M. G. Tedoradze

Hybrid heterostructures based on aromatic polyimide and semiconductor CdSe quantum dots for photovoltaic applications

A nanohybrid photoactive material based on aromatic polyimide (PI) doped with CdSe quantum dots (QDs) has been developed to be used in photovoltaic solar cells. The solar cell is based on a heterostructure of an ITO electrode covered with a layer of Cu–phthalocyanine and a layer of a PI–QD composite. The photovoltaic properties of the CuPc/PI:CdSe hybrid heterostructure at various QD concentrations in the PI matrix have been studied. Luminescent and transmission electron microscopy analyses have shown that the optimal QD mass concentration is 60%. The efficiency of the solar cell based on optimized PI:CdSe structures approaches those for the structures based on conventional MEH-PPV organic semiconductor. Moreover, the photovoltaic characteristics of the solar cell remain stable in the air for a long time (120 h). This is expected to considerably simplify the technology of manufacturing these hybrid solar cells. The mechanisms of the excitation and charge transfer from QDs to the organic semiconductors and...

Photovoltaic devices based on palladium(II) meso-tetra(benzo-15-crown-5)porphyrinate

The properties of photovoltaic cells containing an MEH-PPV composition with palladium(II) meso-tetra(benzo-15-crown-5)porphyrinate as an electron-conduction layer and copper(II) phthalocyanine as a hole transport layer were studied. The influence of the environment and a top-electrode metal on the operation efficiency was also examined. It was found that oxygen at the fabrication steps affects in different manners the formation of open-circuit voltage and the performance of the device. A certain correlation between the properties of electrodes and the photoelectromotive force was established. The highest conversion efficiency of 0.02 electrons per incident photon was obtained for samples that additionally contained an amorphous selenium layer applied over the aforementioned conducting layers.

Optical and Electrical Characteristics of Polymer Films Modified with Nanostructured Silver Aggregates

To study the formation of a new dispersed phase in polymer layers, the absorption of radiation-generated silver aggregates in cellophane films was examined. Stable silver nanoparticles were prepared by the radiation-chemical reduction of silver ions in a solution of inverted micelles of the composition AgNO3(AgClO4)/H2O/AOT/octane. On irradiation of cellophane films immersed in a micellar solution, the formed silver aggregates Agm+nbecame incorporated into the films. The modified films exhibited a stable yellow color. The intensity of an optical absorption band of the films with λmax∼ 420–440 nm increased proportionally to the radiation dose absorbed by an aqueous micellar solution. The light sensitivity of these films was examined. A 35-min exposure of the films at λ = 365 nm resulted in an increase in the intensity of the main absorption band by 17% and in a bathochromic shift of the maximum. The electrical characteristics of modified films were determined depending on the radiation dose. It was found that the incorporation of nanostructured silver clusters exhibiting the characteristic optical absorption band with λmax∼ 420–440 nm increased the conductivity of cellophane films by two to three orders of magnitude.

Optically and chemically amplified photoresists based on poly(hydroxyaminoester)s

Processes for both optical and autocatalytic chemical amplification of a latent image have been realized in the polymer donor poly(hydroxyaminoester) in the presence of the electron acceptor hexabromodimethylsulfone and the chemical sensitizes dimethylaminobenzaldehyde. This resulted in a negative photoresist with a sensitivity as high as 0.2–0.5 mJ cm–2.

The Effect of a Nanosize TiO x Layer on the Performance of an Organic Solar Cell

This work studies the role of a cathodic TiOx buffer layer in operation of a photovoltaic organic solar cell (OSC) based on a photoactive layer with a bulk heterojunction. Using a liquid solution to obtain a TiOx layer is of current interest for simplification of process technologies of successive formation of OSC layers. It is found that the optimum thickness of the TiOx layer is 10 nm; at this thickness, the efficiency of the OSC reaches the value of 4.36%. The effect of air oxygen on the OSC samples is studied and it is found that samples with a TiOx buffer layer undergo degradation to a lesser extent as compared to the samples with no such layer. The effect of oxygen on operation of the photovoltaic device is discussed.

The conduction switching effect in thin polymer layers

The effect of pressure-induced and field-induced conduction switching in thin polymer layers was experimentally studied. Conduction switching was observed in thin layers of poly(diphenylene phthalide), polyvinylcarbazole, some aromatic polyimides, and methoxypoly(phenylene-vinylene). It was found that conduction switching depends in a critical manner on the formation mode of the metal/polymer contact.

Polymer light-sensitive layers for photochemical etching of Al films

Abstract The dry photochemical etching of aluminum films has been studied using the etchers (Opal Blue dye and acids), which are produced by illumination of the light-sensitive polymer layers cast on top of these films. These layers, consisting of different polymer binders, ferrocene [(C 5 H 5 ) 2 Fe], diphenylamine (DPA) and tetrabromomethane (CBr 4 ) have a high light-sensitivity owing to autocatalytic post-exposure accumulation of etchers. In this process the catalytic system Fe(III)/Fe(II) is formed directly from components dissolved in the polymer binder as a result of photochemical reaction. The Al film having a thickness of 0.65 μm is dissolved into the polymer layers completely after exposure H 0 = 4 mJ cm −2 to 365 nm.

Dry photochemical etching of Bi films

Illumination of a light-sensitive polymer layer cast on top of a Bi film leads to etching in situ of the metallic film. The greater the exposure, the less the film thickness. The layer consists of a polymer binder, aromatic amines (Am)[namely diphenylbenzylamine (DPBA), diphenylamine (DPA) or dibenzylaniline (DBA)] and hexabromodimethylsulfone (HBMS), forming light-sensitive charge-transfer complexes Am-HBMS. Initial exposure to 365 and 436 nm light, followed by exposure to 650nm light results in amplification with a consequently high sensitivity for the photoetching process (ca. 3 × 10–4 J cm–2).

Engineering of hybrid heterostructures from organic semiconductors and quantum dots for advanced photovoltaic applications

Semiconductor quantum dots (QDs) are characterized by high extinction coefficients adjustable by varying the nanoparticle size and a high quantum yield of charge generation. They have the advantage of efficient charge transfer from QDs to organic semiconductors. An advanced photovoltaic cell where a SnO2/ITO electrode is covered with layers of CdSe QDs integrated in a polyimide (PI) organic semiconductor (about 100 nm thick) and Cu–phthalocyanine (20–40 nm thick) has been developed.Laser-induced photoluminescence analysis has permitted the optimization of the QD concentration in the PI matrix. Special attention has been paid to the electrode surface quality, including the effect of oxygen-plasma treatment of the transparent SnO2/ITO electrode surface on the heterostructure photoconductivity. The mechanisms of excitation and charge transfers from QDs to the organic semiconductor and their effects on the efficiency of solar radiation conversion to electricity are discussed. Photovoltaic study of the structures developed has been performed, and the effect of the Cu–phthalocyanine layer on their photoconductivity has been estimated. The photovoltaic efficiency of optimized PI–CdSe hybrid structures approaches that of the best performing systems based on the MEH–PPV organic semiconductor. Incorporation of CdSe QDs in MEH–PPV has been demonstrated to increase the photovoltaic efficiency of the system by 50%, thus allowing the development of novel QD-based inorganic/organic hybrid materials with considerably improved photovoltaic properties.

Effect of metal nanoparticles on the optical properties of the solutions of porphyrinates and MEH-PPV polymer

The interactions of metal nanoparticles, which were synthesized in inverse micelles, with a number of porphyrinate molecules and a poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) polymer in solutions were examined by spectrophotometry in order to study the effects of various additives on the efficiency of sun energy absorption and conversion by photosensitive polymer layers. The optical absorption and luminescence spectra of the solutions of Ag, Pd, and Pt nanoparticles and the solutions of Pd(II) and Pt(II) meso-tetra(benzo-15-crown-5)porphyrinates and the MEH-PPV polymer were measured previously.