FIELD OF INVENTION
[0002] The invention disclosed herein relates, in general, to organic solar cells. More specifically, the present invention relates to a method of manufacturing an organic solar cell.
BACKGROUND
[0003] An organic solar cell is a device that converts solar energy into electrical energy due to the presence of an organic photoactive layer. The organic photoactive layer is capable of generating excitons, i.e., bound electron-hole pairs, on receiving solar energy in the form of light. These electron-hole pairs dissociate into charge carrying electrons and holes, and thereby generate electricity. An anode layer and a cathode layer are provided on either sides of the organic photoactive layer to collect these charge carriers and utilize them in external electric circuits in the form of current.
[0004] The anode and the cathode layers are provisioned while manufacturing the organic solar cell. Generally, the anode layer, the cathode layer and the organic photoactive layer are provided on a substrate that acts as a structural component and provides strength to the organic solar cell. An example of a material used for the substrate is glass.
[0005] The process of manufacturing an organic solar cell involves taking the substrate, and depositing on it, the anode layer, the organic photoactive layer and the cathode layer by using one or more of the processes, like, sputtering, pasting, organic vapor phase deposition, and the like. In an exemplary general scenario, the anode layer may be deposited by using sputtering, the organic photoactive layer may be deposited by using organic vapor phase deposition and the cathode layer may again be deposited by sputtering. In each such process, multiple parameters have to be controlled with precision to ensure the quality of the deposited layer.
[0006] Thus, by using different processes for depositing different layers, a number of parameters to be controlled increases significantly. Additionally, using different processes for depositing different layers makes the entire process of manufacturing the organic solar cell more time consuming, as significant time is required for non-productive tasks like transporting and setup activities between productive deposition processes.
[0007] In real-life applications, multiple organic solar cells are connected in series or parallel to generate the required electricity. Therefore, a provision to extract contacts from the anode layer and the cathode layer has to be provided while manufacturing the organic solar cell. Since, the cathode layer does not have any layer above it; therefore, a contact can be easily derived from the cathode layer. However, the anode layer is hidden beneath the organic
photoactive layer and the cathode layer. Therefore to obtain a contact from the anode layer a selected portion of the cathode layer and the organic photoactive layer has to be removed. Generally, the selected portion is removed by an etching process after selectively masking a remaining portion that does not have to be removed. The masking and the etching processes increase the cost of manufacturing as well as the chances of deterioration in a quality of the organic solar cell by accidental removal of an extra portion of the cathode layer and the organic photoactive layer.
[0008] According to the foregoing discussion, it can be observed that the existing processes of manufacturing the organic solar cell have one or more limitations. Firstly, they may require a significant number of parameters to be controlled corresponding to different processes involved. Secondly, they may require time to be spent on non-productive tasks like the transporting and the setting-up of work-in-progress product between the deposition processes. Thirdly, the manufacturing process may incur higher cost due to involvement of processes like masking and etching. Fourthly, there are chances of deteriorated quality of the organic solar cell if the masking and etching processes do not go well. Fifthly, a manufacturing facility for the entire process of manufacturing the organic solar cell as per the state of the art described above may require higher capital investment, since multiple equipments may be required for different processes.
[0009] There is therefore a need for a method of manufacturing an organic solar cell, which overcomes some or all of the limitations identified above.
BRIEF DESCRIPTION OF FIGURES
[0010] The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The invention may best be understood by reference to the following description, taken in conjunction with the accompanying drawings. These drawings and the associated description are provided to illustrate some embodiments of the invention, and not to limit the scope of the invention.
[0011] FIGs. la and lb are diagrammatic illustrations of various components of an exemplary organic solar cell in two exemplary arrangements;
[0012] FIG. 2 is a flow chart describing an exemplary method for manufacturing an organic solar cell as per the prior art, i.e., the state of the art prior to the present invention;
[0013] FIG. 3 is a flow chart describing a method for manufacturing an organic solar cell, in accordance with an embodiment of the present invention;
[0014] FIGs. 4a, 4b, 4c and 4d are diagrammatic illustrations of a process for depositing an anode layer by imparting a centrifugal force, in accordance with some embodiments of the present invention;
[0015] FIG. 5 is a flow chart describing a method for manufacturing an organic solar cell, in accordance with another embodiment of the present invention;
[0016] FIG. 6 is a diagrammatic illustration of a wiping process to facilitate obtaining an electrical contact from the anode layer, in accordance with an exemplary embodiment of the present invention;
[0017] FIG. 7 is a diagrammatic illustration of a process for depositing an organic photoactive layer by imparting a centrifugal force, in accordance with some embodiments of the present invention; and
[0018] FIG. 8 is a flow chart describing a method for manufacturing an organic solar cell, in accordance with yet another embodiment of the present invention.
[0019] Those with ordinary skill in the art will appreciate that the elements in the figures are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated, relative to other elements, in order to improve the understanding of the present invention.
[0020] There may be additional structures described in the foregoing application that are not depicted on one of the described drawings. In the event such a structure is described, but not depicted in a drawing, the absence of such a drawing should not be considered as an omission of such design from the specification.
SUMMARY
[0021] The instant exemplary embodiments provide a method for manufacturing an organic solar cell.
[0022] Some embodiments provide a method for manufacturing the organic solar cell in which a reduced number of parameters are needed to be controlled.
[0023] Some embodiments provide a cost-effective method for manufacturing the organic solar cell.
[0024] Some embodiments provide a method for manufacturing the organic solar cell, such that a capital investment for a manufacturing facility to implement the method is less.
[0025] In some embodiments, a method for manufacturing an organic solar cell is provided. The method includes providing a substrate that is less than 900 square centimeters in size, and depositing an anode layer on the substrate by imparting a centrifugal force to an anodic solution disposed on the substrate. Thereafter, the method includes depositing on the anode layer, an organic photoactive layer that enables conversion of solar energy into electrical energy. Thereafter, the method involves depositing a cathode layer on the organic photoactive layer to form a power-generating sub-assembly, and encapsulating said power-generating sub-assembly to obtain the organic solar cell.
[0026] In some embodiments, each layer from the anode layer, the organic photoactive layer and the cathode layer is deposited by disposing a corresponding solution at a corresponding desired location and applying a centrifugal force to the corresponding solution.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
[0027] Before describing the present invention in detail, it should be observed that the present invention utilizes a combination of method steps and apparatus components related to a method of manufacturing an organic solar cell. Accordingly the apparatus components and the method steps have been represented where appropriate by conventional symbols in the drawings, showing only specific details that are pertinent for an understanding of the present invention so as not to obscure the disclosure with details that will be readily apparent to those with ordinary skill in the art having the benefit of the description herein.
[0028] While the specification concludes with the claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawings, in which like reference numerals are carried forward.
[0029] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting but rather to provide an understandable description of the invention.
[0030] The terms "a" or "an", as used herein, are defined as one or more than one. The term "another", as used herein, is defined as at least a second or more. The terms "including" and/or "having" as used herein, are defined as comprising (i.e. open transition). The term "coupled" or "operatively coupled" as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.
[0031] Referring now to the drawings, there is shown in FIG. la, a diagrammatic illustration of various components of an organic solar cell 100a. The organic solar cell 100a is shown to include a substrate 102, an anode layer 104, an organic photoactive layer 106, a cathode layer 108 and an encapsulation 110.
[0032] The substrate 102 provides strength to the organic solar cell 100a. An example of a material of the substrate 102 includes, but is not limited to, glass. In some exemplary embodiments, during real life applications, the organic solar cell 100a is placed in a way that the substrate 102 is facing the sun and all the sun light falling on the organic solar cell 100a is incident on the substrate 102. In these embodiments, the substrate 102 is made of a transparent material so that it allows maximum light to pass through itself and reach the subsequent layers.
[0033] The organic photoactive layer 106 is responsible for converting light energy into electrical energy. Photons present in the sun light received by the organic photoactive layer 106 generate excitons, i.e., bound electron-hole pairs, within the organic photoactive layer 106. These bound electron-hole pairs dissociate into free electrons and holes within the organic photoactive layer 106. The free electrons and holes act as the charge carriers that are responsible for generating electricity.
[0034] The anode layer 104 acts as an electrode that attracts free electrons towards itself, thereby, assisting in generation of electricity. Similarly, the cathode layer 108 acts as an electrode that attracts free holes towards itself, thereby, assisting in generation of electricity. In some exemplary embodiments, during real life applications, when the organic solar cell 100a is placed in a way that the substrate 102 is facing the sun and all the sun light falling on the organic solar cell 100a is incident on the substrate 102, the anode layer 104 is preferably made of a transparent material so that it allows maximum light to pass through itself and reach the organic photoactive layer 106.
[0035] In some cases, commercially available organic solar cells have additional layers to enhance their efficiency. For example, some organic solar cells have a hole-transport layer between the anode layer 104 and the organic photoactive layer 106 to increase the transport of holes towards cathode, thereby increasing the efficiency. FIG. lb illustrates an embodiment of such an organic solar cell 100b. The organic solar cell 100b is shown to include the hole-transport layer 112.
[0036] Further, the commercially available organic solar cells may also have additional layers like an electron-transport layer to further enhance the performance and the efficiency of the commercially available organic solar cells. Although the present invention has been described with essential layers in the organic solar cell, it will be readily apparent to those with ordinary skill in the art that additional layers including, but not limited to, the hole-transport layer and the electron-transfer layer, can be deposited in the organic solar cell without deviating from the scope of the present invention.
[0037] Further, in real life applications, multiple organic solar cells are either connected in parallel or series. Electrical contacts are provided at the anode layer 104 and the cathode layer 108 in the organic solar cell 100a or 100b to enable such connections between the multiple organic solar cells.
[0038] All the above mentioned layers are encapsulated using the encapsulation 110 to obtain the organic solar cell 100a or 100b.
[0039] FIG. 2 is a flow chart describing an exemplary method 200 for manufacturing the organic solar cell 100a or 100b as per the prior art, i.e., the state of the art prior to the present invention.
[0040] The method for manufacturing the organic solar cell 100a or 100b as per the prior art is initiated at step 202. At step 204, the substrate 102 is provided. Thereafter, at step 206, the anode layer 104 is deposited on the substrate. As per the state of the art, the anode layer 104 is deposited on a substrate of large size, which is then cut into multiple smaller-sized substrates with the anode layer, such that each of the small-sized substrates with anode layer 104 can be used to manufacture an organic solar cell. Therefore, in the state of the art the anode layer 104 is, generally, deposited by using methods suitable for substrates of larger sizes. Accordingly, a spin-coating process is, generally, not used for coating the anode layer 104.
[0041] At step 208, the organic photoactive layer 106 is deposited on the anode layer 104. Thereafter, at step 210, the cathode layer 108 is deposited on the organic photoactive layer 106 forming a power generating sub-assembly 109 that includes the substrate 102, the anode layer 104, the organic photoactive layer 106 and the cathode layer 108.
[0042] Thereafter, electrical contacts need to be extracted from the anode layer 104 and the cathode layer 108. Since the cathode layer 108 is not hidden under any other layer, an electrical contact can be extracted easily from the cathode layer 108. However, the anode layer 104 is hidden beneath the cathode layer 108 and the organic photoactive layer 106, therefore, the electrical contact cannot be extracted from the anode layer 104 without removing a selected portion of the cathode layer 108 and the organic photoactive layer 106.
[0043] Therefore, to selectively remove the selected portion of the cathode layer 108 and the organic photoactive layer 106, a remaining portion of the power generating sub-assembly 109 is masked at step 212, and thereafter, the selected portion of the cathode layer 108 and the organic photoactive layer 106 is removed, at step 214, by an etching process to expose the anode layer 104 hidden beneath them. The electrical contacts can then be extracted from the anode layer 104 as well as the cathode layer 108.
[0044] Thereafter, at step 214, the power generating sub-assembly 109 is encapsulated by using the encapsulation 110. The method is terminated at step 216.
[0045] FIG. 3 is a flow chart describing a method 300 for manufacturing the organic solar cell 100a or 100b, in accordance with an embodiment of the present invention. For the purpose of this description, the method 300 is explained for manufacturing of the organic solar cell 100a. However, it will be readily apparent to those with ordinary skilled in the art that the method 300 can also be applied, without deviating from the scope of the invention, for manufacturing the organic solar cell 100b or another organic solar cell with other additional layers.
[0046] The method 300 for manufacturing the organic solar cell 100a is initiated at step 302. At step 304, the substrate 102 is provided. A size of the substrate is less than 900 square centimeters in area. By limiting the size of the substrate to less than 900 square centimeters it is ensured that parameters for a spin-coating process, which will be applied in subsequent steps of the method 300, can be easily controlled. In an exemplary scenario, the substrate 102 is cleaned of any impurities prior to being used for manufacturing the organic solar cell 100a.
[0047] Examples of a material of the substrate include, but are not limited to, glass. Generally, a thickness of the glass substrate used in method 300 is 0.5 millimeter.
[0048] Thereafter, at step 306, the anode layer 104 is deposited on the substrate 102 by applying a centrifugal force to an anodic solution disposed on the substrate 102. An example of a material of the anode layer 104 includes, but is not limited to, carbon nanotubes, preferably, single-walled carbon nanotubes. Using carbon nanotubes, preferably single-walled carbon nanotubes, for the anode layer 104 may include one or more advantages. Firstly, a high work function of the single-walled carbon nanotubes ensure efficient hole collection to generate electricity. Secondly, single-walled carbon nanotubes have a higher optical transparency in a broad spectral range from Ultraviolet, to far visual and into near-Infrared range. Thirdly, a film formed of carbon nanotubes is significantly flexible. Generally, a thickness of the anode layer 104 of carbon nanotubes may range between 10 to 100 nanometers.
[0049] When the material for the anode layer 104 is carbon nanotubes, a solution of carbon nanotubes or an adhesive liquid containing carbon nanotubes can be used as the anodic solution.
[0050] The deposition of the anode layer 104 by applying centrifugal force can be implemented through the spin-coating process. Referring now to FIG. 4a and FIG. 4b, there is shown a diagrammatic illustration of the spin-coating process for depositing the anode layer 104 on a rectangular substrate. Similarly, in FIG. 4c and FIG. 4d, there is shown a diagrammatic illustration of the spin-coating process for depositing the anode layer 104 on a circular substrate. Although the FIGs. 4a, 4b, 4c and 4d show the spin-coating process being implemented on substrates of rectangular and circular shape only, it will be readily apparent to those skilled in the art that the spin-coating process can be implemented on substrates of any shape, including, but not limited to, hexagonal, octagonal and elliptical, without deviating from the scope of the invention.
[0051] For the purpose of this description, the spin-coating process in accordance with this invention is described by referring to FIG. 4c and FIG. 4d, i.e., using the substrate 102 of a circular shape. Description of steps of the method 300 will remain substantially similar when the spin-coating process is implemented using substrates of other shapes, i.e., when the substrate 102 is of a shape other than circular. FIG. 4c shows a top view of a manufacturing set-up 400b where the spin-coating process can be implemented, in accordance with this invention, and FIG. 4d shows the front view of the manufacturing set-up 400b. The manufacturing set-up 400b is shown to include a nozzle 402 and a spindle 404. The substrate 102 is positioned on the spindle 404, preferably, when the spindle 404 is stationary. Thereafter, the nozzle 402 disposes the anodic solution on the substrate 102, while the spindle 404 is simultaneously rotating about an axis 406 that also passes through the substrate 102, thus imparting a centrifugal force in radially outward direction 408. The centrifugal force forces the anodic solution to spread uniformly on the substrate 102 and form the anode layer 104. A thickness and a uniformity of the anode layer 104 can be controlled by controlling some parameters of the spin-coating process, including, but not limited to, a speed of rotation of the spindle 404 and a mass flow rate of the anodic solution being disposed by the nozzle 402.
[0052] After the anode layer 104 is deposited, the organic photoactive layer 106 is deposited on the anode layer 104 at step 308. The organic photoactive layer 106 can be deposited by using any of the processes like, sputtering, pasting, organic vapor phase deposition, spin-coating and the like.
[0053] Examples of the materials used for the organic photoactive layer 106, include, but are not limited to, polyphenylene vinylene, copper phthalocyanine, carbon fullerenes and fullerene derivatives such as Phenyl-C61 -butyric acid methyl ester, i.e., PCBM. Generally, a thickness of the organic photoactive layer 106 is 100 nanometers.
[0054] While using the method to manufacture the organic solar cell 100b, the hole-transport layer 112 is also deposited prior to depositing the organic photoactive layer 106. In this embodiment the hole-transport layer 112 is deposited on the anode layer 104, and the organic

photoactive layer 106 is subsequently deposited on the hole-transport layer 112. The hole-transport layer 112 can be deposited by using any of the processes like, sputtering, pasting, organic vapor phase deposition, spin-coating and the like.
[0055] Examples of a material of the hole-transport layer 112, include, but are not limited to, Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate), i.e., PEDOT: PSS. Generally, a thickness of the hole-transport layer 112 may range between 80 to 200 nanometers.
[0056] Thereafter, at step 310, the cathode layer 108 is deposited on the organic photoactive layer 106. The cathode layer 108 can be deposited by using any of the processes like, sputtering, pasting, organic vapor phase deposition, spin-coating and the like.
[0057] Examples of a material used for the cathode layer include, but are not limited to, Aluminium doped Zinc Oxide, a conducting ink of Aluminium and a eutectic solution of Indium/Gallium.
[0058] In an embodiment, an electron-transport layer may also be deposited prior to depositing the cathode layer 108 on the organic photoactive layer 106. In this embodiment the electron-transport layer is deposited on the organic photoactive layer 106, and the cathode layer 108 is subsequently deposited on the electron-transport layer. The electron-transport layer can be deposited by using any of the processes like, sputtering, pasting, organic vapor phase deposition, spin-coating and the like. The electron-transport layer increases the transport of electrons towards the anode layer 104, thereby increasing the efficiency of the organic solar cell 100b.
[0059] Although the present invention has been described with essential layers in the organic solar cell, it will be readily apparent to those with ordinary skill in the art that additional layers including, but not limited to, the hole-transport layer and the electron-transfer layer, can be deposited in the organic solar cell without deviating from the scope of the present invention.
[0060] The substrate 102, the anode layer 104, the organic photoactive layer 106, the cathode layer 108 collectively form a power generating sub-assembly 109. While using the method 300 to manufacture the organic solar cell 100b, where the hole-transport layer 112 is also deposited between the anode layer 104 and the organic photoactive layer 106, the power generating sub-assembly 109 includes the substrate 102, the anode layer 104, the hole-transport layer 112, the organic photoactive layer 106 and the cathode layer 108.
[0061] As mentioned in the foregoing sections of the description, in commercial or real-life applications, multiple organic solar cells are connected with each other to generate the required electricity. To facilitate such connection in the manufactured organic solar cells, electrical contacts need to be provided in the anode layer 104 and the cathode layer 108. Since the cathode layer 108 is not hidden under any other layer, the electrical contact can be extracted easily from
the cathode layer 108. However, the anode layer 104 is hidden beneath the cathode layer 108 and the organic photoactive layer 106, therefore, the electrical contact from the anode layer 104 is extracted by removing a selected portion of the cathode layer 108 and the organic photoactive layer 106 from the power generating sub-assembly 109.
[0062] At step 312, the power generating sub-assembly 109 is encapsulated by covering the power generating sub-assembly 109 with the encapsulation 110. In an embodiment, the encapsulation 110 includes a glass cover with a water-absorbent getter material on a surface of the glass cover that which faces the power generating sub-assembly 109. The encapsulation 110 is configured to cover the power generating sub-assembly 109 completely. In an embodiment, the water-absorbent getter material is spin-coated on the glass cover. The water-absorbent getter material prevents the organic solar cell 100a or 100b from being affected by humidity or moisture in a surrounding.
[0063] In one embodiment, the organic solar cell is thermally cured after the encapsulation 110 encapsulates the power generating sub-assembly 109.
[0064] The organic solar cell 100a or 100b is thus formed by the method 300, which includes providing the substrate 102 that is less than 900 square centimeters in size, depositing the anode layer 104 on the substrate by imparting the centrifugal force to the anodic solution disposed on the substrate, depositing on the anode layer 104, the organic photoactive layer 106, depositing the cathode layer 108 on the organic photoactive layer 106 to form the power-generating sub-assembly, and encapsulating said power generating sub-assembly 109 to obtain the organic solar cell.
[0065] The method 300 is terminated at step 314.
[0066] FIG. 5 is a flow chart describing a method 500 for manufacturing the organic solar cell 100a or 100b, in accordance with another embodiment of the present invention. In this embodiment all the layers, i.e., the anode layer 104, the hole-transport layer 112, the organic photoactive layer 106 and the cathode layer 108 are deposited by using the spin-coating process explained in conjunction with FIG. 4. Additionally, in this embodiment, the electrical contact at the anode layer 104 is obtained by removing a selected portion of the cathode layer 108 and the organic photoactive layer 106 by a wiping process, explained in conjunction with FIG. 6.
[0067] For the purpose of this description, the method 500 is explained for manufacturing of the organic solar cell 100a. However, it will be readily apparent to those with ordinary skilled in the art that the method 500 can also be applied, without deviating from the scope of the invention, for manufacturing the organic solar cell 100b or another organic solar cell with other additional layers. Additionally, some steps, and corresponding description, of the method 500 are similar to the method 300. Therefore, subsequent description of the method 500 describes the
steps that are different from the method 300, and may not be elaborate about the steps that are similar to the method 300. Details for the steps that are similar to method 300 can be referred from the description of FIG. 3.
[0068] The method 500 is initiated at step 502. At step 504, the substrate 102 is positioned on the spindle 404, preferably when the spindle 404 is stationary. Thereafter, the anode layer 104 is deposited by using the spin-coating process at step 506. In a preferred embodiment, the nozzle 402 disposes the anodic solution at the center of the substrate, while simultaneously rotating the spindle 404 about the axis 406, i.e., the longitudinal axis of the spindle 406 that also passes through the substrate 102. By disposing the anodic solution at the center of the substrate 102, the anode layer 104 thus formed will completely cover the substrate 102.
[0069] Thereafter, at step 508, the organic photoactive layer 106 is deposited on the anode layer 104 by applying centrifugal force to a solution containing an organic photoactive material. In this embodiment, the nozzle 402 disposes the solution containing an organic photoactive material at the center of the anode layer 104, while simultaneously rotating the spindle 404 about the axis 406. By disposing the solution containing an organic photoactive material at the center of the anode layer, the organic photoactive layer 106 thus formed will completely cover the anode layer 104.
[0070] Thereafter, at step 510, the cathode layer 108 is deposited on the organic photoactive layer 106 by applying centrifugal force to the cathodic solution. The nozzle 402 disposes the cathodic solution at the center of the organic photoactive layer, while simultaneously rotating the spindle 404 about the axis 406. By disposing the cathodic solution at the center of the organic photoactive layer 106, the cathode layer 108 thus formed will completely cover the organic photoactive layer 106.
[0071] Thereafter, the selected portion of the cathode layer 108 and the organic photoactive layer 106 is wiped off to extract contact at the anode layer 104, at step 512. FIG. 6 shows an exemplary equipment that can be used to perform a wiping process. The equipment is shown to include one or more wiping arm 602, such that a motion of the one or more wiping arms is pre-controlled or controllable. Each wiping arm 602 has a wiping portion 604 that includes a solution suitable to dissolve a layer to be removed.
[0072] To remove the selected portion from the cathode layer 108, a solution capable of dissolving and removing the cathode layer 108 is provided on the wiping portion 604 of the each wiping arm 602. Then the each wiping arm 602 is moved on the selected portion of the cathode layer 108 to remove the selected portion of the cathode layer 108. Thereafter, to remove the selected portion from the organic photoactive layer 106, a solution capable of dissolving and removing the organic photoactive layer 106 is provided on the wiping portion 604 of the each
wiping arm 602. Then the each wiping arm 602 is moved on the selected portion of the organic photoactive layer 106 to remove the selected portion of the organic photoactive layer 106.
[0073] When the selected portion of the cathode layer 108 and the organic photoactive layer 106 is removed, a portion of the anode layer 104 that was hidden beneath the selected portion of the cathode layer 108 and the organic photoactive layer 106 becomes accessible. This enables extraction of electrical contact from the anode layer 104.
[0074] Electrical contacts from the cathode layer 108 and the anode layer 104 are extracted. Thereafter, at step 514, the power generating sub-assembly 109 is encapsulated by covering it with the encapsulation 110.
[0075] In an embodiment of method 500, each layer, i.e., the anode layer 104, the organic photoactive layer 106, the cathode layer 108 and the hole-transport layer 112, can be cured thermally after it is applied by the spin-coating process and before a subsequent layer is applied on it.
[0076] Thereafter the method terminates at step 516.
[0077] FIG. 8 is a flow chart describing a method 800 for manufacturing the organic solar cell 100a or 100b, in accordance with yet another embodiment of the present invention. In this embodiment all the layers, i.e., the anode layer 104, the hole-transport layer 112, the organic photoactive layer 106 and the cathode layer 108 are deposited by using the spin-coating process explained in conjunction with FIG. 4. Additionally, in this embodiment, the organic photoactive layer 106 and the cathode layer 108 are not made to cover the anode layer 104 completely. Therefore, in this embodiment, no removal of the cathode layer 108 or the organic photoactive layer 106 is required to extract electrical contact from the anode layer 104.
[0078] For the purpose of this description, the method 800 is explained for manufacturing of the organic solar cell 100a. However, it will be readily apparent to those with ordinary skilled in the art that the method 800 can also be applied, without deviating from the scope of the invention, for manufacturing the organic solar cell 100b or another organic solar cell with other additional layers. Additionally, some steps, and corresponding description, of the method 800 are similar to the method 300 or the method 500. Therefore, subsequent description of the method 800 describes the steps that are different from the method 300 or the method 500, and may not be elaborate about the steps that are similar to the method 300 or the method 500. Details for the steps that are similar to the method 300 or the method 500 can be referred from the description of FIG. 3 and FIG. 5.
[0079] The method 800 is initiated at step 802. At step 804, the substrate is positioned on the spindle 404, preferably when the spindle is stationary. Thereafter, the anode layer 104 is
deposited by using the spin-coating process at step 806. In a preferred embodiment, the anodic solution is disposed at the center of the substrate, while simultaneously rotating the spindle 404 about the axis 406, i.e., the longitudinal axis of the spindle 404 that also passes through the substrate 102. By disposing the anodic solution at the center of the substrate, the anode layer 104 thus formed will completely cover the substrate 102.
[0080] Thereafter, at step 808, the solution containing an organic photoactive material is disposed at a point that is radially outward from a center of the anode layer. For example, referring to FIG. 7, the solution containing an organic photoactive material is disposed at a point 702, located at a radial distance of 'x' units from the center of the anode layer. In this embodiment, the centrifugal force will make the solution containing an organic photoactive material spread in the radially outward direction 408 from the point 702, thereby, leaving a circular portion of radius 'x' of the anode layer 104 uncovered from the organic photoactive layer 106 thus formed.
[0081] At step 810, the cathodic solution is disposed at a point that is radially outward from the center of the organic photoactive layer 106. For example, the cathodic solution is disposed at the point 702 (refer FIG. 7), located at a radial distance of 'x' units from the center of the anode layer 104. In this embodiment, the centrifugal force will spread the cathodic solution in the radially outward direction 408 from the point 702, thereby, leaving a circular portion of radius 'x' of the anode layer 104 uncovered from the cathode layer 108 thus formed.
[0082] Thereafter, at step 812, electrical contacts are extracted from the cathode layer and the anode layer, without requiring removal of the selected portion of the cathode layer 108 and the organic photoactive layer 106. Thereafter, at step 814, the power generating sub-assembly 109 is encapsulated by covering it with the encapsulation 110. The method terminates at step 816.
[0083] Various embodiments, as described above, provide a method for manufacturing an organic solar cell, which has several advantages. One of the several advantages of some embodiments of this method is that it requires a reduced number of parameters to be controlled. For example, in the embodiment where all the layers are deposited by spin-coating process, then the entire method can be controlled by controlling only parameters related to spin-coating, i.e., speed of rotation of the spindle, rate of flow of solutions from the nozzle and, if required, the radial distance 'x' from the center. Another advantage of this embodiment is that all the layers can be deposited by using the same manufacturing set-up, thereby enabling reduced capital investment on a manufacturing facility implementing the method. Yet another advantage of some embodiments is that chances of deterioration of a quality of the organic solar cell are reduced, since the processes like masking and etching are eliminated in some embodiments of the present invention. For the same reason, the method according to the present invention is faster as well.
[0084] Another advantage of some embodiments of the method of present invention is the cost-effectiveness, since certain embodiments the processes like masking and etching can be eliminated.
[0085] While the invention has been disclosed in connection with the preferred embodiments shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is not to be limited by the foregoing examples, but is to be understood in the broadest sense allowable by law.
[0086] All documents referenced herein are hereby incorporated by reference.

CLAIMS
What is claimed is:
1. A method for manufacturing an organic solar cell, the method comprising:
providing a substrate, wherein a size of said substrate is less than 900 square centimetre;
depositing an anode layer on said substrate by imparting centrifugal force to an anodic solution disposed on said substrate;
depositing an organic photoactive layer on said anode layer, said organic photoactive layer enabling conversion of solar energy into electrical energy;
depositing a cathode layer on said organic photoactive layer to form a power-generating sub-assembly; and
encapsulating said power-generating sub-assembly to obtain said organic solar cell.
2. The method as recited in claim 1 further comprising depositing a hole-transport layer on said anode layer.
3. The method as recited in claim 1, wherein said anodic solution comprises carbon nanotubes.
4. The method as recited in claim 3, wherein said forming an anode layer comprises:
disposing said anodic solution on said substrate;
spinning said substrate about an axis passing through said substrate to impart said centrifugal force to said anodic solution, wherein said spinning is continued till a predefined thickness of anodic solution is uniformly applied on said substrate; and
curing said anodic solution to form said anode layer.
5. The method as recited in claim 1, wherein said cathode layer is selected from the group consisting of Aluminium doped Zinc Oxide, a conducting ink of Aluminium and a eutectic solution of Indium/Gallium.
6. The method as recited in claim 1, wherein providing said substrate comprises providing a glass substrate.
7. The method as recited in claim 1 further comprising removing impurities from said substrate prior to forming said anode layer.
8. The method as recited in claim 1, wherein depositing said organic photoactive layer comprises imparting centrifugal force to a solution comprising an organic photoactive material.
9. The method as recited in claim 1, wherein depositing said cathode layer comprises imparting centrifugal force to a cathodic solution.
10. The method as recited in claim 1 further comprising removing a selected portion of the cathode layer and the organic photoactive layer to expose a portion of the anode layer and extract an electrical contact.