1. Field of Invention
The present disclosure relates to photovoltaic devices and, more particularly, to photovoltaic devices produced by an electrochemical deposition process onto two or more electrodes, each including a contact pad and a number of parallel wires connected to the contact pad, the wires of the different electrodes being interdigitated.
2. Description of Related Art
Photovoltaic or solar devices may be used to convert light directly into electrical current. This conversion may be accomplished via the conjunction of n-type and p-type semiconducting materials that separate electron-hole pairs which are created when light is absorbed by the photovoltaic device.
Three generations of photovoltaic devices currently exist. First generation photovoltaic devices may have thicknesses in a range of from about one hundred (100) micrometers to hundreds (100s) of micrometers. First generation devices are generally thicker than subsequent generations because they are generally based on silicon, and the indirect bandgap of silicon may require thicknesses within this range for the effective capture of light. If these devices were much thinner, much of the light might simply pass through the device instead of being absorbed by the silicon material.
Second generation devices may incorporate thin films of direct bandgap semiconducting materials. Such materials may include cadmium telluride or copper indium gallium diselenide for the p-type material. This p-type material may be classified as an absorber and may constitute the majority of the photovoltaic device. Lower costs may be possible using thin films since thin film materials may be deposited using a variety of techniques and less material is required to effectively absorb incident light. On the other hand, decreased efficiency in light conversion may result when thin film devices are compared to crystalline silicon devices.
Third generation devices may include three-dimensional (3D) micro- or nano-scale structures (e.g., nano-wires and nano-rods in polymers) to improve their efficiency. Use of such third-generation devices is predicated on their having an even lower cost than second generation devices and/or higher efficiency.
In connection with the development of second and third generation photovoltaic devices, various geometries are either being used or considered. Such geometries may include a geometry pursuant to which electrical contacts for extracting charge carriers (holes and electrons) are located on opposing surfaces of the thin film.
In some cases, third generation devices may contain nanoparticles that are dispersed during fabrication, as opposed to being grown on the substrate of the device itself. A drawback to this dispersed configuration exists in that it may be a challenge to ensure uninterrupted connectivity of all constituent regions to an electrode. It may also be a challenge to connect said nanoparticles to the correct electrode.
These second and third generation geometries may have drawbacks in that the electrode on the side of the photovoltaic device that faces the sun may block some of the incoming light, thus adversely affecting the photovoltaic device's performance while also increasing its cost and processing complexity.
Advances have been made to address shortcomings associated with the blockage of incoming light caused by the front contacts (on the surface that faces the sun) in first generation devices. Devices that use interdigitated contacts on the back surface (surface not facing the sun) may eliminate light blockage caused by the front contacts. Silicon-based devices have been explored for more than thirty years. Such devices can use line or point contacts created through multiple lithographic patterning (masking) and deposition steps to create localized doping on the back surface of silicon wafers. The doped regions connect to metal busbars also located on the back surface for extraction of electrical current.
Sequential masking steps may also be used to create two interleaved arrays of n-type and p-type doped spots (point contacts) on the back surface of a silicon wafer, which may minimize recombination on the area that interfaces between metal and semiconductor.
Such back surface interdigitated contacts on silicon wafers may be optimized by spacing the lines on which the doped regions fall to a distance on the order of 50 micrometers to 100 micrometers, which is similar to the silicon semiconductor thickness. This length scale may be beneficial in light of sequential masking steps required to create interleaved doping and structures.
Analogous back-contact geometries for thin film devices with micrometer-scale thickness may require a contact (electrode) pitch that is at or below a few micrometers. Accordingly, a process that self-aligns the wires of the electrodes, e.g., by fabricating them simultaneously in a single lithographic patterning, may be preferable to one that requires multiple lithographic patternings. For example, a process has been described for silicon-based devices that uses localized etch-back through the n-region to the p-region and subsequent metal deposition onto both the remaining n-surface and the exposed p-surface with dimensions of tens and hundreds of micrometers. This process relies on controlled undercutting of the etched semiconductor to avoid shorting of metal depositing on the upper n-type surface and the recessed p-type surface. Accordingly, this process may be more difficult to implement on a large scale with thin film devices.
There is a need for thin film photovoltaic devices that incorporate back contacts and that eliminate the blockage of incoming light caused by the front contacts.
There is further need for photovoltaic devices with back contacts that can be fabricated with reduced costs when compared to those requiring multiple lithographic patternings.
The present disclosure addresses the foregoing deficiencies of the prior art by providing a three-dimensional thin film photovoltaic device with self-aligned back contacts that are used for carrier collection when the device is illuminated. The back contacts are interdigitated electrodes that are also used for fabrication of the device.
In accordance with one embodiment of the present disclosure, an electrodeposition method is provided for forming three dimensionally structured thin film photovoltaic devices. The method comprises the steps of providing at least two interdigitated electrodes on an insulating substrate, each of the at least two interdigitated electrodes including a plurality of interdigitated wires having pitches of less than ten micrometers. In a first step, the method comprises electrodepositing one or more thin films of one or more of a first semiconducting material onto a first interdigitated electrode, wherein the first semiconducting material is one of an n-type or p-type material. In a second step, the method comprises depositing one or more thin films of one or more of a second semiconducting material onto at least a second interdigitated electrode until the deposits on the first interdigitated electrode and the second interdigitated electrode impinge upon each other, wherein the second semiconducting material is the other of an n-type or p-type material. After fabrication of the photovoltaic device, at least two of said at least two interdigitated electrodes serve as the back contacts for carrier extraction when the device is in use.
In accordance with another embodiment of the present disclosure, an electrodeposition method is provided for forming a multijunction three dimensionally structured thin film photovoltaic device with self-aligned back contacts. The method for forming a multijunction device comprises providing at least two interdigitated electrodes on an insulating substrate, each of the at least two interdigitated electrodes including a plurality of interdigitated wires having pitches of less than ten micrometers, wherein the at least two interdigitated electrodes include a first interdigitated electrode and a second electrode. In a first step, the method comprises electrodepositing one or more thin films of one or more of a first semiconducting material onto the first interdigitated electrode without impingement upon any other of the at least two interdigitated electrode, the first semiconducting material being one of an n-type or p-type material.
In a second step, the method for forming a multijunction device comprises electrodepositing one or more thin films of one or more of a second semiconducting material onto at least said first interdigitated electrode but without impinging upon said second interdigitated electrode, the second semiconducting material being the other type of an n-type or p-type material. In a third step, the method comprises electrodepositing one or more thin films of one or more of a third semiconducting material onto either the first or second interdigitated electrode without impinging on the other of the first or second interdigitated electrode, the third semiconducting material being either the same type as the first semiconducting material if electrodeposited on the first interdigitated electrode, or the same type as the second semiconducting material if electrodeposited on the second interdigitated electrode, wherein the third semiconducting material is either an n-type or p-type material.
In a fourth step, the method for forming a multijunction device comprises depositing one or more thin films of one or more of a fourth semiconducting material onto one or more of the at least two interdigitated electrodes, wherein the depositing occurs at least until the thin films on the first interdigitated electrode and the second interdigitated electrodes impinge upon each other, wherein the fourth semiconducting material is the other of said either an n-type or p-type material electrodeposited in the third step. After fabrication of the multijunction photovoltaic device, at least two of said at least two interdigitated electrodes serve as the back contacts for carrier extraction when the device is in use.
In accordance with yet another embodiment of the present disclosure, a three dimensionally structured thin film photovoltaic device is provided with self-aligned back contacts that are formed by electrodeposition on interdigitated electrodes used in the device's manufacture. The device comprises an insulating substrate, and at least two interdigitated electrodes on the insulating substrate, the at least two interdigitated electrodes including a plurality of interdigitated wires having pitches of less than ten micrometers, wherein the at least two interdigitated electrodes include a first interdigitated electrode and a second interdigitated electrode. The device also comprises one or more electrodeposited thin film layers of one or more of a first semiconducting material on the first interdigitated electrode, wherein the first semiconducting material is either an n-type or p-type material. The device further comprises one or more deposited thin film layers of one or more of a second semiconducting material on the second interdigitated electrode, wherein the deposits on the first interdigitated electrode and the second interdigitated electrode impinge upon each other, wherein the second semiconducting material is the other of an n-type or p-type material. After fabrication, at least two of said at least two interdigitated electrodes are configured to serve as the back contacts for carrier extraction, when the device is in use.
In accordance with still another embodiment of the present disclosure, a three dimensionally structured thin film multijunction photovoltaic device is provided with self-aligned back contacts that are formed by electrodeposition on interdigitated electrodes used in the device's manufacture. The multijunction device comprises an insulating substrate, and at least two interdigitated electrodes on the insulating substrate, the at least two interdigitated electrodes including a plurality of interdigitated wires having pitches of less than ten micrometers. The at least two interdigitated electrodes include a first interdigitated electrode and a second interdigitated electrode. The device also comprises one or more electrodeposited thin film layers of one or more of a first semiconducting material on the first interdigitated electrode without impingement upon any of the other interdigitated electrodes, wherein the first semiconducting material is one of an n-type or p-type material.
The multijunction device also comprises one or more electrodeposited thin film layers of one or more of a second semiconducting material on at least said first interdigitated electrode but without impinging upon the second interdigitated electrode, wherein the second semiconducting material is the other of an n-type or p-type material. The multijunction device further comprises one or more electrodeposited thin film layers of one or more of a third semiconducting material on either the first or second interdigitated electrode without impinging upon the first and second interdigitated electrodes, the third type being either the same type as the first type if electrodeposited on the first interdigitated electrode or the same type as the second type if electrodeposited on the second interdigitated electrode, wherein the third semiconducting material is either an n-type material or a p-type material.
The multijunction device still further comprises one or more deposited layers of one or more of a fourth semiconducting material on one or more of the interdigitated electrodes such that the deposits on at least the first interdigitated electrode and the second interdigitated electrodes impinge upon each other, and wherein the fourth semiconducting material is the other of said either an n-type or p-type material as the third semiconducting material. After fabrication, at least two of said at least two interdigitated electrodes are configured to serve as the back contacts for carrier extraction when the device is in use.
These, as well as other objects, features and benefits will now become clear from a review of the following detailed description of illustrative embodiments and the accompanying drawings.
The present disclosure is directed to three dimensionally structured thin film photovoltaic devices with self-aligned back contacts. Fabrication of this photovoltaic device includes an electrodeposition process on at least one of two or more interdigitated electrodes.
The electrodeposition process described herein applies to existing technologies for production of interdigitated electrodes to create a new and unobvious self-aligned electrochemical deposition process.
Interdigitated damascene wires with a pitch below 100 nanometers (nm) are regularly fabricated in interdigitated comb-like electrode structures to study leakage current in microelectronics applications. It is also known to deposit micrometer pitch interdigitated electrodes on top of semiconductors to form metal-semiconductor-metal structures for photodetectors. However, in accordance with the present disclosure, such patterned electrically conducting wires on an insulating substrate may serve as the active electrodes for electrodeposition of zero or more metals on one or more electrodes and electrodeposition of one or more semiconductors on one or more electrodes for fabrication of the device. After fabrication and when the device is in use, these same electrodes can serve as the back contacts for carrier collection.
Referring now to
For purposes of the present disclosure, pitch is defined as the distance between the centers of two adjacent interdigitated wires. For example, in
Referring now to
As shown in diagram A of
The electrodeposition process may be adapted to produce a structure in which n-type and p-type materials in the immediately preceding paragraph are reversed, i.e., n-type is replaced by p-type and p-type is replaced by n-type. The electrodeposition process described in connection with
CdTe may be electrodeposited using a codeposition technique, resulting in near-stoichiometric CdTe. This CdTe deposition process may incorporate use of an electrolyte that is relatively concentrated in cadmium (Cd) and dilute in telluride (Te).
A deposition potential may be selected so that elemental Te deposits from a solution that has only Te salts, but elemental Cd does not deposit from a solution having only Cd salts. A range of deposition potentials is available so that whenever a Te atom deposits a Cd atom reacts with it as a result of the enthalpy of reaction of Cd and Te, thus creating a CdTe deposit. By using Te that is relatively dilute when compared to Cd, a well controlled composition can result.
Electrodeposition may be accomplished in a primary aqueous electrolyte, with constituents including the metal salt of the metal to be deposited. A primary electrolyte for the present electrodeposition process may have a concentration of 0.1 mol/L Cd+2, which may be found by adding 3(CdSO4).8H2O salts (99.999% by mass) to 18 megaohms (MΩ)cm water. The primary electrolyte may also be saturated with Te−4 by adding TeO2 (99.999% by mass) until a surplus of oxide powder is visible at the bottom of the deposition cell. The resulting electrolyte may contain about 0.1 mmol/L Te−4 based on the tellurium Pourbaix diagram and solution pH of 2.0, acquired by adding sulfuric acid.
Referring now to
Referring now to
Substrate 390 may be a planar or patterned substrate. If a planar substrate is used, any material suitable for the intended photovoltaic device may be used. For example, metal-coated oxidized silicon wafers may be used for the CdTe deposition process. Substrates with evaporated gold and iridium coatings may be used as well, and may include an underlying titanium adhesion layer.
Substrate 390 is made of an electrically insulating material, e.g., glass, one or more polymers, silicon wafers with an oxidized surface, or metal foil coated with an insulating layer. If substrate 390 is a patterned substrate, any insulating material suitable for the intended photovoltaic device may be used. For example, the patterned substrate may be obtained from thermally oxidized silicon wafers that were lithographically patterned with arrays of interdigitated electrodes. The electrodes may be gold or platinum, and may have heights in the range of 25 nm to 150 nm, with a 5 nm titanium adhesion layer. The area containing the interdigitated wires may be 5 mm by 5 mm, with their metal lines being 5 mm long and adjacent lines being alternately connected to one of two planar contact areas (contact pads).
Any array geometry suitable for the intended photovoltaic device may be used. For example, the array geometries may be classified as fine or intermediate. The fine pitch may have, e.g., 1.3 micrometer wide lines with 0.7 micrometer wide spaces between the lines. In other words, there may be a 2 micrometer pitch between adjacent lines and 4 micrometer pitch between the closest lines on the same electrode. The intermediate pitch may have 1.5 micrometer wide lines with 2.5 μm wide spaces between adjacent lines. As per the example, the pitch may be greater, or less than, twice the wire width.
In the case of either planar or patterned substrates, electroplaters tape may be used to mask the surface of substrate 390 while electrodeposition occurs. This masking may restrict the region over which deposition could occur on electrodes 305 and 310. Separate electrical connections may be made to the two interdigitated electrodes for patterned substrates. Their potentials may be independently controlled and associated deposition currents may be separately measured. Referring back to
Thin films material may be electrodeposited onto substrate 390 using the custom-made rotating electrode 330 that holds individual specimens, each substrate 390 being approximately 8 mm to 11 mm on a side. The substrates may be planar and unpatterned or, alternatively, patterned. For purposes of the present disclosure, thin film deposition describes a technique pursuant to which a film is deposited which has a thickness in the range of about 1 nm to tens (10s) of micrometers. Such thin film techniques are known in the art.
Depositions may be conducted with the substrate 390 rotating at 60 revolutions per minute (rpm) to define hydrodynamics. The electrolyte temperature may be held at 50° C. to 90° C. Substrate 390 may be inserted into the electrolyte with a droplet of 18 MΩcm water on the surfaces of substrate 390 to reduce the risk of contamination during immersion through the electrolyte/air interface. Potentials may be applied after several seconds of rotation to allow the resistive water to be displaced from the substrate prior to deposition.
For deposition on planar substrates, the impact of potential on the electrical properties of electrodeposited CdTe has been noted previously. That is, n-type material may be deposited at more negative potentials (nearer the reversible potential for Cd electrodeposition, i.e., the highest potential for which Cd electrodeposits in the particular electrolyte and conditions) and p-type material may be deposited at more positive potentials (nearer the reversible potential for Te electrodeposition).
It is significant that deposition characteristics are potential dependent. Also as-deposited n-type CdTe materials type-convert to p-type CdTe after annealing. Moreover, devices using CdTe materials deposited at more positive potentials may exhibit lower quantum efficiencies. It should also be noted that low concentrations of elements such as copper or indium can be added to the electrolyte to create doped CdTe semiconductors.
Referring now to
For patterned substrates, depositions on patterned substrates may be conducted using In-doped electrolyte of nominal concentration 0.4 μmol/L In−3. Indium may create n-type CdTe if it displaces Cd on a Cd sublattice site. It is also possible that Indium can be added to other acid electrolytes to create In-doped CdTe.
Photovoltaic devices require differentiation of the two or more interdigitated electrodes in order to separate electron/hole pairs formed by absorption of light. If the CdTe type varies in a step-wise fashion from p→n with increasing potential, then this differentiation can be accomplished through the application of different potentials to the interdigitated electrodes during electrodeposition to surround one electrode with n-type material and the other with p-type semiconductor. Formation of such internal homojunctions during CdTe electrodeposition has been explored extensively in planar geometries. If the type varies from p++→p+→p→n→n+→n++ with increasing potential then systematic variation of the potentials on the two electrodes can create more complex structures. The n-type and p-type materials can be deposited simultaneously from a single electrolyte by applying appropriate potential histories to the two electrodes. If deposition on both electrodes can be controlled arbitrarily then depositions can also be carried out sequentially in two or more separate electrolytes.
The process for electrodeposition on interdigitated electrodes may also be used for heterojunction devices. The heterojunction device creation process could be a two-step process that deposits two dissimilar or different semiconducting materials, e.g., CdS and CdTe. For purposes of the present disclosure, dissimilar or different materials are those having different chemical compositions. However, materials such as n-type CdTe and p-type CdTe are not considered dissimilar or different. Fabrication of heterojunction devices could require a variation on the process disclosed for homojunction devices. More particularly, n-type CdS could be electrodeposited on one electrode in one electrolyte. P-type CdTe could then be deposited on one or both electrodes in a second electrolyte or uniformly across the entire specimen surface including on both electrodes through any thin film deposition process including, but not limited to sputter deposition, close-cell sublimation, evaporation or chemical vapor deposition.
Point contacts, rather than line contacts may also be accessible with additional lithography prior to electrodeposition of the photovoltaic materials, e.g., by masking the electrodes with insulating lines orthogonal to the metallization lines.
The process for electrodeposition on interdigitated electrodes could be used to create multijunction devices, in addition to homojunction and heterojunction devices.
Referring now to
Referring now to
The photovoltaic device may include more than two electrodes. Referring now to
During semiconductor deposition, the multijunction device may be formed by depositing four materials 485, 481, 482, 483. Referring now to
Referring now to
During fabrication of the photovoltaic device, independent control of CdTe deposition on the electrodes 520 and 540 is demonstrated in this figure which illustrates a substrate 540 in planview after 15 minutes (min) of deposition with one gold (Au) electrode 510 held at −1.0 Vss and the other electrode 540 held at −0.2 Vss. One set of alternating wires in specimen 510 is wider (and thicker) due to CdTe deposition. Deposition is only evident on the electrode held at the more negative potential which falls within the range of conditions for CdTe codeposition.
Referring now to
Referring now to
The electrodes of
Referring now to
As per
Referring now to
The contact metallizations for the n-type and p-type semiconductors may be differentiated through the deposition of 90 nm of indium (In) onto one electrode prior to CdTe deposition. Indium deposition may be conducted in an indium-sulfate containing electrolyte of pH 2 obtained through additions of sulfuric acid to 18MΩcm water: electrode potentials were −1.0 V and −0.1 V for the plated and unplated electrodes, respectively. An intermediate dip between the In and CdTe depositions in 18 MΩcm water of pH 2 (also through addition of sulfuric acid) may be used to minimize cross-contamination between the In and CdTe. The more negative potential may be applied to the same electrode for both the In and CdTe depositions, placing the n-type CdTe over the In.
The photovoltaic devices that resulted from the process using electrodeposition on interdigitated electrodes showed systematic variations in performance. In interpreting device performance, the planar films on both Au and Ir were considered both as-deposited and after annealing. Energy dispersive x-ray spectroscopy measurements obtained from scanning electron microscope (SEM) images of planar deposits indicate the thin film specimens are essentially-stoichiometric CdTe. Measurements conducted on individual wires of a device with intermediate pitch Au electrodes (deposition parameters detailed in Table I) also indicate near-stoichiometric CdTe on both electrodes. Annealing of CdTe on Au substrates led to substantial interdiffusion of the Au and CdTe. This could eliminate the incorporated p-n junction on the patterned specimens with Au electrodes and other materials, monolithic or composite, may be considered as more thermally stable or otherwise more desirable electrodes.
The dielectric function for as-deposited and annealed (at 300° C. for 20 minutes) planar CdTe films was determined by variable angle spectroscopic ellipsometry. A multisample analysis was performed with two films deposited for 30 min and 60 min in the primary electrolyte at −0.8 V and 50° C. and specimen rotation rate of 60 rpm with resulting film thicknesses of approximately 120 nm and 230 nm.
The dielectric function for the CdTe bulk was determined by a wavelength fit of the imaginary part of the dielectric function ∈=∈1∈2 with the real part ∈1 derived from a Kramers-Kronig transform based on the numerical integration of ∈2. Referring now to
Referring now to
X-ray diffraction results for CdTe films studied in a θ-2θ geometry exhibit narrowing and a shift of the diffraction peaks of the as-deposited CdTe upon annealing. The narrowing in particular is consistent with the material improvements suggested by the ellipsometric data.
Referring now to
Measurements were taken for the photovoltaic devices that were fabricated through electrodeposition on interdigitated electrodes. Performance of these photovoltaic devices was measured in terms of external quantum efficiency (EQE). EQE may be defined as the ratio of the number of charge carriers collected by the photovoltaic to the number of photons of a given energy shining on the photovoltaic device from outside.
When sunlight illuminates a photovoltaic device, the photons of light are absorbed by the semiconductor(s) of the photovoltaic device. Negatively charged electrons are moved from the valence band of the semiconductor(s) into the conduction band. Contact between thin layers of n-type and p-type semiconductors and their respective contact with different electrodes encourages motion of the negatively charged electrons and positively charged holes toward different electrodes. The photovoltaic device thus converts the solar energy into usable electricity.
In the fabricated devices, charge carrier extraction is accomplished by the same electrodes that were used for device fabrication. Electrons and holes are extracted at different electrodes.
External quantum efficiencies (EQE) in the range of 300 nm to 1100 nm were determined by illumination of a 2 mm diameter region toward the center of the fabricated devices. The spectral response SR(λ), in amps/watt, was obtained from the ratio of the sample photocurrent to that of a NIST-traceable, calibrated Si photo diode under equivalent lighting, multiplied by the known response, in amps/watt, of the photodiode. External quantum efficiencies as a function of wavelength were then calculated using EQE=(hc/qλ)SR(λ), where h is Planck's constant, c is the speed of light in vacuum, q is the elementary charge and λ is the wavelength.
Referring now to
Data for the first 5000 seconds of CdTe deposition on the intermediate pitch device with two Au electrodes is shown in
As determined by cross-section examination, and indicated in Table I, the different deposition rates in the earlier times of the 5000 seconds resulted in different CdTe thicknesses on the two electrodes of the two fine pitch devices.
Unsurprisingly, all four devices exhibit low efficiencies in the as-deposited state, although the devices with thinner CdTe exhibit broader spectral responses. The low values may be due to the fact that electrodeposited CdTe is typically annealed, often in the presence of compounds such as CdCl2, to improve its properties. Because there was a substantial variation in the maximum efficiencies of intermediate pitch specimens as a function of position on the device, the maximum values of efficiencies for the specimens are not deemed to be significant. Also, because no antireflection coating was used, the front surface reflectivity of the films represents a significant loss.
The optical response of a back contact photovoltaic cell is a complex interplay between the optical characteristics of the film and the electrical characteristics. The film properties determine the absorption depth and front surface reflectivity. Electrical characteristics include interface recombination velocities and minority carrier diffusion lengths. However, the gross characteristics of the EQE curves in
Such interpretations would be consistent with earlier reports of efficiency in electrochemically deposited planar devices. These reports show that EQE peaks at less than 10% and 2% for 1 μm thick CdTe electrodeposited on CdS at potentials 125 mV and 250 mV more positive than the Cd reversible potential, respectively. For the measured Cd reversible potential of approximately −1.07 Vss, the potential histories summarized in Table I involve values as much as 350 mV positive of the Cd reversible value, and the majority of deposition is between 100 mV and 200 mV positive, even without correcting for resistive voltage drop through the films during deposition.
The efficiencies and general spectral responses in
Because improved microstructure was observed through spectroscopic ellipsometry and X-ray diffraction upon annealing, one could anticipate significant improvement in device performance following thermal treatment. For the homojunction devices fabricated, the benefits of microstructural changes obtained through annealing may be offset by type-conversion of part or all of the deposit as well as diffusion from the gold contacts, where applicable. Deposition of different material(s) on one or both of the electrodes might enable improvement through annealing by differential doping around the contacts as well as improve the electrical properties of the contacts. The contact(s) may also be capped with conducting oxide or nitride (or such a coating may be grown through reaction of the contact) to decrease recombination and/or act as a diffusion barrier if their presence does not degrade the deposition process.
In accordance with the present disclosure, both homojunction and heterojunction photovoltaic devices may be created through electrodeposition on interdigitated electrodes. Such photovoltaic devices can take many forms. However, all of these devices share a common attribute: the interdigitated electrodes may be used both for deposition of one or more semiconductors and as backside contacts for carrier collection from the photovoltaic devices.
The versatility of the electrodeposition process and back contact geometry is evident, including control of materials properties through applied potential in one or more electrolytes.
As described herein, a single lithographic patterning procedure for fabricating micrometer scale, interdigitated back contact devices may be extrapolated from demonstrated CdTe homojunction devices to heterojunction-based devices containing a broad range of materials. The use of lithography to define the geometry also enables a systematic transition from second-generation planar, thin film with contact geometries to third generation geometries with nanostructuring.
While the specification describes particular embodiments of the present invention, those of ordinary skill can devise variations of the present invention without departing from the inventive concept.
The subject matter of this patent application was invented by employees of the United States Government. Accordingly, the United States Government may manufacture and use the invention for governmental purposes without the payment of any royalties.