Synthesis and characterization of triphenylamine-based organic dyes for dye-sensitized solar cells

We synthesized three organic dyes (DYE 1, DYE 2, and DYE 3) containing triphenylamine (TPA) moieties as electron donors and cyanoacrylic acid moieties as electron acceptors, designed at the molecular level, and developed them for use in dye-sensitized solar cells (DSSCs). Among all the dyes, DYE 2 exhibited the highest overall solar-energy-to-electricity conversion efficiency of 4.06% with a short-circuit photocurrent density of 11.15 mA cm^?2, an open-circuit voltage of 0.64 V, and a fill factor of 0.57 under AM 1.5 irradiation with 100 mW cm^?2 simulated sunlight. The results indicate that the organic dyes are promising in the development of DSSC.     

Fabrication and characterization of cuprous oxide: fullerene solar cells

Cuprous oxide (Cu₂O)-based solar cells with fullerene (C₆₀) were fabricated on indium tin oxide (ITO) by a spin-coating method. The microstructure and cell performance of the solar cells with the Cu₂O:C₆₀ structure was investigated. A photovoltaic device based on an ITO/Cu₂O:C₆₀ bulk heterojunction structure fabricated by the spin-coating method provided short-circuit current density of 0.11 mA cm^?2 and open-circuit voltage of 0.17 V under an Air Mass 1.5 illumination. The microstructures of the Cu₂O active layer were examined by using X-ray diffraction and transmission electron microscopy. The energy levels of the present solar cells are also discussed.     

Synthesis and characterization of new electroluminescent molecules containing carbazole and oxadiazole units

The synthesis of new molecules containing both electron and hole transporter units is reported. This class of compounds, named OC, may be used for assembling electroluminescent devices made by a single organic layer. The active moieties are the carbazole, as the hole transporter unit, and the oxadiazole, as the electron transporter unit. The chemical formulation and the complex geometry of the molecular frame allow good solubility in chlorinate solvents and the preparation of homogeneous films by spinning technique.Photoluminescence of molecules, both in solution and in film, occurs in the blue region of visible spectra, the exact peak position of emission depending on the pendants attached to the oxadiazole unit. The electroluminescence occurs in a higher wavelength region, with a blue-green emission. The electroluminescent devices consist in the simple sequence ITO–OC–Al and ITO–PEDOT–OC–Al.     

Synthesis and characterization of red phosphorescent-conjugated polymers containing charged iridium complexes and carbazole unit

A series of homogeneous red-light phosphorescent polymers with charged iridium (Ir) complex in the backbones and carbazole unit on the side were synthesized by Suzuki polycondensation. These polymers are made up of three repeat units: (i) charged iridium (Ir) complex; (ii) 9,9-dihexylfluorene; (iii) 9,9-bis(N-carbazolyl-hexanyl)-fluorene. Their structures have been identified by nuclear magnetic resonance (NMR) and elemental analysis. All chelating polymers displayed good thermal stability, redox reversibility and film formation. Compared with our former study on these charged Ir complex containing polymers, the addition of carbazole unit has a strong influence on their hole injection and charge attraction ability as well as the host–guest energy transfer efficiency.     

Synthesis and characterization of dendritic poly(l-lysine) containing porphyrin–fullerene moieties

Amphiphilic l-lysine dendrons containing porphyrin and fullerene bearing amino acids with the ratio of 2:0, 2:1 and 1:1 were synthesized and characterized using UV–visible absorption spectroscopy, fluorescence emission spectroscopy and transmission electron microscopy. Photoluminescence spectra of these dendrimers showed photoluminescence quenching due to photoinduced electron transfer from porphyrin to fullerene moieties. Transmission electron microscopic observation evidenced the self-association of these dendrimers in water. Controllable and reversible dissociation and re-aggregation of some of the water soluble dendrimers have been investigated using electronic absorption and fluorescence spectra upon the addition of 2-hydroxypropyl-β-cyclodextrin and 1-adamantanecarboxylic acid in their aqueous dispersion. Enhanced ellipticity of dendritic porphyrin–fullerene conjugate compared to that only dendritic porphyrin indicates intramolecular porphyrin–fullerene interactions.     

Synthesis and electro-optical properties of carbazole derivatives for organic device applications

Two materials, DNCz and TCzPB, which contain carbazole moieties and exhibit high band gap energies, were synthesized via CN coupling and Suzuki coupling reactions, respectively. The ionization potential and electron affinity of the synthesized TCzPB were measured at 5.89 and 2.39 eV, respectively, implying that it is suitable for a host material. A doped multilayer device, ITO/DNTPD/NPD/TCzPB + Ir(ppy)₃/BCP/Alq₃/LiF/Al, exhibited a bright green emission with a maximum luminance of 27,200 cd/m² (17.6 cd/A at 18.0 V) when the synthesized TCzPB was used as the host material for a phosphorescent green dopant. The compound DNCz exhibited similar electronic energy levels to those of NPD, and was applied as a hole-transporting material. Bright green light originated from the Alq₃ layer was observed in the double layer device, ITO/DNCz/Alq₃/LiF/Al. The high hole-transporting property of DNCz was also demonstrated.     

Synthesis and characterization of aniline copolymers containing carboxylic groups and their application as sensitizer and hole conductor in solar cells

Copolymers of m-aminobenzoic acid and o-anisidine doped with p-toluenesulphonic acid in different proportions were successfully synthesized by oxidative polymerization. The copolymers were characterized by FT-IR, UV–vis, ¹H NMR and EPR spectroscopies, cyclic voltammetry, conductivity and SEM. The copolymer with equivalent amounts of the monomers o-anisidine and m-aminobenzoic acid presented the highest conductivity, The EPR analyses and SEM images show that this copolymer provides more homogeneous films with particle size distribution of approximately 1–2 μm. The copolymer with a high fraction of o-anisidine gives rises to films with larger particle sizes and a more defined electrochemical process. The m-aminobenzoic acid monomer was intentionally chosen in order to promote a better electronic coupling between the conducting copolymer and the TiO₂ surface. The copolymers were tested as both sensitizers and hole conducting materials in dye-sensitized solar cells. The device assembled using the copolymer with the highest proportion of m-aminobenzoic acid units as sensitizer produced the highest photocurrent (I_sc = 0.254 mA cm^?2) and photovoltage (V_oc = 0.252 V) at 100 mW cm^?2. The energy diagram shows that although the electronic injection from the conducting polymer excited state is an allowed process the regeneration of the positive charges created after the electron transfer process is forbidden, thus explaining the low efficiency of solar energy conversion. When this copolymer was applied as a hole conducting material, an improvement in the V_oc to 0.4 V, was observed, indicating that this material is more suitable for charge transport when applied in this type of solar cells.     

Synthesis,characterization, and electrical,electrochemical and gas sensing properties of a novel cyclic borazine derivative containing three phthalocyaninato zinc(II) macrocycles

A novel borazine derivative of trinuclear phthalocyanine has been prepared by following the multistep reactions of unsymmetrically substituted phthalocyanines. 4-(4-Amino-3-nitrophenoxy)phthalonitrile (3) which is one of the precursor molecules of the phthalocyanine was obtained from 4-nitrophthalonitrile (1) and 4-amino-3-nitrophenol (2) with K₂CO₃ in DMF at 50 °C. The zinc(II) phthalocyanine (5) containing an unsymmetrical substituted 4-amino-3-nitrophenoxy group was synthesized by statistical condensation of two different phthalonitriles. 4-(4-Amino-3-nitrophenoxy)phthalonitrile (3) and 4,5-bis(hexylthio)phthalonitrile (4) were cyclotetramerized with zinc acetate in DMF at 170–180 °C to yield 2-(4-amino-3-nitrophenoxy)-9,10,16,17,23,24-hexa(hexylthio)phthalocyanine zinc(II) complex (5), which was then separated by column chromatography on silica gel. The unsymmetrically substituted compound was reduced to the diamine form (6) using hydrazine hydrate in the presence of Pd/C catalyst, and the product was purified with chromatographic separation. Compound 6 was then reacted with triisopropoxyborane in refluxing xylene to give 5H,12H,19H-tris[2-(3,4-diaminophenoxy)-9,10,16,17,23,24-hexa(hexylthio)phthalocyaninato zinc(II) diazaborolo] borazine (7). The resulting product was purified by column chromatography on silica gel. All the target unsymmetrical phthalocyanines and borazine derivative were characterized by elemental analysis, IR, UV–vis, and ¹H NMR. Boron and zinc(II) percents in 7 were quantified with ICP-MS. Impedance spectroscopy and dc measurements were performed on spin coated 5–7 films as a function of temperature (293–400 K). The dc results showed an activated conductivity dependence on temperature. The ac results gave a temperature dependent frequency exponent s. The results were compared with the prediction of the Quantum Mechanical Tunelling and Correlated Barrier Hopping models. The ac conductivity of the films was well represented by the form Aω^s. Gas sensing properties of the films for the volatile organic compounds (VOCs) (chloroform, acetone, carbontetrachloride and ammonia) were also investigated in the temperature range from 293 to 400 K. The operating temperature had a considerable effect on sensing characteristics. Maximum sensitivity to VOCs were observed at room temperature for all films. Cyclic voltammetry of compounds 6 and 7 in solution indicated that these compounds have similar voltammetric behaviour.     

Synthesis and electrochemical characterization of a new polymer constituted of alternating carbazole and oxadiazole moieties

We report herein the synthesis and electrochemical characterization of a novel copolymer containing an electron rich carbazole moiety and an electron deficient oxadiazole unit—poly[N-(2′-ethylhexyl)-carbazole-3,6-diyl-1″,3″,4″-oxadiazole-2″,5″-diyl] (PCO). PCO can be dissolved in THF, CHCl₃, xylene, and DMSO. The structure of the polymer is confirmed by FT-IR, NMR and elemental analysis. The optical and electronic properties of the polymer are investigated by UV–Vis absorption spectroscopy and photoluminescence spectroscopy as well as cyclic voltammetry. The results show that the polymer films emit greenish-blue light (λ_max 485 nm) upon UV excitation. Both p-doping and n-doping processes are observed in cyclic voltammetric investigation. A comparison between the properties of polycarbazole and polycarbazole–oxadiazole has been presented.     

Application of a novel microwave plasma treatment for the sintering of nickel oxide coatings for use in dye-sensitized solar cells

In this study the use of microwave plasma sintering of nickel oxide (NiO_x) particles for use as p-type photoelectrode coatings in dye-sensitized solar cells (DSSCs) is investigated. NiO_x was chosen as the photocathode for this application due to its stability, wide band gap and p-type nature. For high light conversion efficiency DSSCs require a mesoporous structure exhibiting a high surface area. This can be achieved by sintering particles of NiO_x onto a conductive substrate. In this study the use of both 2.45 GHz microwave plasma and conventional furnace sintering were compared for the sintering of the NiO_x particles. Coatings 1 to 2.5 μm thick were obtained from the sintered particles (mean particle size of 50 nm) on 3 mm thick fluorine-doped tin oxide (FTO) coated glass substrates. Both the furnace and microwave plasma sintering treatments were carried out at ~ 450 °C over a 5 min period. Dye sensitization was carried out using Erythrosin B and the UV–vis absorption spectra of the NiO_x coatings were compared. A 44% increase in the level of dye adsorption was obtained for the microwave plasma sintered samples as compared to that obtained through furnace treatments. While the photovoltaic performance of the DSSC fabricated using the microwave plasma treated NiO_x coatings exhibited a tenfold increase in the conversion efficiency in comparison to the furnace treated samples. This enhanced performance was associated with the difference in the mesoporous structure of the sintered NiO_x coatings.     

Cross-linkable fullerene interfacial contacts for enhancing humidity stability of inverted perovskite solar cells

In situ cross-linking encapsulation has been demonstrated to be an efficient strategy for enhancing the humidity stability of perovskite solar cells(PSCs). In this study, a novel cross-linkable fullerene derivative, namely1-(p-benzoate-(p-methylvinylbenzene)-indolino[2,3][60]fullerene(FPPS), was readily synthesized from commercially available building blocks in two steps. This FPPS was employed as an interfacial modifier on perovskite surfaces in inverted planar p–i–n PSCs. Owing to the fast interfacial charge extraction and efficient trap passivation,PSCs based on the cross-linked FPPS(C-FPPS) exhibited excellent performance. The PSCs had a top-performing power conversion efficiency(PCE) of 17.82% with negligible hysteresis, compared to the control devices without C-PFFS(16.99%). Moreover, the strong water resistance of the C-FPPS interfacial layer distinctly enhances the ambient stability of PSC devices, exhibiting a t80(the time required to reach 80% of the initial PCE) of 300 h under high-humidity conditions. This significantly surpasses the control devices, whose t80 was only 130 h. These results demonstrate that cross-linkable fullerene derivatives can be promising interfacial materials for designing high-efficiency, hysteresis-free, air-stable PSCs.     

Synthesis and light-emitting properties of polyfluorene copolymers containing a hydrazone derivative as a comonomer

Poly[9,9-bis(2′-ethylhexyl)fluorene-2,7-diyl] (PBEHF) and a series of fluorene copolymers containing a hydrazone comonomer, poly{9,9-bis(2′-ethylhexyl)fluorene-2,7-diyl-co-[aza(2,7-fluorene-9-ylidene)methyl]diphenylamine} [poly(BEHF-co-FDPA)], were synthesized through Ni(0)-mediated polymerization. The synthesized polymers were characterized and their photophysical, electrochemical, and electroluminescent properties were investigated. Interestingly, the copolymer containing only 1% FDPA, poly(99BEHF-co-1FDPA), was found to exhibit photoluminescence (PL) emission that is significantly red-shifted with respect to that of the PBEHF homopolymer. All the copolymers exhibit PL emission maxima in the yellow region of the spectrum in the range from 530 to 540 nm, whereas the PBEHF homopolymer film produces maximum PL emission in the deep blue region at 424 nm. Light-emitting devices were fabricated in an ITO/PEDOT:PSS (50 nm)/polymers (80 nm)/Ca (50 nm)/Al (200 nm) configuration. The electroluminescence (EL) spectra of these devices consist of similar wavelengths to those found in the PL results; however, the EL devices constructed from the copolymers exhibited device performances that were significantly better than that of the device using the PBEHF homopolymer. This enhancement of performance is due to a more efficient charge carrier balance in the devices, which arises because of the effective exciton confinement (or charge carrier trapping) in the FDPA groups.     

Synthesis,characterization and electrical conductivity of a novel conjugated Schiff base macrocycle containing 1,3,4-oxadiazole ring

A new conjugated Schiff base macrocycle containing 1,3,4-oxadiazole ring was prepared by elimination of a tosyl group from a sulfonamide under basic conditions. This synthetic method will provide access to a wide variety of novel conjugated Schiff base macrocycles. The reaction mechanism was examined. The macrocycle has a highly conjugated ring structure and high thermal stability and was doped with iodine to form a stable conducting complex with a conductivity of 10⁻² S/cm. It can be used as semiconductive material.     

Investigation of new PPV-type polymeric materials containing fluorene and thiophene units and their application in organic solar cells

New poly(p-phenylenevinylene) (PPV)-type conducting polymers containing different concentrations of thiophene and fluorene functional units were investigated in this work and the photophysical and electrochemical properties were evaluated. We observed a dependence of these properties on the concentration of thiophene units in the polymer backbone. The hole mobilities were estimated to be on the order of 10^?6 cm² V^?1 s^?1. The polymers were combined with different concentrations of a soluble fullerene derivative (PCBM) and applied in bulk-heterojunction photovoltaic cells. The effects of PCBM concentration and of annealing (post-production treatment) on these devices were investigated. The best results were obtained for the materials containing higher concentrations of thiophene units.     

Using a molten organic conducting material to infiltrate a nanoporous semiconductor film and its use in solid-state dye-sensitized solar cells

We describe a method to fill thin films of nanoporous TiO₂ with solid organic hole-conducting materials and demonstrate the procedure specifically for use in the preparation of dye-sensitized solar cells. Cross-sections of the films were investigated by scanning electron microscopy and it was observed that a hot molten organic material fills pores that are 10 μm below the surface of the film. We characterized the incident photon to current conversion efficiency properties of the solid TiO₂/organic dye/organic hole-conductor heterojunctions and the spectra show that the dye is still active after the melting process.     

Synthesis and characterization of light-emitting materials composed of carbazole,pyrene and fluorene

A series of ethynyl-linked π-conjugated light-emitting molecules with good photoluminescence properties were designed and synthesized through Pd/Cu-catalyzed Sonogashira coupling reaction. The main structure comprised of different fluorophors (pyrene, carbazole, and fluorene), which were linked with triple bonds in order to be screened for high emission efficiency. Optical properties of these synthesized compounds (I_a–I_f) were examined in solutions, thin films and solid states, respectively. All of them showed relative high quantum yields both in solutions (Φ_s: 0.70–0.83) and in films (Φ_f: 0.17–0.34). Light-emitting diode using I_e as an emissive layer was fabricated in the ITO/poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS)/I_e/2, 2′, 2″-(1, 3, 5)-benzene-triyl)tris[1-phenyl-1H-benzimidazole] (TPBI)/Al configuration. The maximum emission wavelength of the device was 496 nm. The maximum luminance and electroluminescence efficiency was 1000 cd/m² and 0.41%, respectively.     

Preparation and characterization of novel dumbbell-like [60]fullerene polystyrene derivatives

The novel dumbbell-like [60]fullerene polystyrene derivatives were prepared by reaction of the “living” dianionic polystyrene with the fullerene core in C₆H₆/THF mixed solvents. The products were characterized by UV–VIS, FTIR, GPC and elemental analysis and it was proved that the products obtained under certain experimental conditions were linear dumbbell macromolecular structures. The GPC analysis showed that C₆₀-styrene copolymers and the pure polystyrene have nearly the same molecular weights. The TGA and EA results indicated that all of the copolymers have approximately the same C₆₀ contents.     

Synthesis and characterization of organic photorefractive glass

Bifunctional molecule, which possesses photoconductive and electrooptic properties in one molecule, was synthesized as a new photorefractive material. Carbazole as a photoconductive moiety was covalently bound to thiophene derivative as an electrooptic chromophore via a flexible alkyl chain. The sample prepared from the mixture of bifunctional molecule (89 wt.%), 2,4,7-trinitro-9-fluorenone (1 wt.%) and ethylcarbazole (10 wt.%) showed good photorefractive property. The 50 μm thick film showed the maximum diffraction efficiency of 65% at 70 V/μm, corresponding to a refractive index modulation (Δn) of ca. 4.5×10⁻³.     

Relationship between structure and optoelectrical properties of organic–inorganic hybrid materials containing fullerene derivatives

Novel lead iodide-based layered perovskite compounds, which contain fullerene derivatives, N-methyl-2-(4-ammoniumphenyl)-fulleropyrrolidine iodide (AmPF) and N-(n-dodecyl)-2-(4-ammoniumphenyl)-fulleropyrrolidine iodide (C12AmPF), in their organic layers were fabricated as thin solid films by spin-coating. The XRD profiles showed that (AmPF)PbI₄ molecules were arranged in a closer-packing form, compared with (C12AmPF)PbI₄. The photoluminescence spectra of thin films suggested the presence of energy transfer between C₆₀ moiety and lead(II) iodide layers, which led to the disappearance of fluorescence peak at 517 nm and the appearance of a new fluorescence peak at 780 nm. (AmPF)PbI₄ and (C12AmPF)PbI₄ films exhibited photoconductivity when ultraviolet light was irradiated, and the photocurrent values with applying 1.0 V bias voltage were 1.77 μA and 1.48 × 10^?2 μA, respectively.