High efficiency photovoltaic cells

Abstract

Novel structures of photovoltaic cells (also called as solar cells) are provided. The cells are based on nanoparticles or nanometer-scaled wires, tubes, and/or rods, which are made of electrical materials covering semiconductors, insulators, and also metallic in structure. These photovoltaic cells have large power generation capability per unit physical area over the conventional cells. These cells will have enormous applications such as in space, commercial, residential and industrial applications.

Claims

1. A photovoltaic cell comprising: a substrate with three-dimensional protrusions, wherein the cross-sectional shape of the three-dimensional protrusions is cylindrical; a first electrode disposed on the substrate; wherein the first electrode coating the three-dimensional protrusions and wherein the first electrode conforms to the contour of the three-dimensional protrusions; an absorption layer disposed on the first electrode; and a second electrode disposed on the absorption layer, wherein the absorption layer comprises: a layer of a plurality of nanoparticles, wherein the nanoparticles are semiconductor of p- or n-type; and wherein the layer of a plurality of nanoparticles is disposed on the first electrode; a layer of continuous electronic material disposed upon the layer of the plurality of nanoparticles and electrically connected to the first electrode or the second electrode, wherein the layer of continuous electronic material is a semiconductor of the opposite conductivity type as the layer of a plurality of nanoparticles; wherein the layer of a plurality of nanoparticles and the layer of continuous electronic material forming cylindrical shaped electrical junctions.

2. The photovoltaic cell of claim 1, wherein the layer of a plurality of nanoparticles are stacked into more than one layer.

3. The photovoltaic cell of claim 1, wherein the layer of a plurality of nanoparticles is of different material or different size.

4. The photovoltaic cell of claim 2, wherein each layer of a plurality of nanoparticles comprises nanoparticles of a different material or different size from at least one other of the layers of nanoparticles.

5. The photovoltaic cell of claim 1, wherein the nanoparticles are rods, tubes, wires, or spheres.

6. The photovoltaic cell of claim 1, wherein the layer of a plurality of nanoparticles are comprised of material selected from the group consisting of Si, Ge, InP, GaAs, CdSe, CdS, ZnO, ZnTe, ZnCdTe, CuInSe, CuSe, InGaAs, and any combination thereof.

7. A photovoltaic cell comprising: a substrate with three-dimensional protrusions, wherein the cross-sectional shape of the three-dimensional protrusions is cylindrical; a first electrode disposed on the substrate; wherein the first electrode coating the three-dimensional protrusions and wherein the first electrode conforms to the contour of the three-dimensional protrusions; an absorption layer disposed on the first electrode; and a second electrode disposed on the absorption layer, wherein the absorption layer comprises: a layer of a plurality of nanoparticles, wherein the nanoparticles are semiconductor of p- or n-type; a layer of first continuous electronic material disposed upon the layer of the plurality of nanoparticles and electrically connected to the second electrode; and a layer of second continuous electronic material disposed and electrically connected to the first electrode, wherein the layer of plurality of nanoparticles is disposed on the layer of second continuous electronic material; wherein the layer of a plurality of nanoparticles and the layer of second continuous electronic material forming cylindrical shaped electrical junctions; wherein the layer of first continuous electronic material is a semiconductor of p- or n-type, and wherein the layer of second continuous electronic material is a semiconductor of the opposite conductivity type as the layer of first continuous electronic material.

8. The photovoltaic cell of claim 7, wherein the layer of a plurality of nanoparticles are stacked into more than one layer.

9. The photovoltaic cell of claim 7, wherein the layer of a plurality of nanoparticles is of different material or different size.

10. The photovoltaic cell of claim 8, wherein each layer of a plurality of nanoparticles comprises nanoparticles of a different material or different size from at least one other of the layers of nanoparticles.

11. The photovoltaic cell of claim 7, wherein the nanoparticles are rods, tubes, wires, or spheres.

12. The photovoltaic cell of claim 7, wherein the layer of a plurality of nanoparticles are comprised of material selected from the group consisting of Si, Ge, InP, GaAs, CdSe, CdS, ZnO, ZnTe, ZnCdTe, CuInSe, CuSe, InGaAs, and any combination thereof.

13. A photovoltaic cell comprising: a substrate with three-dimensional protrusions, wherein the cross-sectional shape of the three-dimensional protrusions is cylindrical; a first electrode disposed on the substrate; wherein the first electrode coating the three-dimensional protrusions and wherein the first electrode conforms to the contour of the three-dimensional protrusions; an absorption layer disposed on the first electrode; and a second electrode disposed on the absorption layer, wherein the absorption layer comprises: a layer of first continuous electronic material disposed upon a layer of second continuous electronic material, wherein the layer of second continuous electronic material is disposed upon and electrically connected to the first electrode; wherein the layer of a first continuous electronic material and the layer of second continuous electronic material forming cylindrical shaped electrical junctions; and a layer of a plurality of nanoparticles disposed upon the layer of first continuous electronic material, wherein the layer of first continuous electronic material is a semiconductor of p- or n-type; wherein the nanoparticles are semiconductor of p- or n-type; and wherein the layer of second continuous electronic material is a semiconductor of the opposite conductivity type as the nanoparticles.

14. The photovoltaic cell of claim 13, wherein the layer of a plurality of nanoparticles are stacked into more than one layer.

15. The photovoltaic cell of claim 13, wherein the layer of a plurality of nanoparticles is of different material or different size.

16. The photovoltaic cell of claim 13, wherein each layer of a plurality of nanoparticles comprises nanoparticles of a different material or different size from at least one other of the layers of nanoparticles.

17. The photovoltaic cell of claim 13, wherein the nanoparticles are rods, tubes, wires, or spheres.

18. The photovoltaic cell of claim 13, wherein the layer of a plurality of nanoparticles are comprised of material selected from the group consisting of Si, Ge, InP, GaAs, CdSe, CdS, ZnO, ZnTe, ZnCdTe, CuInSe, CuSe, InGaAs, and any combination.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be explained in more detail in conjunction with the appended drawings wherein:

(2) FIG. 1A is the schematic showing the cross-sectional view of a conventional photovoltaic cell structure. This is the explanatory diagram showing the prior-art of today's photovoltaic cell. FIG. 1B shows the light intensity behavior inside prior-art semiconductor materials.

(3) FIG. 2A is the schematic showing the nanoparticle structures which illustrate the benefits of achieving a significantly high ratio of surface area to volume used in the simulation. FIG. 2B is the simulation results, showing the ratio of the surface area T to the volume A as a function of diameter of the nanoparticle d with the gap between the particles gas the parameter.

(4) FIGS. 3A and 3B are the schematics showing the cross-sectional views of a photovoltaic cell structure comprising the nanoparticles in the first embodiment, in accordance with the present invention.

(5) FIGS. 4A, 4B, and 4C are the schematics showing the cross-sectional views of photovoltaic cell structures comprising nanoparticles in the second embodiment, in accordance with the present invention.

(6) FIGS. 5A and 58 are the schematics showing the cross-sectional views of a photovoltaic cell structures comprising layers of nanoparticles of different sizes and types in the third embodiment, in accordance with the present invention.

(7) FIG. 6 is the schematic showing the cross-sectional view of a photovoltaic cell structure based on the nanoparticles layer and the cylindrical structure, in the fourth embodiment, in accordance with the present invention.

(8) FIG. 7 is the schematic showing the cross-sectional view of a photovoltaic cell structure based on the nano-scaled cylindrical blocks, in the fifth embodiment, in accordance with the present invention.

(9) FIG. 8 is the schematic showing the cross-sectional view of a photovoltaic cell structure based on the nano-scaled blocks embedded into the polymer, in the sixth embodiment, in accordance with the present invention.

(10) FIGS. 9A, 9B, 9C, and 9D are the schematics showing the fabrication process flow for flexible photovoltaic cells comprising a nanoparticle layer as the absorption layer, in the seventh embodiment, in accordance with the present invention.

(11) FIGS. 10A, 10B, 10C, and 10D are the schematics showing an alternate fabrication process flow for flexible photovoltaic cells comprising nanoparticles embedded into the polymer layer, in the eighth embodiment, in accordance with the present invention.

(12) FIGS. 11A, 11B, 11C, 11D, and 11E are the schematics showing an alternate fabrication process flow for photovoltaic cells comprising nano-scaled wires/blocks formed on the dielectric or semiconductor substrate, in the ninth embodiment, in accordance with the present invention.

(13) FIGS. 12A and 12B are the schematics showing the formation of the semiconductor-metal nanoparticles, as required by FIG. 11 for fabricating the photovoltaic cell.

DETAILED DESCRIPTION

(14) According to the present invention it is our object to provide several photovoltaic cell structures that increase the surface area, which would increase the junction area, and also cover a wide range of the solar spectrum in order to increase conversion efficiency to as high as >60%. Before proceeding to give the detailed explanation of the photovoltaic cell structures and their manufacturing, simulation results are given to show the benefits of increasing the surface area and using the nanoparticles in the photovoltaic cell.

(15) FIGS. 2A and 21 are the schematics representing the layer 202 formed with the nanoparticles. The layer 202 represents the absorption layer in the photovoltaic cell. FIG. 2B shows the simulation results as function of the nanoparticle diameter d with gap g between two nanoparticles as the parameter in FIG. 2A, nn number of nanoparticles are arranged in aa sized layers with thickness t. T/A is the ratio of the surface area of the total nanoparticles T to the volume (aat=A). It is assumed that if we could make the nn number of nanoparticles 204 on the aa-area surface. Increase of the ratio indicates the increasing increment of the surface area Tin the proposed cell, as compared to the conventional photovoltaic cell, which is usually flat. As depicted in FIG. 2B, by reducing the gap g and the nanoparticle diameter d, the ratio increases significantly. For example, if the particle gap g is kept to 5 nm and the particle diameter d is kept to 5 nm, over 750 times the surface area can be achieved as compared to a conventional 5 cm5 cm photovoltaic cell.

(16) According to the preferred embodiment illustrated in FIGS. 3A and 3B, a photovoltaic cell comprising a nanoparticle based layer 301 acts as the absorption layer, sandwiched by top metal contact 303a and bottom metal contact 303b, formed on the supporting substrate 300. The nanoparticles 302 can be formed as the layer (not shown here) acting as the absorption layer. The nanoparticles 302 can be embedded into the electronic material 304, creating electrical conduction. The electronic material 304 can be semiconductor material or conductive polymer material, which may create the junction (n or p type junction) with the nanoparticles 302. A single or plurality of layers may be require to make the junction (not shown here). The electronic material 304 can be a separate material or electronic materials of p or n type. The electronic material 304 and the supporting substrate 300 are further electrically connected to electrodes 303a and 303b, respectively. The electrodes 303a and 303b are intended to serve as common electrodes which connect all nanoparticles 302. The electrode 303a is provided for the electronic material 304 or junction. The electrode 303a can be transparent (not shown here) and can be formed on the electronic material 304 or junction. The interface between the nanoparticle 302 and the electronic material (or junction) 304 form pn- or Schottky junctions where built-in potential for both electrons and holes is generated. The nanoparticles could be made of any kind of semiconductor material of a few nanometers in size, which could create the quantum confinement effect. Absorption of a broad range of the solar spectrum is possible by utilizing different sizes and different semiconductor nanoparticles. Substrate 300 could be semiconductor, glass, or polymer.

(17) According to this invention, alternatively the nanoparticle based layer 301 can be formed various ways as shown in FIGS. 4A, 4B, and 4C. As shown, the nanoparticle based layer 401 (401a, 401b, and 401c) acting as the absorption layer, can be formed by stacking nanoparticles 402 which are either of same size (402a), different size (402b), or different type (402c), Alternatively, the nanoparticles 402 (402a, 402b, and 402c) can be embedded into the electronic conducting material (not shown here). In way of an example not way of limitation, the nanoparticles 402 can be made of semiconductor material (n- or p-type) and the electric conduction material (not shown here) that is on or surrounds the nanoparticles 402 can be made of p-type semiconductor. Incident light 406 (FIG. 4C) enters the photovoltaic cell through either the electrode 403a or on the material or junction substrate 400. (In FIG. 4C, the incident light 406 enters the photovoltaic cell through the electrode 403a). The incident light 406 travels through the nanoparticle based layer 401, and the substrate 400. The light absorbed by both nanoparticles 402 and the electronic material (not shown here) generates numerous electrons (not shown here). Each nanoparticle 402 helps form the junction all over the surface of the electronic material (not shown here), and helps to collect the carriers without allowing recombination. Utilizing the nanoparticles 402 helps to collect the carriers with less or even no recombination by increasing the junction area. It should be pointed out that electrons are apparently generated all over the region along the thickness of the electric material and the nanoparticles 402. It also should be pointed out that holes are apparently generated all over the region along the thickness of the absorption layer 401.

(18) Unlike a conventional solar cell, the solar cells shown in FIGS. 4A, 4B, and 4C have junctions all over the nanoparticles 402, which create an equivalent to multiple junctions across the thickness of the absorption layer 401. Increasing the thickness would help to absorb photon flux perpendicular to the front contact. As the particle size is nano-scaled, absorption of a broad range of the spectrum can be possible and almost all carriers can be collected, as the junctions are formed a few nanometers apart. It is apparent that utilizing the solar cell shown in FIGS. 3 and 4 can (i) reduce the recombination, (ii) absorb all photo flux, and (iii) cover a broad range of the spectrum, thereby increasing the conversion efficiency.

(19) According to the preferred embodiment illustrated in FIGS. 5A and 5B, a photovoltaic cell comprising a plurality of absorption layers 501 based on nanoparticles of different types 508, 510, and 512 are formed on the bottom contact 503b which is on the substrate 500. The only difference here, when compared to FIGS. 3 and 4, is that the absorption layer 501 consists of multiple layers of nanoparticles of different type and different sizes 508, 510, 512. Similar to FIGS. 3 and 4, the surface area of the junction for receiving light 506 is also increased which causes a reduction of the photogenerated carrier recombination and the absorption of all photo-flux incident on the surface, thereby increasing the conversion efficiency. Note here that by utilizing multiple layers of nanoparticles of different type and sizes, absorption of the full solar spectrum can be possible and, ideally, the conversion efficiency can be increased to 100%.

(20) Apparent advantages of this invention over conventional photovoltaic cells are directly associated with the fact that, unlike conventional photovoltaic cells, multiple discrete junctions are created for collecting all photogenerated carriers created in the absorption layer 501, regardless of where they are generated. According to this invention, recombination can be eliminated (ideally) and all photon flux can be absorbed (ideally), and the conversion efficiency can be 100% and still >50% when using Si. Conventionally, as explained in the description of the prior art shown in FIG. 1, a conventional photovoltaic cell, where electrical-junctions are perpendicular to the direction to which incident light travels, the photogenerated carriers generated in the region far away from electrical-junctions need to diffuse much longer distances (diffusion-length) than those photogenerated carriers generated near the junctions, thus they have a greater chance to recombine without contributing to photovoltaic effects. Therefore, in this invention, PCCE is expected to be much higher than that of conventional photovoltaic cells. In addition, it is evident that the total effective area that contributes to the photovoltaic effect in this invention can be increased significantly by a few orders (>3000) considering a 5 nm diameter with a gap of 0 nm for a 5 cm5 cm size cell.

(21) According to this invention, in way of an example not way of limitation, the supporting substrate 500 can be ceramics, glass, polymer or any kind of semiconductor on which transparent or nontransparent metal contact 503b is made. Alternatively, supporting substrate 500 can be metal which also acts the metal contact. For this case, copper, stainless steel, Aluminum, or alloyed metal can be used. According to this invention, the nanoparticles 508, 510, 512 can be any kind of semiconductor or compound semiconductors, having absorption capabilities in the desired spectrum region. By utilizing the quantum confinement effect, which is dependent on the size of the nanoparticle, the absorption range can be extended in the blue and red-shift of their parent bulk type materials. For nanoparticles, Si, Ge, InP, GaAs, CdSe, CdS, ZnO, ZnTe, ZnCdTe, CuInSe, CuSe, InGaAs, etc. can be used.

(22) According to this invention, in a way of an example not way of limitation, the nanoparticles 508, 510, 512 can be stacked to form the absorption layer 501. Alternatively, the electronic conduction material can be used to embed the nanoparticles 508, 510, 512. The electrical conduction material can be the sol-gel layer or any conductive polymer. The top metal contact 503a can be transparent or non-transparent metal. Indium-tin-oxide (ITO) can be used as the transparent metal contact. Alternatively, the electrical conduction layer can be formed onto the absorption layer 501 to create the junction.

(23) In an alternative preferred embodiment shown in FIG. 6, photovoltaic cell comprises a substrate 600 with three-dimensional protrusions wherein the cross-sectional shape of the three-dimensional protrusions is cylindrical, absorption layer 601 based on the nanoparticles 602, electrical conduction layer 604, and top and bottom metal contacts 603a and 503h, respectively. The supporting substrate 600 can be flexible or rigid substrate formed by molding, casting, or etching. The substrate 600 can be polymer, semiconductor or ceramic, or glass type material. Alternatively, supporting substrate 600 can be metal, which can also work as the bottom contact (not shown here). The nanoparticles 602 and the electrical conduction material 604 form the absorption layer 601. The incident beam 606 is absorbed by both the electrical conduction material 604 and the nanoparticles 602, which generate the electrons (and holes), which are in turn collected by the metal contacts 603a and 603b. The junction created by the electrical conduction material 604 and nanoparticles 602 helps sweep away the generated carriers to the contacts 603a and 603b. The electronic material 604 is further electrically connected to electrodes 603a and 603b, which are intended to serve as common electrodes that connect all cylindrical shaped electrical junctions. The electrode 603a is on the electronic material 604. The interface between the nanoparticles 602 and the electronic material 604 form pn- or Schottky junctions, which can be assumed to be multiple discrete junctions inside the conduction material 604.

(24) Photogenerated electrons in the electronic material 604, made of p- and n-type semiconductor or conductive polymer, then diffuse toward the junction created by conduction material 604 and nanoparticles 602. At the junctions, the diffused electrons are swept away by built-in potential, thus photovoltaic effects set in. Common advantages already described for the photovoltaic cells in FIGS. 3, 4, and 5, can be achieved in this embodiment as well. The only differences in FIG. 6 are that the supporting substrate 600 shape is cylindrical and single or multiple layered nanoparticles are used to increase the combined surface to volume ratio significantly.

(25) According to this invention, in way of an example not way of limitation, the supporting substrate 600 can be semiconductors such as Ge, GaAs, GaN, InP, GaN, CdTe, or ZnO or polymer or metal.

(26) In the preferred embodiment shown in FIG. 7, a photovoltaic cell comprises a plurality of nanometer(s) scaled cylinders 714 which are electrically connected to a substrate 700. The nano-meter(s) scaled cylinders 714 are surrounded by an electronic material 716, having metallic electrical conduction and forming the junction in the interface of 716 and 714. The electronic material 716 and the supporting substrate 700 are further electrically connected to electrodes 703a and 703b. The electronic conduction material 716, used to make the junction with nano-meter (s) scaled rods/wires 714, is electrically isolated with the bottom contact 703b by dielectric 718. The planarization dielectric (polymer) 720 is on which the metal electrical contact 703a is formed. The electrode 703a is intended to serve as a common electrode that connects all rods 714. The electrode 703a is provided for the electronic material 716. The interface between the nanometer(s)-scale rods 714 and the electronic material 716 form pn- or Schottky junctions, thus there are pn- or Schottky junctions outside of the nanometer(s)-scale rods 714.

(27) In an alternative preferred embodiment shown in FIG. 8, a photovoltaic cell comprises a plurality of nanometer(s)-scaled rods (or wires) 822 embedded into the electrical conduction material 804 acting as the absorption layer 801, which is electrically connected to a substrate 800. The micrometer(s) or nanometer(s)-scaled rods (or cylinders) 822 are surrounded by an electronic material 804 having electrical conduction. The electronic material 804 can be a separate material in which nanometer-scaled rods or wires 822 are embedded. The electronic material 804 and the supporting substrate 800 are further electrically connected to electrode 803a on the non-substrate side and electrode 803b on the substrate side. The interface between the nanometer(s)-scale rods 822 and the electronic material 804 form junctions, thus creating built-in-potential for collecting photogenerated carriers and transferring them to the electrodes. The main difference between the photovoltaic cell shown in FIG. 8 and others of FIGS. 3, 4, 5, and 6, is that the nanometer(s) scaled rods or wires 822 are separately synthesized and are embedded into the electronic material 804 formed on the supporting substrate 800. For example, the nanorods or wires 822 can be semiconductors like, Si, Ge, InP, GaAs, Cds, Cdse, CdTe, ZnO, Znse, ZnS, etc., or combinations thereof, separately synthesized either by epitaxial growth in a vacuum deposition system or chemically formed from the solutions.

(28) According to this invention, in way of an example not way of limitation, the supporting substrate 800 can be Ge, GaAs, GaN, CdTe, ZnO, Cu, Al.sub.2O.sub.3, AlN, glass, polymer, metal, etc. The electronic material 804 can be conductive polymer or a sol-gel based semiconductor. Note here that use of the nanometer-scaled rods or wires 822 helps not only increase the junction area but also helps transfer the generated carriers to the electrodes 803a and 803b before recombination. The rods or wires 822 inside the conductive polymer help to transfer the carriers through the rods. By varying the size (diameter) of the nanometer scaled rods (or wires) 822, a quantum confinement effect can be created and thereby absorption of broad spectral ranges can be possible.

(29) FIGS. 9A, 9B, 9C and 9D are the schematics showing the fabrication process of the flexible photovoltaic cell based on nanoparticles contained in the absorption layer, according to this invention, wherein the similar numerals in FIG. 9 represents the similar parts in FIGS. 3, 4, 5, and 6, so that similar explanations are omitted. According to this invention, supporting substrate 900 can be semiconductor such as Si, Ge, GaAs, InP, etc., polymer, or glass. The metal 903b acting as the contact in the photovoltaic cells, is formed onto the substrate 900. The metal 903b can be pressed and a rolling technique can be used, utilizing the roller 930. To make a firm connection with the substrate, epoxy or glue can be used. The absorption layer 901, comprising the nanoparticles embedding into the conducting polymer, is formed on the metal contact 903b. To form the absorption layer 901, spin coating or press and rolling techniques can be used. Alternatively, a printing technique or ink-jettable technique can also be used to form the absorption layer 901. With proper heat treatment, the top contact 903a can be formed. It is noted here that the instead of using the substrate 900, alternatively the absorption layer 901 can be directly formed onto the metal 903b by using the printing or ink-jettable technique. The advantages of this process are that low-cost and high efficiency flexible photovoltaic cells can be fabricated.

(30) FIGS. 10A, 10B, 10C, and 10D are the schematics showing the fabrication process of the photovoltaic cell based on nanoparticles contained in the absorption layer 1001, according to this invention, wherein the similar numerals in FIG. 10 represent similar parts in FIGS. 3, 4, 5, and 6, so that similar explanations are omitted. According to this invention, a layer of nanoparticles 1002 is formed on the substrate 2000 by chemical synthesis. A thin layer (not shown here) may be required in between substrate 2000 and the nanoparticle 1002, to increase the sticking coefficient. The layer of nanoparticles 1002 then transferred to the foreign substrate 1000 with metal electrode 1003b, on which the photovoltaic cell is to be made. The transfer of the nanoparticles 1002 to the foreign substrate 1000, can be done by heat or imprinting treatment. According to this invention, foreign substrate 1000 can be a semiconductor such as Si, Ge GaAs, InP, etc., polymer, or glass. Alternatively, the layer of nanoparticles 1002 can be directly transferred to the metal which could act as the substrate and also as the contact for the photovoltaic cell. Alternatively, without using the transferring process described in FIGS. 10A and 10B, the nanoparticle 1002 layer can be formed using printing or ink-jettable printing processes. The absorption layer 1001 comprising the nanoparticles 1002 embedding into the conducting polymer 1004 is formed on the metal contact 1003b. To form the absorption layer, spin coating or press and rolling techniques, as mentioned earlier, can be used. Alternatively, printing or ink-jettable techniques can also be used to form the absorption layer 1001. After proper heat treatment, the top contact 1003a is formed. It is noted here that the instead of using the substrate 1000, alternatively the absorption layer 1001, can be directly formed onto the metal 1003b, using printing or ink-jettable techniques. The advantages of this process are that low-cost and high efficiency flexible photovoltaic cells can be fabricated.

(31) FIGS. 11A, 11B, 11C, 11D, and 11E are the schematics showing the fabrication process of the photovoltaic cell based on nanoscaled rods or wires 1114 formed on the supporting substrate 1100, according to this invention, wherein the similar numerals in FIG. 11 represent similar parts in FIG. 7, so that similar explanations are omitted. According to this invention, nano-meter sized metal-semiconductor compounds 2100 are formed on the substrate 1100 with the metal electrode 1103b. The metal-semiconductor compounds can be formed either on the substrate 1100 by chemical synthesis, or transferred to the substrate 1100 by imprinting or heat treatment processes. According to this invention, the metal-semiconductor compounds 2100 have semiconductor and metal attached together. The semiconductor portion is attached to the substrate and the metal portion acts as the catalytic and is on top of the semiconductor. They are periodically organized onto the substrate 1100 with metal contact 1103b by imprinting or lithography processes. With chemical vapor deposition, the nano-scaled rods 1114 are formed. A dielectric layer, such as silicon-oxide or silicon nitride layer 1118, is used to isolate the junction formed by the electronic material 11116 and nano-rods 1114.

(32) To make the pn-junctions of dissimilar type (p or n), electronic material 1116 is used. For example, if the rod-material 1114 is n-type Si, then p-type Si is to be formed as the electronic material 1116. This can be formed by the diffusion of p-dopants into the n-type substrate. The interface of 1114/1116 forms the junction which has the built-in-potential to create the photovoltaic effect on a large surface area. Finally, a passivation or conformal layer of dielectric or polymer 1120 is formed on the electronic material 1116 after proper chemical mechanical processes. The final stage is to make the planarization using insulator layer 1120 and contact 1113a.

(33) FIGS. 12A and 12B are the schematics showing the formation of the semiconductor-metal interface onto the desired substrate 1200, for example glass for fabricating the photovoltaic cell as explained in FIG. 11, according to this invention, Here, the nano-silicon particles are formed uniformly onto the desired substrate 1200 with the metal contact 1203b. Nano-silicon particles made separately by chemical synthesis can be used for this purpose. This is followed by the nanometal attachment on to the nano-silicon particles, as shown in FIG. 12B. The nanometal onto the nano-silicon acts as the catalytics for forming the nano-rods, as explained in FIG. 11B.

(34) According to this invention, the absorption layer formed by the electronic material and the nanoparticles or nanometer(s) scaled rods, explained in FIGS. 3 thru 11 is a single layer used to form the junctions. By varying the diameter of the nanoparticles or the nano-rods used in the absorption layer, absorption of a wide range of the solar spectrum is possible, which increases the power generation.

(35) According to this invention, as explained in FIGS. 3 thru 11, the nanoparticles or nano-rods are used to increase the junction area, so the junction can be extended closer to the region where the photogenerated carriers are formed. The 3-dimensional structures can be used as part of the electronic material to form the junctions. This structure can be formed utilizing a suitable substrate. The substrate can be used to form the structure where junctions are formed, utilizing the other electronic materials formed on to the 3D structures.

(36) According to this invention, the nanoparticles or rods could be GaN materials (n or p type) and the dozens of materials could be In.sub.1-xGa.sub.xN (p or n type, opposite the GaN rods). By increasing the Ga contents, the band-gap of InGaN can be increased to 3.4 eV, which is the same as that of GaN. By increasing the in content in InGaN, the band gap can be reduced to 0.65 eV. Photons with less energy than the band gap will slip right through. For example, red light photons are not absorbed by high-band-gap semiconductors, while photons with an energy higher than the band gap are absorbed, for example, blue light photons in a low-band-gap semiconductortheir excess energy is wasted as heat.

(37) According to this invention, alternatively the nanoparticles or rods could be III-V based materials (n or p type), for example InP, and the dozens of the materials could be III-V based material like In.sub.1-xGa.sub.xAs (p or n type, opposite the InP rods). In this case, by adjusting the In contents, the band gap can be tuned and thereby a wide spectrum of the solar energy can be absorbed.

(38) According to this invention, alternatively the nanoparticles or rods could be II-V based materials (n or p type), for example CdTe, and the dozens of the materials could be II-VI based material like CdZnS (p or n type, opposite the CdTe rods) or Zn(Cd)Te/ZnS based materials. In this case, by adjusting the Zn contents, the band gap can be tuned and thereby a wide spectrum of the solar energy can be absorbed.

(39) According to this invention, alternatively the nanoparticles or rods could be Si or amorphous Silicon materials (n or p type) and the dozens of the materials could be Si: Ge alloy (p or n type, opposite the Si rods). In this case, by adjusting the Ge contents, the band gap can be tuned and thereby a wide spectrum of solar energy can be absorbed.

(40) According to this invention, alternatively the nanoparticles or rods could be Si, InP, or CdTe (n or p type) and dozens of different materials could make the junction with the rods (wires or tubes) and each type of material would have a specific band gap for absorbing a specific range of the solar spectrum. In this way a wide range of the solar spectrum can be absorbed, and by increasing the junction area (due to use of the rods, wires, or tubes), the electrical power generation could be increased tremendously (50 times and beyond).

(41) According to this invention, the nanoparticles or nanometer(s)-scale wires, mentioned in the preferred embodiments, can be any kind of electronic materials, covering semiconductor, insulator, or metal.

(42) According to this invention, the nanometer sized nanoparticles or rods can be made from semiconductors such as Si, Ge, or compound semiconductors from III-V or II-VI groups. As an example for rods, wires, or tubes, InP, GaAs, or GaN III-V compound semiconductors can be used and they can be made using standard growth processes, for example, MOCVD, MBE, or standard epitaxial growth. According to this invention, the self-assembled process can also be used to make wires, rods, or tubes and their related pn-junction in order to increase the junction area. These rods, wires, or tubes can be grown on the semiconductors (under same group or others), polymers, or insulators. Alternatively, according to this invention, these rods, wires, or tubes, can be transferred to the foreign substrate or to the layer of foreign material. The foreign substrate or the layer of material can be any semiconductor such as Si, Ge, InP, GaAs, GaN, ZnS, CdTe, CdS, ZnCdTe, HgCdTe, etc. The substrate can also cover all kinds of polymers or ceramics such as AlN, Silicon-oxide, etc.

(43) According to this invention, the nanometer sized nanoparticles or rods, based on an II-VI compound semiconductor can also be used. As an example CdTe, CdS, Cdse, ZnS, or ZnSe can be used, and they can be made using standard growth processes, for example, sputtering, evaporation, MOCVD, MBE, or standard epitaxial growth or chemical synthesis. According to this invention, the self-assembled process can also be used to make nanoparticles or wires, and their related pn-junctions to increase the junction area. These rods, wires, or tubes can be grown on the semiconductors (under same group or others), polymers, or insulators. Alternatively, according to this invention, these rods, wires, or tubes, can be transferred to the foreign substrate or to the layer of foreign material. The foreign substrate or the layer of material can be any semiconductor such as Si, Ge, InP, GaAs, GaN, ZnS, CdTe, CdS, ZnCdTe, HgCdTe, etc. The substrate can also cover all kinds of polymers or ceramics such as AlN, Silicon-oxide, etc.

(44) According to this invention, the nanometer sized rods, wires, or tubes can be made from carbon type materials (semiconductors, insulators, or metal like performances), such as carbon nano-tubes, which could be single or multiple layered. They can be made using standard growth processes, for example, MOCVD, MBE, or standard epitaxial growth. According to this invention, the self-assembled process can also be used to make wires, rods, or tubes and their related pn-junction in order to increase the junction area. These rods, wires, or tubes can be grown on the semiconductors (under same group or others), polymers, or insulators. Alternatively, according to this invention, these rods, wires, or tubes, can be transferred to the foreign substrate or to the layer of foreign material. The foreign substrate or the layer of material can be any semiconductor such as Si, Ge, InP, GaAs, GaN, ZnS, CdTe, CdS, ZnCdTe, HgCdTe, etc. The substrate can also cover all kinds of polymers or ceramics such as AlN, Silicon-oxide, etc.

(45) Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that the particular embodiments shown and described by way of illustration are in no way intended to be considered limiting. Therefore, reference to the details of the preferred embodiments is not intended to limit their scope.

(46) Although the invention has been described with respect to specific embodiments for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modification and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching here is set forth.

(47) The present invention is expected to be found practically useful in that the novel photo-voltaic cells have higher power generation capability (25 times and beyond) when compared with that of the conventional cells. The proposed invention can be used for fabricating wide solar panels for both commercial and space applications.