Poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene)(MEH-PPV) /Nitrogen Containing Derivatives of Fullerene Composites: Optical Characterization and Application in Flexible Polymer Solar Cells

New soluble organofullerenes were synthesized by the reaction of organic amines and azides with the [60]fullerene. The comparative investigations of the IR- and optical absorption spectra of blends MEH-PPV/fullerene derivative in solutions and in films showed no ground-state interaction between the components. Photoluminescence (PL) experiments, and photocurrent-voltage measurements were performed on model photovoltaic (PV) cells. We found that PL of MEH-PPV is completely quenched by a small admixture of fullerene derivative which assumes a high efficiency of charge separation in the composite material. The photocurrent in the PV device containing fullerene derivative is two orders of magnitude higher than that in pure MEH-PPV. An attempt to observe the magnetic field spin effect (MFSE) on the photocurrent in MEH-PPV/fullerene composites was made.     

Poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene)(MEH-PPV)/Nitrogen containing derivatives of fullerene composites: Optical characterization and application in flexible polymer solar cells

New soluble organofullerenes were synthesised by the reaction of organic amines and azides with the [60]fullerene. The comparative investigations of the IR- and optical absorption spectra of blends MEH-PPV/fullerene derivative in solutions and in films showed no ground-state interaction between the components. Photoluminescence (PL) experiments, and photocurrent-voltage measurements were performed on model photovoltaic (PV) cells. We found that PL of MEH-PPV is completely quenched by a small admixture of fullerene derivative which assumes a high efficiency of charge separation in the composite material. The photocurrent in the PV device containing fullerene derivative is two orders of magnitude higher than that in pure MEH-PPV. An attempt to observe the magnetic field spin effect (MFSE) on the photocurrent in MEH-PPV/fullerene composites was made.     

Determining the optical absorption edge in organic semiconductor composites with a bulk heterojunction by the constant photocurrent method

Spectral dependences of photoconductivity in thin layers of polyconjugated polymers (PCDTBT, PTB7) and their composites with a fullerene derivative (PC₇₀BM), which are promising for the development of organic solar cells, have been studied. It was found that the photoconductivity in the polymeric composite exceeds that in the polymer in the whole spectral range under study and the edge of the photoconductivity spectrum is shifted to the long-wavelength part of the spectrum. Use of the constant photocurrent method made it possible to obtain spectral dependences of the absorption coefficients and determine the optical gap width of the materials studied.     

Fullerene containing polymers: a review on their synthesis and supramolecular behavior in solution

Due to the theoretical importance and potential applications of fullerene, numerous fullerene derivatives have been developed to enhance its solubility and processability. This article provides an overview on fullerene containing polymers, from synthesis to their physicochemical properties in solution. Due to the unique chemical structure of fullerene, different fullerene containing polymeric architecture can be synthesized through various kinds of conjugating techniques, where fullerene can be located either on the backbone or the branch chain. Recently, the successful development of azido coupling and atom transfer radical addition (ATRA) makes it possible to synthesize "controlled" and well-defined fullerene containing polymers. Experimental results indicated that fullerene containing polymers not only increase the solubility of fullerene in solution, but also retain the conjugating properties of fullerene molecules. By blocking well-defined functional polymers onto fullerene molecules, different types of stimuli-responsive amphiphilic systems can be achieved. However, the large bulk volume and high hydrophobicity of fullerene gives rise to the large aggregates with different morphologies produced in solution, which can be tuned by changing external stimuli, such as pH, temperature, salt, and co-solvents. Interestingly, fullerene containing anionic polymers could induce the formation nano-scale fractal pattern, but not fullerene containing cationic polymers, which is evident from morphological studies.     

Similar Behavior Between Polyfullerenes and Charged Polymers. Extreme Polyelectrolyte Effects in Gel Permeation Chromatography Studies

Fullerene polymers with high fullerene contents were studied by use of gel permeation chromatography (GPC). Surprisingly, the polymer samples exhibit the chromatographic behavior that is characteristic of charged polymers. The extreme poly electrolyte effects observed for the fullerene polymers are rationalized in terms of localized charges in the polymer structures due to large polarizibilities of the polymeric fullerenes.     

Molecular packing and solar cell performance in blends of polymers with a bisadduct fullerene

We compare the solar cell performance of several polymers with the conventional electron acceptor phenyl-C61-butyric acid methyl ester (PCBM) to fullerenes with one to three indene adducts. We find that the multiadduct fullerenes with lower electron affinity improve the efficiency of the solar cells only when they do not intercalate between the polymer side chains. When they intercalate between the side chains, the multiadduct fullerenes substantially reduce solar cell photocurrent. We use X-ray diffraction to determine how the fullerenes are arranged within crystals of poly-(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) and suggest that poor electron transport in the molecularly mixed domains may account for the reduced solar cell performance of blends with fullerene intercalation.     

Photoinduced charge transfer through films containing poly(hexylthiophene), phthalocyanine, and porphyrin-fullerene layers

Efficient photoinduced interlayer electron transfer from a phthalocyanine derivative, ZnPH4, to porphyrin cation of a porphyrin-fullerene donor-acceptor dyad was demonstrated by using time-resolved photovoltage technique. Multicomponent thin films with desired layer arrangements were constructed by the Langmuir-Blodgett and spin-coating methods in order to study charge transfer in solid state. As a contradiction to the photovoltage experiments, the dyad monolayer in the film structure did not enhance the current amplitude in electrochemical photocurrent measurements. This is associated with a weak electronic interaction between fullerene and aqueous electrolyte, reducing the photocurrent generation. The use of poly(3-hexylthiophene) as a hole conducting layer was shown to improve photocurrent yield of the device by forming efficient heterojunction together with the ZnPH4 layer.     

Fabrication and characteristics of polyfluorene based organic photodetectors using fullerene derivatives

The characteristics of organic photodetectors (OPDs) by solution process using one of the polyfluorene derivatives poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) and two fullerene derivatives [6-6]phenyl-C61-butyric acid methyl ester (PCBM) or N-Ts aziridinofullerene (TsAF) are investigated. F8T2:PCBM devices showed good rectifying characteristics in a dark state and photosensitive characteristics, and fast frequency responses. Weight ratio of 1:1 device showed larger photocurrent than 1:4 device and obtained over 50 MHz of cutoff frequency under reverse bias voltage of 10 V. This result suggests that F8T2:PCBM device can be applied to a photodetector for detecting several tens of megahertz optical signals under blue light irradiation. The polarity of J–V characteristics of F8T2:fullerene derivative device is strongly affected by charge injection and extraction between fullerene derivative and electrodes.     

Construction of long-wavelength-light photocurrent generation system based on self-assembled monolayer of cobaltadithiolene [60]fullerene complex

[60]Fullerene pentaester and pentaacid derivatives bearing cobaltadithiolene dyes were successfully synthesized under mild reaction conditions. Self-assembled monolayers (SAMs) of the pentaacid derivative were prepared by an immersion method and the photocurrent generation properties of the SAMs were measured. Due to the introduction of the light-absorbing cobaltadithiolene moiety, the range of available wavelengths for photoelectric conversion was extended to lambda = 700 nm, which is longer than that of conventional penta(organo)[60]fullerene carboxylic acids.     

Star‐like Fullerene Containing Poly(Vinylpyrrolydone) Derivatives: Chloroform Solution Properties

Abstract

Star‐like fullerene C₆₀ derivatives with different branch number, synthesized by the reaction of fullerene with poly(vinylpyrrolydone) (PVP) macromolecules bearing the terminal amino‐groups, were investigated in solution by the viscometry, dielectric, and electrooptical Kerr‐effect methods in comparison with the ordinary linear PVPs of the same molecular mass. It was shown that covalent linkage of branches to fullerene through amino‐groups leads to appearance of a polar and optically anisotropic nanoparticle (amine‐substituted C₆₀) in the center of the coil of star‐like polymers that radically changes dielectric and electrooptical properties of the initial polymer. Effect of fullerene on the dimension of polymer coil had been detected also.     

Hierarchical nanomorphologies promote exciton dissociation in polymer/fullerene bulk heterojunction solar cells

PTB7 semiconducting copolymer comprising thieno[3,4-b]thiophene and benzodithiophene alternating repeat units set a historic record of solar energy conversion efficiency (7.4%) in polymer/fullerene bulk heterojunction solar cells. To further improve solar cell performance, a thorough understanding of structure-property relationships associated with PTB7/fullerene and related organic photovoltaic (OPV) devices is crucial. Traditionally, OPV active layers are viewed as an interpenetrating network of pure polymers and fullerenes with discrete interfaces. Here we show that the active layer of PTB7/fullerene OPV devices in fact involves hierarchical nanomorphologies ranging from several nanometers of crystallites to tens of nanometers of nanocrystallite aggregates in PTB7-rich and fullerene-rich domains, themselves hundreds of nanometers in size. These hierarchical nanomorphologies are coupled to significantly enhanced exciton dissociation, which consequently contribute to photocurrent, indicating that the nanostructural characteristics at multiple length scales is one of the key factors determining the performance of PTB7 copolymer, and likely most polymer/fullerene systems, in OPV devices.     

Photosensitization of nanoporous TiO2 film with porphyrin-linked fullerene

A porphyrin-linked fullerene derivative, which included COOH groups in its fullerene unit, Por-C₆₀(COOH) was synthesized in order to investigate the possibility of promoting the photosensitization of TiO₂. Por-C₆₀(COOH) molecules produced higher photocurrent per molecule than tetrakis(4-carboxyphenyl)-porphyrin molecules. A dye-sensitized solar cell using Por-C₆₀(COOH), in which a C₆₀ unit was introduced between the porphyrin unit and TiO₂, yielded an improvement in energy conversion for light collection.     

Recent Advances in n‐Type Polymers for All‐Polymer Solar Cells

All‐polymer solar cells (all‐PSCs) based on n‐ and p‐type polymers have emerged as promising alternatives to fullerene‐based solar cells due to their unique advantages such as good chemical and electronic adjustability, and better thermal and photochemical stabilities. Rapid advances have been made in the development of n‐type polymers consisting of various electron acceptor units for all‐PSCs. So far, more than 200 n‐type polymer acceptors have been reported. In the last seven years, the power conversion efficiency (PCE) of all‐PSCs rapidly increased and has now surpassed 10%, meaning they are approaching the performance of state‐of‐the‐art solar cells using fullerene derivatives as acceptors. This review discusses the design criteria, synthesis, and structure–property relationships of n‐type polymers that have been used in all‐PSCs. Additionally, it highlights the recent progress toward photovoltaic performance enhancement of binary, ternary, and tandem all‐PSCs. Finally, the challenges and prospects for further development of all‐PSCs are briefly considered.     

Photophysics and photochemistry of colloidal poly (p-phenylinevinylene) (PPV) polymer

The photophysical and photochemical behaviour of colloidal PPV polymers has been investigated by emission and photoelectrochemical studies. Emission studies indicated an increased conjugation length for PPV polymers on going from solution to the solid state. The quenching of the emission of PPV polymer by iodine can be used to probe the hole transfer by PPV–iodide complex with subsequent formation of I^*−. To elucidate the role of hole trapping in the process of photo-generation charge separation in various PPV/OTE electrodes, various electrolytes have been used. The values of photon-to-photocurrent conversion efficiency (IPCE) were evaluated from the short circuit photocurrent measurements at different excitation wavelengths. The close match between the IPCE and the absorption spectra shows that the photosensitization mechanism is operative in extending the photocurrent response of OTE/PPV into the visible. The maximum IPCE observed in the present experiments was 1.5% in the wavelength region of 425 nm which commensurates well with the reported values [M. Jonforsen, I. Ahmad, T. Johansson, J. Larsson, L.S. Roman, M. Svensson, O. Inganas, M.R. Andersson, Synth. Met. 119 (2001) 185]. From the photoelectrochemical response of an OTE/PPV electrode to visible light irradiation, the generation of photovoltage and photocurrent was prompt and was reproducible under several on–off cycles of illumination. Optimization of redox couple, electrolyte and film thickness is essential for improving the performance of PPV-based photoelectrochemical cells.     

Device based on the coupling of an organic light-emitting diode with a photoconductive material

We have realized a device based on the coupling of an organic light-emitting diode (with tri(8-hydroxyquinoline)aluminium for light emission) as an input unit with a photoconductive material as an output unit. Various photoconductive materials like pentacene, Cu-phtalocyanine and fullerene were investigated under green light illumination with an emission peak at 550 nm. Photocurrent measurements versus light intensity and bias voltage (applied between two 50 μm distant indium-tin oxide bottom electrodes for the current to flow through the materials) were realized at room temperature a photocurrent gain around 4 is obtained when the materials are subjected to a luminance of about 5000 cd/m² and for bias voltage of − 50 V. Besides, it was shown that to obtain a device with a fast photocurrent response by switching the light off and on, it is necessary to apply a bias voltage higher than − 200 V in these conditions, the gain is multiplied by a factor of 3.     

Stirring Up Acceptor Phase and Controlling Morphology via Choosing Appropriate Rigid Aryl Rings as Lever Arms in Symmetry‐Breaking Benzodithiophene for High‐Performance Fullerene and Fullerene‐Free Polymer Solar Cells

Two series of new polymers with medium and wide bandgaps to match fullerene (PC₇₁BM) and fullerene‐free 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene (ITIC) acceptors are designed and synthesized, respectively. For constructing the key donor building blocks, the effective symmetry‐breaking strategy is employed. Two common aromatic rings (thiophene and benzene) are chosen as one side substituted groups in the asymmetric benzodithiophene (BDT) monomers. In addition, another rigid benzene ring is inserted between aryl and thioether in the side chains, which results in larger twisting and destroying the aggregation and forming longer lever arms. As a result, highly ordered polymers (PBDTsTh‐FBT and PBDTsPh‐FBT) with strong aggregation properties can blend well with roughly spherical PC₇₁BM, while amorphous polymers (PBDTsThPh‐BDD and PBDTsPhPh‐BDD) with long and rigid aryl rings show good miscibility with elongated ITIC, and finally, both devices exhibit excellent power conversion efficiencies over 10%. Thus, it clearly shows that the asymmetric BDT unit is an excellent donor building block to construct highly efficient photovoltaic polymers. Meanwhile, this work demonstrates that it is not necessary that high‐performance fullerene‐free polymer solar cells (PSCs) require highly ordered microstructures in the blending films, different from the fullerene‐based PSCs.     

Thin polymerized C60 coatings deposited in electrostatic field via electron-beam dispersion of fullerite

The aim of the present study is to clarify the charge composition of fullerite C₆₀ electron-beam dispersion (EBD) products and investigate the influence of fullerene ions and electrons on the structure of the deposited coatings by applying an additional electrostatic field to the substrates. It was found that C₆₀ EBD products contain positive fullerene ions and electrons. By using Raman and attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, laser desorption/ionization mass-spectrometry and atomic force microscopy, it was shown that the assistance of the electrons additionally accelerated up to 300 eV results in the formation of a mixture of dumb-bell- and peanut-shaped C₆₀ polymers. The assistance of the positive fullerene ions additionally accelerated up to 300 eV leads to the formation of highly cross-linked random 3D networks of covalently bonded fullerene molecules.     

C<Subscript>60</Subscript> end-functionalized four-armed polymers: synthesis and optical limiting properties

A series of bromo-terminated four-armed homopolymers [polystyrene (PSt) and poly(methyl methacrylate) (PMMA)], prepared by atom transfer radical polymerization (ATRP), were subsequently functionalized with fullerene C₆₀ by atom transfer radical addition (ATRA) reaction using CuBr/2,2′-bipyridine (bipy) as the catalyst system. The C₆₀ end-capped four-armed polymer derivatives were then characterized by gel permeation chromatography (GPC), UV–vis, FT-IR, thermal gravimetric analyses (TGA) and differential scanning calorimeter (DSC). Another technique of synthesizing C₆₀-functionalized four-armed polymers from azide functional polymers was also applied for comparison. The optical limiting behavior of C₆₀ end-capped four-armed polymers prepared via ATRA reaction were measured in THF solution at 532 nm. Both groups of fullerene-functionalized polymers (C₆₀-PSts and C₆₀-PMMAs) are provided with optical limiting properties.     

Synthesis of High-Molecular-Weight [60]Fullerene Pearl-Necklace Polyamides Derived from Equatorial [60]fullerenobisacetic Acid

A series of [60]fullerene pearl-necklace polyamides, consisting of equatorial-[60]fullerenobisacetic acid and various chromophoric aromatic diamines, were synthesized by a phosphorylation route using large amounts of triphenyl phosphite and pyridine as condensing reagents with stepwise addition of the condensing reagents. In the present polymers, [60]fullerene pearls and diamine linkers were attached to one another by cyclopropane connectors. The polyamides had weight-average molecular weights (M_w)of 4.5-5.0×10⁴ g/mol and inherent viscosities (n_inh) of 0.3-0.4 dL/g in N, N-dimethylacetamide (DMAc) at 30 °C. They had glass transition temperatures at 30-125 °C and decomposition temperatures at 300-310 °C. The UV-VIS spectra in DMAc exhibited broad absorption with λ_max at 310-390 nm tailing to longer wavelengths.     

Investigation of gas diffusion through films of fullerene-containing poly(phenylene oxide)

A study is made of the possibility of using fullerene-containing polymers as materials for gas-separating membranes. Fullerene-containing poly(phenylene oxide) was prepared and its density and free volume were estimated. The coefficients of gas permeability and the selectivity factors for separation of air into oxygen and nitrogen were measured for poly(phenylene oxide) having various fullerene contents. A correlation is established between the change in the transport properties and the free volume. It is shown that modifying poly(phenylene oxide) with fullerene is potentially useful for improving the transport properties of the membranes. Pis’ma Zh. Tekh. Fiz. 25, 14–19 (July 26, 1999)