Performance Of DSSCs Research Articles

Synergistic effects of inter- and intra-particle porosity of TiO2 nanoparticles on photovoltaic performance of dye-sensitized solar cells

We investigated the effects of the inter- and intra-particle porosity of TiO2 nanoparticles (NPs) on the resulting photovoltaic performance of DSSCs. Solid and porous TiO2 NPs with controlled intra-particle porosity were fabricated using Brij-58-templated aerosol-gel and calcination processes. The fabricated solid and porous TiO2 NPs were stacked as thin films with inter-particle porosity using ethyl cellulose-templated screen-printing and calcination processes. Controlling the inter-particle porosity of TiO2 NPs was found to be much more effective than controlling the intra-particle porosity of TiO2 NPs for supporting the maximization of the number of dye molecules. The DSSCs composed of porous photoactive layer with porous TiO2 NPs were found to have the best power conversion efficiency. This suggests that the TiO2 NPs with porous structures, due to the controlled formation of both inter- and intra-particle porosity, can maximize the light harvesting of DSSCs through better dye adsorption and effective light trapping.

Improved performance induced by in situ ligand exchange reactions of copper bipyridyl redox couples in dye-sensitized solar cells.

Copper bipyridyl redox couples are intresting mediators for dye-sensitized solar cells (DSSCs). Here we show that the electrolyte additive 4-tert-butylpyridine (TBP) actually substitutes common bidentate ligands on the Cu(ii) species to form [Cu(TBP)4]2+, which is a poor electron acceptor and thus allows high voltages and charge collection efficiencies to be achieved.

The impact of heteroatom substitution on cross-conjugation and its effect on the photovoltaic performance of DSSCs - a computational investigation of linear vs. cross-conjugated anchoring units.

The unusual bonding pattern and proximal heteroatom substitution in π-cross conjugation produced distinct changes in the energy levels and photophysical behaviour of the dyes. To seek an understanding of the origin of these fluctuations, we have carried out a detailed computational investigation on a series of D-π1-π2 (A1)-A2 structured dyes comprised of common donor-spacer (auxiliary acceptor) units but varied the anchoring parts. In this study, we introduced a novel dimethylamino substituted fluorene-based triarylamine donor unit and evaluated its donating strength. Based on the comparison of DFT computed energy levels with experimental results, we have proposed an orbital splitting pattern to explain the energy level and photophysical properties of the linear vs. cross-conjugated dyes with respect to the linking position of the anchoring unit and benzo[1,2,5]thiadiazole (BTD) substitution. The smallest HOMO-LUMO gap of B3 mainly originated from the weak overlap of the directionality mismatch of the orbital interaction imposed by cross-conjugation. The inefficient overlap in B3 can possibly influence the energy levels but failed to enhance the charge transfer transitions upon photoexcitation. On the other hand, β-heteroatom substitution in bridged dyes partially enhanced π-delocalization over the cross conjugation and produced a significant ICT absorption with an optoelectronic response in the NIR region. BTD acceptor substitution increased the HOMO-LUMO gap of the bridged dyes. NBO analysis was performed to corroborate our predictions. DOS-PDOS analysis of the dyes@TiO2 was employed to investigate the electron injection rate of linear vs. bridged dyes. The anchoring pattern and large torsional deviation of the carboxylate anchoring group upon TiO2 adsorption drastically decreased the photovoltaic performance of the bridged dyes. The results obtained from this study provided a detailed understanding of how to surmount the cross-conjugation with the aid of β-heteroatom substitution. These design guidelines would be helpful in developing novel NIR dyes with better hole mobility for various optoelectronic applications. Furthermore, π-delocalization over the cross-conjugation concept opens a new pathway in the field of functional molecular devices to increase the charge conductance over several orders of magnitude with a significant reduction of destructive quantum interference at the molecular junction.

Enhancing photovoltaic performance of DSSCs sensitized with Ru-II complexes by D–π–A configured carbazole based co-sensitizers

Simple D–π–A architectured carbazole based dyes, P1–4, were employed as co-sensitizers in DSSCs sensitized with Ru-II complexes, viz.NCSU-10 and N3. The results revealed that, the NCSU-10 sensitized devices displayed improved photovoltaic performance when co-sensitized with P1 and P3.

Optical and Photovoltaic Properties of Thieno[3,2-b]thiophene-Based Push-Pull Organic Dyes with Different Anchoring Groups for Dye-Sensitized Solar Cells.

The effect of anchoring groups on the optical and electrochemical properties of triphenylamine-thienothiophenes, and on the photovoltaic performance of DSSCs photosensitized with the prepared dyes, was studied using newly synthesized compounds with cyanoacetic acid or rhodanine-3-acetic acid groups. Precursor aldehydes were synthesized through Suzuki cross-coupling, whereas Knoevenagel condensation of these with 2-cyanoacetic acid or rhodanine-3-acetic acid afforded the final push–pull dyes. A comprehensive photophysical study was performed in solution and in the solid state. The femtosecond time-resolved transient absorption spectra for the synthesized dyes were obtained following photoexcitation in solution and for the dyes adsorbed to TiO2 mesoporous films. Information on conformation, electronic structure, and electron distribution was obtained by density functional theory (DFT) and time-dependent DFT calculations. Triphenylamine–thienothiophene functionalized with a cyanoacetic acid anchoring group displayed the highest conversion efficiency (3.68%) as the dye sensitizer in nanocrystalline TiO2 solar cells. Coadsorption studies were performed for this dye with the ruthenium-based N719 dye, and they showed dye power conversion efficiencies enhanced by 20–64%. The best cell performance obtained with the coadsorbed N719 and cyanoacetic dye showed an efficiency of 6.05%.

Exploring the relevance of thiophene rings as bridge unit in acceptor-bridge-donor dyes on self-aggregation and performance in DSSCs.

The possibility of dye charge recombination in DSSCs remains a challenge for the field. This consists of: (a) back-transfer from the TiO2 to the oxidized dye and (b) intermolecular electron transfer between dyes. The latter is attributed to dye aggregation due to dimeric conformations. This leads to poor electron injection which decreases the photocurrent conversion efficiency. Most organic sensitizers are characterized by an Acceptor-Bridge-Donor (A-Bridge-D) arrangement that is commonly employed to provide charge separation and, therefore, lowering the unwanted back-transfer. Here, we address the intermolecular electron transfer by studying the dimerization and photovoltaic performance of a group of A-Bridge-D structured dyes. Specifically, eight famous sulfur containing π-bridges were analyzed (A and D remained fixed). Through quantum mechanical and molecular dynamics approaches, it was found that the formation of weakly stabilized dimers is allowed. The dyes with covalently bonded and fused thiophene rings as Bridges, 6d and 7d as well as 8d with a fluorene, would present high aggregation and, therefore, high probability of recombination processes. Conversely, using TiO2 cluster and surface models, delineated the shortest bridges to improve the adsorption energy and the stability of the system. Finally, the elongation of the bridge up to 2 and 3 units and their photovoltaic parameters were studied. These results showed that all the sensitizers are able to provide similar photocurrent outcomes, regardless of whether the bridge is elongated. © 2017 Wiley Periodicals, Inc.

Enhanced DSSCs performance of TiO2 nanostructure by surface passivation layers

Rutile titanium oxide (TiO2) synthesized in copper containers, was spin-coated with different surface passivation layers such as magnesium oxide (MgO), calcium carbonate (CaCO3), zirconium oxide (ZrO2), and tin oxide (SnO2). The deposition of these passivation layers on TiO2 confirmed with the help of XRD and EDX analysis, leads to changes in surface morphology induced by the passivation layers demonstrated by FE-SEM imaging. The highest photoconversion efficiency obtained for TiO2 electrode with MgO passivation layer (6.05%), respective incident photon conversion efficiency was 52%. After introduction of passivation layers on the TiO2 nanostructure, electron lifetime increased from 0.48 ms to 0.65 ms and charge transfer resistance decreased from 36.9 Ω cm (pristine TiO2 electrode) to 20.16 Ω cm (MgO passivation layer).

Fabrication of green dye-sensitized solar cell based on ZnO nanoparticles as a photoanode and graphene quantum dots as a photo-sensitizer

Zero-dimensional graphene quantum dots (GQDs) consist of single- or few-layer graphene with a size less than 20 nm and stand for a new type of QDs with unique properties combining the graphene nature and size-resulted quantum effects. GQDs possess unique optical and electronic properties, and in particular possess a band-gap less than 2.0 eV because of quantum confinement and edge effects. In this study, we investigated the performance of DSSCs using different thicknesses of ZnO nanoparticles as a photo-anode and GQDs as a green photosensitizer. The current voltage (I-V) test results indicate that the performance of DSSCs is improved by increasing the thickness of the photo-anode and the thickness of 40 μm shows the highest efficiency for DSSC device based on ZnO nanoparticles photo-anodes. The DSSC using ZnO nanoparticles as a photo-anode with thickness of 40 μm shows almost same efficiency when we replaced N-719 with GQDs which is confirmed that using GQDs as an alternative to ruthenium based dyes is a new approach for DSSCs.

Structure-property relationships: Influence of number of anchoring groups in triphenylamine-carbazole motifs on light harvesting and photovoltaic performance for dye-sensitized solar cells

Three novel organic sensitizers were molecularly designed and synthesized based on triphenylamine (TPA), as the core donor (DTPA), linked to one, two or three carbazole (DCarb) moieties with different number of anchoring groups (AG) to generate: DTPA-π-DCarb-A (DE1), DTPA(π-DCarb-A)2 (DE-2) and DTPA(π-DCarb-A)3 (DE-3). The primary goal of this study was to investigate the influence of bridging different number of DCarb and AG, through π-spacer, with TPA on the photovoltaic performance in DSSCs. The molar extinction coefficient increased with increasing the number of DCarb and A. DE-3 showed the greatest light harvesting in solution and when anchored onto TiO2. Hence, the increase in the number of DCarb and AG led to better light harvesting and stronger electronic coupling with TiO2, which reflected positively on the photovoltaic properties, and this is the first systematic study of its kind involving TPA-π-carbazole motif. DE-3 achieved the best efficiency of 5.44% and showed IPCE of 74% at 470 nm. The Voc increased with increasing the number of anchoring groups. Equilibrium molecular geometries and frontier molecular orbitals studied by DFT and TD-DFT calculations were in excellent agreement with experiments, which showed enhanced electronic coupling with TiO2 and photovoltaic performance as the number of anchoring groups increased.

Revealing the limiting factors that are responsible for the working performance of quasi-solid state DSSCs using an ionic liquid and organosiloxane-based polymer gel electrolyte

We report a study on quasi-solid-state–dye-sensitized solar cells (QSS–DSSCs) with polymer gel electrolytes (PGEs) that are composed of an organosiloxane hybrid polymer gel and imidazolium ionic liquid. The ionic diffusion coefficients of these PGEs are smaller than those of the pure ionic liquid, which may explain the observation of decreased cell performances in the DSSCs using these PGEs. However, from more detailed electrochemical impedance spectroscopy (EIS) studies, there is a strong evidence that the cell performance is also limited by inefficient charge transfer and charge transport inside the mesoporous TiO2 layer. This is indicated by the absence of transmission line characteristics in the observed Nyquist plots. The present experimental results then indicate that the lack of electrolyte penetration into the mesoporous TiO2 layer, due to the PGE rheology behavior caused by the siloxane-based polymer gel used here, is another crucial limiting factor for the photovoltaic performance of DSSCs using this kind of PGE. We consider that this kind of gel phase effect may be also observed in DSSCs using other types of gel electrolytes, including polyionic liquids.

Dye-sensitized solar cell based on TiO2/MnO2 composite film as working electrode

The purpose of this study is to develop DSSC based on TiO2/MnO2 composite film as working electrode. The working electrodes were prepared by the doctor blade method and their characteristics were investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-Vis spectroscopy. Moreover, the performance of DSSCs was performed under simulated AM 1.5G solar illumination using 100 mW/cm2. The indirect band gap of TiO2 pure, TiO2/MnO2 and TiO2/MnO2 6% films are 3.29, 2.98 and 2.81 eV, respectively. The highest power conversion was 0.018 % which corresponds to TiO2/MnO2 6% composite film. The results suggest that the MnO2 added to the semiconductor TiO2 can improve the efficiency of the DSSCs.

Synthesis of TiO2 NRs - ZnO Composite for Dye Sensitized Solar Cell Photoanodes

Composite of TiO2 NRs - ZnO were synthesized for DSSCs photoanode materials. TiO2 NRs was synthesized from TiO2 anatase by mechanochemical technique using ball milling process with agitation speed of 1000 rpm. While, the further hydrothermal refluxing process was conducted at 120°C under various concentration of NaOH in aqueous solution. The starting material of ZnO was prepared from ZnSO4.7H2O as a precursor. The hydrothermal treated TiO2 was added to the ZnO powder in a certain composition of 1:1, 1:2 and 2:1 (w/w), and the mixtures were then annealed at 400°C. The resulting material was characterized by X-ray diffraction (XRD), Surface area analyzer (SAA), Transmission electron microscopy (TEM), and Thermogravimetry/Differential thermal analysis (TG/DTA). The TiO2 revolution occurs from anatase phase into brookite phase. Rutile TiO2 phase was increasing when the NaOH was added at about 12 M. Nanograf of TEM showed the optimum condition for the formation of TiO2 NRs was obtained when 12 M NaOH was used. Structural transformation to 1D nanorods of TiO2 capable increase surface area up to 79 m2/g. TiO2 NRs–ZnO composite was prepared from TiO2 NRs and ZnO using comparation of TiO2 NRs: ZnO = 1:1, 1:2, dan 2:1. Anatase phase TiO2 as a single phase TiO2 was obtained in the TiO2–ZnO composite (1:1 w/w) upon heating the sample until 400°C. Difference TiO2 NRs-ZnO composite materials were investigated as good photovoltaic materials. Evaluation of the performance of DSSCs was conducted by I-V Keithley 2602A measurement indicate that photoanode built of TiO2 NRs - ZnO thin film has a higher solar cell efficiency than that of TiO2 thin film photoanode.

Comparative study on N,N-di-p-tolylaniline-based D-π-A1-π-A2 sensitizers by tuning the auxiliary acceptor for dye-sensitized solar cells

We report the synthesis and DSSCs performance of two dye sensitizers XD1 and XD2 with D-π-A1-π-A2 structure bearing difluorobenzo[c][1,2,5]thiadiazole (DFBT) and diketopyrrolopyrrole (DPP)-based as auxiliary acceptor moieties. The effect of DFBT or DPP on the photophysical, electrochemical, and photovoltaic properties of the target dyes were investigated. It is found that DPP-containing XD2 achieve higher Jsc result from its wider absorption spectrum ranging from visible to near-infrared region, higher molar absorption coefficient in the low-energy region and stronger photocurrent generation as compared to the DFBT-containing XD1. Additionally, the longer electron lifetime and increased charge recombination resistance of XD1 make it achieves higher Voc. The photovoltaic properties of the DSSCs are synthetically influenced by Jsc and Voc. Eventually, the investigation of photovoltaic performance of DSSCs indicates that XD1 obtains slightly higher power conversion efficiency (PCE) of 5.04%, but the PCE of the DSSCs based on the dye XD2 with 1 mM CDCA as co-adsorbent is increased to 6.14%.

Synthesis of highly photo-catalytic and electro-catalytic active textile structured carbon electrode and its application in DSSCs

Due to the growing need of portable smart devices, textile based solar cells have gained widespread attention in the field of wearable electronics. Here, we have demonstrated facile fabrication of metal free DSSCs by printing cotton, polyester and linen fabric counter electrodes with highly photo catalytic and electro catalytic active mesoporous carbon composite composed of highly conductive acid functionalized multi-walled carbon nanotubes decorated with mesoporous activated charcoal. Different mesoporous carbon structures were formulated by varying the concentration of activated charcoal intercalated in the acid functionalized MWCNT matrix. The mesoporous carbon composite with high level of porosity and oxygen rich surface exhibits low charge transfer resistance and excellent electro-catalytic activity for the reduction of tri-iodide ions. The mesoporous carbon composite exhibited 52% higher photo catalytic activity than the acid modified MWCNT. Besides that, in-depth comparison was carried out in between different kinds of textile fabrics coated with the carbon composite. The slight variation in the microporous structures and surface characteristics of cotton, polyester and linen fabrics led to marginal difference in the electrochemical and photovoltaic performance of DSSCs. High mobility of gel electrolyte within the porous structure of mesoporous carbon and textile fabrics assembly demonstrated low RCT of 0.82Ω, 0.77Ω and 1.37Ω for cotton, polyester and linen respectively. The obtained photovoltaic conversion efficiency of cotton, polyester and linen based DSSCs using gel electrolyte were 6.06%, 6.26% and 5.80% respectively. The suggested TCO and Pt free DSSC assemblies paved a way to the facile fabrication of textile based DSSC.

The investigation of the central metal effects on the porphyrin-based DSSCs performance; molecular approach

In this work, we have investigated the insertion of the different metal atoms, -Ca, -Mg and -Zn, into the porphyrin-based dyes for access to more efficient photovoltaic processes in the dye-sensitized solar cells. The photovoltaic processes have been described through the electronic properties of the dyes in the ground and excited states and quantum chemistry descriptors of them. The structural, electronic and spectroscopic properties of the dyes have been obtained by using the natural bond orbital, density functional theory (DFT) and time-dependent-DFT calculations. The preference of applying the metalloporphyrins, especially the Ca-porphyrin complex, in the solar cell is correlated with more proper photovoltaic properties than the free-base porphyrin. Proper photovoltaic properties of the metalloporphyrins are originated from the acceptable electronic chemical potential, electrophilicity indices and electron injection force from the dye to TiO2.

Growth and characterization of ZnO nanostructure on TiO2-ZnO films as a light scattering layer for dye sensitized solar cells

In the present work, we studied the effect of light scattering layer on the performance of DSSCs. TiO2-ZnO thin films were coated onto FTO glass substrate by spin coating technique as a photoanode for DSSCs. ZnO nanorods with flower structures were potentiostatically grown on TiO2-ZnO films at various potentials from −1.1 to 1–1.3V as a light scattering layer. XRD patterns reveal that as the deposition potentials increase the growth of ZnO nanorods increases along with (101) plane orientation. FE-SEM images display agglomerated grains and nanorods with flower structures for TiO2-ZnO film, and ZnO has grown on TiO2-ZnO film at a deposition potential of −1.3V. UV–vis spectra confirm the TiO2-ZnO with ZnO nanorods having a higher light scattering effect, absorbance and dye loading than that of another film. The efficiency of the DSSCs consisting of without and with scattering layer is estimated to be 0.79 and 1.81%, respectively.

Photovoltaic Performance of Co-doped CuCrO2 for p-type Dye-sensitized Solar Cells Application

For the first time, Co-doped CuCrO2+δ non-stoichiometric nanocrystals with δ≈0.1 aresynthesized bylow-temperature hydrothermal method. The synthesis mechanism proposed and the structural characterizations have confirmed that the excess oxygen from delafossite structure is given by the specific hydrothermal conditions (temperature, pressure and molarity of basic solution). The decreasing of the observed electrical resistivity in the non-stoichiometric nanocrystals is enhanced by Co-subtitution. Thus, hydrothermal synthesis has allowed to obtain doped delafossite nanocrystalline compound with excess oxygen and mixed valancies of both sites (A and B sites) and could open the study of its cumulative effect on physical properties. The performance of p-type DSSCs based on Co-doped CuCrO2+δnanocrystals photocathodeswas made using two type of dye: Coumarin C343 and Ruthenium N719. The short-circuit density (Jsc) is notably increased by approximately 60% when N719 is used as dye.

The influence of inserted thiophene into the (π-A'-π)-bridge on photovoltaic performances of dye-sensitized solar cells

A series of metal-free D-π-A'-π-A type organic dyes have been designed by inserting one or two thiophene between the (π-A'-π)-bridge and the donor and/or acceptor moieties based on BZTP-1. The influence of inserted thiophene into the (π-A'-π)-bridge on photovoltaic performances of sensitizer was investigated in detail using the density functional theory (DFT) and its time-dependent density functional theory (TD-DFT) methods. Calculated results show that increasing the length of the conjugated-linker leads to a high planarity and very narrow HOMO-LUMO energy gap. Especially, dye T-T-BZTP-T-T that forms by inserting two thiophenes into two sides of BZTP exhibits the most obvious red-shifted and the strongest absorption, which leads to a high Voc. Moreover, we find that these dyes show a good character of electron injection and dye regeneration owing to the ideal ΔGinject, μnormal and ΔGreg. Therefore, the insertion of thiophene into the (π-A'-π)-bridge has a better influence on photovoltaic performance of designed dyes compared with BZTP-1. We hope the present work will be helpful for future experimental synthesis of organic dyes to improve the performance of DSSCs.

High efficiency dye sensitized solar cell made by carbon derived from sucrose

Carbon materials represent an attractive alternative to platinum based counter electrodes in DSSCs. Graphitic carbon produced from carbonization of sucrose has been used for making counter electrode for DSSCs. It was observed that increment in thickness of carbon counter electrode improves the performance of DSSCs. Electrochemical impedance spectroscopy, Tafel polarization and cyclic voltammetry measurements suggest that sucrose derived carbon based counter electrode shows fast reduction rate of I3− compare with platinum based counter electrode. DSSCs based on sucrose derived carbon exhibit high power conversion efficiency (PCE) of 9.96% and fill factor (FF) of 0.72 which is higher than PCE of 9.39% and FF of 0.67 of the cells with platinum (Pt) based counter electrode.

Anionic ancillary ligands in cyclometalated Ru(ii) complex sensitizers improve photovoltaic efficiency of dye-sensitized solar cells: insights from theoretical investigations

Comprehensive understanding of the impact of anionic ligands in Ru complex dyes on the performance of DSSCs by theoretical calculations.