We report electroabsorption studies of electric fields in organic light emitting diodes made form substituted poly(para phenylene vinylene) derivatives and solar cells made form zinc phthalocyanine (ZnPc) and perylenetetracarboxylic diimide (PTCDI). The electric field in LEDs is not proportional to the applied bias due to the development of an internal electric field during operation that opposes the applied bias. This counter field is weaker for devices measured in vacuum than for those measured in an ambient atmosphere and is no longer apparent for devices that were prepared and tested under an inert atmosphere. We also observed that the built-in potential increased with operating time. The combination of these two processes leads to an increase in the turn-on voltage of organic LEDs with increasing operating time. We have detected an electric field at the electrode/organic LEDs with increasing operating time. We have detected an electric field at the electrode/organic interface of organic solar cells which is insensitive to the external DC bias. The interface field has a different spectral signature from that of the bulk of the two layers and is attributed to charged transfer-induced dipoles. Rectifying behavior due to the formation of a pn junction under illumination is observed in bilayer solar cells, but not single layer devices made from ZnPc or PTCDI.
ZnO thin films with electrical resistance as low as 10-3 (Omega) (DOT)cm and transparency of 90 - 95% have been prepared by spray pyrolysis of zinc acetate solutions. However, a careful optimization of all deposition conditions is needed in order to obtain films with these values. Thermal decomposition of precursor, the influence of preparation conditions on the film properties and on the film formation mechanism are studied. The stepwise thermal destruction of Zn(CH3CO2)2(DOT)2H2O is recorded and it is shown, that single solid phase ZnO is the only decomposition product at temperatures higher than 590 K in air. Three characteristic temperature regions were distinguished in the film growth process exhibiting each a different mechanism of crystal growth and leading to different thin film qualities. The optical, structural, morphological and electrical properties of sprayed films are mainly determined by growth temperature and are in dependence on the concentration of dopants. This can be explained on the basis of changes in the growth mechanisms and chemical purity of the films.
The possibility is demonstrated to manufacture by the recrystallization of initial powders in different molten fluxes different A2B6 powders with the qualities acceptable for monograin layer construction. Several technologies of formation of monograin layers and optoelectronic devices were developed and studied. It is shown, that insufficient electronic parameters of semiconductor sensors and solar cells designed as monograin layers are connected with the insufficient cleaning of surfaces of crystals in the monograin layer.
The `modular optoelectronic multispectral/stereo scanner' (MOMS-02) is a second generation pushbroom scanner, flown during the D2 mission aboard Space Shuttle flight STS-55. Besides a three line along-track stereo device, the sensor is equipped with multispectral modules that provide data in 4 wavebands covering the visible and near-infrared range. The mission took place during April/May 1993 and provided data of approximately 8 Mio. km2. Data have been acquired in different modes at a mean altitude of 296 km that results in a mean GIFOV of 4.5 m X 4.5 m for the nadir looking panchromatic module and 13.5 m X 13.5 m for the multispectral and tilted panchromatic modules. Centering and widths of all bands for the spectral and panchromatic modules have been newly designed. The narrower and distinct positioned bandpasses allow a more detailed recording of vegetational targets and improve discrimination of various rock/soil types independently of the very high spatial resolution. The results of investigated MOMS-02 data with regard to technical parameters and distinct applications are discussed within this paper.
The modular optoelectronic multispectral/stereo scanner (MOMS-02) is a second generation instrument, flown during the D2 mission aboard Space Shuttle flight STS-55. The sensor provided multispectral data in four wavebands covering the visible and near-infrared range. In addition, MOMS-02 is equipped with a three line along-track stereo device that recorded for/aft and nadir panchromatic data. Centering and widths of all bands for the spectral and panchromatic modules have been newly designed. Thus, the narrower and distinct positioned bandpasses allow a somewhat more distinct recording of vegetational targets in the VIS/NIR range and an improvement in discrimination of various rock/soil types independently of the very high spatial resolution. The bandpass used for the panchromatic modules has also been rearranged to optimize for the contrast of vegetation to rock/soil targets. Entropy, SNR, and PSF performances are comparable to operational sensors like HRV or TM. However, data of band 3 are slightly weaker in their performance especially in the SNR. First imagery are presented on the basis of a merging concept for high resolving panchromatic and multispectral data.
MOMS-02/D2, as a continuation of MOMS-01, has been developed for digital mapping of the Earth's surface from space. The camera will be flown on-board the second German Spacelab Mission D2 which is presently scheduled for launch in September 1992. The special characteristic of this camera is the combination of high-resolution panchromatic images for 3- dimensional geometric information with multispectral images for thematic applications. With this concept MOMS-02 is fundamentally different from all existing remote sensing systems and thus pursues new and independent goals.