Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Reexamination Certificate
2000-02-08
2001-08-28
Diamond, Alan (Department: 1753)
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
C136S252000, C136S258000, C257S040000, C257S052000, C257S053000, C257S049000, C257S431000, C257S461000, C438S082000, C438S057000, C438S096000, C438S097000, C250S200000, C313S498000, C313S499000, C313S501000, C252S299300, C252S299010, C429S111000
Reexamination Certificate
active
06281430
ABSTRACT:
This invention relates to electronic devices having a structure on a nanometer scale and especially optoelectronic devices such as photovoltaic cells, photodetectors, electroluminescence devices and electrochromic devices. It especially relates to such devices comprising bicontinuous phase separated the structures.
Bicontinuous phase separated systems with phase separation on a nanometer scale have received increasing attention during the last years. Especially, systems incorporating nanostructured titanium oxide and an organic semiconductor or a fluid electrolyte have been proposed for use as dye sensitized solar cells, electroluminescent devices and electrochromic devices. In these systems the interface between the two phases is up to several hundred times larger than in the conventional flat layer systems. An increased interface between the two phases is advantageous in many respects, for example in that it improves the charge separation in solar cells or the charge carrier injection in batteries or electroluminescent devices. Although these advantages can be realized by the nanoparticle titanium oxide structure according to the prior art, the use of titanium oxide or metal oxides in general has a disadvantage in that it implies a sintering step in a temperature range of about 450° C. to 500° C., requiring that the carrier of such structures is thermally stable at these elevated temperatures. This excludes polymer substrates which would be desirable otherwise because of their low weight and their low cost.
J. J. M. Halls et al., Nature 376 (1995), 498 proposed a photovoltaic cell comprising two continuous separated phases of conjugated polymers. In order to prepare this cell, a solution of a mixture of polymers was spincast onto a substrate. The mixture spontaneously separated into a dendritic bicontinuous phase with phase separation on a nanometer scale. Accordingly, the average distance between the point of light absorption and the junction between the two polymer phases was reduced to be less than the mean free paty of the quasiparticles created by the light absorption. In a solar cell prepared by the above-mentioned process each phase was in contact with both electrodes. In a further paper by M. Granström et al., Nature 395 (1998), 257 it was proposed to apply each of the two polymers to a separate substrate coated with an appropriate electrode and laminate the two parts thus created together in order to form a solar cell.
Although these approaches overcome the problem of a high temperature sintering step encountered with the metal oxide structures, they still have a drawback in that the interface between the two phases is established in a random manner so that the potential benefits of an interface having variations on a nanometer scale can not be fully achieved.
It is the object of the present invention to provide a method of preparing an electronic structure having variations on a nanometer scale with high predictability and in a controlled manner and to provide a new class of such structures having more precisely defined features on a nanometer scale.
This object is accomplished by an electronic device comprising two adjacent regions of materials with different electric properties, which is characterized in that one of the regions is formed by a columnar structure of a discotic liquid crystal material, said structure having interspaces defined between columns of said discotic liquid crystal material, said interspaces being part of the other region and comprising a second material having electric properties different from that of said discotic liquid crystal. Preferably, the columnar structure is stabilized, e.g. by cross-linking or by other suitable means, so that it is especially thermally and chemically stable and the columnar order is not destroyed or disturbed during the operation of the device, e.g. when heating up. A typical length scale for the interspaces is less than 100 nm and for most applications less than 10 nm.
Said two regions may form a bicontinuous phase separated system, the two phases interleaving each other in the region of the columns.
The invention may provide that the interspaces are filled with an amorphous phase.
Alternatively, it may be provided that the device comprises intercalated columns of two different discotic materials.
According to a specific embodiment said discotic material and said second material filling the interspaces between the columns of said discotic material are of a different conductivity type (p-type, n-type) so that a p-n junction is formed in the region of said columns.
The discotic material may especially be chosen from the group consisting of phthalocyanines and triphenylenes.
Especially said discotic material may comprise a triphenylene substituted with an acceptor group. It is preferred that said acceptor group is a trifluorosulphonic acid derivate.
The electronic device according to the invention can be an optoelectronic device, especially a photovoltaic cell, a photodetector, an electroluminescent device or an electrochromic device.
According to an embodiment of a photovoltaic cell the discotic columnar phase is preferably formed by a phthalocyanine. The conductive substrate onto which said columnar structure is deposited is preferably transparent to light and may consist of e.g. tin-doped indium oxide (ITO) or fluorine-doped tin oxide (FTO). Said interspaces between the columns are preferably filled with an amorphous phase of n-type oxadiazole.
In an embodiment as an electroluminescent device said columnar discotic structure is preferably formed by a triphenylene derivative.
The electronic device according to the invention can especially be an image sensor comprising a plurality of light detecting regions, each comprising a columnar structure of a discotic material as described above, and be adapted for detecting different light wavelengths in different light detecting regions.
The invention also provides a method of forming an electronic structure and for producing electronic devices comprising such structures, said method comprising the steps of
applying a first layer of essentially parallely oriented discotic molecules to a substrate,
depositing a second layer of a discotic material on said first layer, the material of said second layer being capable of forming a columnar discotic phase on the material of said first layer, said second layer containing interspaces between columns of discotic material opening to the surface of this layer,
introducing a second material having electric properties different from those of the material of said second layer into at least some of the interspaces of said second layer.
The method may especially provide the step of cross-linking the molecules of the second layer at least in the longitudinal direction of a column. The materials may be made crosslinkable by substitution with groups such as epoxide or ethylene, which react with one another to create an insoluble network of covalently bonded molecules. The crosslinking may be effected by thermal radiation, by irradiation with X-rays or by ultraviolet (UV) radiation.
According to a preferred embodiment said first layer is linked to said substrate by chemisorption. In addition or alternatively the substrate may be treated with a surface modifying agent, especially an agent affecting the wettability and/or surface tension of the substrate. Suitable materials may be chosen from the group consisting of siloxanes, alkylthiols and polyimides. Said surface modifying agent is advantageously doped with charge transport material. As a further additional or alternative step the surface of the substrate may be prepared with a suitable surface geometry, e.g. by creating cavities with essentially parallel longitudinal axes. This may especially result in a step-like surface structure. Such structures may be prepared e.g. by oblique evaporation of SiO
X
.
The invention can provide that a second layer deposited on said first layer is treated with a solvent to introduce defects, thereby creating or increasing interspaces between the columns
Lupo Donald
Nelles Gabrielle
Yasuda Akio
Diamond Alan
Frommer William S.
Frommer & Lawrence & Haug LLP
Russell Mark W.
Sony International (Europe) GmbH
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