Absorption panchromatic

As already shown, the sensitized spectra follow the dye absorption. Most of the dyes have sufficiently narrow absorption bands. This does not permit us to obtain the panchromatic sensitivity in the sufficiently broad spectral range. It was proposed to use the polymers with conjugated bonds as sensitizers [21]. The broad diffuse absorption spectra are inherent to such compounds. One can expect higher thermal stability from such sensitizers. In addition the application of binder may be omitted from the preparation of the photosensitive layers, for example, in electrophotography. Polymers with triple bonds, polyphenylenes and polyoxiphenylenes were used as sensitizers [10, 14, 278-280]. The typical results are shown in Fig. 47. The main rules for photoconductivity sensitized by polymers were the same as for the dyes. Optimum sensitization was obtained at the concentration of the sensitizer of 10 1-10-2 g/cm3 relative to the polymeric photoconductor weight. 

The ratio of photo- to dark current was as high as 200—300 with panchromatic light intensity of 20-30 W/cm2 the photocurrents reached 10 7 A/cm2 at electric fields of 4—5 x 10s V/cm. In these polymers the absorption spectra coincide with the photoconductivity action spectra. 

A further fundamental prerequisite is a high extinction coefficient in the visible range of the solar spectrum. The absorption spectrum has to be chosen such that either a broad band is provided by a given sensitizer or more than one sensitizer has to be used to efficiently cover the solar spectrum (panchromatic sensitization) [95-97]. 

These materials show low bandgap, appropriate HOMO/LUMO energy levels (Figure 1.29), modest mobility, and panchromatic (broad absorption) features, making them potential candidate for optoelectronic applications. 

J. W. Jung, F. Liu, T. P. Russell, W. H. Jo, Semi-crystalline Random Conjugated Copolymers with Panchromatic Absorption for Highly Efficient Polymer Solar Cells. Energy Environ. Sci. 2013, 6, 3301. 

Carey Lea failed to find any sensitising action of dyes on ferric oxalate, potassium chromate, uranyl nitrate, etc. The research of J. M. Eder was fundamental in the study of sensitisation by dyestuffs. J. J. Acworth found a rough correlation between the absorption maximum of a coloured silver bromide gelatin plate and the maximum of chemical activity in the region of the spectrum, although this was always displaced towards the violet. The development of this work into panchromatic plates is well known. 

The coordination of dendritic oligothiophene-appended pyridines 25-27 to RuPc 28 gave rise to dyes possessing a panchromatic absorption in the visible range (Figure 18)." These compounds were incorporated into... 

As it is well known, calculations on the solar spectrum impinging on the Earth surface demonstrate that the ideal photosensitizer for a system that would absorb the maximum fraction of energy (somewhat above 1000 nm) would absorb near infrared photons, and of course, all of the photons above that limit. Thus, new sensitizers are continuously prepared with a maximum in the NIR for the use in solar cells. However, organic light absorbers have relatively narrow bandwidths separated by deep minima, which makes it difficult to obtain panchromatic absorption in a single organic semiconductor. 

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