Fullerene Layer Research Articles

Photophysical Study of a Self-Assembled Donor–Acceptor Two-Layer Film on TiO2

The self-assembled monolayer (SAM) technique was employed to fabricate a two-layer donor-acceptor film on the surface of TiO2. The approach is based on using donor and acceptor compounds with anchoring groups of different lengths. The acceptor, a fullerene derivative, has a carboxyl anchor attached to the fullerene moiety via a short linker that places the fullerene close to the surface. The donor, a porphyrin derivative, is equipped with a long linker that can penetrate between the fullerenes and keep porphyrin on top of the fullerene layer. The two-layer fullerene-porphyrin structures were deposited on a mesoporous film of TiO2 nanoparticles by immersing the TiO2 film sequentially into fullerene and porphyrin solutions. Transient absorption spectroscopy studies of the samples revealed that after the selective photoexcitation of porphyrin a fast (<5 ps) intermolecular electron transfer (ET) takes place from porphyrin to the fullerene layer, which confirms the formation of the interlayer donor-acceptor interface. Furthermore, in the second step of ET the fullerene anions donate electrons to the TiO2 nanoparticles. The latter reaction is relatively slow with an average time constant of 230 ps. It involves roughly half of the primary generated charges, and the second half relaxes by the interlayer charge recombination. The resulting state with a porphyrin cation and electron in TiO2 has an extremely long lifetime and recombines with an average time constant of 23 ms.

A Hybrid CuI/Fullerene Heterojunction in Transparent Flexible Photovoltaic Cells

We report on the fabrication and testing of multilayer thin-film photovoltaic cells based on a hybrid cuprous iodide/fullerene (CuI/C60) heterojunction. The cells were prepared by thermal evaporation of components on flexible polyethylene terephthalate (PET) substrates. The 0.4-V open circuit voltage (Uoc) arising at the junction does not depend on the thickness of the fullerene layer and on the introduction of a blocking layer at cathode. However, these changes strongly affect the short circuit current. A distinctive feature of such cells is high transparency in the entire visible range, which makes them potentially interesting for application in tandem (or multijunction) photovoltaic structures in order to enhance Uoc.

Characteristics of fullerene-based diode structures on polymer and glass substrates

Chemical structure of the top Al/C60 interface in Al/C60/ITO sandwich structures (Al is the thermally deposited top aluminum layer, C60 is the thermally deposited fullerene layer, ITO is the double indiumtin oxide, the role of the substrate is played by Lavsan (polyethylene terephthalate), or glass) is studied by time-of-flight secondary mass spectrometry (ToF-SIMS) with depth profiling. The study is stimulated by the recently found specific features of the photovoltaic effect in fullerene-containing sandwich structures on glass or polymer substrates. It is found that the chemical composition of the top Al/C60 interface is not the same on different substrates. This leads to differences in the photovoltaic conversion parameters for more complex thin-film structures with a molecular heterojunction.

The fabrication of polyfluorene and polycarbazole-based photovoltaic devices using an air-stable process route

We report a comparative study based on the fabrication of polymer:fullerene photovoltaic (PV) devices incorporating carbazole, fluorene, and a PTB based co-polymer. We have explored the efficiency and performance of such devices when the active polymer:fullerene layer is deposited by spin-casting either under nitrogen or ambient conditions. We show that PV devices based on carbazole and fluorene based materials have very similar power conversion efficiencies when processed under both air and nitrogen, with other photobleaching measurements suggesting that such materials have comparatively enhanced photostability. Devices based on the PTB co-polymer, however, have reduced efficiency when processed in air.

Origin and elimination of photocurrent hysteresis by fullerene passivation in CH3NH3PbI3 planar heterojunction solar cells.

The large photocurrent hysteresis observed in many organometal trihalide perovskite solar cells has become a major hindrance impairing the ultimate performance and stability of these devices, while its origin was unknown. Here we demonstrate the trap states on the surface and grain boundaries of the perovskite materials to be the origin of photocurrent hysteresis and that the fullerene layers deposited on perovskites can effectively passivate these charge trap states and eliminate the notorious photocurrent hysteresis. Fullerenes deposited on the top of the perovskites reduce the trap density by two orders of magnitude and double the power conversion efficiency of CH(3)NH(3)PbI(3) solar cells. The elucidation of the origin of photocurrent hysteresis and its elimination by trap passivation in perovskite solar cells provides important directions for future enhancements to device efficiency.

Binary short-range colloidal assembly of magnetic iron oxides nanoparticles and fullerene (nC60) in environmental media.

Colloidal assembly of nC60 fullerene with naturally abundant magnetic iron oxide NPs will affect their fate and transformation in environmental media. In solution, fullerene association to aggregating iron oxide NPs/clusters greatly enhanced the overall colloidal stability. Development of depletion-mediated structured fullerene layers between pure and surface modified γFe2O3 NPs possibly resulted in such stabilization. Here, we also report that on air-water interface, association of fullerene to pure and humic acid (HA7) coated γFe2O3 NPs led to the formation of ordered assemblies, e.g., binary wires and closed-packed "crystalline" and "glassy" structures in the presence and absence of electrolytes suggesting immobilization of the former. The interaction of fullerene to Fe3O4 NPs and clusters also produced ordered assemblies along with amorphous aggregates. Fullerene interaction with Fe3O4 NPs in low concentration of HA1 and Na(+) at pH 6 formed dendritic growth and polycrystalline circular assemblies on air-water interface. HRTEM study further revealed that the monolayer circular assemblies were highly ordered but structural degeneracy was evident in multilayers. Therefore, interfacial assemblies of fullerene with iron oxide NPs resulted in short-range periodic structures with concomitant immobilization and reduction in availability of the former, especially in soils or sediments rich in the latter.

Time-resolved neutron reflectometry and photovoltaic device studies on sequentially deposited PCDTBT-fullerene layers.

We have used steady-state and time-resolved neutron reflectometry to study the diffusion of fullerene derivatives into the narrow optical gap polymer poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) to explore the sequential processing of the donor and acceptor for the preparation of efficient organic solar cells. It was found that when [6,6]-phenyl-C61-butyric-acid-methyl-ester (60-PCBM) was deposited onto a thin film of PCDTBT from dichloromethane (DCM), a three-layer structure was formed that was stable below the glass-transition temperature of the polymer. When good solvents for the polymer were used in conjunction with DCM, both 60-PCBM and [6,6]-phenyl-C71-butyric-acid-methyl-ester (70-PCBM) were seen to form films that had a thick fullerene layer containing little polymer and a PCDTBT-rich layer near the interface with the substrate. Devices composed of films prepared by sequential deposition of the polymer and fullerene had efficiencies of up to 5.3%, with those based on 60-PCBM close to optimized bulk heterojunction (BHJ) cells processed in the conventional manner. Sequential deposition of pure components to form the active layer is attractive for large-area device fabrication, and the results demonstrate that this processing method can give efficient solar cells.

Crystallinity Effects in Sequentially Processed and Blend-Cast Bulk-Heterojunction Polymer/Fullerene Photovoltaics

Although most polymer/fullerene-based solar cells are cast from a blend of the components in solution, it is also possible to sequentially process the polymer and fullerene layers from quasi-orthogonal solvents. Sequential processing (SqP) not only produces photovoltaic devices with efficiencies comparable to the more traditional bulk heterojunction (BHJ) solar cells produced by blend casting (BC) but also offers the advantage that the polymer and fullerene layers can be optimized separately. In this paper, we explore the morphology produced when sequentially processing polymer/fullerene solar cells and compare it to the BC morphology. We find that increasing polymer regioregularity leads to the opposite effect in SqP and BC BHJ solar cells. We start by constructing a series of SqP and BC solar cells using different types of poly(3-hexylthiophene) (P3HT) that vary in regioregulary and polydispersity combined with [6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM). We use grazing incidence wide-angle X-ray ...

Suppressed charge recombination in inverted organic photovoltaics via enhanced charge extraction by using a conductive fullerene electron transport layer.

Conductive fullerene electron-transporting layers (ETLs) are developed to facilitate the solution processing of highly efficient inverted OSCs with power conversion efficiency (PCE) reaching 9.6%. Its high conductivity also allows devices to be fabricated independently of the ETL thickness (up to ca. 50 nm). Transient photovoltage (TPV) measurements are used to shed light on how these conductive ETLs help suppress charge recombination in solar cells.

Phase transitions at high pressure in the fullerene C60 molecular donor-acceptor complex {Hg(dedtc)2}2 · C60

Raman spectra of crystals of the molecular fullerene C60 donor-acceptor complex {Hg(dedtc)2}2 · C60 (fullerene with mercury diethyldithiocarbamate) have been measured at a pressure up to 8.4 GPa and at room temperature. A phase transition has been revealed in the pressure range of 1.2–2.0 GPa, which is accompanied by a splitting of the degenerate intramolecular phonon modes Hg(1)-Hg(4) and Hg(7)-Hg(8), as well as by a softening of the Hg(2) mode of the fullerene C60. As the pressure further increases to the maximum value, the intensity of the bands varies smoothly. A decrease in the pressure leads to the reverse transition to the initial state at 1.2 GPa. The splitting of the degenerate modes Hg(1)-Hg(8) and the softening of the Hg(2) modes resemble their behavior in the formation of dimers in fullerite crystals and indicate the possible formation of dimers in two-dimensional fullerene layers under hydrostatic compression of the {Hg(dedtc)2}2 · C60 complex.

Formation of hexagonal fullerene layers from neutral and negatively charged fullerenes in {(Ph3P)3Au(+)}2(C60(•-))2(C60)·C6H4Cl2 containing gold cations with the C3v symmetry.

Fullerene salt {(Ph3P)3Au(+)}2(C60(•-))2(C60)·C6H4Cl2 (1) containing (Ph3P)3Au(+) cations with the C3v symmetry has been obtained as single crystals. Hexagonal corrugated fullerene layers formed in 1 alternate with the layers consisting of (Ph3P)3Au(+) and C6H4Cl2 along the c axis. According to IR spectra and peculiarities of the crystal structure, the charge on fullerenes in the layers is evaluated to be -1 for two and close to zero for one C60. These fullerenes have different cationic surroundings, and positively charged gold atoms approach closer to C60(•-). Charged and neutral fullerenes are closely packed within hexagonal layers with an interfullerene center-to-center distance of 10.02 Å and multiple short van der Waals C···C contacts. The distances between C60(•-) are essentially longer with an interfullerene center-to-center distance of 10.37 Å due to corrugation of the layers, and no van der Waals contacts are formed in this case. As a result, each C60(•-) has only three negatively charged fullerene neighbors with rather long interfullerene distances providing only weak antiferromagnetic interaction of spins in the fullerene layers with a Weiss temperature of -5 K.

Cyanine dye polyelectrolytes for organic bilayer solar cells

Polyelectrolytes composed of an anionic sulfoethyl methacrylate/methacrylate backbone and cationic cyanine dyes counter ions are synthesized. The effective reaction sequence is confirmed by NMR spectroscopy and consists of a thermal radical copolymerization to obtain the polymer backbone (Mn ∼ 40 kg mol−1), followed by deprotonation of the sulfoethyl group and a salt metathesis reaction with elimination of silver halide to incorporate the dye. With increasing cyanine content (20–50% of polymer repeating units) polyelectrolytes become insoluble in apolar solvents. This allows the fabrication of simple solution-processed bilayer organic solar cells, where an electron acceptor fullerene layer is coated from the orthogonal solvent chlorobenzene onto an underlying polyelectrolyte electron donor layer. The optimization of solar cells is described, and photo-CELIV measurements are used to identify the low hole mobility in the polyelectrolyte layer as the main reason that currently limits solar cell performance to ∼0.9%.

Metallic and Mott insulating spin-frustrated antiferromagnetic states in ionic fullerene complexes with a two-dimensional hexagonal C60·- packing motif.

(MDABCO(+))(C60(·-))(TPC) (1), in which MDABCO(+) is N-methyldiazabicyclooctanium, TPC is triptycene, and both have threefold symmetry, is a rare example of a fullerene-based quasi-2D metal and contains closely packed hexagonal fullerene layers with interfullerene center-to-center distances of 10.07 Å at 300 K. Evidence for the metallic nature of 1 was obtained by optical and microwave conductivity measurements on single crystals. The metal is characterized by a nontypical Drude response and relatively large optical mass (m*/m0 =6.7). The latter indicates a narrow-band nature, which is consistent with the calculated bandwidth of 0.10-0.15 eV. The coexistence of metallic and antiferromagnetic nonmetallic 2D layers was observed in 1 above 200-230 K. It was assumed that the nonmetallic layers undergo a transition to the metallic state below 200 K due to ordering of the fullerene and cationic sublattices. New layered complex (MQ(+))(C60(·-))(TPC) (2) with a hexagonal arrangement of C60(·-) was obtained by increasing the interfullerene distance with the bulkier N-methylquinuclidinium cations (MQ(+)) having threefold symmetry. The structure of 2 is characterized by increased interfullerene center-to-center distances in the layers (10.124, 10.155, and 10.177 Å at 250 K). Unit-cell doubling parallel to the 2D layer (along the b axis) was observed at low temperatures. In contrast to metallic 1, 2 exhibits a nonmetallic spin-frustrated state with an antiferromagnetic interaction of spins (the Weiss temperature is -27 K) and no magnetic ordering down to 1.9 K. It was supposed that the expanded interfullerene distances in the triangular arrangement decrease the bandwidth and suppress metallic conductivity in 2, and thus a Mott-Hubbard insulating state with antiferromagnetically frustrated spins results.

Fullerenes as adhesive layers for mechanical peeling of metallic, molecular and polymer thin films.

We show that thin films of C60 with a thickness ranging from 10 to 100 nm can promote adhesion between a Au thin film deposited on mica and a solution-deposited layer of the elastomer polymethyldisolaxane (PDMS). This molecular adhesion facilitates the removal of the gold film from the mica support by peeling and provides a new approach to template stripping which avoids the use of conventional adhesive layers. The fullerene adhesion layers may also be used to remove organic monolayers and thin films as well as two-dimensional polymers which are pre-formed on the gold surface and have monolayer thickness. Following the removal from the mica support the monolayers may be isolated and transferred to a dielectric surface by etching of the gold thin film, mechanical transfer and removal of the fullerene layer by annealing/dissolution. The use of this molecular adhesive layer provides a new route to transfer polymeric films from metal substrates to other surfaces as we demonstrate for an assembly of covalently-coupled porphyrins.

Thermally evaporated fullerene (C70) to bridge the charge transport in between nanostructured zinc oxide and conjugated copolymer in hybrid solar cell

We have investigated the effect of incorporating thin fullerene (C70) layer in between nanostructured ZnO and conjugated co-polymer PCDTBT (Poly [[9-(1-octylnonyl)-9H–carbazole-2,7-diyl]-2,5-thophenediyl-2,1,3-benzothiadiazole- 4,7-diyl-2,5-thiophenediyl]) for photovoltaic device performance. The addition of the fullerene layer enhances the electron transfer at the heterojunction from polymer to the metal oxide. The reason for the enhanced performance is investigated and it is observed that the fullerene layer can improve charge transfer process thorough the reduction of the trap induced interfacial recombination. The fullerene introduction is also helping in effective charge transfer (CT) excitons dissociation and transport at the interface. Encouraging improvement of the device performance was observed with the incorporation of C70 in this kind of hybrid solar cells.

Photodynamic inactivation of enveloped virus in protein plasma preparations by solid-phase fullerene-based photosensitizer

The problem of transfusion-transmitted infections still remains serious and actual for health care despite the detailed testing of donors. Human immunodeficiency virus, hepatitis B and C viruses and human cytomegalovirus are among the most dangerous pathogens that can be transmitted with blood. Previously, a composition consisting of fullerene layer applied on silica gel particles was shown to inactivate influenza virus up to complete loss of infectivity. In the present study the unit has been developed with source of irradiation whose spectrum is appropriate for solid-phase fullerene. The ability of the unit to inactivate the enveloped influenza virus in protein fraction of donor blood has been studied. It was shown that at optimized conditions complete inactivation of enveloped virus of extremely high initial titer (7.0-9.5 log 10 EID 50/0.2 mL) in the solution of albumin was achieved after as short time as 30 min of irradiation. This process did not affect the oxidative metabolism of neutrophils and membranes of erythrocytes evaluated by NBT reduction test and morphological analysis of erythrocytes, respectively. The data obtained suggests that the method described can be recommended for further development and optimization of the procedure of inactivation of viruses in the preparations of the plasma of donor blood.

PHOTONIC ANALYSIS OF SEMICONDUCTOR FIBONACCI SUPERLATTICES: PROPERTIES AND APPLICATIONS

Abstract—In this paper, we theoretically study the phase treatment of reflected waves in onedimensional Fibonacci photonic quasicrystals composed of nano-scale fullerene and semiconductor layers. The dependence of the phase shift of reflected waves for TE mode and TM mode on the wavelength and incident angle is calculated by using the theoretical model based on the transfer matrix method in the infrared wavelength region. In the band gaps of supposed structures, it is found that the phase shift of reflected wave changes more slowly than within the transmission band gaps. Furthermore, the phase shift decreases with the incident angle increasing for TE mode, and increases with the incident angle increasing for TM mode. Also, for the supposed structures it is found that there is a band gap which is insensitive to the order of the Fibonacci sequence. These structures open a promising way to fabricate subwavelength tunable phase compensators, very compact wave plates and phase-sensitive interferometry for TE and TM waves.

Insertion of fullerene layer for bulk heterojunction organic photovoltaic cell fabricated by electrospray deposition method

AbstractAn improved power conversion efficiency (PCE) of bulk heterojunction organic photovoltaic cell (OPV) was achieved by inserting an n‐type [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) layer between the active layer and a metal electrode. The controlled substrate temperature was found to be a useful parameter for the multilayer structure (active layer/ PCBM) by the electrospray deposition method. Under optimized substrate temperature during the PCBM deposition, a multilayer structure could be formed, and the PCE was improved up to 1.94%.magnified image(© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Tandem organic photovoltaics incorporating two solution-processed small molecule donor layers

We develop a partially solution-processed small molecule tandem organic photovoltaic cell using an organic/inorganic interlayer structure that provides efficient charge recombination while protecting underlying layers from degradation due to attack from solvents applied during the deposition of subsequent sub-cells. Each sub-cell consists of a functionalized squaraine (fSQ) blend donor that is cast from solution, followed by evaporation of other functional layers. The first fSQ layer is cast from chloroform, while the second is cast from a tetrahydrofuran, thereby minimizing dissolution of the relatively insoluble, underlying fullerene layer that acts to protect the first donor layer. Solvent vapor annealing increases the sub-cell performance while decreasing the damage caused by spin-coating of the second fSQ layer, both of which result from increased film crystallinity that reduces the rate of solvent penetration. The tandem cell has a power conversion efficiency of 6.2% ± 0.3% and an open circuit voltage nearly equal to the sum of the constituent sub-cells.

Ordered Structures from Crystalline Carbon Disulfide Solvates of the Nano-Tubular Fullerenes D5h(1)-C90 and D5h-C70

The structures of three crystalline solvates, D5h(1)-C90·CS2, D5h-C70·3CS2, and 2(D5h-C70)·3CS2, of nanotubular fullerenes have been determined by single crystal X-ray diffraction. Despite the marked tendency for fullerenes to disorder, the carbon cages in all three structures are fully ordered at 100(2) K for D5h(1)-C90·CS2 and 90 K for the other two crystals. Moreover, the carbon disulfide molecules are also ordered, except for the case of D5h(1)-C90·CS2, where there is a minor disorder in the solvate location. The molecular packing in D5h(1)-C90·CS2 reflects the nanotubular nature of the fullerene component with channels of alternating fullerenes and carbon disulfide molecules running along the crystallographic b axis. The molecular packing arrangements for D5h-C70·3CS2 and 2(D5h-C70)·3CS2 do not show such channels. In D5h-C70·3CS2, the carbon disulfide molecules form chains that snake between the fullerenes and along the crystallographic a axis. In 2(D5h-C70)·3CS2, there are two crystallographically distinct fullerene cages, which are segregated into individual layers. Within each layer, the fullerenes show hexagonal close packing and the carbon disulfide molecules form chains that snake between the fullerene layers in a zigzag fashion. The presence of diiodine in solution was essential for the formation of crystals of D5h-C70·3CS2 and 2(D5h-C70)·3CS2 that were suitable for structure determination, although no diiodine was incorporated in these crystals.