Sensitizers For DSSCs Research Articles

Molecular engineering of carbazole-fluorene sensitizers for high open-circuit voltage DSSCs: Synthesis and performance comparison with iodine and cobalt electrolytes

A rational molecular engineering strategy was set up to prepare an original series of efficient carbazole-based sensitizers for dye-sensitized solar cells. The new D–π–A dyes, including a fluorene core in the π-bridge, auxiliary thienyl groups on the donor and multiple anti-stacking chains, showed particularly favorable optoelectronic properties for DSSC application. Accordingly, the new dyes achieved up to 6.5% power conversion efficiency in standard devices (7.5 μm-thick transparent TiO2 and iodine-based electrolyte). The dyes were afterwards employed in thin-film devices (2 μm-thick transparent TiO2) and tested in the presence of three different electrolytes including I3−/I−, [CoII(bpy)3(PF6)2]/[CoIII(bpy)3(PF6)3] or [CoII(bpy-pz)2(PF6)2]/[CoIII(bpy-pz)2(PF6)3] as redox mediators. Overall performance under these conditions was around 4% PCE, whatever the electrolyte. However, remarkable open-circuit voltages were observed with cobalt-based electrolytes. In particular, with [Co(bpy-pz)2] the three dyes afforded VOC above 800 mV, even reaching as high as 919 mV, thus compensating the slight decrease in photocurrent arising from the low-mobility of the Co-complexes.

New efficient tert-butyldiphenyl-4H-pyranylidene sensitizers for DSSCs

Three triarylamine-free new dyes based on a tert-butylphenyl-4H-pyranylidene ring have been synthesized and successfully used as sensitizers for DSSCs.

A "click-chemistry" approach for the synthesis of porphyrin dyads as sensitizers for dye-sensitized solar cells.

Two novel porphyrin dyads (9 and 11) consisting of two zinc-metallated porphyrin units, covalently linked at their peripheries through 1,2,3-triazole containing bridges and functionalized by a terminal carboxylic acid group, have been synthesized via "click" reactions, which are Cu-catalyzed Huisgen 1,3-dipolar cycloadditions between azide- and acetylene-containing porphyrins. Photophysical and electrochemical measurements, together with DFT calculations, showed that the two dyads possess suitable frontier orbital energy levels for use as sensitizers in DSSCs. The 9 and 11 based solar cells were fabricated resulting in power conversion efficiencies (PCEs) of 3.82 and 5.16%, respectively. As shown by photovoltaic measurements (J-V curves) and incident photon to current conversion efficiency (IPCE) spectra of the two solar cells, the higher PCE value of the latter is attributed to its enhanced photovoltaic parameters, and particularly its enhanced short circuit current (Jsc). This is related to the stronger absorption profile of the sensitizing dyad 11 (the dyad with the shorter triazole containing bridge) and the higher dye loading of the corresponding solar cell. Furthermore, electrochemical impedance spectra (EIS) demonstrated that the 11 based solar cell exhibits longer electron lifetime (τe) and more effective suppression of the recombination between the injected electrons and the electrolyte.

A triazine di(carboxy)porphyrin dyad versus a triazine di(carboxy)porphyrin triad for sensitizers in DSSCs.

Two porphyrin-chromophores, i.e. triad PorZn-(PorCOOH)(2)-(piper)2 (GZ-T1) and dyad (PorZn)(2)-NMe2 (GZ-T1), have been synthesized and their photophysical and electrochemical properties have been investigated. The optical properties together with the appropriate electronic energy levels, i.e. the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels, revealed that both porphyrin assemblies can function as sensitizers for dye sensitized solar cells (DSSCs). The and -based DSSCs have been prepared and studied using 20 mM CDCA as coadsorbent and were found to exhibit an overall power conversion efficiency (PCE) of 5.88% and 4.56%, respectively (under an illumination intensity of 100 mW cm(-2) with TiO(2) films of 12 μm). The higher PCE of the -sensitized DSSC, as revealed from the current-voltage characteristic under illumination and the incident photon to current conversion efficiency (IPCE) spectra of the two DSSCs, is mainly attributed to its enhanced short circuit current (J(sc)), although both the open circuit voltage (V(oc)) and the fill factor are improved too. The electrochemical impedance spectra (EIS) demonstrated a shorter electron transport time, longer electron lifetime and higher charge recombination resistance for the DSSC sensitized with the dye as well as a larger dye loading onto the TiO(2) surface.

Thiazolo[5,4-d]thiazole-based organic sensitizers with strong visible light absorption for transparent, efficient and stable dye-sensitized solar cells

Five thiazolothiazole-based dyes, bearing electronrich ProDOT groups, were used as sensitizers in thin-layer DSSCs (active area: 0.25–3.6 cm2; TiO2 thickness: 3.0–6.5 μm), giving efficiencies up to 7.71% coupled with excellent stability over 1000 h.

Organic dyes with a fused segment comprising benzotriazole and thieno[3,2-b]pyrrole entities as the conjugated spacer for high performance dye-sensitized solar cells.

Sensitizers with a fused segment comprising electron deficient benzotriazole () and electron rich thiophene or thieno[3,2-b]pyrrole entities as the conjugated spacer have been synthesized for dye-sensitized solar cells (DSSCs). The power conversion efficiency (PCE) increases with elongation of the conjugated spacer, and the dye with the dithieno[3,2-b]pyrrolobenzotriazole spacer has the best efficiency of 8.14%, which is comparable with that of an -based DSSC (8.03%). After coadsorbed with 1 mM CDCA, the efficiency was improved to 8.4%. The J-aggregation of the dye results in light harvesting at a longer wavelength spectral region and increasing the photocurrent of the cell.

Linearly π-conjugated oligothiophenes as simple metal-free sensitizers for dye-sensitized solar cells

Oligothiophenes with a terminal acceptor anchoring group can act as simple and efficient metal-free sensitizers for DSSCs.

Utilization of electron‐deficient thiadiazole derivatives as π-spacer for the red shifting of absorption maxima of diarylamine-fluorene based dyes

This study is carried out to design diarylamine-fluorene dyes by incorporating electron‐deficient thiadiazole derivatives. Quantum chemical calculations are performed to study the geometries, electronic structures and absorption spectra of the dyes. Interaction of dyes with TiO2 cluster is also studied. The effects of the electron‐deficient units on the spectra and electrochemical properties have been investigated. Dyes D1–D4 display remarkably enhanced spectral response in the red portion of the solar spectrum as compared with reference compound D0. The newly designed dyes demonstrate desirable energetic and spectroscopic parameters and may lead to efficient metal‐free organic dye sensitizers for DSSCs.

Red shifting of absorption maxima of phenothiazine based dyes by incorporating electron-deficient thiadiazole derivatives as π-spacer

This study was carried out to design phenothiazine based dyes by incorporating electron-deficient thiadiazole derivatives as π-spacer. Density functional theory and time-dependent density functional theory calculations of the geometries, electronic structures and absorption spectra of the dyes before and after binding to titanium oxide were carried out. Effects of the electron-deficient units on the spectra and electrochemical properties have been investigated. Compared with the reference compound CS1A, Dyes 1–4 display remarkably enhanced spectral responses in the red portion of the solar spectrum. The newly designed dyes demonstrate desirable energetic and spectroscopic parameters, and may lead to efficient metal-free organic dye sensitizers for DSSCs.

New metal-free organic dye for DSSC devices prepared by electros-pray method: synthesis, characterization and device preparation

Two new metal-free organic dyes CBR and CI with carbazole as electron-donor, thiophene as p- conjugated bridge and 2-cyanoacrylic acid as electron-acceptor and anchor group have been designed and synthesized. After characterized by 1 H NMR, MALDI-TOF, IR and absorption, they were used as sensitizers for DSSCs, in which the TiO 2 anode was prepared by electrospray method. Compared with CBR, the DSSC based on CI showed better performances ( J SC , V OC , FF , and η ). Under AM 1.5 G irradiation, its short circuit current increased nearly 2.6 times, with the power conversion efficiency improving from 1.0% to 2.3%. This is mainly due to the reduction of a CH 2 in the molecular structure, which increased effective conjugation between donor and acceptor, benefiting for the electron transfer from donor to acceptor as well as lowering the material bandgap. Because CBR and CI have stronger absorption in the region of 350-450 nm, they were selected as co-sensitized dye with the conventional dye N719. The power conversion efficiency improved from 5.2% (N719) to 5.6% (CBR-N719) and 6.7% (CI-N719).

Impacts of Temperature on the Stability of Tropical Plant Pigments as Sensitizers for Dye Sensitized Solar Cells

Natural dyes have become a viable alternative to expensive organic sensitizers because of their low cost of production, abundance in supply, and eco-friendliness. We evaluated 35 native plants containing anthocyanin pigments as potential sensitizers for DSSCs. Melastoma malabathricum (fruit pulp), Hibiscus rosa-sinensis (flower), and Codiaeum variegatum (leaves) showed the highest absorption peaks. Hence, these were used to determine anthocyanin content and stability based on the impacts of storage temperature. Melastoma malabathricum fruit pulp exhibited the highest anthocyanin content (8.43 mg/L) followed by H. rosa-sinensis and C. variegatum. Significantly greater stability of extracted anthocyanin pigment was shown when all three were stored at 4°C. The highest half-life periods for anthocyanin in M. malabathricum, H. rosa-sinensis, and C. variegatum were 541, 571, and 353 days at 4°C. These were rapidly decreased to 111, 220, and 254 days when stored at 25°C. The photovoltaic efficiency of M. malabathricum was1.16%, while the values for H. rosa-sinensis and C. variegatum were 0.16% and 1.08%, respectively. Hence, M. malabathricum fruit pulp extracts can be further evaluated as an alternative natural sensitizer for DSSCs.

Dye-sensitized solar cells based on triazine-linked porphyrin dyads containing one or two carboxylic acid anchoring groups

Porphyrin dyads, covalently linked by 1,3,5-triazine, either with one or two carboxylic acid groups, were synthesized and used as sensitizers in DSSCs, resulting in power conversion efficiency higher than 5%.

Theoretical study on the light harvesting efficiency of zinc porphyrin sensitizers for DSSCs

DFT and TDDFT calculations have been carried out to investigate the effect of donor and acceptor groups on the electronic properties of zinc-porphyrin sensitizers. The calculated results show that increasing the electron releasing strength of a meso-donor group opposite to a meso substituted acceptor group increases the light harvesting efficiency and short circuit current density.

Theoretical investigation of phenothiazine–triphenylamine-based organic dyes with different π spacers for dye-sensitized solar cells

Three phenothiazine–triphenylamine-based organic dyes (CD-1, CD-2 and CD-3) are designed based on the dye WD-8. The geometries, electronic structures, and electronic absorption spectra of these dyes before and after binding to TiO2 are studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The calculated geometries indicate that these dyes show good steric hindrance effect which is advantage to inhibit the close intermolecular π–π aggregation effectively. The lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy levels of these dyes could ensure positive effect on the process of electron injection and dye regeneration. The simulated spectra of CD-1∼3 show better absorption than that of WD-8 in the low energy zone. All the calculated results demonstrate that these dyes could be used as potential sensitizers for DSSCs and show better performances than WD-8.

New simple panchromatic dyes based on thiadiazolo[3,4-c]pyridine unit for dye-sensitized solar cells

Three new organic D–A–π–A photosensitizers with thiadiazolo[3,4-c]pyridine moiety incorporated between non-planar triarylamine and cyanoacrylic acid, have been developed and applied in dye-sensitized solar cells. It has been demonstrated that the incorporation of electron-withdrawing thiadiazolo[3,4-c]pyridine unit can effectively tune the HOMO and LUMO energy levels, extending the absorption spectra into the deep-red region and covering the whole visible region. The photoresponse of the cells based on the three dyes reached above 800 nm, a value which is comparable to the incident photon-to-current conversion efficiency onset of the established dye N719. Typically, three different bulky electron-donating units such as triphenylamine, N,N-bis(9,9-dimethylfluoren-2-yl)aniline and 4-(hexyloxy)-N-(4-(hexyloxy)phenyl)-N-phenylaniline were utilized to investigate their influences on the photovoltaic performances of DSSCs. The results indicate that the introduction of the strongest electron-donating 4-(hexyloxy)-N-(4-(hexyloxy)phenyl)-N-phenylaniline unit can further red-shift the intramolecular charge transfer band and enhance the light-harvesting properties, as well as retard the electron recombination between electrons at the TiO2 and oxidized species of dye or I3− in the electrolyte. Under simulated AM 1.5G irradiation, the cell based on the dye derived from 4-(hexyloxy)-N-(4-(hexyloxy) phenyl)-N-phenylaniline produced a short-circuit photocurrent of 14.19 mA cm−2, an open-circuit photovoltage of 0.462 V, a fill factor of 0.64, corresponding to a power conversion efficiency of 4.20%. Though the power conversion efficiency is still low, the methodology of tuning the HOMO and LUMO energy levels by incorporation of an electron-withdrawing thiadiazolo[3,4-c]pyridine unit in such D–A–π–A dyes could be generally applied to design more efficient panchromatic sensitizers in DSSCs.

Synthesis, photo-electrochemical properties and dye-sensitized solar cell performance of d–π–A structured porphyrins

Abstract Two new dye sensitizers 5-(N,N-4-(diphenylamino)phenyl)-10-(4-(tert-butyl-2-cyanoacrylate)phenyl)porphyrin (TP) and 5-(N, N-4-(bis(4-butylphenyl) amino) phenyl)-10-(4-(tert-butyl-2-cyanoacrylate)phenyl)porphyrin (BUTP) with cyanoacrylic acid as electron acceptor were synthesized and researched. BUTP has strong absorption in a wide range of 300–726 nm. DSSCs sensitized by BUTP displayed a power conversion efficiency (η) 5.33%, JSC 12.21 mA cm−2, Voc 0.68 V, FF 0.65, under the illumination of AM 1.5 G. Spectral properties, electrochemical properties, photovoltaic and electrochemical impedance properties of TP and BUTP were also investigated. Considering its simple synthesis, both TP and BUTP were qualified sensitizers for DSSCs.

Tetraaryl ZnII Porphyrinates Substituted at β‐Pyrrolic Positions as Sensitizers in Dye‐Sensitized Solar Cells: A Comparison with meso‐Disubstituted Push–Pull ZnII Porphyrinates

A facile and fast approach, based on microwave-enhanced Sonogashira coupling, has been employed to obtain in good yields both mono- and, for the first time, disubstituted push-pull Zn(II) porphyrinates bearing a variety of ethynylphenyl moieties at the β-pyrrolic position(s). Furthermore, a comparative experimental, electrochemical, and theoretical investigation has been carried out on these β-mono- or disubstituted Zn(II) porphyrinates and meso-disubstituted push-pull Zn(II) porphyrinates. We have obtained evidence that, although the HOMO-LUMO energy gap of the meso-substituted push-pull dyes is lower, so that charge transfer along the push-pull system therein is easier, the β-mono- or disubstituted push-pull porphyrinic dyes show comparable or better efficiencies when acting as sensitizers in DSSCs. This behavior is apparently not attributable to more intense B and Q bands, but rather to more facile charge injection. This is suggested by the DFT electron distribution in a model of a β-monosubstituted porphyrinic dye interacting with a TiO2 surface and by the positive effect of the β substitution on the incident photon-to-current conversion efficiency (IPCE) spectra, which show a significant intensity over a broad wavelength range (350-650 nm). In contrast, meso-substitution produces IPCE spectra with two less intense and well-separated peaks. The positive effect exerted by a cyanoacrylic acid group attached to the ethynylphenyl substituent has been analyzed by a photophysical and theoretical approach. This provided supporting evidence of a contribution from charge-transfer transitions to both the B and Q bands, thus producing, through conjugation, excited electrons close to the carboxylic anchoring group. Finally, the straightforward and effective synthetic procedures developed, as well as the efficiencies observed by photoelectrochemical measurements, make the described β-monosubstituted Zn(II) porphyrinates extremely promising sensitizers for use in DSSCs.

Novel expanded porphyrin sensitized solar cells using boryl oxasmaragdyrin as the sensitizer

Oxasmaragdyrin boron complexes were prepared and applied in DSSCs. The HOMO-LUMO energy gap analyses and theoretical calculations revealed that these expanded porphyrins are ideal sensitizers for DSSCs. A device containing oxasmaragdyrin-BF2 as the sensitizer achieves an energy conversion efficiency of 5.7%.

Novel Ruthenium Complex with Terpyridine Derivative for DSSCs

In this work, we designed and investigated theoretically novel ruthenium(II) complex (Bu4N)[Ru(DMFAdctpy)(NCS)3]; (DMFAdctpy : 2-(6-(5-(4-(bis(9,9-dimethyl-9H-fluoren-2-yl)amino)phenyl)pyridin-2-yl)-4-carboxypyridin-2-yl)pyridine-4-carboxylic acid) with DMFAdctpy as an anchoring group and a highly conjugated ancillary ligand to increase absorption ability in the long wavelength region compared to the N3 dye([Ru(dcbpy)2(NCS)2]); (dcbpy (4,4′-dicarboxy-2,2′-bipyridine)). The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to gain insight into the factors responsible for photovoltaic properties as dye sensitizer. The absorption spectrum of these dyes with terpyridine derivative is more red-shifted and broad than that of N3, especially, in the region between 400 nm and 650 nm. This is attributed to the extension of the π-conjugated system of insertion terpyridine ligands. Molecular orbital analysis confirmed that the HOMOs of (Bu4N)[Ru(DMFAdctpy)(NCS)3] localized over the NCS ligand orbitals. The LUMO, LUMO+1 and LUMO+2 are mainly localized over the dctpy ligand. However, the LUMO+3 is delocalized on the DMFA moiety. Due to the panchromatic and red-shifted absorption spectrum, these novel ruthenium complexes are expected to good candidates as dye sensitizers for DSSCs.

Effect of linker used in D–A–π–A metal free dyes with different π-spacers for dye sensitized solar cells

Two novel D–A–π–A metal free dyes with triphenylamine as donor, dithiophene-diketo-pyrrolo-pyrrole as acceptor unit, thiophene and phenyl π-conjugated bridges and a cyanoacetic acid as electron acceptor (TDPP1 and TDPP2 were denoted for thiophene and phenyl π-conjugated bridge, respectively) have been designed and used as sensitizers for DSSCs. Incorporation of dithiophene-diketo-pyrrolo-pyrrole, reduces the band gap significantly. The influence of π-conjugated bridge on optical and electrochemical properties were investigated. Results demonstrated that the absorption band of TDPP with thiophene π-conjugated bridge has red shifted due to the enhancement of electron donating ability of π-conjugated bridge. The DSSC based on TDPP1 shows prominent power conversion efficiency about 4.81%, which is higher that for TDPP2 (3.42%). The electrochemical impedance spectroscopy analysis reveal that the charge recombination resistance at the TiO2/dye/electrolyte interface for the DSSC based on TDPP1 is higher than that for TDPP2, which improves both Jsc and Voc. The PCE of the DSSC based on TDPP1 is further improved up to 6.34%, when deoxycholic acid (DCA) was employed as coadsorbant.