Novel D-π-A system based on zinc porphyrin dyes for dye-sensitized solar cells: Synthesis, electrochemical, and photovoltaic properties

We have designed and synthesized novel zinc porphyrin dyes which have a D-π-A system based on porphyrin derivatives containing a triphenylamine (TPA) electron-donating group and a phenyl carboxyl anchoring group substituted at the meso position of the porphyrin ring, yielding the push-pull porphyrins as the most efficient green dye for dye-sensitized solar cell (DSSC) applications. The synthesis and characterization of a novel D-π-A system based on zinc-porphyrin derivatives have been investigated through their photophysical and photoelectrochemical studies. A large red-shift of the absorption maxima due to introduction of the TPA moiety at the meso position of the porphyrin ring was expected in the D-π-A porphyrins, but the absorption maxima of HKK-Por dyes were a little red-shifted in contrast to Zn[5,-10,15-triphenyl-20-(4-carboxylphenyl)-porphyrin], due to the tilted structure between TPA and the porphyrin unit. Under the photovoltaic performance measurement, the maximum incident photon-to-current conversion efficiency (IPCE) value of the DSSC based on HKK-Por 5 was slightly higher than the efficiencies of the DSSCs based on other HKK-Por dyes due to the introduction of the alkoxy group into the TPA moiety at the meso position of the porphyrin ring. A maximum photon-to-electron conversion efficiency of 3.36% was achieved with the DSSC based on HKK-Por 5 dye (J_SC = 9.04 mA/cm², V_OC = 0.57 V, FF = 0.66) under AM1.5 irradiation (100 m Wcm⁻²).     

Triphenylamine-based organic dyes containing a 1,2,3-triazole bridge for dye-sensitized solar cells via a ‘Click’ reaction

Three new organic dyes with one, two and three branched D-π-A structures derived from an electron donating triphenylamine core and connected by 1,2,3-triazole group to an electron deficient cyanoacrylate system have been conveniently synthesized via a ‘Click’ reaction. It was found that all three dyes show UV-vis absorptions in the 300-500 nm range with high molar extinction coefficients. A red-shift of UV-vis absorption band was observed in the solid thin film compared with the dioxane solution. Dye-sensitized solar cell devices based on the dyes were fabricated and tested. The one branched triphenylamine-based dye exhibits the highest energy conversion efficiency. Increase of the branched D-π-A structure around the triphenylamine core results in the decrease of energy conversion efficiency of the dyes, which can be attributed to less attachment of the dyes onto TiO₂ photoanode with the enlarged molecular size of the corresponding multibranched structure.     

Multi-alkylthienyl appended porphyrins for efficient dye-sensitized solar cells

Four porphyrin dyes, incorporating multi-alkylthienyl appended porphyrins as the electron donor, the 2-cyanoacrylic acid as the electron acceptor, and different π-conjugated spacer, have been synthesized for dye-sensitized solar cells (DSSCs). All the porphyrin dyes studied in this work exhibit red-shifted and broadened electronic spectra respect to the reference P_Zn as expected. By the introduction of thienyl groups at the meso-positions, the energy level of E_ox (excited-state oxidation potentials) is significantly shifted to the positive compared with the reference P_Zn, indicating a decreased HOMO–LUMO gap. The highest power conversion efficiency of the four dyes based on DSSCs reached 5.71% under AM 1.5 G irradiation.     

Multi-alkylthienyl appended porphyrins for efficient dye-sensitized solar cells

Four porphyrin dyes, incorporating multi-alkylthienyl appended porphyrins as the electron donor, the 2-cyanoacrylic acid as the electron acceptor, and different π-conjugated spacer, have been synthesized for dye-sensitized solar cells (DSSCs). All the porphyrin dyes studied in this work exhibit red-shifted and broadened electronic spectra respect to the reference P_Zn as expected. By the introduction of thienyl groups at the meso-positions, the energy level of E_ox (excited-state oxidation potentials) is significantly shifted to the positive compared with the reference P_Zn, indicating a decreased HOMO-LUMO gap. The highest power conversion efficiency of the four dyes based on DSSCs reached 5.71% under AM 1.5 G irradiation.     

A Novel Alkoxysilyl Azobenzene Dye Photosensitizer with Alkylamino Group for Dye-Sensitized Solar Cells

A newly designed alkoxysilyl azobenzene dye with alkylamino group, 4-diethoxyphenylsilyl-4′-dimethylaminoazobenzene, was synthesized and examined as the photosensitizer for a dye-sensitized solar cell (DSSC). The novel azobenzene dye exhibited a strong absorption band in the visible region, and the solar cell using the dye as the sensitizer showed an incident monochromatic photon-to-current conversion efficiency (IPCE) value of 66 % at 440 nm and a light-to-electric energy conversion efficiency of 2.2 % under simulated sunlight irradiation of AM-1.5G one sun condition. The energy conversion efficiency obtained here is the highest value among those reported so far for azobenzene-sensitized solar cells, indicating the potential of alkoxysilyl dyes as photosensitizers for DSSCs.     

Tunable molecular weights of poly(triphenylamine‐2,2′‐bithiophene) and their effects on photovoltaic performance as sensitizers for dye‐sensitized solar cells

Despite the huge progress achieved over the past decade, the relationship between the molecular weights of dyes and the performance of dye‐sensitized solar cells (DSSCs) remains unclear. In this article, we report on the fine control of the number‐average molecular weight (M_n) of poly(triphenylamine‐2,2′‐bithiophene) (PPAT) dyes with cyanoacrylic acid moieties as acceptors. We found a correlation between the M_n and photovoltaic performance of these polymers when they were used for DSSC applications. In this study, three samples (PPAT‐01, PPAT‐02, and PPAT‐03) with different M_n values (M_ns = 1700, 2800, and 3500 g/mol) were prepared through the control of the polymerization time and characterized by analytical gel permeation chromatography and NMR. Under the same experimental conditions, the overall cell efficiency of the oligomer dyes showed a nonmonotonic tendency with increasing molecular weight. The power‐conversion efficiencies were 2.81% for PPAT‐01, 4.72% for PPAT‐02, and 1.88% for PPAT‐03. UV absorption measurements proved that PPAT‐03 formed aggregation, whereas PPAT‐01 and PPAT‐02 were in the monolayer state adsorbed on TiO₂. The larger aggregation decreased charge transfer; thus, poor photoelectric conversion performance was observed. Furthermore, a higher molecular weight reduced the amount of PPAT‐03 adsorbed on TiO₂, and this had a crucial effect on the performance of the cells because of the reduced photocurrent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44182.     

Organic dyes incorporating low-band-gap chromophores based on π-extended benzothiadiazole for dye-sensitized solar cells

A series of new π-conjugated organic dyes (HKK-BTZ1, HKK-BTZ2, HKK-BTZ3 and HKK-BTZ4), comprising triphenylamine (TPA) moieties as the electron donor and benzothiadiazole moieties as the electron acceptor/anchoring groups, was synthesized for the use in dye-sensitized solar cells (DSSCs). TPA units are bridged to benzothiadiazole with single(S), double(D) and triple bonds(T) in different derivatives. And HKK-BTZ1 was modified by introducing alkoxy group of TPA unit, because the bulky alkoxy group is a strong donating group for the more red shift and for reducing aggregation of dyes in TiO₂ film. The structure-property relationship was investigated. Under standard global AM 1.5 G illumination, a maximum photo-to-electron conversion efficiency of 7.30% was achieved with the DSSC based on dye HKK-BTZ4 (J_SC = 17.9 mA/cm⁻², V_OC = 0.62 V, FF = 0.66), while the Ru dye N719-sensitized DSSC showed an efficiency of 7.82% with a J_SC of 17.5 mA/cm⁻², a V_OC of 0.62 V, and a FF of 0.72.     

Carbazole based hole transporting materials for solid state dye sensitizer solar cells: role of the methoxy groups

The synthesis of new organic hole transporting materials (HTMs) based on 3,6‐disubstituted 9H‐carbazole‐3,6‐diamine,N,N,N′,N′‐tetraphenyl‐9‐(4‐methoxyphenyl) derivatives and their applications in solid state dye sensitizer solar cells (DSSCs) are described. The effect of the methoxy group localized on the para position of the diphenylamine moieties on the thermal, electronic and electrochemical properties and photovoltaic performance is discussed. In solid state DSSCs, utilization of the aforementioned HTMs in combination with the dye D102 (TiO₂/D102/HTM/Au) shows a positive influence of the methoxy group on the photovoltaic conversion efficiency compared with unsubstituted diphenylamine grafted groups. A study on the concentration of the HTM is also carried out and shows an optimal concentration around 200 mg mL^?1. Without further optimization, the best device gives a power conversion efficiency of 1.75% under AM 1.5 solar irradiation (100 mW cm^?2).     

Novel Self-assembled Isonicotinic Acid Derivative and Zinc Porphyrin Dyads and Applications in Dye Sensitized Solar Cells

A new self-assemblies based on double-deck dyes ZnTPP-Wi (i?=?1–3) were synthesized and applied in dye-sensitized solar cells (DSSCs). Anchoring molecules (Wi i?=?1–3) consisting of phenyl carboxyl acid and cyanoacetic acid group. Capping layer dyes zinc meso-tetraphenylporphine (ZnTPP) with anchoring molecules Wi through axially coordination bonds of Zn-to-ligand self-assemblies solar cells devices. We herein report a consisting acylamide and cyanoacetic acid group W3 as an anchoring molecule for the axial coordination with upper zinc porphyrin ZnTPP. W3 was synthesized by introducing acylamide and cyanoacetic acid groups may inhibit adverse dye aggregation and improving electrons are effectively injected into the TiO₂ semiconductor surface. Thus, W3 anchoring molecules can be used to fabricate efficient solar cells with ZnTPP porohyrin dye, achieving good photoelectric performance, indicative of their general applicability in fabricating good-performance DSSCs. The assembled modes were also verified by transmission electron microscopy (TEM). The photoelectrochemical efficiencies for dye ZnTPP-W3 are best than those of self-assembly dyes prevailingly ascribed to larger J_sc and V_oc.

     

Synthesis, Characterization, and Photovoltaic Properties of Soluble TiOPc Derivatives

We have synthesized soluble TiOPc derivatives containing alkoxy groups for use as additives in dye-sensitized solar cells (DSSCs). The DSSC devices containing these TiOPc derivatives exhibited short-circuit current densities of 8.49~10.04 mA/cm² and power conversion efficiencies of 2.73~3.62 % under AM 1.5 illumination and 100 mW/cm² irradiation.     

Dye-sensitized solar cells based on double-layered TiO2 composite films and enhanced photovoltaic performance

Dye-sensitized solar cells (DSSCs) are fabricated based on double-layered composite films of TiO₂ nanoparticles and hollow spheres. The photoelectric conversion performances of DSSCs based on nanoparticles/nanoparticles (PP), hollow spheres/hollow spheres (HH), hollow spheres/nanoparticles (HP), and nanoparticles/hollow spheres (PH) double-layered films are investigated, and their photo-electric conversion efficiencies are 4.33, 4.72, 4.93 and 5.28%, respectively. The enhanced performance of TiO₂ nanoparticles/hollow spheres double-layered composite film solar cells can be attributed to the combined effect of following factors. The light scattering of overlayer hollow spheres enhances harvesting light of the DSSCs and the underlayer TiO₂ nanoparticle layer ensures good electronic contact between film electrode and the F-doped tin oxide (FTO) glass substrate. Furthermore, the high surface areas and pore volume of TiO₂ hollow spheres are respectively beneficial to adsorption of dye molecules and transfer of electrolyte solution.     

Wool-acid dye covalent bonding: the effect of water-soluble carbodiimides

Wool dyed with acid dyes has low wash fastness because of the weak, secondary forces between the fibre and the dye molecule. The amount of covalently fixed dye increases when aftertreating the dyed wool samples with carbodiimides. Several water-soluble carbodiimide derivatives proved to be effective for this purpose. They were synthesised by our method involving the use of: N-propyl-N′-(3-trimethyl-ammoniumpropyl)-carbodiimide-iodide, N-cyclohexyl-N′-(3-trimethylammonium-propyl)-carbodiimide-iodide, and N-cyclohexyl-N′-(2-morpholinoethyl)-carbodiimide-methyl-p-toluene-sulphonate. No damage occurred in the fibre structure during the treatment. The effect of both the carbodiimides and the dyes (Sandolan Fast Blue P-L, Egacyd Yellow T) is discussed.     

The influence of anatase-rutile mixed phase and ZnO blocking layer on dye-sensitized solar cells based on TiO2nanofiberphotoanodes

High performance is expected in dye-sensitized solar cells (DSSCs) that utilize one-dimensional (1-D) TiO₂ nanostructures owing to the effective electron transport. However, due to the low dye adsorption, mainly because of their smooth surfaces, 1-D TiO₂ DSSCs show relatively lower efficiencies than nanoparticle-based ones. Herein, we demonstrate a very simple approach using thick TiO₂ electrospun nanofiber films as photoanodes to obtain high conversion efficiency. To improve the performance of the DSCCs, anatase-rutile mixed-phase TiO₂ nanofibers are achieved by increasing sintering temperature above 500°C, and very thin ZnO films are deposited by atomic layer deposition (ALD) method as blocking layers. With approximately 40-μm-thick mixed-phase (approximately 15.6?wt.% rutile) TiO₂ nanofiber as photoanode and 15-nm-thick compact ZnO film as a blocking layer in DSSC, the photoelectric conversion efficiency and short-circuit current are measured as 8.01% and 17.3?mA?cm^?2, respectively. Intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy measurements reveal that extremely large electron diffusion length is the key point to support the usage of thick TiO₂ nanofibers as photoanodes with very thin ZnO blocking layers to obtain high photocurrents and high conversion efficiencies.     

Quasi solid state dye-sensitized solar cells with modified TiO2 photoelectrodes and triphenylamine-based dye

Quasi solid state dye-sensitized solar cells (DSSCs) have been fabricated with organic sol or TiCl₄ modified TiO₂ and porous TiO₂ photoanode and a triphenylamine-based dye (TPAR3) used as photosensitizer. Dark current measurements suggested that both modified TiO₂ photoelectrodes had significantly reduced the recombination rate of photoelectrons due to the reduced bare FTO surface in comparison to porous photoelectrode. The DSSC based on modified TiO₂ photoelectrodes showed improved photovoltaic parameters compared to the porous TiO₂ photoelectrode. The overall power conversion efficiency (PCE) is 3.27%, 4.73% and 6.8% for porous, TiCl₄ modified and sol modified TiO₂ photoelectrodes, respectively. The improved PCE with modified TiO₂ electrodes was attributed to the formation of a compact layer. This effectively improves adherence of TiO₂ to FTO surface, providing a larger TiO₂/FTO contact area and reducing the electron recombination by blocking the direct contact between redox electrolyte and the conductive FTO surface and enhances the electron collection efficiency.     

New heteroleptic benzimidazole functionalized Ru-sensitizer showing the highest efficiency for dye-sensitized solar cells

We designed and synthesized a new ruthenium complex using terpyridine as an anchoring ligand and BOC (tert-butyloxycarbonyl) protected bidentate benzimidazole derivative as an ancillary ligand, coded as GS7. The complex was characterized using ¹H NMR, FTIR, elemental analysis, UV–vis spectrophotometer, and cyclic voltammetry. We also tested photovoltaic performance of this complex for dye-sensitized solar cell (DSSCs). GS7 when used as a sensitizer for DSSCs with iodine triiodide electrolyte, showed a J_sc of 15.25 mA cm^− 2, a V_oc of 0.576 V, a FF of 0.691 and overall power conversion efficiency of (η) 6.07%.     

The use of poly(vinylpyridine-co-acrylonitrile) in polymer electrolytes for quasi-solid dye-sensitized solar cells

Poly(vinylpyridine-co-acrylonitrile) (P(VP-co-AN)) was used to form polymer electrolytes for dye-sensitized solar cells (DSSCs). The effects of P(VP-co-AN) on the photovoltaic performances of DSSCs have been investigated with nonaqueous electrolytes containing alkali-iodide and iodine. It was found that the effect of P(VP-co-AN) on V_oc closely related to its amount in the electrolyte. Lower amount of P(VP-co-AN) was benefit for the construction of a solar cell containing P(VP-co-AN) with higher energy conversion efficiency. Chemically crosslinking solidification with backbone polymer P(VP-co-AN) amount of 3% fabricated quasi-solid DSSCs with 10% increased conversion efficiencies with relative to that of the initial liquid DSSCs.     

Enhancement of the photoelectric performance of dye-sensitized solar cells using Ag-doped TiO<Subscript>2</Subscript> nanofibers in a TiO<Subscript>2</Subscript> film as electrode

For high solar conversion efficiency of dye-sensitized solar cells [DSSCs], TiO₂ nanofiber [TN] and Ag-doped TiO₂ nanofiber [ATN] have been extended to be included in TiO₂ films to increase the amount of dye loading for a higher short-circuit current. The ATN was used on affected DSSCs to increase the open circuit voltage. This process had enhanced the exit in dye molecules which were rapidly split into electrons, and the DSSCs with ATN stop the recombination of the electronic process. The conversion efficiency of TiO₂ photoelectrode-based DSSCs was 4.74%; it was increased to 6.13% after adding 5 wt.% ATN into TiO₂ films. The electron lifetime of DSSCs with ATN increased from 0.29 to 0.34 s and that electron recombination was reduced.     

Iodine-free organic dye sensitized solar cells with in situ polymerized hole transporting material from alkoxy-substituted TriEDOT

An alkoxy-substituted ethylenedioxythiophene (EDOT) trimer is designed and synthesized which has shown a low oxidation potential of 0.50 V versus saturated calomel electrode (SCE). In situ polymerization of the trimer in a thin layer electrolytic cell using organic dye adsorbed on TiO₂ as the working electrode yielded alkoxy-substituted poly(ethylenedioxythiophene) (PEDOT). With D149 as the dye sensitizer and the in situ polymerized polymer as hole-transporting material (HTM), dye sensitized solar cells (DSSCs) were fabricated to show a typical power conversion efficiency of 3.97% under AM 1.5 G (100 mW cm⁻²) illumination. The results show good promise of in situ polymerized conjugated polymers as HTM for iodine/iodide redox-free DSSC applications.     

Synthesis of ruthenium complex and its application in dye-sensitized solar cells

An amphiphilic bipyridyl ligand, 4,4′-dicarboxy-octyl-2,2′-bipyridine, and its ruthenium(□) complex (termed as S8) were synthesized and characterized by UV/Vis, IR and NMR spectroscopy. The performance of this S8 complex as charge transfer photo-sensitizer in TiO₂-based dye-sensitized solar cells was studied under standard AM 1.5 sunlight and by using an electrolyte consisting of 0.70 M 1,2-dimethyl-3-propyl-imidazolium iodide, 0.10 M LiI, 40 mM iodine and 0.125 M 4-tert-butylpyridine in acetonitrile. Aliphatic chains linking to carboxylate groups of S8 act as an effective electron donor and carboxylate groups act as an effective electron withdrawing between the TiO₂ layer and the carboxylate linking TiO₂ layer leading to increasing of electron density at this interface, which is attributed to increasing efficiency of electron injection to the TiO₂ conduction band from the excited state of dye. The complex, S8, gave a photocurrent density of 13.02 mA/cm², 0.60 V open circuit voltage and 0.69 fill factor yielding 5.36% efficiency. The S8 dye with aliphatic chain improved conversion efficiency of the resulting DSSCs compared with a cell fabricated using the N3 dye.     

Hydrothermal Growth and Application of ZnO Nanowire Films with ZnO and TiO2 Buffer Layers in Dye-Sensitized Solar Cells

This paper reports the effects of the seed layers prepared by spin-coating and dip-coating methods on the morphology and density of ZnO nanowire arrays, thus on the performance of ZnO nanowire-based dye-sensitized solar cells (DSSCs). The nanowire films with the thick ZnO buffer layer (~0.8–1 μm thick) can improve the open circuit voltage of the DSSCs through suppressing carrier recombination, however, and cause the decrease of dye loading absorbed on ZnO nanowires. In order to further investigate the effect of TiO₂ buffer layer on the performance of ZnO nanowire-based DSSCs, compared with the ZnO nanowire-based DSSCs without a compact TiO₂ buffer layer, the photovoltaic conversion efficiency and open circuit voltage of the ZnO DSSCs with the compact TiO₂ layer (~50 nm thick) were improved by 3.9–12.5 and 2.4–41.7%, respectively. This can be attributed to the introduction of the compact TiO₂ layer prepared by sputtering method, which effectively suppressed carrier recombination occurring across both the film–electrolyte interface and the substrate–electrolyte interface.