Vlad V. Travkin

First tellurium-containing phthalocyanine analogues: strong effect of tellurium on spectral, redox and conductivity properties of porphyrazines with annulated chalcogenodiazole ring(s)

The first tellurium-containing phthalocyanine analogues have been prepared and spectroscopically characterised: the Mg(II) complex of tetra(1,2,5-telluradiazolo)porphyrazine and a low-symmetry tert-butyl substituted Mg(II) tribenzoporphyrazine with one fused 1,2,5-telluradiazole ring. It was observed that the introduction of Te atom(s) reduces the energy of the Q-transition, facilitates the reduction of the macrocycle and strongly increases the conductivity of thin films.

Organic photovoltaic cells on polymeric substrates with buffer nanolayers

Prototypes of organic photovoltaic cells based on the planar “subphthalocyanine/fullerene” heterojunction were fabricated using flexible polymeric substrates. Current-vs-voltage characteristics in the dark and under illumination were recorded and basic photovoltaic parameters were derived. It was shown that introduction of the (top) barrier layer composed of Alq3 molecules under the cathode significantly lowers the parasitic resistances in the cells, so that fill factor rises up to 55%. If the (bottom) buffer InClPc layer is deposited onto the anode (ITO), then the open circuit voltage of cells increases from 0.47 to 0.83 V. The highest power conversion efficiency was achieved in OPVC with both top and bottom interfacial layers (∼1%).

Depth profiling of fullerene-containing structures by time-of-flight secondary ion mass spectrometry

A new variant of depth profiling for thin-film fullerene-containing organic structures by the method of time-of-flight (TOF) secondary ion mass spectrometry (SIMS) on a TOF.SIMS-5 setup is described. The dependence of the yield of C60 molecular ions on the energy of sputtering ions has been revealed and studied. At an energy of sputtering Cs+ ions below 1 keV, the intensity of C60 molecular ions is sufficiently high to make possible both elemental and molecular depth profiling of multicomponent (multilayer) thin-film structures. Promising applications of TOF-SIMS depth profiling for obtaining more detailed information on the real molecular composition of functional organic materials are shown.

Photovoltaic properties of Schottky-barrier cells utilizing sub-phthalocyanine layer

We have fabricated and tested Schottky-type photovoltaic cells based on chloro(sub-phthalocyaninato)boron(III) complex, SubPcBCl. The vacuum-deposited SubPcBCl layer was sandwiched between standard glass/ITO substrate and evaporated Au, Ag or Al top metallic electrode. Performance of such cells depends on the work function of the cathode material. Power conversion efficiency of the non-optimized cells with Al cathode approaches ~0.01% under 1 sun illumination. The photovoltaic effect takes place even if gold is used as top electrode.

Phthalocyanine-Based Schottky-Type Photovoltaic Cells with Magnetron Sputtered Al Electrodes

This work addresses the use of a sputtering technique for fabricating the top contacts to conventional sandwich-type ITO\phthalocyanine\Al cells. Current-vs-voltage characteristics of these cells measured both in dark and under illumination are compared with those of identical cells, but bearing a thermally evaporated Al cathode. The greatly improved efficiency is revealed in the former case: in particular, the fill factor increased by a factor of three.

Tandem photovoltaic cells with a composite intermediate layer

We have fabricated and tested tandem photovoltaic cells containing series-connected subcells of the “oxide–organic semiconductor–metal” type. The organic semiconductors were two phthalocyanine dyes (SubPc and PcVO); Al or Ag:Mg were used as capping metallic electrodes. A semitransparent composite metal–oxide layer formed by molybdenum oxide MoOx deposited over an ultrathin Al layer is used to join the subcells. Additionally, a MoOx layer deposited onto glass/ITO substrates serves as an anode buffer in the front subcell, and LiF deposited onto the dye layers serves as a cathode buffer in the front or rear subcells. Upon optimization of the thickness and composition of the intermediate layer, the open circuit voltage Uoc amounts to 1.6 V reflecting total summation of the contributions from the each of the subcells at a wide spectral coating from 300–1000 nm. The fill factor in the tandem cell is not worse than in individually made single cells with the same scheme or in disconnected subcells.

The Effect of a Substrate on the Current-vs-Voltage Characteristics of Thin-Film Sandwich Structures Based on Buckminsterfullerene

We analyze the current-vs-voltage (J-V) characteristics of ITO/C60/Al sandwich cells, where ITO is the double indium tin oxide, C60 is the buckminsterfullerene and Al is the thermally evaporated top aluminum electrode. These cells were obtained on either glass/ITO or polyethyleneterephthalate/ITO substrates (or, optionally, on glass/ZnO substrates) in a parallel process under identical conditions. However, the J-V dependences in each series behave very differently. The results are discussed in terms of the migration of admixtures from a bulk substrate material toward the top metallic electrode, thus modifying the photovoltaic properties of cells.

Prototypes of photovoltaic cells based on subphthalocyanine with a lower buffer layer

Prototype organic photovoltaic cells containing a planar subphthalocyanine/fullerene heterojunction are fabricated. Their current-voltage characteristics are measured and basic photoconversion parameters are estimated. It was found that the morphology and conductive properties of the photoactive phthalocyanine layer depend on the presence and nature of the molecular sublayer on the anode surface onto which it is deposited. The use of indium chloride phthalocyanine as a sublayer increases the photoconversion efficiency in cells by a factor of 15.

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.

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.