the tube oxide, and thus to strongly im…
We fabricate photo-anodes by transferring anodic TiO2 nanotube membranes in tube-top-down configuration on FTO glass, and use them for constructing frontside illuminated dye-sensitized solar cells. Prior to solar cell construction, the tube-based photo-anodes are crystallized at different temperatures (400-800°C), and the effects of tube electron transport properties on the photovoltaic performance of the solar cells are investigated. We show that improved solar cell efficiencies (up to ca. 8.0%) can be reached by high-temperature treatment of the tube membranes. Consistently with electron tra…
We report an optically gated transistor composed of CdSe nanocrystals (NCs), sensitized with the dye Zinc beta-tetraaminophthalocyanine for operation in the first telecom window. This device shows a high ON/OFF ratio of six orders of magnitude in the red spectral region and an unprecedented 4.5 orders of magnitude at 847 nm. By transient absorption spectroscopy, we reveal that this unexpected infrared sensitivity is due to electron transfer from the dye to the CdSe NCs within 5 ps. We show by time-resolved photocurrent measurements that this enables fast rise times during near-infrared optical…
Plasmonic core-shell nanoparticles (PCSNPs) can function as nanoantennas and improve the efficiency of dye-sensitized solar cells (DSSCs). To achieve maximum enhancement, the morphology of PCSNPs need to be optimized. Here we precisely control the morphology of Au@TiO2 PCSNPs and systematically study its influence on the plasmonic enhancement effect. Enhancement mechanism was found to vary with the thickness of TiO2 shell. PCSNPs with thinner shell enhance the current due to plasmonic effect, whereas particles with thicker shell improve the voltage due to increasing semiconducting character. W…
Effect of Mixed Ratios of Mangosteen Peel (Garcinia mangostana L.) and Grass Jelly Leaf (Cyclea barbata L. Miers) Natural Dyes on the Performance of Dye-Sensitized Solar Cells (DSSC)
In this work, using the DFT and TDDFT, we have theoretically studied the electronic and optical properties of the two recently synthesized coadsorbents Y1 and Y2, which were aimed to enhance the efficiency of the black dye-sensitized solar cells. To determine the solvatochromic shifts, both the implicit and mixed implicit-explicit models have been used. The connection between the solvatochromic shifts and the changes of dipole moments in the excitation process is discussed. The difference in excitation charge transfer is utilized to explain the experimentally observed difference in $J_{sc}$ fo…
TiO2 nanorods have been prepared on ITO substrates by dc reactive magnetron sputtering technique. The hydroxyl groups have been introduced on the nanorods surface. The structure and the optical properties of these nanorods have been studied. The dye-sensitized solar cells (DSSCs) have been assembled using these TiO2 nanorods as photoelectrode. And the effect of the hydroxyl groups on the properties of the photoelectric conversion of the DSSCs has been studied.
Dye sensitized Solar cells (DSSCs) were fabricated with four naturally occurring anthocyanin dyes extracted from naturally found fruits/ juices (viz. Indian Jamun, Plum, Black Currant and Berries) as sensitizers. Extraction of anthocyanin was done using acidified ethanol. The highest power conversion efficiencies (η) of 0.55% and 0.53% were achieved for the DSSCs fabricated using anthocyanin extracts of blackcurrant and mixed berry juice. Widespread availability of these fruits/juices, high concentration of anthocyanins in them and ease of extraction of anthocyanin dyes from these commonly ava…
We report on the effect of the strong spin orbit coupling and the Lorentz force on the efficiency of TiO2 based dye sensitized solar cells. Upon inclusion of Ho2O3, due to the strong spin orbit coupling of the rare earth Ho3+ ion, we do see 13 percent enhancement in the efficiency. We attribute such an enhancement in power conversion efficiency to the increased lifetime of the photo-excited excitons. Essentially, a Ho3+ ion accelerates the phenomenon of the spin rephasing or the intersystem crossing of the excitons in a photosensitizer. Increase in the absorbance and decrease in the photolumin…
We study within the many-body Green's function $GW$ and Bethe-Salpeter formalisms the excitation energies of several coumarin dyes proposed as an efficient alternative to ruthenium complexes for dye-sensitized solar cells. Due to their internal donor-acceptor structure, these chromophores present low-lying excitations showing a strong intramolecular charge-transfer character. We show that combining $GW$ and Bethe-Salpeter calculations leads to charge-transfer excitation energies and oscillator strengths in excellent agreement with reference range-separated functional studies or coupled-cluster…
Propionitrile electrolyte solutions mixed with sulfolane or with 1-ethyl 3-methyl imidazolium tetracyanoborate (ionic liquid) are optimized for Co(bpy)3+/Co(bpy)2+-mediated DSCs working at low illumination intensity.
Concentration spectral manifestation of the ionic and neutral dyes encapsulated in mesoporous silicate films was studied. The mesoporous dyed SiO2 film was prepared by sol-gel technology with use as surfactant the amphiphilic three-bloc copolymer Pluronic P123. It was discovered when dye concentration exceeds mesoporous one the new spectral bands appear that are distinct from the initial monomolecular predecessors. To explain the phenomena guess is formulated and proved that origin of new spectrums is obliged to formation of the ionic pairs, excimers and excitons with participation of dye mole…
The conversion efficiency of dye-sensitized solar cells (DSSCs) is optimized by modifying the optical design and improving absorbance within the cell. These objectives are obtained by creating different sized cavities in TiO2 photoanode. For this purpose, carbon nanospheres with diameters 100-600 nm are synthesized by hydrothermal method. A paste of TiO2 is mixed with various amounts of carbon nanospheres. During TiO2 photoanode sintering processes at 500C temperature, the carbon nanospheres are removed. This leads to random creation of cavities in the DSSCs photoanode. These cavities enhance …
In the present work we grow anodic TiO$_2$ nanotube layer with tube diameter ~ 500 nm and an open tube mouth. We use this morphology in dye-sensitized solar cells (DSSCs) and show that these tubes allow the construction of hybrid hierarchical photoanode structures of nanotubes with a defined and wall-conformance TiO2 nanoparticles decoration. At the same time, the large diameter allows the successful establishment of an additional (insulating) blocking layer of SiO$_2$ or Al$_2$O$_3$. We show that this combination of hierarchical structure and blocking layer significantly enhances the solar ce…
A measurement method of constant-current-discharging voltage decay is established to characterize the band bending effect in the heterojunction of conducting glass/TiO2 for typical dye-sensitized solar cells. Furthermore, a dark-state electron transport regarding the TiO2 conduction band bending is proposed based upon the viewpoints of thermionic emission mechanism, which suggests an origin of the band bending effect in a theoretical model. This model quantitatively agrees well with our experimental results and indicates that both the Fermi level decay in TiO2 and the potential difference acro…
Visible light-driven production of fuels and value-added chemicals is currently one of the most intensely investigated research topics across various scientific disciplines, due to its potential to ease the World s dependence on fossil fuels. In this perspective, we recapitulate some of the main features of dye-sensitized photocatalytic systems aimed at solar H$_2$ production, focusing in particular on TiO$_2$-based three-component assemblies with organic sensitizers. Relevant aspects include the structural and electronic properties of the sensitizers, the nature of the semiconductor and the h…
In the present work, a light-controlled device cell is established based on the dye-sensitized solar cell using nanocrystalline TiO2 films. Voltage-current curves are characterized by three types of transport behaviors: linear increase, saturated plateau and breakdown-like increase, which are actually of the typical performances for a photo-gated transistor. Moreover, an asymmetric behavior is observed in the voltage-current loops, which is believed to arise from the difference in the effective photo-conducting areas. The photovoltaic voltage between the shared counter electrode and drain (VCE…
We report on the effect of ligand exchange of copper sulphide selenide as well as copper selenide nanocrystals with the organic pi-system Cobalt beta-tetraaminophthalocyanine and analyse changes in the structural, optical as well as electric properties of thin films of these hybrid materials. A strong ligand interaction with the surface of the nanocrystals is revealed by UV-vis absorption and Raman spectroscopy. Grazing-incidence small-angle X-ray scattering studies show a significant contraction in the interparticle distance upon ligand exchange. For copper-deficient copper selenide, this con…
Dye-sensitized solar cells (DSSCs) are gaining considerable interest as alternatives to the semiconductor-based thin film solar cells. The noble metal platinum (Pt) is conventionally used as counter electrode (CE) material for fabricating DSSCs. Since Pt is expensive and scarce, new materials have been explored to develop cost-effective Pt-free counter electrodes for DSSCs. Two-dimensional (2D) graphene-based counter electrodes have achieved the highest known power conversion efficiency (η) of 13%, which has stimulated research activities in 2D layered transition metal dichalcogenides (TMDs) f…
The excited-state properties in a series of coumarin solar cell dyes are investigated with a long-range-corrected (LC) functional which asymptotically incorporates Hartree-Fock exchange. Using time-dependent density functional theory (TDDFT), we calculate excitation energies, oscillator strengths, and excited-state dipole moments in each of the dyes as a function of the range-separation paramenter, mu. To investigate the acceptable range of mu and assess the quality of the LC-TDDFT formalism, an extensive comparison is made between LC-BLYP excitation energies and approximate coupled cluster si…
Photo-gated transistors based on dye-sensitized nanocrystalline titanium dioxide thin film are established. A transistor-like transport behavior characterized by the linear increase, saturated plateau, and breakdown-like increase in the voltage-current curve is achievable with a low driven bias for the present device. The response current exhibits a linear dependence on the intensity of gated light, and the measured maximum photosensitivity is approximately 0.1 A/W. The dynamic responses for various light frequencies and their dependences on the load resistances are investigated as well. The c…
Computational Design of Metal-Free Porphyrin Dyes for Sustainable Dye-Sensitized Solar Cells Informing Energy Informatics and Decision Support
Dinajpur Government College（迪纳杰布尔政府学院）；UiT The Arctic University of Norway（挪威北极大学）；Hajee Mohammad Danesh Science and Technology University（哈吉·穆罕默德·达内什科学与技术大学）；Daffodil International University（达芬奇国际大学）
Recently, some new series of heteroleptic ruthenium-based dyes, the so-called RD dyes, were designed and synthesized showing better performances compared to the well-known homoleptic N719. In this work, using the density-functional theory and its time-dependent extension, we have investigated the electronic structure and absorption spectra of these newly synthesized dyes, and compared the results to those of N3 dye to describe the variations of the properties due to the molecular engineering of ancillary ligand. We have shown that the calculation results of the absorption spectra for these dye…
We calculate from first principles the O1s core-level shifts for a variety of atomistic models of the interface between TiO2 and the dye N3 found in dye-sensitized solar cells. A systematic comparison between our calculations and published photoemission data shows that only interface models incorporating hydrogen bonding between the dyes are compatible with experiment. Based on our analysis we propose that at the TiO2/N3 interface the dyes are arranged in supramolecular assemblies. Our work opens a new direction in the modeling of semiconductor/dye interfaces and bears on the design of more ef…
The surface states of the active TiO2 layer is crucial while fabricating an efficient solar cell. This work experimentally analyses the effect of exposing TiO2 based electron transport layer (ETL) to the ultraviolet-ozone (UV-O3) and optimizes the exposure time for improving power conversion efficiency (PCE) of fabricated dye-sensitized solar cells (DSSCs). These results demonstrate that the performance of DSSCs can be improved significantly by UV-O3 exposure of sintered TiO2 photoanode surface, with the duration of exposure being a critical parameter. Fabricated devices show 33.01 % increase …
We present the manipulation of magnetic and electrical properties of (Ga,Mn)As by the adsorption of dye-molecules as a first step towards the realization of light-controlled magnetic-semiconductor/dye hybrid devices. A significant lowering of the Curie temperature with a corresponding increase in electrical resistance and a higher coercive field is found for the GaMnAs/fluorescein system with respect to (Ga,Mn)As. Upon exposure to visible light a shift in Curie temperature towards higher values and a reduction of the coercive field can be achieved in photo-sensitized (Ga,Mn)As. A mayor change …
Excitonic effects due to electron-hole coupling play a fundamental role in renormalising energy levels in dye sensitised and organic solar cells determining the driving force for electron extraction. We show that first-principles calculations based on many-body perturbation theory within the GW-BSE approach provide a quantitative picture of interfacial excited state energetics in organic dye-sensitized TiO2 , delivering a general rule for evaluating relevant energy levels.To perform GW-BSE calculations in such large systems we introduce a new scheme based on maximally localized Wannier functio…
Beyond Panchromatic Absorption: Deciphering the Excited-State Maze from Light Absorption to Photocatalysis in Dye-Sensitized MOFs
Institute for Aqua Regeneration, Shinshu University（信州大学水再生研究所）；Department of Materials Chemistry, Faculty of Engineering, Shinshu University（信州大学工学部材料化学系）
In the present work we introduce a path to the controlled construction of DSSCs based on hierarchically structured single walled, self-organized TiO2 layers. In a first step we describe a simple approach to selectively remove the inner detrimental shell of anodic TiO2 nanotubes (NTs). This then allows controlled well-defined layer-by-layer decoration of these TiO2-NT walls with TiO2 nanoparticles (this in contrast to conventional TiO2 nanotubes). We show that such defined multiple layered decoration can be optimized to build dye sensitized solar cells that (under back-side illumination conditi…
Optimizing the photovoltaic efficiency of dye-sensitized solar cells (DSSC) based on staggered gap heterojunctions requires a detailed understanding of sub-band gap transitions in the visible from the dye directly to the substrate's conduction band (CB) (type-II DSSCs). Here, we calculate the optical absorption spectra and spatial distribution of bright excitons in the visible region for a prototypical DSSC, catechol on rutile TiO$_2$(110), as a function of coverage and deprotonation of the OH anchoring groups. This is accomplished by solving the Bethe-Salpeter equation (BSE) based on hybrid r…
Structural colors are a result of the scattering of certain frequencies of the incident light on micro- or nanoscale features in a material. This is a quite different phenomenon from that of colors produced by absorption of different frequencies of the visible spectrum by pigments or dyes, which is the most common way of coloring used in our daily life. However, structural colors are more robust and can be engineered to span most of the visible spectrum without changing the base material, only its internal structure. They are abundant in nature, with examples as colorful as beetle shells and b…
We report the atomic layer deposition of titanium dioxide on carbon nanosheet templates and investigate the effects of post-deposition annealing in a helium environment using different characterization techniques. The crystallization of the titanium dioxide coating upon annealing is observed using in-situ X-ray diffraction. The (micro)-structural characterization of the films is carried out by scanning electron microscopy and advanced transmission electron microscopy techniques. Our study shows that the annealing of the atomic layer deposition processed and carbon nanosheets templated titanium…
The interaction of the dye molecule N3 (cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4'-dicarboxylato)-ruthenium(II)) with the ultra-thin oxide layer on a AlNi(110) substrate, has been studied using synchrotron radiation based photoelectron spectroscopy, resonant photoemission spectroscopy (RPES) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). Calibrated X-ray absorption and valence band spectra of the monolayer and multilayer coverages reveal that charge transfer is possible from the molecule to the AlNi(110) substrate via tunnelling through the ultra-thin oxide layer and i…
The electron transport layer (ETL) plays a fundamental role in perovskite solar cells. Recently, graphene-based ETLs have been proved to be good candidate for scalable fabrication processes and to achieve higher carrier injection with respect to most commonly used ETLs. In this work we experimentally study the effects of different graphene-based ETLs in sensitized MAPI solar cells. By means of time-integrated and picosecond time-resolved photoluminescence techniques, the carrier recombination dynamics in MAPI films embedded in different ETLs is investigated. Using graphene doped mesoporous TiO…
The performance of organometallic perovskite solar cells has rapidly surpassed that of both conventional dye-sensitised and organic photovoltaics. High power conversion efficiency can be realised in both mesoporous and thin-film device architectures. We address the origin of this success in the context of the materials chemistry and physics of the bulk perovskite as described by electronic structure calculations. In addition to the basic optoelectronic properties essential for an efficient photovoltaic device (spectrally suitable band gap, high optical absorption, low carrier effective masses)…
The use of graphene-based electrodes is burgeoning in a wide range of applications, including solar cells, light emitting diodes, touch screens, field-effect transistors, photodetectors, sensors and energy storage systems. The success of such electrodes strongly depends on the implementation of effective production and processing methods for graphene. In this work, we take advantage of two different graphene production methods to design an advanced, conductive oxide- and platinum-free, graphene-based counter electrode for dye-sensitized solar cells (DSSCs). In particular, we exploit the combin…
