Transparent flat body e.g. for panel comprising LCD or window pane having controllable transparency, has active layer between two electrodes enclosed by covering layer

The invention relates to a light-permeable flat body with two transparent cover layers which enclose between them an active layer that changes its light permeability in an electric field between two electrode layers, optionally subdivided into sections, and with a photovoltaic element connected to the electrode layers, preferably via a control stage, which has a having photoactive layer between two electrode layers.

Light-permeable flat bodies, such as those formed by liquid crystal displays or window panes with controllable light-permeability, have an active layer that changes its light-permeability in an electric field between two electrode layers, optionally subdivided into sections, via which the electric field required to control the active layer is applied at least in sections. When liquid crystals are used, the essentially layer-parallel liquid crystal molecules form nematic rotary cells, the liquid crystal molecules rotating in the field direction when an electric field is applied and returning to the twisted structure after the electric voltage has been switched off from the field-oriented state. By using polarization filters on both cover layers of the active layer, the field-oriented state can be made visible through light absorption. Electrochromic active layers, on the other hand, are based on the interaction of two colorless or only slightly colored, oxidizable on the one hand and reducible on the other hand, one of which is reduced under the influence of an electrical voltage and the other is oxidized, at least one of these substances becoming colored. After the voltage has been switched off, the two original redox substances form back again, with a discoloration or lightening of the color. Since comparatively low electrical energies are required to build up the electric field to control the light transmittance of the active layer, regardless of the structure of the active layer, photovoltaic elements are ideal for the energy supply, especially since, due to the light sensitivity of photovoltaic elements, a simple, independent control of the light transmittance of the active layer can be achieved . The disadvantage of the photovoltaic elements used for this purpose is that they must have a sufficiently large receiving area for light radiation in order to ensure the necessary energy supply. The space required for this increases with decreasing efficiency. This applies in particular to photovoltaic elements whose photoactive layer is not built up in the conventional way on silicon, but on conjugated plastics in which single and double bonds alternate. This results in energy bands comparable to semiconductors with regard to the electron energy, so that they can be converted from the non-conductive to the metallically conductive state by doping. To improve the efficiency of the energy conversion of photovoltaic polymer cells from a conjugated polymer, it is known (US Pat. No. 5,670,791 A) to build up the photoactive layer from two molecular components, namely a conjugated polymer component as electron donor and a fullerene as electron acceptor. This measure made it possible to largely avoid the usual charge carrier recombination, which leads to a considerable increase in efficiency, but which is still low compared to photovoltaic elements based on silicon.

The invention is therefore based on the object of supplying a transparent flat body of the type described above with the energy required for controlling the active layer via a photovoltaic element, with a comparatively low construction effort and without providing additional space for the arrangement of the photovoltaic element have to.

The invention solves the problem posed by the fact that the photoactive layer of the photovoltaic element consists in a manner known per se of two translucent molecular components, that one of the two electrode layers of the active layer is at the same time one of the electrode layers of the photovoltaic element and that the two transparent cover layers are both the photovoltaic Include element and the active layer between them.

Since a photovoltaic element with a photoactive layer of two translucent molecular components is used as an electron donor and electron acceptor, the translucent flat body itself can serve as a carrier for the photovoltaic element, so that the photovoltaic element extends over the entire surface of the translucent flat2

AT 409 902 B body can extend. In this way, sufficient electrical energy for controlling the active layer of the transparent flat body can be made available even with a comparatively low efficiency of the energy conversion. Despite the comparatively large-area photovoltaic element, the construction effort remains low because one of the two electrode layers of the active layer of the translucent flat body is used as an electrode for the photovoltaic element, the photoactive layer of which is thus built up on one electrode layer of the translucent flat body. This means that not only do transparent cover layers between the active layer of the light-permeable flat body and the photoactive layer of the photovoltaic element become superfluous, but also that the considerable effort required to produce a separate electrode layer for the photovoltaic element on the side of the active layer of the light-permeable flat body can be dispensed with. Both the active layer of the translucent flat body and the photoactive layer of the photovoltaic element are enclosed between two common, transparent cover layers, which in turn allows the translucent flat body and the photovoltaic element to be sealed together.

Since, in general, the energy supply of the flat body, which can be controlled with regard to its light permeability, should be ensured regardless of the light permeability selected in each case, it is advisable to arrange the photovoltaic element on the side of the active layer facing a light source.

In the drawing, the subject matter of the invention is shown by way of example, namely a light-permeable flat body according to the invention is shown in a schematic cross section.

According to the illustrated embodiment, the translucent flat body has two transparent cover layers 1, 2 made of glass or plastic, which enclose between them on the one hand an active layer 3 for controlling the light permeability and on the other hand a photoactive layer 4 of a photovoltaic element 5. The active layer 3 can be constructed in the usual way as an electrochromic layer, which can be exposed to an electric field between two adjacent electrode layers 6 and 7, via which the light permeability of the active layer 3 is controlled. These electrode layers 6 and 7 preferably consist of an indium tin oxide (ITO), but in contrast to conventional flat bodies that can be controlled with regard to their transparency, in particular window panes, only one of the two electrode layers 6, 7 is applied to a transparent cover layer 1. The electrode layer 6 facing away from the cover layer 1 is at the same time an electrode layer for the photovoltaic element 5, the other electrode layer 8 of which is assigned to the cover layer 2. The photoactive layer 4 of the photovoltaic element 5, which can have a multilayer structure, consists of a conjugated polymer as an electron donor and a fullerene as an electron acceptor. While the hole-collecting electrode layer 6 consists of a transparent, conductive oxide, the electron-collecting electrode layer 8 of the photovoltaic element 5 can consist of aluminum which is vapor-deposited onto the photoactive layer 4. Due to the small layer thickness, the metallic electrode layer 8 is also translucent.

With the excitation of the conjugated polymer by irradiated light, electrons are released to the fullerene of the photoactive layer 4, which leads to a corresponding build-up of voltage. Since the electrode layer 8 is electrically connected to the electrical connection 10 of the electrode layer 7 of the active layer 3 via an electrical connection 9, the voltage build-up in the photoactive layer 4 due to the common electrode layer 6 causes an electric field between the electrode layers 6 and 7, which creates the chemical Controls the reaction of the redox substances of the active layer 3 and thus their color behavior. To influence this control, a corresponding control stage 11 can be switched into the electrical connection of the two electrical connections 9 and 10.

If the active layer 3 is not made up of electrochromic substances, but is created on the basis of liquid crystals, the mode of operation of the active layer 3 changes, but not its control via the photovoltaic element 5. The cover layers 1 and 2 must, however, be provided with corresponding polarization layers 12 and 13, as indicated by dash-dotted lines in the drawing, in order to be able to use the alignment of the liquid crystal molecules in the direction of the electric field for shading the translucent flat body.

AT 409 902 B

Although the light-permeable flat body is shown in the form of a window pane in the drawing, the invention is not restricted to this embodiment, but can also be used in connection with a liquid crystal display. For this purpose, the electrode layer 7 is to be subdivided accordingly and the parts are to be controlled separately from one another in order to obtain a display by controlling individual liquid crystal cells of the liquid crystal cells of the active layer 3 arranged in a matrix pattern.

The combination of an active layer 3 for controlling the light permeability with a photovoltaic element 5 for supplying energy to the control of the active layer 3 in a common, light-permeable flat body creates simple construction conditions that allow an electrode layer 6 to be shared between the active layer 3 and the photoactive layer 4 as well the transparent cover layers 1 and 2 for the two layers 3 and 4 allow. In addition, the two layers 3 and 4 can be sealed together, because only the edge-side gap between the cover layers 1 and 2 needs to be sealed with a seal. The mutual spacing of the cover layers 1 and 2 can be ensured by means of spacers, which preferably carry the electrical connections 9 and 10.