Source: http://www.google.com/patents/US6340789?dq=6,250,774
Timestamp: 2014-09-23 03:08:11
Document Index: 698518214

Matched Legal Cases: ['art 8', 'art 16', 'art 8', 'art 16', 'art 16', 'art 8']

Patent US6340789 - Lamination and controlled joining of semiconductor layers - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign in<nobr>Advanced Patent Search</nobr>PatentsThe invention concerns optically absorptive photonic devices and in particular photovoltaic and photoconductive devices. It is particularly concerned with devices formed from multiple semiconducting layers, e.g., organic semiconducting polymers. Such a device has two central semiconductive layers which...http://www.google.com/patents/US6340789?utm_source=gb-gplus-sharePatent US6340789 - Lamination and controlled joining of semiconductor layersAdvanced Patent SearchPublication numberUS6340789 B1Publication typeGrantApplication numberUS 09/646,325Publication dateJan 22, 2002Filing dateFeb 2, 1999Priority dateMar 20, 1998Fee statusPaidAlso published asCN1258827C, CN1298554A, DE69934786D1, DE69934786T2, EP1064686A1, EP1064686B1, WO1999049525A1Publication number09646325, 646325, US 6340789 B1, US 6340789B1, US-B1-6340789, US6340789 B1, US6340789B1InventorsKlaus Petritsch, Magnus GranstromOriginal AssigneeCambridge Display Technology LimitedExport CitationBiBTeX, EndNote, RefManPatent Citations (16), Non-Patent Citations (12), Referenced by (57), Classifications (24), Legal Events (7) External Links: USPTO, USPTO Assignment, EspacenetLamination and controlled joining of semiconductor layersUS 6340789 B1Abstract The invention concerns optically absorptive photonic devices and in particular photovoltaic and photoconductive devices. It is particularly concerned with devices formed from multiple semiconducting layers, e.g., organic semiconducting polymers. Such a device has two central semiconductive layers which have been laminated together so as to form a mixed layer between the first and second semiconductive layers, while retaining at least some of the first and second semiconductive layers on either side of the mixed layer.
29. A device as claimed in claim 13, wherein at least one of the semiconductive materials comprises an azo-dye consisting of azo chromofore (�N═N�) linking aromatic groups.
FIELD OF THE INVENTION The present invention relates to optically absorptive photonic devices and in particular photovoltaic and photoconductive devices and their formation. Embodiments of the invention relate particularly to devices formed from multiple semiconducting layers, preferably composed of organic semiconducting polymers.
BACKGROUND OF THE INVENTION Semiconductive photovoltaic devices are based on the separation of electron-hole pairs formed following the absorption of a photon. An electric field is generally used for the separation. The electric field may arise from a Schottky contact where a built-in potential exists at a metal-semiconductor interface or from a pn junction between p-type and n-type semiconductive materials. Such devices are commonly made from inorganic semiconductors especially silicon which is used in monocrystalline, polycrystalline or amorphous forms. Silicon is normally chosen because of its high conversion efficiencies and the large industrial investments which have already been made in silicon technology. However, silicon technology has associated high costs and complex manufacturing process steps resulting in devices which are expensive in relation to the power they produce.
�Two-layer organic photovoltaic cell�, Applied Physics Letters 48(2), Jan. 13, 1986, C. W. Tang, U.S. Pat. No. 4,164,431 and U.S. Pat. No. 4,281,053 describe multi-layer organic photovoltaic elements. These devices are formed in a layer by layer fashion. A first organic semiconductive layer is deposited on an electrode, a second organic semiconductive layer is deposited on the first organic layer and an electrode is deposited on the second organic layer. The first and second organic semiconductive layers are electron acceptors and hole acceptors. In the following, an �electron accepting material� refers to a material which due to a higher electron affinity compared to another material is capable of accepting an electron from that material. A �hole accepting material� is a material which due to a smaller ionisation potential compared to another material is capable of accepting holes from that other material. The absorption of light in organic photoconductive materials results in the creation of bound electron-hole pairs, which need to be dissociated before charge collection can take place. The material considerations for organic devices are different compared to inorganic devices, where the electron and holes created by the absorption of a photon are only weakly bound. The dissociation of the bound electron-hole pair is facilitated by the interface between the layer of material which acts as a hole acceptor and the layer of semiconductive material which acts as an electron acceptor. The holes and electrons travel through their respective acceptor materials to be collected at the electrodes.
The designing of photovoltaic devices which are fabricated in a layer by layer fashion is limited. When one organic layer is deposited on top of another organic layer, the second layer must be added in such a way that the previously deposited layer is not affected in a detrimental way. Consequently solvents used for subsequent layers are limited in order not to dissolve the previous layer completely or destroy it in other ways. �Efficient photodiodes from interpenetrating polymer networks�, Nature, vol 376, Aug. 10, 1995, page 498-500, J. J. M. Halls et al, and U.S. Pat. No. 5,670,791 describe the formation of a photovoltaic device by depositing a single layer comprising a blend of first and second semiconductive polymers and the deposition of a second electrode on top of that layer. The first semiconductive polymer acts as a electron acceptor and the second semiconductive polymer acts as a hole acceptor. The first and second semiconductive polymers form respective continuous networks that interpenetrate so that there is a continuous path through each of the semiconductive polymers and a charge carrier within one of the first and second semiconductive polymers can travel between the first and second electrodes without having to cross into the other semiconductive polymer. However, these devices do not show the high efficiency that would be expected if the devices worked as ideally envisaged. This may be due to the fact that it is likely that at least one of the polymers can extend through the whole device, thereby creating a parallel system of single material diodes.
SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved photovoltaic device.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is the chemical structure of the organic polymer POPT;
DESCRIPTION OF THE PREFERRED EMBODIMENT FIGS. 4a, 4 b, 4 c and FIG. 5 illustrate the manufacture of a photovoltaic or photconducting device 20. The device 20 has a first component part 8 and a second component part 16 which are laminated together as illustrated in FIG. 4c. The first component part 8 is illustrated in FIG. 4a and has a first self-supporting substrate 2, a first electrode 4 and a first semiconductive layer 6. The second component part 16 is illustrated in FIG. 4b and has a second self-supporting substrate 10, a second electrode 12 and a second semiconductive layer 14. On lamination, a mixed layer 28 containing material from the first and second semiconductive layers is formed at the interface of the first semiconductive layer 6 and the second semiconductive layer 14 as illustrated in FIG. 5.
The material of the first semiconductive layer 6 acts as an electron donor while the material of the second semiconductive layer 14 acts as an electron acceptor in this material combination. Semiconducting polymers which can act as electron acceptors are e.g. polymers, containing CN�or CF3 groups like CN-PPV, MEH-CN-PPV, CF3 substituted ones or Buckminsterfullerene (C60) alone or functionalised to enhance solubility. Semiconducting polymers which do not contain such or other electron withdrawing groups can often act as hole acceptors, for instance the following polymers (and their derivatives) or copolymers containing units of the following polymers (and derivatives): poly(phenylene), poly(phenylene vinylene), poly(thiophene), poly(silane), poly(thienylene vinylene) and poly(isothianaphthene).
Other suitable semiconductive m ate rials include : organometallic polymers; phthalocyanines, perylenes, naphthalocyanines, squaraines, merocyanines and their respective derivatives; and azo-dyes consisting of azo chromofore (�N═N�) linking aromatic groups.
The first substrate 2 and first electrode 4 and/or the second electrode 12 and the second substrate 10 are transparent to allow light to reach the mixed layer. On illumination the device is capable of supplying either electric power or�under applied bias voltage�a light dependent current.
EMBODIMENT 1 A first method of forming the device 20 will be explained with reference to FIG. 4a. A glass substrate 2 is covered with indium tin-oxide, ITO, to form the first electrode 4. The ITO surface is cleaned using acetone and methanol. An organic polymer solution is prepared by dissolving 10 milligrams of regioregular POPT (poly(3- (4-octylphenyl) thiophene)), the chemical structure of which is illustrated in FIG. 1, in 2 milliliters of chloroform. The solution is filtered with 0.45 micrometer filters and then spincoated onto the ITO surface to give a thickness of between 40 and 150 nm. The polymer covered substrate is then heated from room temperature to 230� C. at a rate of 4� C. per minute and maintained at 230� C. for 30 minutes. This heating occurs in a vacuum chamber with a gas pressure of below 10−5 torr and induces a phase transition in the POPT which shifts its absorption to longer wavelengths.
EMBODIMENT 2 In the second embodiment the first semiconductive layer 6 and the second semiconductive layer 14 are formed by a different method. Referring to FIG. 4a, the first semiconductive layer 6 is a polymer blend formed by dissolving 19 milligrams of POPT and 1 milligram of MCP in 4 milliliters of chloroform, filtering the solution using 0.45 micrometer filters, and spincoating the filtered solution on top of the indium tin oxide electrode 4. The second semiconductive layer 14 of the second component part 16 is also a polymer blend. This polymer blend is formed by dissolving 1 milligram of POPT and 19 milligrams of MCP in 4 milliliters of chloroform and filtering the solution using 0.45 micrometer filters. The polymer blend is then spincoated onto the aluminium electrode 12. The method is then the same as previously described. The first component part 8 is heated and the two component parts are laminated together to form the complete device 20.
According to the described methods, the separate first and second semiconductive layers can be individually treated before lamination. Such treatment may involve the inducement of a phase transition in a semiconductive polymer to vary its absorption characteristics, the ordering of the material to improve its transport properties or the doping of the material. Separate annealing of the two components 8 and 16 before their lamination together allows traces of solvent, water and oxygen to be removed. Selective doping (with molecular, polymeric or inorganic dopants) of each layer can represent a very powerful means to decrease the serial resistance and/or create or enhance internal electric fields. The bandgap of the semiconductor layers may be decreased or even removed depending on the degree of doping. Possible dedoping (neutralization) at the interface after the lamination of both substrates may lead to the (re)creation or change of a bandgap and/or transport properties which could enhance the efficiency of such a device. This has partly been discussed in Synthetic Metals 84 (1997) 477-482, Yoshino et al. With the present invention the donor and the acceptor material�and any underlying layers can be separately doped and optimized.
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