Ya. I. Vertsimakha

Properties of the CuInS2 surface and the effect of organic layers

This study is devoted to the properties of the CuInS2 (CIS) surface and the effect of thin organic layers on them. The CIS layers under study feature photosensitivity in the range of 1.5–3 eV. A quadratic approximation of the long-wavelength edge of a spectral dependence of the photovoltage yields the band gap Eg=1.46±0.02 eV. It is shown that the major contribution to the formation of the barrier near the CIS free surface is made by acceptor levels arranged higher than the CIS valence band top by ∼0.1 and ∼0.2 eV. As a polymeric layer is deposited onto the CIS free surface, the potential barrier height slightly decreases, while the carrier transport efficiency simultaneously increases. As an organic p-type semiconductor is deposited onto the CIS free surface, trapping centers are partially neutralized, and the carrier recombination rate on the CIS film surface decreases.

Electronic Processes in the Porous Silicon-Conducting Polymer Heterostructures

The effect of an integrated polymer on the luminescence characteristics of porous silicon (PS)-conducting polymer (CP) heterostructures has been studied. Both n-(100) and p-type (111) PS has been employed in order to prepare the heterostructures. To obtain the integrated polymer layers (polyaniline, polymethoxyaniline, polyphenylacetylene, poly-para-phenylene, poly-N-epoxy-propylcarbazol), the methods of electrochemical polymerization, vacuum deposition, and spin coating have been used. The obtained structures were studied using atom force microscopy and were examined as to the capability to photoluminescence (PL) and cathodoluminescence (CL). It has been found that the presence of a CP layer on the PS surface preserves the “red” PL, but weakens it to 50–90%. The CL spectra of the obtained heterostructures allow us to suggest their capability of electroluminescence in the visible region of the spectrum.

Organic p-n Type Heterostructures Based on the Hexatiopentacene

The major task of our work was to search for new organic p-n-type heterostructures photosensitive in a wide spectral region and with a small recombination rate at the interface. We used photosensitive hexatiopentacene layers as p-type components and methyl perylene pigment, C60 and V2O5 xerogel films as n-type ones. Photovoltage spectra are well described by the Van Opdorp model, which considers the presence of surface states at the free surface and the interface. The diffusion lengths of charge carriers in hexatiopentacene (200 nm) and methyl perylene pigment (40 nm) films are determined. We have shown the perspectivity to use the hexatiopentacene/methyl perylene pigment heterostructures for manufacturing plastic solar cells.

Photoelectrical Properties of Interfaces Between Organic Films and CdSSe

Abstract The paper reviews authors own results obtained on heterostructures (HS) of CdSSe with organic photosensitive films, the attention being given to processes of carrier recombination, to the formation of potential barriers near the interface, and to the effect of oxygen. Photochemical processes near top electrodes are discussed. Experimental results characterizing parameters of barriers in such HS are compared with the energy diagram of ionized states and the Anderson model. It is shown that HS can be successfully used for construction of improved organic gas sensors.

Effect of Ammonia on Optical Absorption of Polyaniline Films

The influence of ammonia on the optical absorption of polyaniline films obtained by the electrochemical method is studied. In the presence of ammonia, the optical spectra of a polymer are found to change due to the appearance of a new absorption band with a maximum at 2.07 eV and a simultaneous decrease in the intensity of bands at 1.57 and 2.91 eV. The kinetics of changes showing the presence of an isobestic point at 2.71 eV is elaborated. The results can be used to optimize the ammonia gas sensors for monitoring the biotechnological processes in the food industry and the environment.

Effect of Polymer Molecular Structure on Photosensitivity of Composites Films Based on Infra-Red Polymethine Dye

The main results of studies of the effect of a polymer molecular structure on the photosensitivity of composites films based on infra-red polymethine dye photosensitive in a wide spectral range including the near IR region are presented. The highest photosensitivity is observed among the studied composites in that with a polyphenylenevinylene polymer matrix. The basic reason for high integral photosensitivity of these composites is the formation of aggregates, for which the energy and efficiency of the photogeneration of charge carriers are comparable or higher than those for quasiisolated molecules of polymethine dyes. The studied polymer composites of polymethine dyes can be used as near IR radiation sensors (800–1400 nm) and IR photoconverters including solar cells.

Organic Iso-Type Double-Layer Heterostructures Based On Pentacene, Hexathiopentacene, and Lead Phthalocyanine

Photovoltaic properties of double-layer iso-type heterostructures based on pentacene, hexathiopentacene, and lead-phthalocyanine are studied. The heterostructures are prepared by thermal deposition on glass substrates at various substrate temperatures (T s ). Under modulated illumination, the sign reversal is observed in photovoltage spectra of pentacene/lead-phthalocyanine heterostructures deposited at T s = 300 K. The properties of these structures are well described by the van Opdorp model for inorganic iso-type heterojunctions. No sign reversal has been observed in pentacene/lead-phthalocyanine, pentacene/hexathiopentacene, and hexathiopentacene/lead-phthalocyanine heterostructures deposited at T s = 370 K, the magnitudes of photovoltage being higher than those in structures prepared at T s = 300 K.

p-n Type Heterostructures Based on N,N′-Dimethyl Perylene-Tetracarboxylic Acid Diimide

Photovoltaic properties of new photosensitive p-n type heterostructures based on N,N′-dimethyl perylene-tetracarboxylic acid diimide and organic [pentacene, hexathiopentacene, lead phthalocyanine] and inorganic [CuI] semiconductors are investigated. The basic attention is focused on the influence of energy diagram parameters and substrate temperatures (T s) during the deposition on the photosensitivity of heterostructures. The maximal photovoltage, minimal surface recombination rate, and structural homogeneity of layers for the heterostructures were obtained at T s = 370 K. The comparison of the obtained results with energy diagram parameters according to the Anderson model (without taking surface states into account) shows a qualitative agreement for two-layered organic p-n heterojunctions.

Influence of modified surface of gaas on properties of heterostructures with organic semiconductors

The electrical, optical and photoelectric properties of organic/inorganic semiconductors heterostructures are investigated depending upon the interface microrelief morphology modified by chemical etching of GaAs. Polishing andanisotropic etchants were used to change it from flat to microtextured(quasigrating-type). The p/n-heterostructures were fabricated by the vacuumevaporation of thin (∼50 nm) pentacene or phthalocyanine of lead filmson modified surface of n-GaAs crystals. A considerable decrease of the optical reflectance and increase of the photosensitivity by a few (1.5-4) times have been obtained for microtextured heterostructures with respect to the flat ones.The results emphasize the importance of GaAs surface chemical microtexturing to future developments of the photocells, based on organic semiconductor/GaAs heterojunction.

Peculiarities of electronic processes at organic photosensitive films interface and prospectives of their practical application

Abstract The peculiarities of potential barrier formation at the interface of organic photosensitive films (OPF) with metals and inorganic semiconductors (IS) are analyzed. The basic attention is given to the effect of an adsorption of oxygen, polymorphic modifications and processes of polarization arising due to the caption of nonequilibrium charge carriers in contact area of a space charge. In view of this the basic reasons for low efficiency of a solar energy conversion and possibility of their practical use are analyzed. Gas detection by change of properties which depend on the parameters of the interface between OPF and metal or IS, allows one to improve the time of response and selectivity of sensors. The use of IS of CdS, CdSe type for creating a blocking barrier at the OPF interface allows one to increase the height of the barrier and sensitivity to gases several times.