MANUFACTURING OF ORGANIC PHOTOACTIVE CELLS
BACKGROUND
The present invention relates, in general, to photoactive cells.
Organic photoactive cells have emerged as an alternative to silicon-based photoactive cells, and have a potential to provide a cheap source of energy. In a conventional method of manufacturing an organic photoactive cell, an electrode is sputter-deposited over a photoactive layer. The deposition of the electrode over the photoactive layer often results in a change in the internal structure of the photoactive layer. This leads to defects in the photoactive layer, and hence, leads to lower efficiencies of such photoactive cells.
Various techniques have been employed to minimize defects generated due to deposition of electrodes. In one conventional manufacturing process, an additional step of annealing is performed after the sputter-deposition of the electrode. However, this makes the manufacturing process complex and time-consuming, as additional steps have to be performed. Another conventional manufacturing process employs alternative techniques, such as thermal evaporation, to deposit the electrode, instead of sputter-deposition. However, these alternative techniques are very time-consuming, and are not suitable for mass manufacturing.
In light of the foregoing discussion, there is a need for a method of manufacturing a photoactive cell that eliminates defects in the photoactive cell, and is suitable for mass manufacturing.

SUMMARY
An object of the present invention is to provide a method of manufacturing a photoactive cell.
Another object of the present invention is to provide a manufacturing method that eliminates defects in the photoactive cell.
Yet another object of the present invention is to provide a manufacturing method that is suitable for mass manufacturing.
Embodiments of the present invention provide a method of manufacturing a photoactive cell. The method includes obtaining a substrate, depositing a first conductive material over the substrate to form a first electrode, coating the first electrode with a photoactive material to form a photoactive layer, coating the photoactive layer with a hole-transport material to form a hole-transport layer, and depositing a second conductive material over the hole-transport layer to form a second electrode.
In accordance with an embodiment of the present invention, the first electrode is deposited using sputter-deposition. As the process of sputter-deposition is performed before the photoactive layer is formed, defects in the photoactive layer are eliminated.
The process of sputter-deposition consumes lesser time, compared to conventional evaporation techniques. This makes the manufacturing method suitable for mass manufacturing.

BRIEF DESCRIPTION OF DRAWINGS
Embodiments of the present invention will hereinafter be described in conjunction with the appended drawings provided to illustrate and not to limit the scope of the claims, wherein like designations denote like elements, and in which:
FIG. 1 depicts a method of manufacturing a photoactive cell, in accordance with
an embodiment of the present invention;
FIG. 2 depicts a system for manufacturing a photoactive cell, in accordance with
an embodiment of the present invention; and
FIG. 3 is a schematic diagram depicting a photoactive cell so manufactured, in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
Various embodiments of the present invention provide a method and system for manufacturing a photoactive cell. A photoactive cell is defined as a cell that is based on activation of electrons occurring due to incident photons.
The method includes obtaining a substrate; depositing a first conductive material over the substrate to form a first electrode; coating the first electrode with a photoactive material to form a photoactive layer; coating the photoactive layer with a hole-transport material to form a hole-transport layer; and depositing a second conductive material over the hole-transport layer to form a second electrode. The method eliminates defects in the photoactive layer that could occur due to deposition of the first electrode and the second electrode.
Referring now to figures, FIG. 1 depicts a method of manufacturing a photoactive cell, in accordance with an embodiment of the present invention. At step 102, a substrate is obtained. Step 102 may, for example, include cleaning the substrate.

The substrate may, for example, be transparent or opaque, as required. The substrate may, for example, be made of any material that is tolerant to moisture, Ultra Violet (UV) radiation, abrasion, and natural temperature variations. Examples of such materials include, but are not limited to, glass, plastics and suitable polycarbonates.
At step 104, a first conductive material is deposited over the substrate to form a first electrode. In accordance with an embodiment of the present invention, step 104 is performed by sputter-depositing the first conductive material over the substrate. In alternative embodiments of the present invention, step 104 could be performed by other alternative processes, such as thermal evaporation and physical vapor deposition.
The first conductive material may, for example, be a transparent conductive oxide, such as Zinc Oxide and Aluminum-doped Zinc Oxide. Alternatively, the first conductive material may be Aluminum, Silver, Calcium and Barium.
In accordance with an additional embodiment of the present invention, step 104 may include sputter-depositing a conductive material over the substrate, and then depositing a low work function material, such as Calcium, Barium, and Lithium Fluoride, over the sputter-deposited conductive material.
At step 106, the first electrode is coated with a photoactive material to form a photoactive layer. In one example, the photoactive material may include an active polymer and a fullerene-based electron acceptor. In another example, the photoactive material may include a nano-particle-based electron acceptor, instead of a fullerene-based electron acceptor.

step 106 may, for example, be performed by spin coating the photoactive material over the first electrode.
In accordance with an embodiment of the present invention, step 106 includes a sub-step of controlling the thickness of the photoactive layer.
In accordance with a specific embodiment of the present invention, step 102 Includes forming grooves on the substrate. These grooves help retain the photoactive material coated on the first electrode at step 106.
In accordance with another specific embodiment of the present invention, a step of depositing a nano-particle layer in-between the first electrode and the photoactive layer may be performed. For example. Titanium Oxide (TIO2) nano-particles may be deposited over the first electrode after step 104. The nano-particle layer improves conductivity between the first electrode and the photoactive layer.
At step 108, the photoactive layer is coated with a hole-transport material to form a hole-transport layer. Examples of the hole-transport material include, but are not limited to, Poly(3,4-ethylenedioxythiophene) (PEDOT), Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS).
In addition, the hole-transport material could be mixed with other polymer derivatives to improve conductivity and to minimize degradation of the hole-transport layer, in accordance with a specific embodiment of the present Invention.
Step 108 may, for example, be performed by spin coating the hole-transport material over the photoactive layer.

In accordance with an embodiment of the present invention, step 108 includes a sub-step of controlling the thickness of the hole-transport layer. The thickness of the hole-transport layer may, for example, be adjusted to allow proper transmission of light, while allowing transportation of charge carriers.
At step 110, a second conductive material is deposited over the hole-transport layer to form a second electrode. The second conductive material may, for example, be a transparent conductive oxide, such as Indium Tin Oxide (ITO), Zinc Oxide (ZnO), and Fluorine-doped Tin Oxide (FTO). Alternatively, a suitable transparent conductive polymer may be used as the second conductive material.
In accordance with an embodiment of the present invention, step 110 is performed by sputter-depositing the second conductive material over the hole-transport layer. In accordance with an embodiment of the present invention, step 110 is performed by a low-power reactive sputtering. In accordance with another embodiment of the present invention, step 110 includes performing a low-power reactive sputtering, followed by a high-power reactive sputtering. In alternative embodiments of the present invention, step 110 could be performed by other alternative processes, such as thermal evaporation and physical vapor deposition.
In accordance with a specific embodiment of the present invention, a step of depositing a nano-particle layer between the hole-transport layer and the second electrode may be performed. The nano-particle layer improves conductivity between the hole-transport layer and the second electrode.
In accordance with an additional embodiment of the present invention, a step of positioning a transparent member over the second electrode may be performed.

In accordance with another additional embodiment of the present invention, a step of encapsulating the substrate, the first electrode, the photoactive layer, the hole-transport layer and the second electrode with a laminate may be performed. The laminate may, for example, be any material that is tolerant to moisture, abrasion, and natural temperature variations. For example, Silicon Oxynitride (SiOxN) may be used as a laminate. In another example, the step of encapsulation may be performed by dispensing glue at the edge of the photoactive cell.
In accordance with an embodiment of the present invention, the photoactive material is capable of producing electron-hole pairs when solar energy is incident on it. Therefore, the photoactive layer is capable of converting solar energy into electricity. The hole-transport layer enables transportation of charge carriers produced in the photoactive layer to the second electrode. Accordingly, the first electrode and the second electrode are formed so as to be capable of collecting electricity generated by the photoactive layer.
In accordance with an embodiment of the present invention, the substrate and the first electrode are substantially transparent, such that solar radiation falling on the substrate passes towards the photoactive layer. For example, a substrate made of a transparent material may be taken at step 102, and a transparent conductive material may be used to deposit the first electrode at step 104. In such a case, the photoactive cell may be arranged in such a manner that solar radiation falls from the side of the substrate. The incident solar radiation passes through the transparent substrate and the transparent first electrode towards the photoactive layer.
In accordance with another embodiment of the present invention, the hole-transport layer and the second electrode are substantially transparent, such that solar radiation falling on the second electrode passes towards the photoactive layer. For example, a transparent hole-transport material may be used to form

the hole-transport layer at step 108, and a transparent conductive material may be used to deposit the second electrode at step 110. In such a case, the photoactive cell may be arranged in such a manner that solar radiation falls from the side of the second electrode. The incident solar radiation passes through the transparent second electrode and the transparent hole-transport layer towards the photoactive layer.
It should be noted here that steps 102-110 are only illustrative and other alternatives can also be provided where steps are added, one or more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein. For example, one or more of the following steps may be added: a step of drying and annealing the photoactive layer before step 108, and a step of drying and annealing the hole-transport layer before step 110.
FIG. 2 depicts a system 200 for manufacturing a photoactive cell, in accordance with an embodiment of the present invention. System 200 includes a substrate obtaining unit 202, a first-electrode depositing unit 204, a photoactive-layer coating unit 206, a hole-transport-layer coating unit 208, and a second-electrode depositing unit 210.
Substrate obtaining unit 202 is configured to obtain a substrate, as required. Substrate obtaining unit 202 may, for example, be configured to clean the substrate.
In accordance with a specific embodiment of the present invention, substrate obtaining unit 202 is configured to form grooves on the substrate.
As described earlier, the substrate may, for example, be transparent or opaque, as required. The substrate may, for example, be made of any material that is tolerant to moisture, UV radiation, abrasion, and natural temperature

variations. Examples of such materials include, but are not limited to, glass, plastics and suitable polycarbonates.
First-electrode depositing unit 204 is configured to deposit a first conductive material over the substrate to form a first electrode. In accordance with an embodiment of the present invention, first-electrode depositing unit 204 is configured to sputter-deposit the first conductive material over the substrate. In alternative embodiments of the present invention, first-electrode depositing unit 204 could be configured to perform other alternative processes, such as thermal evaporation and physical vapor deposition.
The first conductive material may, for example, be a transparent conductive oxide, such as Zinc Oxide and Aluminum-doped Zinc Oxide. Alternatively, the first conductive material may be Aluminum, Silver, Calcium and Barium.
In accordance with an additional embodiment of the present invention, first-electrode depositing unit 204 may be configured to sputter-deposit a conductive material over the substrate, and then deposit a low work function material, such as Calcium, Barium, and Lithium Fluoride, over the sputter-deposited conductive material.
Photoactive-layer coating unit 206 is configured to coat the first electrode with a photoactive material to form a photoactive layer. In one example, the photoactive material may include an active polymer and a fullerene-based electron acceptor. In another example, the photoactive material may include a nano-particle-based electron acceptor, instead of a fullerene-based electron acceptor.
Photoactive-layer coating unit 206 may, for example, be configured to spin coat the photoactive material over the first electrode.

In accordance with an embodiment of the present invention, photoactive-layer coating unit 206 is configured to control the thickness of the photoactive layer.
In accordance with a specific embodiment of the present invention, system 200 also includes an additional unit configured to deposit a nano-particle layer in-between the first electrode and the photoactive layer.
Hole-transport-layer coating unit 208 is configured to coat the photoactive layer with a hole-transport material to form a hole-transport layer. Examples of the hole-transport material include, but are not limited to, Poly(3,4-ethylenedioxythiophene) (PEDOT), Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)(PEDOT:PSS).
In addition, the hole-transport material could be mixed with other polymer derivatives to improve conductivity and to minimize degradation of the hole-transport layer, in accordance with a specific embodiment of the present invention.
Hole-transport-layer coating unit 208 may, for example, be configured to spin coat the hole-transport material over the photoactive layer.
In accordance with an embodiment of the present invention, hole-transport-layer coating unit 208 is configured to control the thickness of the hole-transport layer.
Second-electrode depositing unit 210 is configured to deposit a second conductive material over the hole-transport layer to form a second electrode. The second conductive material may, for example, be a transparent conductive oxide, such as Indium Tin Oxide (ITO), Zinc Oxide (ZnO), and Fluorine-doped Tin Oxide
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(FTO). Alternatively, a suitable transparent conductive polymer may be used as the second conductive material.
In accordance with an embodiment of the present invention, second-electrode depositing unit 210 is configured to sputter-deposit the second conductive material over the hole-transport layer. In accordance with an embodiment of the present invention, second-electrode depositing unit 210 is configured to perform a low-power reactive sputtering. In accordance with another embodiment of the present invention, second-electrode depositing unit 210 is configured to perform a low-power reactive sputtering, followed by a high-power reactive sputtering. In alternative embodiments of the present invention, second-electrode depositing unit 210 could be configured to perform other alternative processes, such as thermal evaporation and physical vapor deposition.
In accordance with a specific embodiment of the present invention, system 200 includes an additional unit configured to deposit a nano-particle layer between the hole-transport layer and the second electrode. The nano-particle layer improves conductivity between the hole-transport layer and the second electrode.
In accordance with an additional embodiment of the present invention, system 200 also includes a positioning unit configured to position a transparent member over the second electrode. The positioning unit may, for example, be a pick-and-place unit that is configured to pick the transparent member, and align and place the transparent member over the second electrode.
In accordance with another additional embodiment of the present invention, system 200 also includes an encapsulating unit configured to encapsulate the substrate, the first electrode, the photoactive layer, the hole-transport layer and the second electrode with a laminate.
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FIG. 2 is merely an example, which should not unduly limit the scope of the claims herein.
FIG. 3 is a schematic diagram depicting a photoactive cell 300, in accordance with an embodiment of the present invention. Photoactive cell 300 includes a substrate 302, a first electrode 304 deposited over substrate 302, a photoactive layer 306 coated over first electrode 304, a hole-transport layer 308 coated over photoactive layer 306, and a second electrode 310 deposited over hole-transport layer 308.
Substrate 302 may, for example, be transparent or opaque, as required. The substrate may, for example, be opaque to one band of wavelength, while being transparent to other bands. For example, a quartz substrate is transparent to UV radiation, while a rock salt substrate is transparent to Infra Red (IR) radiation. In another example, the substrate may be doped with a suitable material that converts radiation of one wavelength to radiation of another wavelength. For example, a fluorescent-doped substrate may be used, as required.
In one example, substrate 302 made of a transparent material may be used, and a transparent conductive material may be used to deposit first electrode 304. In such a case, photoactive cell 300 may be arranged in such a manner that solar radiation falls from the side of substrate 302. As substrate 302 and first electrode 304 are transparent, incident solar radiation passes towards photoactive layer 306.
In another example, a transparent hole-transport material may be used to form hole-transport layer 308, and a transparent conductive material may be used to deposit second electrode 310. In such a case, photoactive cell 300 may be arranged in such a manner that solar radiation falls from the side of second
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electrode 310. As second electrode 310 and hole-transport layer 308 are transparent, incident solar radiation passes towards photoactive layer 306.
First electrode 304 is deposited on the top surface of substrate 302, as shown. In accordance with an embodiment of the present invention, first electrode 304 is deposited by sputter-deposition of a first conductive material over the top surface of substrate 302. The first conductive material may, for example, be a transparent conductive oxide, such as Zinc Oxide and Aluminum-doped Zinc Oxide. Alternatively, the first conductive material may be Aluminum, Silver, Calcium and Barium.
In accordance with an additional embodiment of the present invention, first electrode 304 may be deposited by sputter-depositing a conductive material over substrate 302, and then depositing a low work function material, such as Calcium, Barium, and Lithium Fluoride, over the sputter-deposited conductive material.
Photoactive layer 306 is coated over first electrode 304, as shown. In accordance with an embodiment of the present invention, a photoactive material is spin-coated over first electrode 304 to form photoactive layer 306. In one example, the photoactive material may include an active polymer and a fullerene-based electron acceptor. In another example, the photoactive material may include a nano-particle-based electron acceptor, instead of a fullerene-based electron acceptor.
Hole-transport layer 308 is coated over photoactive layer 306, as shown. In accordance with an embodiment of the present invention, a hole-transport material is spin-coated over photoactive layer 306 to form hole-transport layer 308. Examples of the hole-transport material include, but are not limited to, Poly(3,4-ethylenedioxythiophene) (PEDOT), Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)(PEDOT:PSS).
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In addition, the hole-transport material could be mixed with other polymer derivatives to improve conductivity and to minimize degradation of hole-transport layer 308, in accordance with a specific embodiment of the present invention.
In accordance with an embodiment of the present invention, the thickness of hole-transport layer 308 is adjusted to allow proper transmission of light and transportation of charge carriers simultaneously.
Second electrode 310 is deposited over hole-transport layer 308, as shown. In accordance with an embodiment of the present invention, second electrode 310 is deposited by sputter-deposition of a second conductive material over hole-transport layer 308. The second conductive material may, for example, be a transparent conductive oxide, such as Indium Tin Oxide (ITO), Zinc Oxide (ZnO), and Fluorine-doped Tin Oxide (FTO). Alternatively, a suitable transparent conductive polymer may be used as the second conductive material.
In accordance with an embodiment of the present invention, photoactive cell 300 further includes a transparent member (not shown) positioned over second electrode 310. The transparent member protects second electrode 310 from environmental damage, while allowing electromagnetic radiation falling on its surface to pass towards photoactive layer 306. The transparent member may, for example, be a toughened glass with low iron content. In addition, the transparent member may be coated with an anti-reflective coating to reduce loss of solar energy incident on photoactive cell 300. The anti-reflective coating minimizes reflection occurring at a medium boundary between air and the transparent member.
When solar radiation falls over photoactive layer 306, electron-hole pairs are created in photoactive layer 306. Electrons and holes are separated at an interface between photoactive layer 306 and hole-transport layer 308, thereby generating a voltage. When a load is connected across first electrode 304 and
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second electrode 310, the generated voltage drives current, thereby producing electricity.
It is to be understood that the specific designation for photoactive cell 300 and its various components is for the convenience of the reader and is not to be construed as limiting photoactive cell 300 to a specific size, shape, type, or arrangement of its components.
Embodiments of the present invention provide a method for manufacturing a photoactive cell. The method eliminates defects in a photoactive layer that could occur due to deposition of electrodes.
The electrodes are deposited using a sputter-deposition process, which consumes lesser time compared to conventional evaporation techniques. This makes the manufacturing method suitable for mass manufacturing.
In the description herein for the embodiments of the present invention, numerous specific details are provided, such as examples of components and/or methods, to provide a thorough understanding of the embodiments of the present invention. One skilled in the relevant art will recognize, however, that an embodiment of the present invention can be practiced without one or more of the specific details, or with other apparatus, systems, assemblies, methods, components, materials, parts, and/or the like. In other instances, well-known structures, materials, or operations are not specifically shown or described in detail to avoid obscuring aspects of the embodiments of the present invention.
Reference throughout this specification to "one embodiment", "an embodiment", or "a specific embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of an embodiment of the present invention and not necessarily in all embodiments. Thus, respective appearances of the
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phrases "in one embodiment", "in an embodiment", or "in a specific embodiment" in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics of any specific embodiment of the present invention may be combined in any suitable manner with one or more other embodiments. It is to be understood that other variations and modifications of the embodiments of the present invention described and illustrated herein are possible in light of the teachings herein and are to be considered as part of the spirit and scope of the present invention.
It will also be appreciated that one or more of the elements depicted in the drawings/figures can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application.
As used in the description herein and throughout the claims that follow, "a", "an", and "the" includes plural references unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of "in" includes "in" and "on" unless the context clearly dictates othenA/ise.
The foregoing description of illustrated embodiments of the present invention, Including what is described in the Abstract, is not intended to be exhaustive or to limit the present invention to the precise forms disclosed herein. While specific embodiments of, and examples for, the present invention are described herein for illustrative purposes only, various equivalent modifications are possible within the spirit and scope of the present invention, as those skilled in the relevant art will recognize and appreciate. As indicated, these modifications may be made to the present invention in light of the foregoing description of illustrated embodiments of the present invention and are to be included within the spirit and scope of the present invention.
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Thus, while the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some instances some features of the embodiments of the present invention will be employed without a corresponding use of other features without departing from the scope and spirit of the present invention as set forth. Therefore, many modifications may be made to adapt a particular situation or material to the essential scope and spirit of the present invention. It is intended that the present invention not be limited to the particular terms used in following claims and/or to the particular embodiment disclosed as the best mode contemplated for carrying out this present invention, but that the present invention will include any and all embodiments and equivalents falling within the scope of the appended claims.
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CLAIMS WHAT IS CLAIMED IS:
1. A method of manufacturing a photoactive cell, the method comprising the
steps of:
obtaining a substrate;
depositing a first conductive material over the substrate to form a first electrode;
coating the first electrode with a photoactive material to form a photoactive layer, the photoactive layer being capable of converting solar energy incident on the photoactive layer into electricity;
coating the photoactive layer with a hole-transport material to form a hole-transport layer; and
depositing a second conductive material over the hole-transport layer to form a second electrode, such that the first electrode and the second electrode are capable of collecting electricity generated by the photoactive layer.
2. The method of claim 1, wherein the step of depositing the first electrode
comprises the step of sputter-depositing the first conductive material over the substrate.
3. The method of claim 1, wherein the first conductive material is selected from
the group consisting of Aluminum, Silver, Calcium, Barium, and Zinc Oxide.
4. The method of claim 1, wherein the step of obtaining the substrate comprises
the step of forming grooves on the substrate, to help retain the photoactive material on the first electrode.
5. The method of claim 1 further comprising the step of depositing a nano-particle
layer in-between the first electrode and the photoactive layer.
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6. The method of claim 1, wherein the substrate and the first electrode are
substantially transparent, such that solar radiation falling on the substrate
passes towards the photoactive layer.
7. The method of claim 1, wherein the hole-transport layer and the second
electrode are substantially transparent, such that solar radiation falling on the second electrode passes towards the photoactive layer.
8. The method of claim 1 further comprising the step of positioning a transparent
member over the second electrode.
9. The method of claim 1 further comprising the step of encapsulating the
substrate, the first electrode, the photoactive layer, the hole-transport layer
and the second electrode with a laminate.
10. A method of manufacturing a photoactive cell substantially as herein above
described in the specification with reference to the accompanying drawings.

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