The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "The embodiments relate to an apparatus and a method for spraying layers of organic devices. In particular, the embodiments to spraying layers having multiple components, which for example are not soluble in the same solvent.
"Spray coating serves as a low-cost polymer coating method for producing electronic devices, such as solar cells or photodiodes on an organic basis, as known, for example, from WO 2003/107453 and the publication by
"However, there are materials that have promising electronic properties but are not soluble in the same solvent. It is consequently impossible to produce a bulk heterojunction solution from these materials. Normally, in this case two-layer systems (bilayers) are produced, which however must forgo the positive properties, such as higher efficiencies, of a bulk heterojunction.
"A further problem that frequently occurs is the production of multiply stacked polymer layers (multilayers) which are soluble in the same solvent. In this case (for example tandem OLEDs, tandem OPDs or tandem solar cells), unfortunately, the aforementioned coating methods cannot be used, since the application of a layer re-dissolves the layer lying thereunder, since the material forming the following layer is applied in the same solvent.
"A further disadvantage of the previously known methods is that, depending on the solvent and application method used, with these application methods the maximum layer thickness that can be produced is limited."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "An aspect of the embodiments is therefore to overcome the disadvantages of the prior art and provide an apparatus and a method with which it is possible at low cost to spray multiple components in different or the same solvents simultaneously onto a substrate, thicker layers and/or multiple layers.
"The subject matter of the embodiments, and the solution achieving the aspects, is therefore an apparatus for spraying a sheet-like substrate, including an atomizer, a reservoir and a holder, the apparatus having at least two reservoirs and/or the atomizer having at least two spray heads and/or the apparatus being designed for multiple spraying of the same surface area. Similarly, the subject matter is a method for spraying a sheet-like substrate in which at least two spray heads spray different or the same spraying agents onto one or the same surface area or one spray head repeatedly sprays the same surface area. Finally, the subject matter is an organic electronic device, including a substrate, a lower electrode and an organic active layer with an upper electrode arranged above it, the photoconductive organic layer being obtainable in the form of a bulk heterojunction by an apparatus or a method as described herein.
"For example, an apparatus is designed for multiple spraying of the same surface area if the reservoir is disproportionately large in comparison with the surface area to be sprayed, in which case it is advantageous if the reservoir is fixed and the spray heads are supplied with agent through a supply line, which may also be flexible. Furthermore, an apparatus is designed for multiple spraying of the same surface area if the holder is connected to a mechanism by which the spray head is automatically moved repeatedly back and forth, or if, in a roll-to-roll spray method, the rolls are designed such that a surface area can be drawn back and forth repeatedly under the apparatus for spraying. The rolls of the system are then designed such that they can make the continuous strip that is to be sprayed rotate in both directions. Thus, the substrate is made to pass under the spraying spray head a number of times. This makes it possible for any desired layer thicknesses of the functional polymers of the device to be applied in one coating process step.
"In the present case, an atomizer refers to a part of a spraying apparatus in which the spraying agent is atomized by supplying gas, and in particular ambient air, with or without a compressor. A conventional atomizer has only one, firmly fixed spray head, it being proposed according to the invention that multiple spray heads, which are fed from different or the same reservoir(s), form the atomizer. The geometrical system of the spray heads in the atomizer may be as desired, for example the spray heads may be arranged in the atomizer in a circular or semicircular form. Particularly preferred is the embodiment in which the spray heads can be switched on and off as desired and/or the spray heads can be fixed in various positions.
"According to an advantageous embodiment, the spray heads are movably arranged in the atomizer, so that the alignment and/or the position of the spray heads with respect to the surface area to be sprayed is variable.
"According to an advantageous embodiment , the same spraying agents are applied by different spray heads, so that thick layers are obtained. The application of the functional polymers with the aid of this 'multiple' spraying method allows the production of layers of any desired thickness and can be integrated in high-throughput fabrication processes, such as roll-to-roll methods.
"Consequently, various organic electronic devices, as are the subject matter of the invention, can be produced, for example fully spray-coated solar cells, organic field-effect transistors, organic capacitors, organic electrochromic devices, organic light-emitting diodes or organic photodiodes.
"The layer thickness of the hole conductor and the semiconducting absorber material can be variably changed by spray coating. Thicker layers mean a higher absorption of the incident radiation, which converts into higher efficiencies and, in the case of organic photodiodes, lower dark currents.
"According to a further advantageous embodiment, different spraying agents are fed into the individual spray heads of the apparatus, so that the formation of a layer of multiple components, for example in different solvents, is made possible.
"According to an advantageous embodiment of the apparatus, the spray heads are arranged in a semicircular form. In this case, the ideal spray line is perpendicular to the substrate to be sprayed, so that the spray heads are arranged as closely as possible around this line.
"According to a an embodiment of the method, the spray heads are fixed and the substrate to be sprayed is moved under the spray heads.
"The use of organic electronics is continuously increasing because of the low-cost production methods and the increasing efficiencies of solar cells, LEDs, FETs and photodetectors. In the area of solar cells and photodetectors, a high efficiency is achieved by a blend of different organic materials, known as a composite, including an electron donor (absorber and hole transport components; usually a semiconducting polymer) and an electron acceptor (electron transport component; usually a fullerene)--also known as a 'bulk heterojunction' (BHJ). The separation of the charge carriers takes place at the interfaces of the two materials that form within the volume of the layer as a whole. All composites that can be applied by wet-chemical processes are attractive for the low-cost production of the aforementioned electrical devices.
"The semiconductor solutions may be applied by methods such as spin coating, blade coating, slit coating, dip coating and spray coating.
"Thanks to the flexibility of the organic semiconductors, devices can also be realized on flexible substrates (e.g. PET, PES and PEN) for large-area applications such as in the case of organic solar cells.
"In all the aforementioned devices, a hole conductor, such as poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS for short), is used as an intermediate layer (between the anode and the 'bulk heterojunction'). PEDOT:PSS is usually applied to the bottom electrode (anode), in order to smooth the surface and optimize the injection or extraction of charge carriers (depending on whether it is a light-emitting diode or a solar cell or a photodiode). Moreover, this hole transport layer or electron blocking layer is used as a 'buffer' layer to avoid short-circuits caused by possible 'spikes' in the bottom electrode.
"So far, the PEDOT:PSS layer has usually been applied by spin coating or doctor blading methods and with layer thicknesses in the range of 80-120 nm. The reason for this is to maintain a low surface roughness of the electrode in order to avoid possible short-circuits. However, spin coating and doctor blading entail the disadvantage that only thin layers of the intermediate layer can be applied. The photo-active BHJ layer has also only been applied so far by the aforementioned methods. In the case of the BHJ, the production of a thicker layer is even more important, since a higher absorption of the incident radiation is ensured. In the case of an organic photodiode, a thicker BHJ layer is particularly valuable and also reduces the dark current.
"Thicker layers (>100 .mu.m) are also advantageous for x-ray detection, as already known from the still unpublished DE 10 2008 029 782.8.
BRIEF DESCRIPTION OF THE DRAWINGS
"These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which:
"FIG. 1 shows an embodiment of a spraying apparatus according to the invention, in which a bulk heterojunction is realized,
"FIG. 2a shows a further embodiment of the spraying apparatus, it being possible for example to realize a hole conductor layer of PEDOT:PSS or a thick layer by multiple spraying with the same spraying agent,
"FIG. 2b shows the principle of multiple spray coating with a spray gun,
"FIG. 3 shows a structure of an organic photodiode given by way of example,
"FIG. 4 shows a current/voltage curve of a device of which the organic active layer has been produced by an atomizer which sprays the same surface area simultaneously with multiple spray heads,
"FIG. 5 shows the measurement of an external quantum efficiency of this device; the high quantum efficiency is evidence that a bulk heterojunction has been created,
"FIG. 6 shows the current/voltage curves for two organic photodiodes in comparison, the one photodiode (represented by the triangles) having a sprayed PEDOT:PSS layer and the other having been produced according to the prior art by spin coating,
"FIGS. 7 and 8 show layer thickness measurements with the aid of a profilometer,
"FIG. 9 shows a current-voltage characteristic (dark current and light current) for an organic photodiode."
For additional information on this patent application, see:
Keywords for this news article include: Nanotechnology, Organic Electronic, Emerging Technologies,
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