Narrow Results

The scattering layer in the TiO₂ photoanode (PAs) of dye-sensitized solar cells (DSSCs) is doped with single-layer graphene (G), and DSSC is prepared by doctor blade coating method. A small amount of graphene (0.0016 wt.%) in a graphene aqueous solution (G-AS) and a G-TiO₂ paste was prepared to make 2–20 wt.% of G-AS in the deionized water (DIW). The UV-Vis measurement results show that the TiO₂ scattering layers doped with graphene effectively improve the visible light absorption intensity of DSSC PAs and increase the current density (Jsc) from 13.84 mA/cm² to 16.20 mA/cm². The Electrochemical Impedance Spectroscopy (EIS) measurement showed that the internal structural impedance Rk $(\mathrm{\Omega })$ decreased from 12.086 $(\mathrm{\Omega })$ (without graphene doping) to 9.875 $(\mathrm{\Omega })$ at 5 wt.% of the graphene doping. The photoelectric conversion efficiency (PCE) increased from 6.56% of the original un-doped graphene to the maximum PCE value of 7.57% at 5 wt.%. The results show that the best PCE is obtained when the concentration of G-AS is 5 wt.%.

Well-oriented TiO₂ nanorod (NR) arrays were fabricated directly on conductive side of F/SnO₂ substrates via hydrothermal technique. The effect of growth time on the TiO₂ NR thin film was examined. Field emission scanning electron microscope revealed that NRs exhibited a tetragonal structure with square top facets. Thickness measurements indicated that the thicknesses of the samples increased from 0.234$\mu$m to 1.544$\mu$m as the growth time was extended. The investigation of XRD indicates that the TiO₂ films are single-crystalline type of rutile. The effect of growth time on optical and electrical properties has been studied. With optimum growth time, dye sensitized solar cell (DSSC) efficiency of 1.48% could be reached using 1.544$\mu$m long TiO₂ NR arrays as electrode.

Cheap and efficient dye sensitized solar cells (DSSCs) can be prepared using natural dyes responding in the visible region of solar spectrum. Localized surface plasmon resonance (LSPR) plays a very important role for the improvement in the efficiency of DSSCs by using Plasmonic nanoparticles (PNPs) for exploiting the visible portion of the solar radiation by transferring the energy from dye to PNP. This energy transfers from dye to semiconductor TiO₂ through PNP which increases the overall photo catalytic activity. In the present study, Al-doped TiO₂ photoanodes were prepared via sol–gel route and used for DSSC application. Various natural and synthetic dyes are prepared and the optical transmittance and absorbance of the dyes are measured in the wavelength range of 250–850nm using UV-Vis spectroscopy and they are used in DSSC. Natural dyes extracted from fruits and synthetic dye based on Ruthenium (Ru) metal complex is used as sensitizers. Power conversion efficiency (PCE) of solar cells utilizing different dyes is compared. Out of the various natural dyes, beetroot and strawberry extracts based dyes show good absorbance in the visible range of electromagnetic spectrum. On the other hand, synthetic dyes based on Ru complex show strong absorbance over a wide range of visible spectrum. The absorbance increases with increase in concentration of Ru in ethanol. The extracts of beetroot, strawberry and mixed fruits show a peak in absorbance spectra at 501nm, 416nm and 332nm, respectively, indicating the absorption over a wide range of visible spectrum. Maximum efficiency of DSSCs utilizing PNPs sensitized with beetroot and strawberry dyes are found to be 1.5% and 1.3%, respectively.

The present work aims at a better and deeper insight into the forces that govern the intramolecular charge transfer (ICT) and photo injection processes in dyes for dye sensitized solar cells (DSSC). The geometry, electronic structure, electron density distribution, and absorption spectra, for a selected donor-$\pi$-acceptor (D-$\pi$-A) dye for DSSC were computed and analyzed at a high level of DFT theory. The coplanar geometry of the studied dye (D1) indicates a strong conjugation which facilitates ICT. NBO analyses reveal that this ICT amounts to 0.8e, which is localized on the acceptor and anchoring groups resulting in a marked total delocalization interaction energy. The origin of this stabilization is two-fold; first the $\pi$-charge transfer (CT) interaction from donor to acceptor orbitals and the hyperconjugative interactions involving Rydberg states. The effect of fluorine substituents, in the $\pi$-spacer, on the quantum efficiency of DSSCs was investigated. Gibb’s free energy values, redox potentials, excited state life time, non-linear optical properties (NLO) and driving forces for D1 and its fluorinated derivatives were computed.

Energy collection in photosynthetic microorganisms occurs through vectorial energy transfer along organized assemblies of chromophores. This process has inspired many research groups and yielded numerous examples of self-assembled photoactive structures. Dye sensitization of solar cells usually requires covalent anchoring of dyes onto the surface of metal oxides. A new porphyrin derivative that self-assembles upon non-covalent interaction with a surface has been designed and characterized by AFM. Interaction with metal oxide surfaces is further documented by the sensitization of metal oxide surfaces and the generation of photocurrent in non-optimized dye sensitized solar cells.

Two porphyrin dyads with the donor-π-acceptor molecular architecture, namely (ZnP)-[triazine-gly]-(H₂PCOOH) and (ZnP)-[triazine-Npip]-(H₂PCOOH), which consist of a zinc-metalated porphyrin unit and a free-base porphyrin unit covalently linked at their peripheries to a central triazine group, substituted either by a glycine in the former or a N-piperidine group in the latter, have been synthesized via consecutive amination substitution reactions of cyanuric chloride. The UV-vis absorption spectra and cyclic-voltammetry measurements of the two dyads, as well as theoretical calculations based on Density Functional Theory, suggest that they have suitable frontier orbital energy levels for use as sensitizers in dye-sensitized solar cells. Dye-sensitized solar cells based on (ZnP)-[triazine-gly]-(H₂PCOOH) and (ZnP)-[triazine-Npip]-(H₂PCOOH) have been fabricated, and they were found to exhibit power conversion efficiency values of 5.44 and 4.15%, respectively. Photovoltaic measurements (J–V curves) and incident photon to current conversion efficiency spectra of the two solar cells suggest that the higher power conversion efficiency value of the former solar cell is a result of its enhanced short circuit current, open circuit voltage, and fill factor values, as well as higher dye loading. This is ascribed to the existence of two carboxylic acid anchoring groups in (ZnP)-[triazine-gly]-(H₂PCOOH), compared to one carboxylic acid group in (ZnP)-[triazine-Npip]-(H₂PCOOH), which leads to a more effective binding onto the TiO₂ photoanode. Electrochemical impedance spectra show evidence that the (ZnP)-[triazine-gly]-(H₂PCOOH) based solar cell exhibits a longer electron lifetime and more effective suppression of charge recombination reactions between the injected electrons and electrolyte.

A series of tetraphenyl meso-substituted porphyrins with either p-amino or p-carboxy substituents has been studied as dyes for standard dye-sensitized solar cells (DSSCs). The porphyrins with greater numbers of amino groups generally show greater efficiency, primarily due to higher photocurrents; open-circuit voltage and fill factors are comparable. The most efficient sensitizer was the trans disubstituted zinc porphyrin, with an overall solar energy conversion efficiency of 5.66%, slightly higher than the triamino zinc porphyrin at 5.18%. The improved efficiency is attributed to the well known push–pull effect in porphyrinsensitized DSSCs with electrondonating groups opposite to the electronwithdrawing anchoring (carboxy) groups. It is suggested that porphyrin derivatives with cis diaminophenyl groups show somewhat diminished efficiency due to difficulties with regeneration of the dye from its oxidized form.

A new copper phthalocyanine, namely 9(10),16(17),23(24)-tri-tert-butyl-2-[acetynyl-(4-carboxy)phenyl]phthalocyaninatocopper and its related free base have been synthesized as potential stable blue dyes for dye sensitized solar cells. The molecule structure consists on an unsymmetrically-substituted macrocycle bearing three tert-butyl groups and one phenylethynyl moiety as peripheral substituents and it is analogue to that of a previously published zinc derivative. Chemical and optical characterizations, as well as theoretical calculations of the frontier orbitals of both molecules are discussed. To evaluate the effect of the central metal on the photovoltaic behavior of this dye, the novel molecules have been both tested and confronted with the zinc derivative. This last one has shown efficiency values significantly higher than those previously published with a 2.10% maximum efficiency, while the other two dyes yielded 1.66% and 1.38% maximum efficiency respectively.

In this contribution, different porphyrin derivatives were experimentally synthesized and theoretically analyzed using several electronic structure methods to study the geometrical and electronic properties of A₄, trans-A₂B${}_2$and A₃B porphyrins bearing several functional groups (–OH, –COOH, -3,5-di-$t$Bu, –OCH₂CH₂CH₂COOEt and –OMe) suitable to be employed as dyes in Dye Sensitized Solar Cells (DSSC). A₄ (R $=$ -H, -OMe, -OH, -3,5-di-tert-butyl, –OCH₂CH₂CH₂COOEt) and A₃B (R${}_1=$R${}_2=$R${}_3=$–H; R${}_4=$–OH and R${}_4=$-3,5-di-$t$Bu) porphyrins were synthesized and characterized by UV-vis and ¹H NMR spectroscopies for comparison. The geometrical parameters were analyzed in the ground state and gas phase using the semiempirical method PM6 and the DFT functionals M06-2X and B3LYP, in combination with the 6-31G(d), DZVP and TZVP basis set. For calculations of the electronic and excited state properties, CAM-B3LYP, M06-2X and HSE06, using SMD as solvation model, were applied. This study revealed that HSE06/DZVP protocol is the best methodology to simulate electronic spectra in these porphyrin derivatives. Indeed, whereas substituent groups did not significantly affect the geometrical structure of the porphyrin derivatives studied, they do influence their electronic structures, mainly in the LUMO (lowest unoccupied molecular orbital) energy levels.

The first example of A2B2 tetrabenzoporphyrin (KW-4) was synthesized, characterized and evaluated as a sensitizer for dye-sensitized solar cells. UV-vis and fluorescence spectroscopy revealed red-shifted and broadened absorption spectra of A2B2 tetrabenzoporphyrin as compared with its A2 dibenzo- and A2B2 dibenzoporphyrin analogues, which is a desired feature of dyes for dye-sensitized solar cells. DFT calculations also indicate favorable electron density distribution on the HOMO and LUMO of KW-4. However, the power conversion efficiency of the solar cell based on tetrabenzoporphyrin KW-4 displayed inferior performance than that of the solar cell based on A2 dibenzoporphyrin KW-2. The lower performance of the KW-4 cell was ascribed to two factors: the low lying LUMO energy level leading to less efficient electron injection and the “flat geometry” of the dye on TiO₂ surface facilitating charge recombination and decreasing dye loading. The investigation of anchoring group effect suggests that the acrylic acid group is a better anchoring group than pentadienyl carboxylic acid.

In this paper, the fabrication of PEDOT:PSS-doped graphene oxide (GO) as a hole transport conducting electrode has been discussed. GO has been synthesized by modified Hummer’s method. Formation of GO and structural changes in GO after PEDOT:PSS doping had been confirmed by Raman and XRD analyses. FESEM images depict the morphological changes in GO before and after doping. Bonds in the samples have been analyzed by FTIR. UV-Vis study shows that PEDOT:PSS-doped GO has good transparency in the visible region. Hall measurement indicates that the electrical conductivity in GO is due to the electron transport while the conductivity in PEDOT:PSS-doped GO is due to the hole transport. A new type of DSSC has been proposed with the fabricated hole transport PEDOT:PSS electrode without ITO. The working of the cell with the new hole transport electrode has been explained. Prepared electrodes have been used in the fabrication of DSSC, showing exciting initial results.

Pure nickel nanoparticles with diameter around 100 nm were prepared with a moderate hydrothermal method. The matrix was then selenized into Ni${}_{0.85}$Se particles in a Se vapor without any damage to their original morphologies. The as-prepared N${}_{\mathrm{\text{i}}0.85}$Se and Ni nanoparticles were then used as counter electrodes (CEs) in dye-sensitized solar cells. It was found that the performance of the cell with Ni${}_{0.85}$Se as counter electrode is enhanced by nearly two times in contrast to the one with Ni as CEs. This provides a new method to fabricate optional counter electrode for Pt.

Highly active counter electrodes with controllable morphology create new opportunities for the development of dye-sensitized solar cells. Controllable morphology accompanied by maximization of the use of active substances is a vital challenge. Herein, Integrated MoC quantum dots (QD) on different carbon frameworks to form solid flower-like MoC_QD@SCF, hollow flower-like MoC_QD@HCF1 and MoC_QD@HCF2 with varying degrees of hollowness. The as-prepared MoC_QD@HCF2 counter electrode (CE) displays a splendid tri-iodide reduction reaction (T-IRR). The power conversion efficiency (PCE) of DSSCs with MoC_QD@HCF2 reaches 9.03%, which is higher than that of Pt CE (8.41%), MoC_QD@HCF1 (8.24%) and MoC_QD@SCF (7.81%). This controllable morphology strategy shows potential applications and provides new insights into energy conversion and storage devices.

The first example of A2B2 tetrabenzoporphyrin (KW-4) was synthesized, characterized and evaluated as a sensitizer for dye-sensitized solar cells. UV-vis and fluorescence spectroscopy revealed red-shifted and broadened absorption spectra of A2B2 tetrabenzoporphyrin as compared with its A2 dibenzo- and A2B2 dibenzoporphyrin analogues, which is a desired feature of dyes for dye-sensitized solar cells. DFT calculations also indicate favorable electron density distribution on the HOMO and LUMO of KW-4. However, the power conversion efficiency of the solar cell based on tetrabenzoporphyrin KW-4 displayed inferior performance than that of the solar cell based on A2 dibenzoporphyrin KW-2. The lower performance of the KW-4 cell was ascribed to two factors: the low lying LUMO energy level leading to less efficient electron injection and the “flat geometry” of the dye on TiO₂ surface facilitating charge recombination and decreasing dye loading. The investigation of anchoring group effect suggests that the acrylic acid group is a better anchoring group than pentadienyl carboxylic acid.