HK1144468A - Photovoltaics with interferometric masks - Google Patents

Abstract

An interferometric mask 300 covering the front electrodes 910, 91 1 of a photovoltaic device 900 is disclosed. Such an interferometric mask 300 may reduce reflections of incident light from the electrodes 910, 911. In various embodiments, the mask reduces reflections so that a front electrode 910, 911 pattern appears similar in color to adjacent regions of visible photovoltaic active material.

Description

Photovoltaic device with interferometric mask

Technical Field

The present invention relates generally to the field of photoelectric transducers, such as photovoltaic cells, that convert light energy into electrical energy.

Background

For over a century fossil fuels such as coal, oil and natural gas have provided the primary energy source in the united states. There is an increasing need for alternative energy sources. Fossil fuels are non-renewable energy sources that are rapidly being depleted. Large-scale industrialization in developing countries such as india and china has placed a considerable burden on the availability of fossil fuels. In addition, geopolitical issues can quickly affect the supply of such fuels. Global warming has also received much attention in recent years. Several factors are believed to contribute to global warming; however, widespread use of fossil fuels is considered to be a major cause of global warming. Therefore, there is an urgent need to find a renewable and economically viable energy source that is also environmentally safe. Solar energy is an environmentally safe renewable energy source that can be converted into other forms of energy, such as heat and electricity.

Photovoltaic (PV) cells convert light energy into electrical energy and thus can be used to convert solar energy into electricity. Photovoltaic solar cells can be made very thin and modular. PV cells can range in size from a few millimeters to tens of centimeters. The individual electrical output from one PV cell can range from a few milliwatts to a few watts. Several PV cells can be electrically connected and packaged in an array to generate sufficient electrical power. PV cells can be used in a wide variety of applications, such as to provide power for satellites and other space vehicles, to provide power for residential and commercial assets, to charge automobile batteries, and the like.

While PV devices may reduce reliance on hydrocarbon fuels, widespread use of PV devices has been hampered by inefficiencies and aesthetic issues. Thus, improvements in any of these aspects may increase the use of PV devices.

Disclosure of Invention

Certain embodiments of the present invention include a photovoltaic cell or device integrated with an interferometric mask to darken all or part of the cell or device to appear dark or black to a viewer. Such interference shaded photovoltaic devices may have a more uniform color, making them more aesthetically pleasing and thus more suitable for architectural or architectural applications. In various embodiments, one or more optical resonant cavities and/or optical resonant layers are included in the photovoltaic device, and in particular on the light incident side or front side of the photovoltaic material, to shield the reflective electrode, which may be located on the front surface of the photovoltaic device. The optical resonant cavity and/or layers can include transparent non-conductive materials such as dielectrics, transparent conductive materials, air gaps, and combinations thereof. Other embodiments are possible.

In one embodiment, a photovoltaic device is described that defines a front side upon which light is incident and a back side opposite the front side. The photovoltaic device includes a photovoltaic active layer and a conductor on a front side of the photovoltaic active layer. The interferometric mask is patterned to cover the front side of the conductor.

In another embodiment, a photovoltaic device includes a photovoltaic material and a conductor in front of the photovoltaic material. The photovoltaic device further includes an optical interference cavity located in front of the photovoltaic material and the conductor. The cavity includes a reflective surface in front of the photovoltaic material, an optical resonant cavity in front of the reflective surface, and an absorber in front of the optical resonant cavity. The visible color is substantially uniform across the front side of the photovoltaic device, including portions of the photovoltaic material and the metal conductor.

In another embodiment, a photovoltaic device includes: means for generating an electrical current from incident light on an incident side of the means; means for conducting the generated current; means for interference shielding the conducting means from the incident side of the photovoltaic device.

In another embodiment, a method for manufacturing a photovoltaic device is provided. The method includes providing a photovoltaic generator having a photovoltaic active layer, a patterned front side conductor, and a back side conductor. A plurality of layers is formed over the photovoltaic generator. One or more of the plurality of layers are patterned to define an interferometric modulator overlying the patterned front side conductor.

Drawings

The example embodiments disclosed herein are illustrated in schematic drawings for purposes of illustration only.

FIG. 1 schematically illustrates a theoretical optical interference cavity.

FIG. 2 schematically illustrates a plurality of layers forming one implementation of an optical interferometric modulator.

FIG. 3A is a block diagram of an interferometric modulator ("IMOD") stack, similar to the optical interferometric modulator of FIG. 2, including an absorber layer, an optical resonant cavity, and a reflector.

Fig. 3B schematically illustrates an IMOD in which the optical cavity includes air gaps formed by posts or pillars between absorber and reflector layers.

FIG. 3C illustrates an embodiment of an IMOD in which the optical cavity can be electromechanically adjusted in an "open" state.

FIG. 3D illustrates an IMOD in which the optical cavity can be electromechanically tuned in a "closed" state.

FIG. 4 shows total reflection versus wavelength for an interferometric light modulator having an optical cavity configured to reflect normally incident light and yellow of the reflected light.

Fig. 5 shows total reflection versus wavelength for the case of an optical cavity configured to minimize visible reflection of normally incident light and reflected light.

Fig. 6 shows the total reflection vs. wavelength of an interferometric light modulator, such as that of fig. 5, at an angle of incidence or viewing angle of about 30 degrees from the direction of illumination.

Fig. 7 schematically illustrates a photovoltaic cell including a p-n junction.

Figure 8 is a block diagram schematically illustrating a photovoltaic cell including a deposited thin film photovoltaic active material.

Fig. 9A and 9B are schematic plan and isometric cross-sectional views depicting an exemplary solar photovoltaic device with a visible reflective electrode on the front side.

10A-10G are schematic cross-sectional views illustrating steps in the process of fabricating an embodiment of an Interferometric Modulator (IMOD) mask integrated with a photovoltaic device, wherein the IMOD mask is patterned with a photovoltaic device front electrode.

Fig. 10H is a schematic cross-sectional view of the photovoltaic device of fig. 10G after forming a protective film on the IMOD mask.

11A-11D are schematic cross-sectional views illustrating steps of adding an IMOD mask over a photovoltaic device, wherein layers defining an optical resonant cavity of the IMOD mask remain unpatterned, according to another embodiment.

Fig. 12 is a schematic cross-sectional view of a photovoltaic device having an IMOD mask covering an electrode, wherein the IMOD mask includes a layer patterned slightly wider than the photovoltaic device front electrode, according to another embodiment.

Figures 13A-13E are schematic cross-sectional views illustrating steps in the process of fabricating a thin film photovoltaic device with an integrated IMOD mask on a transparent substrate.

Figure 13F is a schematic cross-sectional view of another embodiment of an IMOD mask integrated with a thin film photovoltaic device on a transparent substrate, wherein the layers defining the optical resonant cavity of the IMOD mask remain unpatterned.

Figure 13G is a schematic cross-sectional view of another embodiment of an IMOD mask integrated on the front side of a transparent substrate opposite the side of the substrate having active photovoltaic material.

Fig. 14A and 14B are schematic cross-sectional views of forming a photovoltaic device with a single crystal semiconductor photovoltaic device, with and without an IMOD mask formed over the front electrode.

Figure 15 is a schematic cross-sectional view of an embodiment of an interferometric-enhanced photovoltaic device with an integrated IMOD mask.

Detailed Description

One problem that has hindered the widespread adoption of Photovoltaic (PV) devices on available surfaces to convert light energy into electrical energy or current is the undesirable aesthetic appearance of the front conductors or electrodes on the PV devices. The high reflectivity of the common front electrode material contrasts with the darker appearance of the active PV material itself and hinders the fusion of the PV device with the surrounding materials. The embodiments described below employ an Interferometric Modulator (IMOD) construction designed to darken, hide, or fuse electrodes, providing an IMOD mask over conductors of a PV device. Light incident on the IMOD mask produces little or no visible reflection in the region of the electrodes due to the principles of optical interference. Interference shadowing effects are governed by the dimensions and basic optical properties of the materials that make up the IMOD mask. Thus, the shading effect is not as prone to fading over time as common dyes or coatings.

Although certain preferred embodiments and examples are discussed herein, it is to be understood that the present subject matter extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. It is intended that the scope of the invention herein disclosed should not be limited by the particular disclosed embodiments. Thus, for example, in any method or process disclosed herein, the acts or operations making up the method/process may be performed in any suitable order and are not necessarily limited to any particular disclosed order. Various aspects and advantages of the described embodiments have been described where appropriate. It is to be understood that not necessarily all such aspects or advantages may be achieved in accordance with any particular embodiment. Thus, for example, it is recognized that various embodiments may be practiced in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may be taught or suggested herein. The following detailed description is directed to certain specific embodiments of the invention. The invention may, however, be embodied in many different forms. The embodiments described herein can be implemented in a wide variety of devices including photovoltaic devices to collect light energy.

In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. As will be apparent from the description below, the embodiments can be implemented in a variety of devices that include photovoltaic active materials.

FIG. 1 illustrates an optical resonant cavity. An example of such an optical cavity is a soap film that can produce a spectrum of reflected colors. The optical cavity shown in figure 1 comprises two surfaces 101 and 102. The two surfaces 101 and 102 may be opposing surfaces on the same layer. For example, the two surfaces 101 and 102 may comprise surfaces on a glass or plastic plate or sheet or a glass or plastic film or any other transparent material. Air or other medium may surround the plate, sheet or film. In the illustrated example, the light is partially reflected and partially transmitted at each of the interfaces 101, 102.

A light ray 103 incident on the front surface 101 of the optical cavity is partially reflected as indicated by the light path 104 and partially transmitted through the front surface 101 along the light path 105. The transmitted light may be partially reflected along optical path 107 and transmitted out of the resonant cavity along optical path 106. The amount of light transmitted and reflected may depend on the refractive indices of the materials forming the optical cavity and the surrounding medium. As will be appreciated by those skilled in the art, the example is simplified by the omission of multiple internal reflections.

For purposes of the discussion provided herein, the total intensity of light reflected from an optical resonant cavity is the coherent superposition of the two reflected light rays 104 and 107. With this coherent addition, both the amplitude and phase of the two reflected beams contribute to the collective intensity. This coherent addition is called interference. The two reflected light rays 104 and 107 may be phase-shifted with respect to each other. In some embodiments, the phase difference between the two waves may be 180 degrees and cancel each other out. The two light beams are said to interfere destructively if the phase and amplitude of the two light rays 104 and 107 are configured to reduce intensity. If, conversely, the phase and amplitude of the two beams 104 and 107 are configured to increase the intensity, the two rays are said to interfere in a rectangular manner. The phase difference depends on the optical path difference of the two paths, which depends on both the thickness of the optical cavity, the refractive index of the material between the two surfaces 101 and 102, and whether the refractive index of the surrounding material is higher or lower than the material forming the optical cavity. The phase difference is also different for different wavelengths in the incident light beam 103. Thus, in some embodiments, an optical resonant cavity can reflect a particular set of wavelengths of incident light 103 while transmitting other wavelengths of incident light 103. Thus, some wavelengths may interfere constructively and some may interfere destructively. In general, the color and total intensity reflected and transmitted by an optical cavity are thus dependent on the thickness and materials forming the optical cavity and the surrounding medium. The wavelengths reflected and transmitted also depend on the viewing angle, the different wavelengths reflected and transmitted at different angles.

In FIG. 2, an optical resonant cavity is defined between two layers. In particular, the absorber layer 201 defines the top or front surface 101 of the optical cavity and the bottom reflector layer 202 defines the bottom or back surface 102 of the optical cavity. The thicknesses of the absorber and reflector layers may be substantially different from each other. For example, the absorber layer 201 will typically be thinner than the bottom reflector layer 202 and designed to be partially transmissive. The absorber and reflector layers may comprise metal. As shown in FIG. 2, a light ray 203 incident on the absorber layer 201 of the optical interference cavity is partially reflected out of the optical interference cavity along each of paths 204 and 207. The illumination field seen by an observer on the front or incident side is a superposition of the two reflected light rays 204 and 207. The amount of light that the device substantially absorbs or transmits out of the device through the bottom reflector 202 can be significantly increased or decreased by varying the thickness and composition of the reflector layers, while the apparent reflected color depends largely on the interference effect dictated by the size or thickness of the optical resonant cavity 101 and the material properties of the absorber layer 201.

In some embodiments, the optical cavity between the front and back surfaces 101, 102 is defined by a layer (e.g., an optically transparent dielectric layer) or layers. In other embodiments, the optical resonant cavity between the front and back surfaces 101, 102 is defined by an air gap or a combination of an optically transparent layer and an air gap. The size of the optical interference cavity can be tuned to maximize or minimize reflection of one or more particular colors of incident light. The one or more colors reflected by the optical interference cavity can be changed by changing the thickness of the cavity. Thus, the color or colors reflected by an optical interference cavity may depend on the thickness of the cavity. When the cavity height is such that a particular wavelength is maximized or minimized by optical interference, the structure is referred to herein as an Interferometric Modulator (IMOD).

In certain embodiments, the optical cavity height between the top absorber and the bottom reflector can be effectively varied, for example, by a microelectromechanical system (MEMS). MEMS include microelectromechanical elements, actuators, and electronics. Microelectromechanical elements may be formed using deposition, etching, and/or other micromachining processes that etch away or remove parts of substrates and/or deposited material layers or that add layers to form electrical and electromechanical devices. Such MEMS devices include IMODs having an electromechanically adjustable optical resonant cavity. IMODs selectively absorb and/or reflect light using the principles of optical interference. In certain embodiments, an interferometric modulator may comprise a pair of conductive plates, one of which is partially reflective and partially transmissive and the other of which is partially or fully reflective. The conductive plates are capable of relative movement upon application of an appropriate electrical signal. In a particular embodiment, one plate may include a stationary layer deposited on a substrate and the other plate may include a metallic membrane separated from the stationary layer by an air gap. As described in greater detail herein, the position of one plate relative to another can change the optical interference of light incident on the interferometric modulator. In this way, the color of light output by the interferometric modulator can be changed.

Using such a MEMS tunable optical interferometric cavity, or IMOD, at least two states can be provided. The first state includes an optical interference cavity having a dimension whereby light of a selected color (based on the size of the cavity) interferes in a phase rectangular manner and is reflected out of the cavity. The second state comprises a visible black state resulting from constructive and/or destructive interference of light so as to substantially absorb visible wavelengths. Alternatively, the two states may be colored and broad-spectrum (white) reflective.

Fig. 3A is a simplified schematic diagram of an IMOD stack 300. As illustrated, the IMOD stack 300 includes an absorber layer 301, a reflector 303, and an optical resonant cavity 302 formed between the absorber layer 301 and the reflector 303. The reflector 303 may, for example, comprise a metal layer (e.g., aluminum) and is typically thick enough to be opaque (e.g., 300 nm). The optical cavity 302 may comprise an air gap and/or one or more optically transparent materials. If the optical resonant cavity 302 is defined by a single layer located between the reflector 303 and the absorber layer 301, a transparent conductor or transparent dielectric may be used. In some embodiments, the optical resonant cavity 302 can include a composite structure including a plurality of materials that can include two or more of an air gap, a transparent conductive material, and a transparent dielectric layer. A possible advantage of multiple layers and/or air gaps is that selected layers of the stack can provide multiple functions in addition to their optical role in the IMOD stack 300, such as device passivation or scratch resistance. In some embodiments, the optical resonant cavity can comprise one or more partially transparent materials, whether conductive or dielectric. Exemplary transparent materials for the optical interference cavity 302 may include Transparent Conductive Oxide (TCO) Indium Tin Oxide (ITO) and/or dielectric silicon dioxide (SiO)₂)。

In this embodiment, light first passes through the IMOD stack 300 by passing into the absorber layer 301. Some light passes through the partially transmissive absorber layer 301, passes through the optical interference cavity 302, and reflects off the reflector 303 again via the optical resonant cavity 302 and via the absorber layer 301.

Referring to FIG. 3B, in other embodiments, the thickness of the optical cavity 302 may comprise an air gap 302 supported by spacers 311, such as rails, posts, or pillars. Within the IMOD 300, the optical resonant or interferometric cavity 302 may be either an air gap that is static, or an air gap that is dynamic, that is, variable use (for example) of MEMS technology.

Interferometric Modulator (IMOD) structures such as those shown in fig. 3A or 3B selectively use optical interference to produce the desired reflected output. This reflected output can be "modulated" by selecting the thickness and optical properties of the optical resonant cavity 302 and the thickness and optical properties of the absorber 301 and reflector 303. MEMS devices may also be used to change the size of the optical resonant cavity 302 to dynamically change the reflected output. Colors observed by an observer looking at the surface of the absorber 301 will correspond to those frequencies that are substantially reflected off the IMOD but are not substantially absorbed or destructively interfered by the layers of the IMOD. The thickness of the optical cavity 302 can be selected to vary the frequencies that interfere but are not substantially absorbed.

Figures 3C and 3D show an embodiment of an IMOD in which the optical resonant cavity (302 in figure 3B) includes an air gap and can be electromechanically altered using MEMS technology. Fig. 3C illustrates the IMOD configured in an "open" state and fig. 3D illustrates the IMOD configured in a "closed" or "collapsed" state. The IMOD illustrated in figures 3C and 3D includes a substrate 320, a thin film stack 330, and a reflective film 303. Thin film stack 330 may include an absorber (corresponding to 303 in fig. 3A and 3B) as well as other layers and materials, such as separate transparent electrodes and dielectric layers. In some embodiments, the thin film stack 330 may be attached to the substrate 320. In the "on" state, the thin film stack 330 is separated from the reflective film 303 by a gap 340. In some embodiments, for example, as illustrated in fig. 3C, gap 340 may be an air gap supported by spacers 311, such as rails, posts, or pillars. In the "on" state, in some embodiments, the thickness of the gap 340 may vary, for example, between 120nm and 400nm (e.g., about 260 nm). Thus, in the "open" state, the optical resonant cavity of figures 3A and 3B includes the air gap along with any transparent layer located over the absorber within the thin film stack 330.

In certain embodiments, the IMOD may be switched from an "open" state to a "closed" state by applying a voltage difference between the thin film stack 330 and the reflective film 303 as illustrated in fig. 3D. In the "closed" state, an optical cavity above the absorber between the thin film stack 330 and the reflective film 303 is defined by, for example, a dielectric layer overlying the absorber in the thin film stack 330, and is typically configured to reflect a "black" or minimal visible reflection. In some embodiments, the thickness of the air gap may generally vary between about 0nm and about 2000nm (e.g., between "open" and "closed" states).

In the "on" state, one or more frequencies of incident light interfere in a phase rectangular manner over the surface of the substrate 320. Thus, some frequencies of incident light are not substantially absorbed within the IMOD but are reflected from the IMOD. Frequencies that reflect off of the IMOD interfere in a rectangular fashion outside of the IMOD. The display colors observed by an observer viewing the surface of the substrate 320 will correspond to those frequencies that are substantially reflected off of the IMOD but not substantially absorbed by the layers of the IMOD. Frequencies that interfere in a rectangular manner but are not substantially absorbed can be varied by varying the thickness of the optical cavity (which includes gap 340), and thus the thickness of the optical resonant cavity.

Fig. 4 illustrates a graph of total reflection of an IMOD (e.g., IMOD 300 of fig. 3A or 3B) versus wavelength as seen from a direction normal or perpendicular to a front surface of the IMOD. The total reflection graph shows a reflection peak at about 550nm (yellow). An observer observing the IMOD will observe the IMOD as yellow. As previously mentioned, the location of the peak of the total reflection curve may be shifted by changing the thickness or material of the optical resonant cavity 302 or by changing the material and thickness of one or more layers in the stack.

FIG. 5 illustrates a total reflection versus wavelength graph of an IMOD over a wavelength range of approximately 400nm to 800nm with an IMOD having an optical cavity thickness selected to minimize reflection in the visible range. The total reflection is observed to be uniformly low over the entire wavelength range. Thus, very little light is reflected off of the interferometric modulator. In some embodiments, the color observed by an observer looking perpendicular at the front surface of the IMOD may be generally black, reddish black, or purple.

Typically, IMOD stacks may have viewing angle dependence. However, when the optical resonant cavity is selected to minimize IMOD reflections in the visible range, the angular dependence tends to be quite low. Figure 6 illustrates total reflection versus wavelength for an IMOD having an optical resonant cavity optimized to minimize visible reflection when the angle of incidence or viewing is 30 degrees. The total reflection is observed to be uniformly low over the entire visible wavelength range. Thus, very little visible light is reflected off of the interferometric modulator. A comparison of fig. 5 and 6 shows that the spectral response of the IMOD having the cavity 302 selected or modulated to minimize visible reflections is substantially the same at normal incidence as at an angle of incidence or viewing of 30 degrees. In other words, the spectral response of a "black" IMOD having a cavity selected to minimize visible reflection does not exhibit a strong dependence on the angle of incidence or viewing angle.

Fig. 7 shows a typical Photovoltaic (PV) cell 700. Typical photovoltaic cells can convert light energy into electrical energy or current. PV cells are an example of a renewable energy source with a small carbon footprint and with less impact on the environment. The use of PV cells can reduce the cost of power generation and provide potential cost benefits. PV cells can have many different sizes and shapes, for example, from less than a postage stamp to several inches wide. Several PV cells can typically be connected together to form a PV cell module that can be up to several feet long and several feet wide. The modules may in turn be combined and connected to form PV arrays of different sizes and power outputs.

The size of the array may depend on several factors, such as the amount of sunlight available in a particular location and the needs of the consumer. The modules of the array may include electrical connections, mounting hardware, power conditioning equipment, and batteries to store solar energy for use when the sun is not shining. The PV device may be a single cell with its attendant electrical connections and peripheral devices, or a PV module or PV array. PV devices may also include functionally incoherent electrical components, such as components powered by the one or more PV cells.

A typical PV cell includes a PV active region disposed between two electrodes. In some embodiments, the PV cell includes a substrate on which a stack of layers is formed. The PV active layer of the PV cell can include a semiconductor material such as silicon. In some embodiments, the active region may include a p-n junction formed by contacting n-type semiconductor material 703 and p-type semiconductor material 704, as shown in fig. 7. Such a p-n junction may have diode-like properties and may therefore be referred to as a photodiode structure.

The one or more PV active layers 703, 704 are sandwiched between two electrodes that provide a current path. The back electrode 705 may be formed of aluminum, silver, or molybdenum, or some other conductive material. The back electrode may be rough and unpolished. The front electrode 701 is designed to cover a large portion of the front surface of the p-n junction to reduce contact resistance and improve collection efficiency. In embodiments where the front electrode 701 is formed of an opaque material, the front electrode 701 is configured to leave an opening over the front side of the PV active layer to allow illumination to impinge upon the PV active layer. In some embodiments, the front electrode can include a transparent conductor, such as, for example, tin oxide (SnO)₂) Or a Transparent Conductive Oxide (TCO) such as Indium Tin Oxide (ITO). The TCO can provide good electrical and conductivity and at the same time is transparent to incoming light. In some embodiments, the PV cell page can include an anti-reflection (AR) coating 702 deposited over the front electrode 701. The AR coating 702 may reduce the amount of light reflected from the front surface of the one or more PV active layers 703, 704.

When the front surface of the active PV material is illuminated, the photons transfer energy to electrons in the active region. The electron may have sufficient energy to enter a conduction band if the energy transmitted by the photon is greater than the band gap of the semiconducting material. An internal electric field is formed as the p-n junction is formed. The internal electric field exerts an influence on energized electrons to cause these electrons to move to generate a current flow in the external circuit 707. The resulting current flow may be used to power various electrical devices, such as the light bulb 706 shown in fig. 7.

In some embodiments, the p-n junction shown in fig. 7 may be replaced by a p-i-n junction in which an intrinsic or undoped semiconducting layer is sandwiched between p-type and n-type semiconductors. The p-i-n junction may have a higher efficiency than the p-n junction. In some other embodiments, the PV cell may include a plurality of junctions.

The PV active layer or layers can be formed from any of a variety of light-absorbing, photovoltaic materials, such as crystalline silicon (c-si), amorphous silicon (α -si), cadmium telluride (CdTe), indium copper selenide (CIS), Copper Indium Gallium Selenide (CIGS), light-absorbing dyes and polymers, polymers dispersed with light-absorbing nanoparticles, group III-V semiconductors such as GaAs, and the like. Other materials may also be used. The light absorbing material or materials in which photons are absorbed and transfer energy to electrical carriers (holes and electrons) are referred to herein as the PV active layer of the PV cell, and this term is intended to encompass multiple active sublayers. The materials used for the PV active layer may be selected depending on the desired performance and application of the PV cell.

In some embodiments, the PV cell can be formed by using thin film technology. For example, in embodiments in which optical energy passes through a transparent substrate, the PV cell may be formed by depositing a first or front TCO electrode layer on the substrate. A PV active material is deposited on the first electrode layer. A second electrode layer may be deposited on the PV active material layer. The layers may be deposited using deposition techniques such as physical vapor deposition techniques, chemical vapor deposition techniques, electrochemical vapor deposition techniques, and the like. Thin film PV cells can comprise amorphous or polycrystalline materials such as thin film silicon, CIS, CdTe, or CIGS. Among many other advantages, some of the advantages of thin film PV cells are small device footprint and scalability of the manufacturing process.

Fig. 8 is a block diagram schematically illustrating a typical thin film PV cell 800. A typical PV cell 800 includes a glass substrate 801 through which light can pass. A glass substrate 801 has deposited thereon a first electrode layer 802, a PV active layer 803 (which is shown to comprise amorphous silicon), and a second electrode layer 805. The first electrode layer 802 may comprise a transparent conductive material, such as ITO. As illustrated, the first electrode layer 802 and the second electrode layer 805 sandwich the thin film PV active layer 803 between them. The illustrated PV active layer 803 comprises an amorphous silicon layer. Amorphous silicon, which serves as the PV material, may include one or more diode junctions, as is known in the art. Furthermore, the one or more amorphous silicon PV layers may include a p-i-n junction with an intrinsic silicon layer sandwiched between a p-doped layer and an n-doped layer.

As illustrated in fig. 9A and 9B, many PV devices employ specular or reflective conductors 910, 911 on the front or light incident side of the device and on the back side of the PV device 900. The conductors on the front or light incident side may include bus electrodes 910 or grid line electrodes 911. When optical energy is absorbed by the PV active material 903, electron-hole pairs are generated. These electrons and holes may generate a current by moving to one or the other of the front electrodes 910, 911 or the back electrode 905, as shown in fig. 9B. The front conductors or electrodes 910, 911 are patterned to both reduce the distance that electrons or holes must travel to reach the electrodes while also allowing sufficient light to pass through to the PV active layer 903. However, the bright reflected lines produced by these electrodes are generally considered to be unattractive, such that PV devices are generally not used in a visible position.

Thus, some of the examples below describe methods of covering the unsightly electrodes to make the electrode pattern appear dark or black to better match the appearance of the exposed PV active area. Furthermore, some embodiments described below provide photovoltaic devices that are uniform in appearance so that they can better blend with surrounding structures (e.g., roof tiles). This can be achieved by darkening portions of the front face of the PV device having patterned electrodes, or by darkening the entire front surface of the photovoltaic device.

One way to darken or otherwise shield the electrodes to inhibit reflection from the conductive layer or electrodes is to use an Interferometric Modulator (IMOD) as a mask while tuning the reflectance to darken and/or blend the electrode with the color appearance of the exposed PV active area. In the IMOD stack, the function of an IMOD reflector (e.g., reflector 303 of fig. 3A or 3B) may be provided by a shielded conductor (e.g., front bus electrode 910 or grid line electrode 911 of fig. 9A and 9B). Light incident on the IMOD mask produces little or no visible reflection in the region of the electrodes due to the principles of optical interference described above. Advantageously, the interference effect is governed by the thickness and materials of the absorber and the optical cavity. Thus, the shading effect is not as prone to fading over time as common dyes or coatings.

Fig. 10A-10G illustrate one example of a process for fabricating a PV device incorporating an IMOD mask on the front electrode. The examples employ deposited PV active material films. In one embodiment, such a photovoltaic device can be formed on a substrate 1010, such as a plastic, glass, or other suitable work piece. As illustrated in fig. 10A, one method for fabricating such a device may include forming a back electrode 1020 on a substrate 1010 using known methods. The metal layer may be deposited to serve as the back electrode 1020 of the photovoltaic device, although non-metallic conductive materials may also be used.

Referring to fig. 10B, the method further includes forming a photovoltaic active material 1030. In the illustrated embodiment, the Photovoltaic (PV) active material 1030 comprises a deposited thin film, although portions of single crystals, semiconductor substrates, and/or epitaxial layers thereon may also be employed in other arrangements. The deposited PV active material can comprise, for example, amorphous silicon thin films that are gaining popularity recently. Amorphous silicon in the form of a thin film may be deposited over a large area by Physical Vapor Deposition (PVD), Chemical Vapor Deposition (CVD), electrochemical vapor deposition, or Plasma Enhanced Chemical Vapor Deposition (PECVD), as well as other methods known to those skilled in the art. As known to those skilled in the art, a PV active material comprising an amorphous silicon layer may comprise one or more junctions having n-doped and/or p-doped silicon and may further comprise p-i-n junctions. Other suitable materials for the PV active material 1030 include germanium (Ge), Ge alloys and alloys such as Copper Indium Gallium Selenide (CIGS), cadmium telluride (CdTe), and group III-V semiconductor materials or tandem multi-junction photovoltaic materials and thin films. Group III-V semiconductor materials include materials such as gallium arsenide (GaAs), indium nitride (InN), gallium nitride (GaN), Boron Arsenide (BAs), and the like. Semiconductor alloys such as indium gallium nitride may also be used. Other photovoltaic materials and devices are also possible. Methods for forming these materials are known to those skilled in the art. As an illustrative example, alloys such as CIGS may be formed by a vacuum-based process in which copper, gallium and indium are co-evaporated or co-sputter coated followed by selenide vapor annealing to form the final CIGS structure. Alternative processes based on non-vacuum are also known to those skilled in the art.

In fig. 10C, a Transparent Conductive Oxide (TCO)1040 is optionally deposited over the PV active material 1030. TCO layers are typically used with photovoltaic materials, especially thin film photovoltaic materials, in order to improve electrode contact with the PV active layer 1030. Functionally, the TCO 1040 forms part of the front electrode that completes the circuit for carrying the current generated by the PV active material 1030, but the more conductive metal conductor that traditionally overlies the TCO 1040 and connects the PV cell to a wider circuit is referred to as the front electrode. As known to those skilled in the art, a common TCO is Indium Tin Oxide (ITO). Methods for forming or depositing ITO are known in the art and include electron beam evaporation, physical vapor deposition, or sputter deposition techniques. Other TCO materials and manufacturing processes may also be used. In other embodiments, the TCO layer may be omitted.

In fig. 10D, a precursor layer 1050 is formed after depositing TCO material 1040. The precursor layer 1050 may include a metal or highly conductive material to act as a front electrode and connect the PV cell into a circuit that carries the current generated by the PV cell. As noted above, these conductors tend to be quite reflective and can detract from the appearance of the PV device and prevent widespread use of the PV device. Typical reflective materials for the precursor layer 1050 include aluminum (Al), molybdenum (Mo), zirconium (Zr), tungsten (W), iron (Fe), silver (Ag), and chromium (Cr).

As shown in fig. 10E, an optical cavity 1060 is formed over the front body 1050. In the illustrated embodiment, optical cavity 1060 is a deposited transparent layer, however, as described above with reference to figures 3A and 3B, in other arrangements, the cavity can include air gaps defined by spacers such as pillars, posts, or rails (see figure 3B); a single transparent conductive or dielectric layer; a composite formed from a plurality of conductive or dielectric transparent layers; or a composite formed by an air gap in combination with one or more transparent layers. An optical resonant cavity with a single layer of transparent material can simplify manufacturing and reduce cost. A composite structure having multiple layers and/or air gaps may employ multiple layers to provide multiple functions in addition to their optical role in the formed IMOD mask, such as device passivation or scratch resistance.

The air gap or composite optical cavity may also provide multiple functions, such as device venting or the ability to employ MEMS to reflect multiple colors (e.g., color mode and black mask mode) or for forming an effectively tunable IMOD mask. In the illustrated embodiment, where the reflector 303 of the IMOD mask also serves as the front electrode of the PV device, the reflector 303 may be used as a fixed electrode for electrostatic actuation, e.g., when the PV device is inactive. The absorber 301 may act as a movable electrode. Those skilled in the art will appreciate that the dual-function interconnects and external circuitry for manipulating electrostatic MEMS operation and current collection from the PV device may be integrated with the active IMOD mask of the PV device.

Optical cavity 1060 for one embodiment is formed of SiO₂Or other transparent dielectric material layer. SiO 2₂A suitable thickness for optical cavity 1060 is 300A(Angstrom) and 1000To produce an interference dark or black effect. For depositing or forming SiO₂Methods of (A) are known in the art, including CVD and othersThe method is carried out. Other suitable transparent materials for forming optical cavity 1060 include ITO, Si₃N₄And Cr₂O₃. Another embodiment of the optical cavity 1060 is made of SiO₂Or other transparent dielectric material. A suitable thickness for the air gap optical cavity 1060 is 450 deg.FAnd 1600To produce an interference dark or black effect.

Referring to fig. 10F, absorber layer 1070 is formed over optical cavity 1060. In the illustrated embodiment, where the constructed IMOD mask is designed to interferometrically darken the appearance of the natural reflective precursor 1050, the absorber layer 1070 may comprise a semi-transparent thickness of a metal or semiconductor layer, for example. The absorber layer may also comprise a material having a nonzero n x k (i.e., a nonzero product of the index of refraction (n) and the extinction coefficient (k)). In particular, chromium (Cr), molybdenum (Mo), titanium (Ti), silicon (Si), tantalum (Ta), and tungsten (W) all form suitable layers. In one embodiment, absorber layer 1070 is 20 a thickAnd 300In the meantime.

Referring to fig. 10G, the stack illustrated in fig. 10F is then patterned using, for example, photolithographic patterning and etching or other suitable techniques to form PV device 1000G as shown in fig. 10G. The resulting Interferometric Modulator (IMOD) mask 300 includes a reflector 303 (which also serves as the front conductor or electrode of the PV device), an optical resonant cavity 302 (which is referred to by reference numeral 1060 prior to patterning), and a patterned absorber 301. In the embodiment of FIG. 10G, the reflector 303, the optical resonant cavity 302, and the absorber 301 are patterned together and thus aligned with each other. In other arrangements, the components of the IMOD mask 300 may have a pattern that differs in some fashion from the pattern of the conductors that serve as the IMOD mask reflectors 303, as will be better understood from the discussion of fig. 12 below. The IMOD mask 300 thus covers the front electrode or reflector 303. The risk of alignment of the IMOD mask 300 with the reflector 303, which acts as the front electrode of the PV device, is that some reflections from the sides of the reflector 303 are minimal when viewed at an acute viewing angle. However, the way the absorber 301 is patterned does not prevent any more light from reaching the PV active layer than does the reflector 303, which is present anyway as the front electrode (as is already the case). Thus, the absorber 301 is patterned in a manner that avoids any further reduction in PV efficiency.

The materials and dimensions of the absorber 301 and the optical resonant cavity 302 are selected to reduce the reflectivity from the underlying reflector 303. Reflectivity is defined as the ratio of the direction normal to the upper surface of the mask 300 [ the intensity of light reflected from the IMOD mask 300 ] to [ the intensity of incident light on top of the IMOD mask 300 ]. Common PV device front electrode materials for the reflector 303 exhibit reflectivities in the range of 30% to 90%. However, the IMOD mask 300 is configured to interferometrically reduce the total reflectivity to less than 10%. Thus, the reflectivity that can be observed over the IMOD mask 300 is less than 10% for the most common reflector 303 material (at this point the reflection tends to appear "gray") and more typically less than 5%. Those skilled in the art will appreciate in view of the disclosure herein that the reflectivity can be reduced to only 1% to 3% by appropriate selection of the materials and dimensions of the absorber 301 and the layers in the optical cavity 302, thus really appearing "black".

Thus, the observer sees little or no light reflected from the front body of the PV device. Thus, the pattern formed by the IMOD mask 300 covering the electrodes may appear dark or black. Alternatively, the structure of the IMOD mask 300 is selected to reflect a color that substantially matches the color of the visible region of the photovoltaic active material adjacent the front conductor. For most PV devices, the PV active area appears rather dark, so that reducing visible reflection by the IMOD mask 300 effectively blends the conductors with the appearance of the PV active area, making it difficult to visually distinguish the two regions of the PV device. However, since the visible region of the PV active material exhibits a color other than dark or black due to non-conventional PV materials or other coatings on the window of the PV active material, the IMOD mask 300 may be configured to reflect other colors in order to match the visible region of the PV active area and create a uniform color or appearance of the PV device.

In one example where the optical cavity 302 includes air gaps defined by spacers such as pillars, posts, or rails (see FIG. 3B), a suitable height for the air gaps used to create the dark or black IMOD mask 300 is at 450And 1600Depending in part on the other materials selected for the IMOD mask 300. In which the optical cavity 302 comprises a dielectric (e.g., SiO) having a refractive index between 1 and 3₂) In another example of (3), a dark or black IMOD mask 300 may be produced having a density at 300And 1000With a dielectric thickness in between.

Referring to fig. 10H, PV device 1000H may include additional layers such as an overlying hard mask, an anti-reflective coating, or a passivation layer without compromising the masking function of the IMOD mask. For example, the dielectric layer 1080 overlying the IMOD mask 300 may comprise SiO₂Or silicon nitride and may serve as a top passivation layer for the PV device. In addition, the dielectric layer 1080 may be provided at a thickness suitable to act as an anti-reflection (AR) layer that may further enhance the black state of the front electrode region. A typical thickness of an AR layer composed of silicon oxide or silicon nitride is about 300 aAnd 1500In the meantime. Since the other layers are positioned between the viewer and the front electrode reflector 303, the selection of materials, optical properties, and thicknesses of the various layers may need to be adjusted to ensure that the interferometric mask 300 produces the desired reflectivity.

Fig. 11A-11D illustrate another embodiment in which an IMOD black mask is formed after patterning the front electrode. Fig. 11A illustrates the PV device structure of fig. 10D after patterning the conductor layer 1050 of fig. 10D, such as by photolithography and etching. Suitable materials for the precursor layer 1050 are described above with reference to fig. 10D. The patterning defines patterned conductors or front electrodes that will also serve as reflectors 303 of the IMOD mask to be formed. The structure may represent, for example, a prefabricated Photovoltaic (PV) device prior to encapsulation. Alternatively, in another embodiment, the PV device can be encapsulated and include a passivation layer (not shown) over the structure of fig. 11A, for example, prior to performing the steps of fig. 11B-11D. In such an arrangement, the materials and dimensions of the subsequently formed optical resonant cavity and absorber should be selected in view of the optical effect of the passivation layer. In other words, the passivation layer (not shown) may be considered as part of the formed composite optical cavity.

Figure 11B shows the structure of figure 11A after forming a blanket layer or composite structure of optical cavity layers 1060 selected to define IMOD masks. As described in the discussion of fig. 10E, the optical cavity layer 1060 can be an air gap defined by spacers such as pillars, posts, or rails (see fig. 3B); a single transparent conductive or dielectric layer; a composite formed from a plurality of conductive or dielectric transparent layers; or a composite formed by an air gap in combination with one or more transparent layers.

Fig. 11C illustrates the structure of fig. 11B after deposition of an absorber layer 1070. Suitable materials and thicknesses for the semi-transparent absorber layer 1070 are discussed above with reference to fig. 10F.

Figure 11D illustrates the structure of figure 11C after patterning the absorber layer 1070 to leave the patterned absorber 301. In the illustrated embodiment, the optical cavity layer 1060 is left as a blanket or unpatterned layer. Thus, the optical cavity layer 1060 is blanket over the PV cell. Absorber 301 is patterned, such as by photolithographic masking and etching, to substantially cover conductor and/or electrode 303.

The resulting structure of FIG. 11D is a PV device 1100 including an interferometer or IMOD mask 300 that includes a patterned reflector 303, a blanket optical cavity layer 1060, and a patterned absorber 301 that also serves as a front conductor or front electrode of the PV device. The blanket optical cavity layer 1060 (which may represent a single layer or a composite structure as described above) may also provide other functions across the area where the PV active layer 1030 is visible or exposed, such as passivation or antireflection of the PV active layer 1030 or optionally intervening TCO layer 1040. The region of the optical cavity layer 1060 between the patterned reflector 303 and the absorber 301 forms the optical cavity 302 of the IMOD mask 300. In the illustrated embodiment, the absorber 301 is patterned to be substantially aligned with the reflector 303.

FIG. 12 shows another embodiment of the present invention in which optical cavity layer 1060 is patterned together with absorber layer 1070 overlying the layers of the PV device as described with reference to FIG. 11C to cover reflector 303 to produce PV device 1200 as shown in FIG. 12. In this embodiment, both the absorber 301 and the optical resonant cavity 302 are patterned to cover the electrodes 303 by extending slightly beyond them. In such an embodiment, the patterned absorber 301 may extend laterally beyond the edges of the electrodes on each side less than 10% of the width of the electrodes, and in one embodiment less than 5% of the width of the electrodes. A wider absorber 301 better ensures coverage to mask reflections from the front conductor/reflector 303 and accommodates reasonable mask angle error levels between the reflector 303 pattern and the absorber 301 pattern. On the other hand, by minimizing the extent to which the absorber 301 is wider than the interference shielded reflector 303, the amount of light reaching the PV active layer 1030, and thus the overall PV device efficiency, may still be high.

In other embodiments not shown, the absorber layer and optical cavity structures may extend over all of the PV devices, but in this case the absorber layer should be very thin (mostly transmissive) in order to minimize the reduction of light reaching the PV active layers. Thus, the degree of dark or "black" effect is sacrificed to some extent when thinning the blanket absorber layer to maximize transmission. In this case, it may also be desirable to employ an additional semi-transparent reflector with relatively high transmission over the PV active layer in order to better match the reflected color to that of the IMOD in the front electrode region.

As discussed with reference to FIG. 10H, the interferometric mask 300 of FIGS. 11D and 12 can also be protected or passivated by other layer or layers formed or deposited over the surfaces of the embodiments.

Fig. 13A-13E depict a process for manufacturing another embodiment of the invention in which a layer of the PV device is formed over a transparent substrate through which light is transmitted into the PV active region. Fig. 13A begins with a suitable optically transparent substrate 1310, such as glass, plastic, or other suitable substrate having suitable optical properties. An absorber layer 1320 is formed or deposited on the back side of the substrate opposite the light incident side or front side. Therefore, in fig. 13A to 13E, light is incident from below. Suitable materials and thicknesses for the semi-transparent absorber layer 1320 are discussed above with reference to the absorber layer 1070 of fig. 10F.

FIG. 13B illustrates the structure of FIG. 13A after forming or depositing an optical cavity layer 1330 over the absorber layer 1320. As described in the discussion of fig. 10E, optical cavity layer 1330 can be an air gap defined by spacers such as pillars, posts, or rails (see fig. 3B); a single transparent conductive or dielectric layer; a composite formed from a plurality of conductive or dielectric transparent layers; or a composite formed by an air gap in combination with one or more transparent layers.

FIG. 13C illustrates further formation or deposition of a conductor layer 1340 over the optical cavity layer 1330. Suitable materials for the conductor layer 1340 are discussed above with reference to the conductor layer 1050 of fig. 10D.

Referring to fig. 13D, the patterned or etched layers 1320, 1330, 1340 form an IMOD mask 300 pattern that is substantially similar to or covers the reflector 303 pattern. Patterning the layer stack defines a patterned conductor or front electrode that will also serve as the reflector 303 of the IMOD mask 300. Although formed on the back side of the substrate, reflector 303 is still forward (closer to the light-incident side) relative to the PV active layer yet to be formed, and thus reflector 303 is said to define the "front conductor" of the PV device.

FIG. 13E illustrates the result of depositing a thin film Photovoltaic (PV) active layer 1350, and then a post-conductor layer 1360, behind or opposite the interferometric mask 300. Suitable materials for the thin film PV active layer are discussed above with reference to fig. 10B, and typically the PV active material includes numerous types of photovoltaic semiconductive materials, such as amorphous silicon. Although not shown, a transparent conductor layer (TCO) such as ITO may be deposited prior to deposition of the PV active layer 1350 in order to improve electrical contact with the front conductor 303 and thus the collection efficiency of the PV device 1300E. The back conductor layer 1360 may include a metal conductive layer, and is typically formed to an opaque thickness.

In the embodiment of fig. 13A through 13E, the interferometric mask 300 of the PV device is formed on the optical structure prior to forming or depositing the PV active material 1350. In this embodiment, the photovoltaic device and the interferometric mask 300 are formed on the side of the optical substrate opposite the light incident or front side of the substrate. Therefore, the order of layer formation may be reversed from that of fig. 10A to 10G. Additional layers (not shown) may include a TCO located between the PV active layer 1350 and the substrate 1310 and an AR coating or hard film located on the front side of the substrate 1310.

FIG. 13F illustrates another embodiment of the present invention. FIG. 13F shows the absorber layer 1320 of FIG. 13A patterned to leave the patterned absorber 301 before forming the optical cavity layer 1370. An optical cavity layer 1370 is then deposited or formed over the patterned absorber 303. As described in the discussion of fig. 10E, the optical cavity layer 1370 can be an air gap defined by spacers such as posts, or rails (see fig. 3B); a single transparent conductive or dielectric layer; a composite formed from a plurality of conductive or dielectric transparent layers; or a composite formed by the combination of an air gap and one or more transparent layers. A layer of conductor material is deposited over the optical cavity layer 1370. The conductor layer may then be patterned to form the front electrode of the PV device 1300F that also serves as the patterned reflector 303 of the IMOD mask 300, while leaving the optical cavity layer 1370 unpatterned on the PV cell. Next, a PV active layer 1350 is formed over the IMOD mask 300 (which includes the front electrode) and a back electrode 1360 is formed over the PV active layer 1350.

The use of the blanket optical cavity layer 1370 in embodiments where light is transmitted through the substrate (as shown in figure 13F) may have several advantages. As mentioned above, Transparent Conductive Oxides (TCO) are typically used to improve the contact between the electrode and the photovoltaic material. In the embodiment of FIG. 13F, the optical cavity structure can include a TCO layer in contact with the front electrode formed by the reflector 303 or from a TCO layer in contact with the front electrode formed by the reflector 303.

Fig. 13G illustrates another embodiment in which the interferometric mask 300 is formed on a light incident side or front side of a transparent substrate 1310, while a front electrode 1390 and a Photovoltaic (PV) active layer 1350 are formed on the back side of the substrate 1310 opposite the light incident side or front side. In this embodiment, due to the thickness of the substrate 1310 between the reflective front electrode 1390 and the absorber 301, the front side IMOD mask 300 is required to include a separate reflector 303 on the front side of the substrate 1310 that is patterned to cover the reflective front electrode 1390 on the other side of the substrate 1310. In this case, the PV device 1300G may have a conventional construction on the back side of the substrate 1310 including a patterned front electrode 1390, TCO layer 1380, PV active layer 1350, and back electrode 1360 sequentially formed on the back surface of the transparent substrate 1310. The front side of the substrate 1310 includes a stack of IMOD masks 300 made up of a separate reflector 303, optical resonant cavity 302, and absorber 301 sequentially formed on the front side of the light transmissive substrate 1310. As with the illustrated embodiment, this IMOD stack would preferably be patterned to cover the precursor 1390 pattern. Since this IMOD mask has its own reflector 303 and absorber 301, it is electrically isolated from the PV active layer 1350 and thus can be separately interconnected to form an electrostatic MEMS IMOD. In this embodiment, the IMOD mask 300 will be able to open and close, as illustrated in fig. 3C and 3D. In this case, the optical resonant cavity 302 may comprise an air gap (340 in FIG. 3C) through which the movable electrode (303 in FIGS. 3C and 3D) can move. In this embodiment, dielectric and other layers, as well as support posts for spacing the movable electrode/reflector from the fixed electrode/absorber, may be formed in front of the substrate 1310 to implement the movable IMOD mask 300 on the light incident side of the substrate 1310, as will be appreciated by those skilled in the art.

Fig. 14A-14B illustrate an embodiment of integrating an IMOD mask with a PV device 1400A in which the photovoltaic material is a single crystal semiconductor substrate and/or a portion of an epitaxial layer formed on such a single crystal substrate. Fig. 14A depicts a Photovoltaic (PV) device 1400B that includes a back electrode 1410, a p-type silicon layer 1420, an n-type silicon layer 1430, a front conductor or electrode 1440, and an anti-reflective coating 1450. As previously mentioned, it is desirable to shield or minimize reflections from the front electrodes 1440 (which may be, for example, bus lines or grid lines of a PV array). Thus, the interferometric mask 300 may be formed on the light incident or front side of the electrode, as shown in FIG. 14B. This can be achieved in a manner similar to those described above, using similar materials. In one embodiment, the process may begin with the inclusion of a silicon substrate or single crystal silicon material with patterned conductors 303 (as in fig. 14B) and forming an IMOD mask 300 thereover. In another embodiment, the process may start with a silicon substrate or single crystal silicon material that includes an active region without a front conductor or electrode pattern, and form the precursor along with the optical resonant cavity 302 and absorber 301 as the reflector 303 using techniques similar to those discussed above with reference to figures 10A-10G and 11A-11D. As previously mentioned, the absorber 301 and the optical resonant cavity 302, or the absorber alone, may be patterned to substantially align with the front electrode/reflector 303 covering the reflector 303, as shown in fig. 14B. In another embodiment, the absorber 301 and optical resonant cavity 302, or the absorber alone, may be patterned to follow the pattern of the front electrode/reflector 303 but wider to cover a larger surface area than the reflector 303. As in fig. 11D and 13F, the optical cavity layer may be unpatterned or blanket over the PV cell, while front electrode/reflector 303 and absorber 301 are patterned. In yet another embodiment, the absorber 301, the optical cavity 302, and/or the front electrode/reflector 303 may be screen printed, in which case they may be formed and patterned simultaneously. The layers of the front electrode/reflector, the optical cavity and the absorber can be screen printed, either simultaneously or separately, in any grouping. In addition, some layers may be patterned by photolithography and etching, while other layers may be screen printed.

The foregoing embodiments teach that the IMOD mask configurations that can be used to interferometrically shield the front electrode of a PV device have a wide variety of configurations. For example, in addition to the thin film and crystalline silicon PV cell and transmissive substrate embodiments described above, an interferometer or IMOD mask may be used to mask reflections from the front electrode of the thin film interference enhanced photovoltaic cell or device.

Fig. 15 illustrates an embodiment of a PV device 1500 in which an interferometric mask 300 masks reflections from a reflector 303 that may serve as a front conductor or electrode of an interference enhanced cell formed on a suitable substrate 1510. In the illustrated embodiment, the conductor 303 is in electrical contact with the active layer 1540 via the TCO layer 1550. In other embodiments, the conductor 303 is in direct electrical contact with the active layer 1540, or is in electrical contact via other layers and materials not shown. Certain embodiments of the interferometric-tuned photovoltaic cell include a reflector 1520 and an optical resonant cavity 1530 disposed behind or opposite the light incident side of the PV active layer 1540. The PV active layer can include a thin film photovoltaic material, such as amorphous silicon, CIGS, or other thin semiconductor film photovoltaic material. The optical properties (dimensions and material properties) of the reflector 1520 and the optical resonant cavity 1530 are selected such that the reflections from the interfaces of the layered PV device 1500 coherently add to create an increased field in the PV active layer 1540 of the photovoltaic cell where the optical energy is converted to electrical energy. Such interference enhanced photovoltaic devices enhance absorption of optical energy in the active region of the interference photovoltaic cell and thus increase the efficiency of the device. In a variation of this embodiment, multiple optical resonant cavities may be employed to individually tune different wavelengths of light and maximize absorption in the PV active layer. The buried optical cavity and/or layers may comprise transparent conductive or dielectric materials, air gaps, or combinations thereof.

While the foregoing detailed description discloses several embodiments of the invention, it is to be understood that this disclosure is only illustrative and not limiting of the invention. It is to be understood that the specific configurations and operations disclosed may differ from those described above, and that the methods described herein may be used in contexts other than semiconductor device fabrication.

Claims (50)

1. A photovoltaic device defining a front side on which light is incident and a back side opposite the front side, the photovoltaic device comprising:

a photovoltaic active layer;

a conductor on the front side of the photovoltaic active layer; and

an interferometric mask patterned to cover the front side of the conductor.

2. The device of claim 1, wherein the interferometric mask is configured such that a color of light reflected from the front side of the interferometric mask substantially matches a color of the photovoltaic active layer visible in a region adjacent to the conductor.

3. The device of claim 1, wherein the interferometric mask is configured such that little or no incident visible light is reflected from the front side of the interferometric mask such that the interferometric mask appears black from a normal viewing angle.

4. The device of claim 1, wherein the interferometric mask is configured such that a reflectivity of the interferometric mask is less than 10%.

5. The device of claim 1, wherein the conductor comprises a bus connecting electrodes of a plurality of photovoltaic cells in an array.

6. The device of claim 1, wherein the conductor comprises an electrode in electrical contact with the photovoltaic active layer.

7. The device of claim 1, wherein the interferometric mask comprises an absorber over an optical resonant cavity over the conductor.

8. The device of claim 7, wherein the optical resonant cavity includes an air gap formed by posts separating the absorber from the conductor.

9. The apparatus of claim 8, wherein the air gap is at a height of about 450 fAnd 1600In the meantime.

10. The device of claim 7, wherein the optical resonant cavity comprises a layer of dielectric material.

11. The device of claim 10, wherein the dielectric material is about 300 a thickAnd 1000In the meantime.

12. The device of claim 10, wherein the dielectric layer has a refractive index between about 1 and 3.

13. The device of claim 10, wherein the dielectric layer is a blanket layer extending across the photovoltaic device.

14. The device of claim 7, further comprising a passivation layer over the absorber.

15. The device of claim 14, wherein the passivation layer comprises silicon dioxide.

16. The device of claim 1, wherein the photovoltaic active layer is selected from the group consisting of: single crystal silicon, amorphous silicon, germanium, group III-V semiconductors, copper indium gallium selenide, cadmium telluride, gallium arsenide, indium nitride, gallium nitride, boron arsenide, indium gallium nitride, and tandem multijunction photovoltaic materials.

17. The device of claim 1, wherein the photovoltaic active layer comprises a thin film photovoltaic material.

18. The device of claim 17, wherein the thin film comprises amorphous silicon.

19. The device of claim 17, wherein the thin film is formed over a backside of a transparent substrate, over the interferometric mask, and over the conductor.

20. The device of claim 19, wherein the conductor is in electrical contact with the photovoltaic material through a Transparent Conducting Oxide (TCO).

21. The device of claim 17, wherein the thin film is formed over a backside of a transparent substrate and over the conductor, and the interferometric mask is formed and patterned over the front side of the transparent substrate.

22. The device of claim 21, wherein the interferometric mask comprises an active MEMS device having a reflector on the front side of the transparent substrate.

23. The device of claim 1, wherein the photovoltaic active layer comprises an interference enhanced photovoltaic device.

24. The device of claim 1, wherein the interferometric mask comprises an active MEMS device.

25. A photovoltaic device defining a front side on which light is incident and a back side opposite the front side, the photovoltaic device comprising:

a photovoltaic material;

a conductor located in front of the photovoltaic material; and

an optical interference mask in front of the photovoltaic material and the conductor, wherein the mask comprises

A reflective surface in front of the photovoltaic material;

an optical resonant cavity in front of said reflective surface; and

an absorber located in front of said optical cavity,

wherein a visible color across the front side of the photovoltaic device including portions of the photovoltaic material and the metal conductor is substantially uniform.

26. The device of claim 25, wherein the optical resonant cavity comprises a composite of two or more of: an air gap, a transparent conductive layer, and a transparent dielectric layer.

27. The device of claim 25, wherein the optical interferometric mask is configured such that little or no incident visible light is reflected such that the photovoltaic device appears black.

28. The device of claim 27, wherein the optical interferometric mask is patterned to cover the metal conductor and expose portions of the photovoltaic material.

29. The device of claim 25, wherein the optical interferometric mask and one or more layers of the conductor are screen printed.

30. The apparatus of claim 25, wherein the conductor is transparent.

31. The device of claim 25, wherein a reflective surface is defined by the conductor.

32. A photovoltaic device, comprising:

means for generating an electrical current from incident light on an incident side of the means;

means for conducting the generated current; and

means for interference shielding the conducting means from the incident side of the photovoltaic device.

33. The device of claim 32, wherein the means for generating the electrical current comprises a semiconductor photovoltaically active material.

34. The device of claim 32, wherein the means for conducting comprises a reflective patterned front electrode in electrical contact with the means for generating electrical current.

35. The device of claim 32, wherein the means for interference shielding comprises a stack comprising an optical resonant cavity and an absorber located above the means for conducting, the optical resonant cavity and absorber configured to interferometrically reduce a reflectivity from the means for conducting.

36. A method of manufacturing a photovoltaic device comprising

Providing a photovoltaic active layer, a patterned front side conductor and a back side conductor to a photovoltaic generator;

forming a plurality of layers over a front side of the photovoltaic generator; and

one or more of the plurality of layers are patterned to define an interferometric modulator overlying the patterned front side conductor.

37. The method of claim 36, wherein forming the plurality of layers comprises forming an absorber and an optical resonant cavity configured to reflect visible light substantially matching a visible spectrum reflected by exposed portions of the photovoltaic active layer.

38. The method of claim 37, wherein the interferometric modulator is configured to appear black from the front side.

39. The method of claim 37, wherein forming the interferometric cavity includes forming an absorber and a dielectric layer.

40. The method of claim 39, wherein patterning comprises patterning the absorber and the dielectric layer.

41. The method of claim 39, wherein patterning includes patterning the absorber to follow a pattern of the patterned front side conductors and leave the dielectric layer as a blanket layer.

42. The method of claim 36, wherein patterning comprises forming the interferometric modulator coextensive with the front side conductor.

43. The method of claim 42, wherein providing the photovoltaic device includes patterning the front side conductor simultaneously with patterning one or more of the plurality of layers.

44. The method of claim 36, wherein forming and patterning the plurality of layers comprises screen printing the plurality of layers in a pattern that follows the patterned front side conductor.

45. The method of claim 37, wherein forming an optical resonant cavity comprises forming an air gap and a spacer.

46. A method of manufacturing a photovoltaic device having a front side on which light is incident and a back side opposite the front side, the method comprising forming an interferometric modulator configured to appear black over the front side of the photovoltaic device.

47. The method of claim 46, wherein the photovoltaic device comprises a front-side reflective conductor, and forming the interferometric modulator comprises forming an absorber, an optical resonant cavity, and a conductor, wherein the absorber and the optical resonant cavity are patterned to follow a pattern of the reflective conductor.

48. The method of claim 47, wherein forming the patterned absorber and optical resonant cavity comprises screen printing.

49. The method of claim 47, wherein the photovoltaic device is formed on a transparent substrate having opposing sides such that the front side reflective conductor and the interferometric modulator are formed on opposing sides of the transparent substrate.

50. The method of claim 46, wherein the photovoltaic device comprises a front-side reflective conductor, and forming the interferometric modulator comprises forming an absorber, an optical resonant cavity, and a conductor, wherein the absorber is patterned to follow a pattern of the reflective conductor.