Patent Publication Number: US-2019198744-A1

Title: Hybrid solar and solar thermal device with embedded flexible thin-film based thermoelectric module

Description:
CLAIM OF PRIORITY 
     This application is a Continuation-in-Part application of co-pending U.S. application Ser. No. 15/808,902 titled FLEXIBLE THIN-FILM BASED THERMOELECTRIC DEVICE WITH SPUTTER DEPOSITED LAYER OF N-TYPE AND P-TYPE THERMOELECTRIC LEGS filed on Nov. 10, 2017, which is a Continuation-in-Part application of co-pending U.S. patent application Ser. No. 14/564,072 titled VOLTAGE GENERATION ACROSS TEMPERATURE DIFFERENTIALS THROUGH A THERMOELECTRIC LAYER COMPOSITE filed on Dec. 8, 2014, which is a conversion application of U.S. Provisional Application No. 61/912,561 also titled VOLTAGE GENERATION ACROSS TEMPERATURE DIFFERENTIALS THROUGH A THERMOELECTRIC LAYER COMPOSITE filed on Dec. 6, 2013, U.S. application Ser. No. 14/711,810 titled ENERGY HARVESTING FOR WEARABLE TECHNOLOGY THROUGH A THIN FLEXIBLE THERMOELECTRIC DEVICE filed on May 14, 2015 and issued as U.S. Pat. No. 10,141,492 on Nov. 27, 2018 and co-pending U.S. application Ser. No. 15/368,683 titled PIN COUPLING BASED THERMOELECTRIC DEVICE filed on Dec. 5, 2016. The content of the aforementioned applications are incorporated by reference in entirety thereof. 
    
    
     FIELD OF TECHNOLOGY 
     This disclosure relates generally to thermoelectric devices and, more particularly, to a hybrid solar and a solar thermal device with embedded flexible thin-film based thermoelectric module. 
     BACKGROUND 
     A solar device (e.g., a solar panel) may utilize a photovoltaic layer including solar cells to convert solar energy into electricity. Although photovoltaic based solar devices provide for scalability in use thereof, the aforementioned devices may be inefficient (e.g., efficiency ≤24%). Another solar device may be solar thermal based, leveraging heat energy of the sun. Although solar thermal installations may be relatively efficient, limitations in efficiency arising out of heat losses due to internal convection may prove to be a compromise therein. 
     SUMMARY 
     Disclosed are methods, a device and/or a system of a hybrid solar and a solar thermal device with embedded flexible thin-film based thermoelectric module. 
     In one aspect, a method of a solar device includes sputter depositing pairs of N-type thermoelectric legs and P-type thermoelectric legs electrically in contact with one another on a flexible substrate to form a thin-film based thermoelectric module. The flexible substrate is aluminum (Al) foil, a sheet of paper, teflon, plastic, polyimide, a single-sided metal clad laminate, or a double-sided metal clad laminate. The method also includes rendering the formed thin-film based thermoelectric module flexible and less than or equal to 100 μm in dimensional thickness based on choices of fabrication processes with respect to layers of the formed thin-film based thermoelectric module including the sputter deposited N-type thermoelectric legs and the P-type thermoelectric legs. 
     Further, the method includes directly coupling the flexible thin-film based thermoelectric module to a layer of heat absorber material or a layer of photovoltaic material configured to receive sunlight such that the flexible thin-film based thermoelectric module is in contact therewith to form the solar device, and leveraging, through the directly coupled flexible thin-film based thermoelectric module, a temperature difference across a first surface of the flexible thin-film based thermoelectric module directly in contact with the layer of heat absorber material or the layer of photovoltaic material and a second surface away therefrom to generate increased solar thermal power and/or electrical power output through the solar device compared to an otherwise equivalent solar device without the formed thin-film based thermoelectric module. 
     In another aspect, a method of a solar device includes forming a flexible thin-film based thermoelectric module of less than or equal to 100 μm in dimensional thickness on a flexible substrate based on choices of fabrication processes and materials with respect to layers of the formed thin-film based thermoelectric module. The flexible substrate is an Al foil, a sheet of paper, teflon, plastic, polyimide, a single-sided metal clad laminate, or a double-sided metal clad laminate. The method also includes directly coupling the flexible thin-film based thermoelectric module to a layer of heat absorber material or a layer of photovoltaic material configured to receive sunlight such that the flexible thin-film based thermoelectric module is in contact therewith to form the solar device. 
     Further, the method includes leveraging, through the directly coupled flexible thin-film based thermoelectric module, a temperature difference across a first surface of the flexible thin-film based thermoelectric module directly in contact with the layer of heat absorber material or the layer of photovoltaic material and a second surface away therefrom to generate increased solar thermal power and/or electrical power output through the solar device compared to an otherwise equivalent solar device without the formed thin-film based thermoelectric module. 
     In yet another aspect, a method of a solar device includes forming a flexible thin-film based thermoelectric module of less than or equal to 100 μm in dimensional thickness on a flexible substrate based on choices of fabrication processes and materials with respect to layers of the formed thin-film based thermoelectric module. The flexible substrate is an Al foil, a sheet of paper, teflon, plastic, polyimide, a single-sided metal clad laminate, or a double-sided metal clad laminate. The method also includes directly coupling the flexible thin-film based thermoelectric module to a layer of heat absorber material or a layer of photovoltaic material configured to receive sunlight such that the flexible thin-film based thermoelectric module is in contact therewith to form the solar device. 
     Further, the method includes leveraging, through the directly coupled flexible thin-film based thermoelectric module, a temperature difference across a first surface of the flexible thin-film based thermoelectric module directly in contact with the layer of heat absorber material or the layer of photovoltaic material and a second surface away therefrom to generate increased solar thermal power and/or electrical power output through the solar device compared to an otherwise equivalent solar device without the formed thin-film based thermoelectric module while enabling retention of an outward physical appearance of the otherwise equivalent solar device. 
     Other features will be apparent from the accompanying drawings and from the detailed description that follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of this invention are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which: 
         FIG. 1  is a schematic view of a thermoelectric device. 
         FIG. 2  is a schematic view of an example thermoelectric device with alternating P and N elements. 
         FIG. 3  is a top schematic view of a thermoelectric device component, according to one or more embodiments. 
         FIG. 4  is a process flow diagram detailing the operations involved in realizing a patterned flexible substrate of a thermoelectric device as per a design pattern, according to one or more embodiments. 
         FIG. 5  is a schematic view of the patterned flexible substrate of  FIG. 4 , according to one or more embodiments. 
         FIG. 6  is a schematic view of the patterned flexible substrate of  FIG. 4  with N-type thermoelectric legs, P-type thermoelectric legs, a barrier layer and conductive interconnects, according to one or more embodiments. 
         FIG. 7  is a process flow diagram detailing the operations involved in sputter deposition of the N-type thermoelectric legs of  FIG. 6  on the patterned flexible substrate (or, a seed metal layer) of  FIG. 5 , according to one or more embodiments. 
         FIG. 8  is a process flow diagram detailing the operations involved in deposition of the barrier layer of  FIG. 6  on top of the sputter deposited pairs of P-type thermoelectric legs and the N-type thermoelectric legs of  FIG. 6  and forming the conductive interconnects of  FIG. 6  on top of the barrier layer, according to one or more embodiments. 
         FIG. 9  is a process flow diagram detailing the operations involved in encapsulating the thermoelectric device of  FIG. 4  and  FIG. 6 , according to one or more embodiments. 
         FIG. 10  is a schematic view of a flexible thermoelectric device embedded within a watch strap of a watch completely wrappable around a wrist of a human being. 
         FIG. 11  is a schematic view of a flexible thermoelectric device wrapped around a heat pipe. 
         FIG. 12  is schematic view of a solar device, according to one or more embodiments. 
         FIG. 13  is a schematic view of another solar device, according to one or more embodiments. 
         FIG. 14  is a schematic view of yet another solar device, according to one or more embodiments. 
         FIG. 15  is a schematic view of still yet another solar device, according to one or more embodiments. 
         FIG. 16  is a process flow diagram detailing the operations involved in realizing the solar devices of  FIGS. 12-15 , according to one or more embodiments. 
     
    
    
     Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows. 
     DETAILED DESCRIPTION 
     Example embodiments, as described below, may be used to provide methods, a device and/or a system of a hybrid solar and a solar thermal device with embedded flexible thin-film based thermoelectric module. Although the present embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the various embodiments. 
       FIG. 1  shows a thermoelectric device  100 . Thermoelectric device  100  may include different metals, metal  1   102  and metal  2   104 , forming a closed circuit. Here, a temperature difference between junctions of said dissimilar metals leads to energy levels of electrons therein shifted in a dissimilar manner. This results in a potential/voltage difference between the warmer (e.g., warmer junction  106 ) of the junctions and the colder (e.g., colder junction  108 ) of the junctions. The aforementioned conversion of heat into electricity at junctions of dissimilar metals is known as Seebeck effect. 
     The most common thermoelectric devices in the market may utilize alternative P and N type legs/pellets/elements made of semiconducting materials. As heat is applied to one end of a thermoelectric device based on P and N type elements, charge carriers thereof may be released into the conduction band. Electron (charge carrier) flow in the N type element may contribute to a current flowing from the end (hot end) where the heat is applied to the other end (cold end). Hole (charge carrier) flow in the P type element may contribute to a current flowing from the other end (cold end) to the end (hot end) where the heat is applied. Here, heat may be removed from the cold end to prevent equalization of charge carrier distribution in the semiconductor materials due to migration thereof. 
     In order to generate voltage at a meaningful level to facilitate one or more application(s), typical thermoelectric devices may utilize alternating P and N type elements (legs/pellets) electrically coupled in series (and thermally coupled in parallel) with one another, as shown in  FIG. 2 .  FIG. 2  shows an example thermoelectric device  200  including three alternating P and N type elements  202   1-3 . The hot end (e.g., hot end  204 ) where heat is applied and the cold end (e.g., cold end  206 ) are also shown in  FIG. 2 . 
     Typical thermoelectric devices (e.g., thermoelectric device  200 ) may be limited in application thereof because of rigidity, bulkiness and high costs (&gt;$20/watt) associated therewith. Also, these devices may operate at high temperatures using active cooling. Exemplary embodiments discussed herein provide for a thermoelectric platform (e.g., enabled via roll-to-roll sputtering on a flexible substrate (e.g., plastic)) that offers a large scale, commercially viable, high performance, easy integration and inexpensive (&lt;20 cents/watt) route to flexible thermoelectrics. 
     In accordance with the exemplary embodiments, P and N thermoelectric legs may be deposited on a flexible substrate (e.g., plastic) using a roll-to-roll process that offers scalability and cost savings associated with the N and P materials. In a typical solution, bulk legs may have a height in millimeters (mm) and an area in mm 2 . In contrast, N and P bulk legs described in the exemplary embodiments discussed herein may have a height in microns (μm) and an area in the μm 2  to mm 2  range. 
     Examples of flexible substrates may include but are not limited to aluminum (Al) foil, a sheet of paper, teflon, plastic, polyimide and a single/double-sided metal (e.g., copper (Cu)) clad laminate. As will be discussed below, exemplary embodiments involve processes for manufacturing/fabrication of thermoelectric devices/modules that enable flexibility thereof not only in terms of substrates but also in terms of thin films/thermoelectric legs/interconnects/packaging. Preferably, exemplary embodiments provide for thermoelectric devices/modules completely wrappable and bendable around other devices utilized in specific applications, as will be discussed below. Further, exemplary embodiments provide for manufactured/fabricated thermoelectric devices/modules that are each less than or equal to 100 μm in dimensional thickness. 
       FIG. 3  shows a top view of a thermoelectric device component  300 , according to one or more embodiments. Here, in one or more embodiments, a number of sets of N and P legs (e.g., sets  302   1-M  including N legs  304   1-M  and P legs  306   1-M  therein) may be deposited on a substrate  350  (e.g., plastic, metal clad laminate) using a roll-to-roll process discussed above.  FIG. 3  also shows a conductive material  308   1-M  contacting both a set  302   1-M  and substrate  350 , according to one or more embodiments; an N leg  304   1-M  and a P leg  306   1-M  form a set  302   1-M , in which N leg  304   1-M  and P leg  306   1-M  electrically contact each other through conductive material  308   1-M . Terminals  370  and  372  may be electrically conductive leads to measure the potential difference generated by a thermoelectric device including thermoelectric device component  300 . 
     Exemplary thermoelectric devices discussed herein may find utility in solar and solar thermal applications. As discussed above, traditional thermoelectric devices may have a size limitation and may not scale to a larger area. For example, a typical solar panel may have an area in the square meter (m 2 ) range and the traditional thermoelectric device may have an area in the square inch range. A thermoelectric device in accordance with the exemplary embodiments may be of varying sizes and/or dimensions ranging from a few mm 2  to a few m 2 . 
     Additionally, exemplary thermoelectric devices may find use in low temperature applications such as harvesting body heat in a wearable device, automotive devices/components and Internet of Things (IoT). Entities (e.g., companies, start-ups, individuals, conglomerates) may possess expertise to design and/or develop devices that require thermoelectric modules, but may not possess expertise in the fabrication and packaging of said thermoelectric modules. Alternately, even though the entities may possess the requisite expertise in the fabrication and packaging of the thermoelectric modules, the entities may not possess a comparative advantage with respect to the aforementioned processes. 
     In one scenario, an entity may create or possess a design pattern for a thermoelectric device. Said design pattern may be communicated to another entity associated with a thermoelectric platform to be tangibly realized as a thermoelectric device. It could also be envisioned that the another entity may provide training with regard to the fabrication processes to the one entity or outsource aspects of the fabrication processes to a third-party. Further, the entire set of processes involving Intellectual Property (IP) generation and manufacturing/fabrication of the thermoelectric device may be handled by a single entity. Last but not the least, the entity may generate the IP involving manufacturing/fabrication of the thermoelectric device and outsource the actual manufacturing/fabrication processes to the another entity. 
     All possible combinations of entities and third-parties are within the scope of the exemplary embodiments discussed herein. 
       FIG. 4  shows the operations involved in realizing a patterned flexible substrate (e.g., patterned flexible substrate  504  shown in  FIG. 5 ) of a thermoelectric device  400  as per a design pattern (e.g., design pattern  502  shown in  FIG. 5 ), according to one or more embodiments. In one or more embodiments, operation  402  may involve choosing a flexible substrate (e.g., substrate  350 ) onto which, in operation  404 , design pattern  502  may be printed (e.g., through inkjet printing, direct write, screen printing) and etched onto the flexible substrate. In one or more embodiments, a dimensional thickness of substrate  350  may be less than or equal to 25 μm. 
     Etching, as defined above, may refer to the process of removing (e.g., chemically) unwanted metal (say, Cu) from the patterned flexible substrate. In one example embodiment, a mask (e.g., a shadow mask) or a resist may be placed on portions of the patterned flexible substrate corresponding to portions of the metal that are to remain after the etch. Here, in one or more embodiments, the portions of the metal that remain on the patterned flexible substrate may be electrically conductive pads, electrically conductive leads and terminals formed on a surface of the patterned flexible substrate.  FIG. 5  shows a patterned flexible substrate  504  including a number of electrically conductive pads  506   1-N  formed thereon. Each electrically conductive pad  506   1-N  may be a flat area of the metal that enables an electrical connection. 
     Also,  FIG. 5  shows a majority set of the electrically conductive pads  506   1-N  as including pairs  510   1-P  of electrically conductive pads  506   1-N  in which one electrically conductive pad  506   1-N  may be electrically paired to another electrically conductive pad  506   1-N  through an electrically conductive lead  512   1-P  also formed on patterned flexible substrate  504 ; terminals  520   1-2  (e.g., analogous to terminals  370  and  372 ) may also be electrically conductive leads to measure the potential difference generated by the thermoelectric device/module fabricated based on design pattern  502 . The aforementioned potential difference may be generated based on heat (or, cold) applied at an end of the thermoelectric device/module. 
     It should be noted that the configurations of the electrically conductive pads  506   1-N , electrically conductive leads  512   1-P  and terminals  520   1-2  shown in  FIG. 5  are merely for example purposes, and that other example configurations are within the scope of the exemplary embodiments discussed herein. It should also be noted that patterned flexible substrate  504  may be formed based on design pattern  502  in accordance with the printing and etching discussed above. 
     Example etching solutions employed may include but are not limited to ferric chloride and ammonium persulphate. Referring back to  FIG. 4 , operation  406  may involve cleaning the printed and etched flexible substrate. For example, acetone, hydrogen peroxide or alcohol may be employed therefor. Other forms of cleaning are within the scope of the exemplary embodiments discussed herein. In one or more embodiments, the aforementioned processes discussed in  FIG. 4  may result in a dimensional thickness of electrically conductive pads  506   1-N , electrically conductive leads  512   1-P  and terminals  520   1-2  being less than or equal to 18 μm. 
     The metal (e.g., Cu) finishes on the surface of patterned flexible substrate  504  may oxidize over time if left unprotected. As a result, in one or embodiments, operation  408  may involve additionally electrodepositing a seed metal layer  550  including Chromium (Cr), Nickel (Ni) and/or Gold (Au) directly on top of the metal portions (e.g., electrically conductive pads  506   1-N , electrically conductive leads  512   1-P , terminals  520   1-2 ) of patterned flexible substrate  504  following the printing, etching and cleaning. In one or more embodiments, a dimensional thickness of seed metal layer  550  may be less than or equal to 5 μm. 
     In one example embodiment, surface finishing may be employed to electrodeposit seed metal layer  550 ; the aforementioned surface finishing may involve Electroless Nickel Immersion Gold (ENIG) finishing. Here, a coating of two layers of metal may be provided over the metal (e.g., Cu) portions of patterned flexible substrate  504  by way of Au being plated over Ni. Ni may be the barrier layer between Cu and Au. Au may protect Ni from oxidization and may provide for low contact resistance. Other forms of surface finishing/electrodeposition may be within the scope of the exemplary embodiments discussed herein. It should be noted that seed metal layer  550  may facilitate contact of sputter deposited N-type thermoelectric legs (to be discussed below) and P-type thermoelectric legs (to be discussed below) thereto. 
     In one or more embodiments, operation  410  may then involve cleaning patterned flexible substrate  504  following the electrodeposition.  FIG. 6  shows an N-type thermoelectric leg  602   1-P  and a P-type thermoelectric leg  604   1-P  formed on each pair  510   1-P  of electrically conductive pads  506   1-N , according to one or more embodiments. In one or more embodiments, the aforementioned N-type thermoelectric legs  602   1-P  and P-type thermoelectric legs  604   1-P  may be formed on the surface finished patterned flexible substrate  504  (note: in  FIG. 6 , seed layer  550  is shown as surface finishing over electrically conductive pads  506   1-N /leads  512   1-P ; terminals  520   1-2  have been omitted for the sake of clarity) of  FIG. 5  through sputter deposition. 
       FIG. 7  details the operations involved in sputter deposition of N-type thermoelectric legs  602   1-P  on the surface finished patterned flexible substrate  504  (or, seed metal layer  550 ) of  FIG. 5 , according to one or more embodiments. In one or more embodiments, the aforementioned process may involve a photomask  650  (shown in  FIG. 6 ) on which patterns corresponding/complementary to the N-type thermoelectric legs  602   1-P  may be generated. In one or more embodiments, a photoresist  670  (shown in  FIG. 6 ) may be applied on the surface finished patterned flexible substrate  504 , and photomask  650  placed thereon. In one or more embodiments, operation  702  may involve sputter coating (e.g., through magnetron sputtering) of the surface finished patterned flexible substrate  504  (or, seed metal layer  550 ) with an N-type thermoelectric material corresponding to N-type thermoelectric legs  602   1-P , aided by the use of photomask  650 . The photoresist  670 /photomask  650  functions are well understood to one skilled in the art; detailed discussion associated therewith has been skipped for the sake of convenience and brevity. 
     In one or more embodiments, operation  704  may involve stripping (e.g., using solvents such as dimethyl sulfoxide or alkaline solutions) of photoresist  670  and etching of unwanted material on patterned flexible substrate  504  with sputter deposited N-type thermoelectric legs  602   1-P . In one or more embodiments, operation  706  may involve cleaning the patterned flexible substrate  504  with the sputter deposited N-type thermoelectric legs  602   1-P ; the cleaning process may be similar to the discussion with regard to  FIG. 4 . 
     In one or more embodiments, operation  708  may then involve annealing the patterned flexible substrate  504  with the sputter deposited N-type thermoelectric legs  602   1-P ; the annealing process may be conducted (e.g., in air or vacuum) at 175° C. for 4 hours. In one or more embodiments, the annealing process may remove internal stresses and may contribute stability of the sputter deposited N-type thermoelectric legs  602   1-P . In one or more embodiments, a dimensional thickness of the sputter deposited N-type thermoelectric legs  602   1-P  may be less than or equal to 25 μm. 
     It should be noted that P-type thermoelectric legs  604   1-P  may also be sputter deposited on the surface finished pattern flexible substrate  504 . The operations associated therewith are analogous to those related to the sputter deposition of N-type thermoelectric legs  602   1-P . Obviously, photomask  650  may have patterns corresponding/complementary to the P-type thermoelectric legs  604   1-P  generated thereon. Detailed discussion associated with the sputter deposition of P-type thermoelectric legs  604   1-P  has been skipped for the sake of convenience; it should be noted that a dimensional thickness of the sputter deposited P-type thermoelectric legs  604   1-P  may also be less than or equal to 25 μm. 
     It should be noted that the sputter deposition of P-type thermoelectric legs  604   1-P  on the surface finished patterned flexible substrate  504  may be performed after the sputter deposition of N-type thermoelectric legs  602   1-P  thereon or vice versa. Also, it should be noted that various feasible forms of sputter deposition are within the scope of the exemplary embodiments discussed herein. In one or more embodiments, the sputter deposited P-type thermoelectric legs  604   1-P  and/or N-type thermoelectric legs  602   1-P  may include a material chosen from one of: Bismuth Telluride (Bi 2 Te 3 ), Bismuth Selenide (Bi 2 Se 3 ), Antimony Telluride (Sb 2 Te 3 ), Lead Telluride (PbTe), Silicides, Skutterudites and Oxides. 
       FIG. 8  details operations involved in deposition of a barrier layer  672  (refer to  FIG. 6 ) on top of the sputter deposited pairs of P-type thermoelectric legs  604   1-P  and N-type thermoelectric legs  602   1-P  and forming conductive interconnects  696  on top of barrier layer  672 , according to one or more embodiments. 
     In one or more embodiments, operation  802  may involve sputter depositing barrier layer  672  (e.g., film) on top of the sputter deposited pairs of the P-type thermoelectric legs  604   1-P  and the N-type thermoelectric leg  602   1-P  discussed above. In one or more embodiments, barrier layer  672  may be electrically conductive and may have a higher melting temperature than the thermoelectric material forming the P-type thermoelectric legs  604   1-P  and the N-type thermoelectric legs  602   1-P . In one or more embodiments, barrier layer  672  may prevent corruption (e.g., through diffusion, sublimation) of one layer (e.g., the thermoelectric layer including the P-type thermoelectric legs  604   1-P  and the N-type thermoelectric legs  602   1-P ) by another layer. An example material employed as barrier layer  672  may include but is not limited to Cr, Ni or Au. Further, in one or more embodiments, barrier layer  672  may further aid metallization contact therewith (e.g., with conductive interconnects  696 ). 
     In one or more embodiments, a dimensional thickness of barrier layer  672  may be less than or equal to 5 μm. It is obvious that another photomask (not shown) analogous to photomask  650  may be employed to aid the patterned sputter deposition of barrier layer  672 ; details thereof have been skipped for the sake of convenience and clarity. In one or more embodiments, operation  804  may involve may involve curing barrier layer  672  at 175° C. for 4 hours to strengthen barrier layer  672 . In one or more embodiments, operation  806  may then involve cleaning patterned flexible substrate  504  with barrier layer  672 . 
     In one or more embodiments, operation  808  may involve depositing conductive interconnects  696  on top of barrier layer  672 . In one example embodiment, the aforementioned deposition may be accomplished by screen printing silver (Ag) ink or other conductive forms of ink on barrier layer  672 . Other forms of conductive interconnects  696  based on conductive paste(s) are within the scope of the exemplary embodiments discussed herein. As shown in  FIG. 8 , a hard mask  850  may be employed to assist the selective application of conductive interconnects  696  based on screen printing of Ag ink. In one example embodiment, hard mask  850  may be a stencil. 
     In one or more embodiments, the screen printing of Ag ink may contribute to the continued flexibility of the thermoelectric device/module and low contact resistance. In one or more embodiments, operation  810  may involve cleaning (e.g., using one or more of the processes discussed above) the thermoelectric device/module/formed conductive interconnects  696 /barrier layer  672  and polishing conductive interconnects  696 . In one example embodiment, the polishing may be followed by another cleaning process. In one or more embodiments, operation  812  may then involve curing conductive interconnects  696  at 175° C. for 4 hours to fuse the conductive ink into solid form thereof. In one or more embodiments, conductive interconnects  696  may have a dimensional thickness less than or equal to 25 μm. 
       FIG. 9  details the operations involved in encapsulating the thermoelectric device (e.g., thermoelectric module  970 )/module discussed above, according to one or more embodiments. In one or more embodiments, operation  902  may involve encapsulating the formed thermoelectric module (e.g., thermoelectric module  970 )/device (with barrier layer  672  and conductive interconnects  696 ) with an elastomer  950  to render flexibility thereto. In one or more embodiments, as shown in  FIG. 9 , the encapsulation provided by elastomer  950  may have a dimensional thickness of less than or equal to 15 μm. In one or more embodiments, operation  904  may involve doctor blading (e.g., using doctor blade  952 ) the encapsulation provided by elastomer  950  to finish packaging of the flexible thermoelectric device/module discussed above. 
     In one or more embodiments, the doctor blading may involve controlling precision of a thickness of the encapsulation provided by elastomer  950  through doctor blade  952 . In one example embodiment, elastomer  950  may be silicone. Here, said silicone may be loaded with nano-size aluminum oxide (Al 2 O 3 ) powder to enhance thermal conductivity thereof to aid heat transfer across the thermoelectric module. 
     In one or more embodiments, as seen above, all operations involved in fabricating the thermoelectric device/module (e.g., thermoelectric device  400 ) render said thermoelectric device/module flexible.  FIG. 10  shows a flexible thermoelectric device  1000  discussed herein embedded within a watch strap  1002  of a watch  1004  completely wrappable around a wrist  1006  of a human being  1008 ; flexible thermoelectric device  1000  may include an array  1020  of thermoelectric modules  1020   1-J  (e.g., each of which is thermoelectric device  400 ) discussed herein. In one example embodiment, flexible thermoelectric device  1000  may serve to augment or substitute power derivation from a battery of watch  1004 .  FIG. 11  shows a flexible thermoelectric device  1100  discussed herein wrapped around a heat pipe  1102 ; again, flexible thermoelectric device  1100  may include an array  1120  of thermoelectric modules  1120   1-J  (e.g., each of which is thermoelectric device  400 ) discussed herein. In one example embodiment, flexible thermoelectric device  1100  may be employed to derive thermoelectric power (e.g., through array  1120 ) from waste heat from heat pipe  1102 . 
     It should be noted that although photomask  650  is discussed above with regard to deposition of N-type thermoelectric legs  602   1-P  and a P-type thermoelectric legs  604   1-P , the aforementioned deposition may, in one or more other embodiments, involve a hard mask  690 , as shown in  FIG. 6 . Further, it should be noted that flexible thermoelectric device  400 / 1000 / 1100  may be fabricated/manufactured such that the aforementioned device is completely wrappable and bendable around a system element (e.g., watch  1004 , heat pipe  1102 ) that requires said flexible thermoelectric device  400 / 1000 / 1100  to perform a thermoelectric power generation function using the system element. 
     The abovementioned flexibility of thermoelectric device  400 / 1000 / 1100  may be enabled through proper selection of flexible substrates (e.g., substrate  350 ) and manufacturing techniques/processes that aid therein, as discussed above. Further, flexible thermoelectric device  1000 / 1100  may be bendable 360° such that the entire device may completely wrap around the system element discussed above. Still further, in one or more embodiments, an entire dimensional thickness of the flexible thermoelectric module (e.g., flexible thermoelectric device  400 ) in a packaged form may be less than or equal to 100 μm, as shown in  FIG. 9 . 
     Last but not the least, as the dimensions involved herein are restricted to less than or equal to 100 μm, the flexible thermoelectric device/module discussed above may be regarded as being thin-film based (e.g., including processes involved in fabrication thereof). 
     In one or more embodiments, thermoelectric device  400 /thermoelectric module  970  may be easily amenable to use in solar devices such as solar panels/flat plate collectors. Solar thermal installations may harvest the heat energy of the sun. The heat then may be used to drive other mechanical systems for power production. One or more embodiments discussed herein may relate to integrating thermoelectric device  400 /thermoelectric module  970  with solar devices such as a solar panel. 
       FIG. 12  shows a solar device  1200  (e.g., a solar panel), according to one or more embodiments. In one or more embodiments, solar device  1200  may include a thermoelectric module  1202  (e.g., thermoelectric module  970 , embodiments of  FIGS. 3-8 ) in a lightweight, paper thin form coupled to (e.g., placed right below) a heat absorber layer  1204  and in contact therewith; one surface  1252  (e.g., a top surface) of thermoelectric module  1202  may directly contact heat absorber layer  1204 . In one or more embodiments, another surface  1254  (e.g., a bottom surface) of thermoelectric module  1202  may contact an internal layer of fluid pipes  1206  (e.g., cold enough to provide for a temperature difference across surface  1252  and surface  1254 ; the fluid pipes may provide for cooling by way of carrying air or a fluid such as water; in certain cases, internal layer of fluid pipes  1206  may be at ambient temperature), as shown in  FIG. 12 . As a temperature difference between surface  1252  and surface  1254  of thermoelectric module  1202  generates a potential difference and, therefore, current, in one or more embodiments, the temperature difference between heat absorber layer  1204  and internal layer of fluid pipes  1206  may be utilized to generate electric power. 
     In one example embodiment, heat absorber layer  1204  may include a metallic material (e.g., Copper, Aluminum) coated with a special material such as TiNOX to efficiently absorb incident solar light energy (e.g., sunlight  1250 ) and effect transformation thereof into heat/thermal energy, thereby resulting in minimal reflection and radiation losses. It should be noted that surface  1254 , in one or more other embodiments, may be in contact with a layer that provides for a temperature difference between surface  1252  and surface  1254 . In other words, any layer that provides for a temperature difference between surface  1252  and surface  1254  may substitute internal layer of fluid pipes  1206 .  FIG. 12  shows a temperature difference providing layer  1206  as the generalized term for the aforementioned “any layer that provides for a temperature difference between surface  1252  and surface  1254 .” 
       FIG. 13  shows another solar device  1300 , according to one or more embodiments. Here, in one or more embodiments, a thermoelectric module  1302  (e.g., thermoelectric module  970 , embodiments of  FIGS. 3-8 ) may be sandwiched between two metallic layers, viz. metallic layer  1304  and metallic layer  1306 , with thermoelectric module  1302  contacting both metallic layer  1304  and metallic layer  1306 ;  FIG. 13  shows thermoelectric sandwich  1350  as including thermoelectric module  1302 , metallic layer  1304  and metallic layer  1306 . Examples of each of metallic layer  1304  and metallic layer  1306  include Copper and Aluminum. Other materials are within the scope of the exemplary embodiments discussed herein. It should be noted that metallic layer  1304  and metallic layer  1306  may be of the same material or of different materials. 
     Also, in one or more embodiments, it should be noted that thermoelectric sandwich  1350  may introduced right behind heat absorber layer  1204  and in contact therewith, as shown in  FIG. 13 . In other words, metallic layer  1304  may contact the metallic layer (e.g., metallic layer  1308 ;  FIG. 13  also shows coating  1310  (e.g., TiNOX discussed above) on top of metallic layer  1308 ; both coating  1310  and metallic layer  1308  may form part or whole of heat absorber layer  1204 ) of heat absorber layer  1204 . In one or more embodiments, solar device  1300  may be similar to solar device  1200 , except for substitution of thermoelectric module  1202  with thermoelectric sandwich  1350 . In one or more embodiments, the specific configuration of solar device  1300  disclosed in  FIG. 13  with thermoelectric sandwich  1350  may warrant only minimal changes to the existing manufacturing process thereof. In certain aspects, in one or more embodiments, thermoelectric sandwich  1350  may be viewed as a thermoelectric module analogous to thermoelectric module  1202 . 
       FIG. 14  shows yet another solar device  1400 , according to one or more embodiments. In one or more embodiments, solar device  1400  may include a photovoltaic (PV) layer  1404  directly on top of heat absorber layer  1204  and in contact therewith. In one or more embodiments, a thermoelectric module  1402  analogous to thermoelectric module  1202  or thermoelectric module  1302  part of thermoelectric sandwich  1350  may be directly coupled to (e.g., placed right below) heat absorber layer  1204  and in contact therewith (refer to the embodiments of  FIGS. 12-13 ). 
     When sunlight  1250  is incident on PV layer  1404 , a large portion of said sunlight  1250  may be absorbed by a semiconductor material of PV layer  1404 , thereby effecting a transfer of energy from photons to electrons. The flow of these electrons may constitute an electric current. This electric current may be utilized to power a grid or another element. It is obvious that PV layer  1404  may include solar cells made of semiconductor material such as Silicon and Cadmium Telluride. Other materials are within the scope of the exemplary embodiments discussed herein. 
     The working of photovoltaic cells is well known to one skilled in the art. Detailed discussion thereof is, therefore, skipped for the sake of convenience and brevity. In one or more embodiments, heat absorber layer  1204  placed below PV layer  1404  may provide for cooling of solar cells within PV layer  1404 . In one or more embodiments, heat absorber layer  1204  may then be able to leverage energy from PV layer  1404  that is unrecoverable without the presence of heat absorber layer  1204  within solar device  1400 . 
     Again, it should be understood that solar device  1400  may be analogous to solar device  1300  and solar device  1200 , except for the inclusion of PV layer  1404  on top of heat absorber layer  1204 . Exemplary embodiments disclosed in  FIG. 14  may not only enable solar device  1400  to produce electricity (because of PV layer  1404 ) but also to leverage a temperature difference across surfaces of thermoelectric module  1402  to simultaneously heat internal layer of fluid pipes  1206  (e.g., water, air, fluid). 
     It should be noted that any combination of a thermoelectric module (e.g., thermoelectric module  1202 , thermoelectric sandwich  1350 , thermoelectric module  1402 ) with PV layer  1404  and heat absorber layer  1204  may be envisioned according to the application toward which a corresponding solar device (e.g., solar device  1200 , solar device  1300 , solar device  1400 ) is targeted.  FIG. 15  shows still yet another solar device  1500 , according to one or more embodiments. Here, PV layer  1404  may directly be on top of a thermoelectric module  1502  (e.g., thermoelectric module  1202 , thermoelectric sandwich  1350 ) and in contact therewith. Again, in one or more embodiments, sunlight  1250  incident on PV layer  1404  may be leveraged to generate electricity; temperature difference across surfaces of thermoelectric module  1402  (e.g., surface  1252  and surface  1254  of thermoelectric module  1202 , metallic layer  1304  and metallic layer  1306  of thermoelectric sandwich  1350 ) may be leveraged to simultaneously heat internal layer of fluid pipes  1206 . 
     While focused solar absorption through heat absorber layer  1204  is missing in solar device  1500  of  FIG. 15 , the advantages of thermoelectric module  970  and the embodiments thereof in  FIGS. 3-8  may still be realized in solar device  1500 , as in solar device  1200 , solar device  1300  and solar device  1400 . Example applications in which solar device  1200 , solar device  1300 , solar device  1400  and/or solar device  1500  may be employed include but are not limited to solar air cooling (temperatures of heat energy required may range from 160-180° C.), solar desalination (temperatures of heat energy required may range from 120-140° C.), solar dehydration (temperatures of heat energy required may range from 120-140° C.) and solar process heating (temperatures of heat energy required may range from 100-200° C.). 
     Thus, in one or more embodiments, thermoelectric module  970  and the embodiments thereof in  FIGS. 3-8  may find use in 24×7 operation of solar devices (e.g., solar device  1200 , solar device  1300 , solar device  1400 , solar device  1500 ) with continuous electric power and solar thermal power generation. The thin-film nature of elements of thermoelectric module  970  and the embodiments thereof in  FIGS. 3-8  may lead to enhancements of existing solar devices (e.g., into solar device  1200 , solar device  1300 , solar device  1400  and/or solar device  1500 ) without changes in looks and/or outward physical appearances thereof; the aforementioned existing solar devices may otherwise be equivalent to solar device  1200 , solar device  1300 , solar device  1400  and/or solar device  1500 . In one or more embodiments, the aforementioned enhancements may provide for increased (e.g., three to fourfold) solar thermal power and/or electrical power output compared to these existing solar devices. 
     In one or more embodiments, thermoelectric module  970  and embodiments thereof in  FIGS. 3-8  may provide for the first cost-effective solar, thermoelectric and solar-thermal panels based on thin-film thermoelectrics. In one or more embodiments, the thin-film basis may provide for negligible increase in weight of the abovementioned enhanced solar devices due to addition of thermoelectric module  970  and embodiments thereof in  FIGS. 3-8 . 
     It should be noted that solar device  1200 , solar device  1300 , solar device  1400  and solar device  1500  may be examples of hybrid solar/thermoelectric and hybrid solar thermal/thermoelectric devices. To generalize, exemplary embodiments may relate to hybrid solar and solar thermal devices with embedded thermoelectric module (e.g., thermoelectric module  1202 , thermoelectric sandwich  1350 , thermoelectric module  1402 , thermoelectric module  1502 ). 
       FIG. 16  shows a process flow diagram detailing the operations involved in realizing a solar device (e.g., solar device  1200 , solar device  1300 , solar device  1400 , solar device  1500 ), according to one or more embodiments. In one or more embodiments, operation  1602  may involve sputter depositing pairs of N-type thermoelectric legs (e.g., N-type thermoelectric legs  602   1-P ) and P-type thermoelectric legs (e.g., P-type thermoelectric legs  604   1-P ) electrically in contact with one another on a flexible substrate (e.g., substrate  350 ) to form a thin-film based thermoelectric module (e.g., thermoelectric module  970  and the embodiments of  FIGS. 3-8 , thermoelectric module  1202 , thermoelectric sandwich  1350 , thermoelectric module  1402 , thermoelectric module  1502 ). 
     In one or more embodiments, the flexible substrate may be an Al foil, a sheet of paper, teflon, plastic, polyimide, a single-sided metal clad laminate, or a double-sided metal clad laminate. In one or more embodiments, operation  1604  may involve rendering the formed thin-film based thermoelectric module flexible and less than or equal to 100 μm in dimensional thickness based on choices of fabrication processes with respect to layers of the formed thin-film based thermoelectric module including the sputter deposited N-type thermoelectric legs and the P-type thermoelectric legs. In one or more embodiments, operation  1606  may involve directly coupling the flexible thin-film based thermoelectric module to a layer of heat absorber material (e.g., heat absorber layer  1204 ) or a layer of photovoltaic material (e.g., PV layer  1404 ) configured to receive sunlight (e.g., sunlight  1250 ) such that the flexible thin-film based thermoelectric module is in contact therewith to form the solar device. 
     In one or more embodiments, operation  1608  may then involve leveraging, through the directly coupled flexible thin-film based thermoelectric module, a temperature difference across a first surface (e.g., surface  1252 , metallic layer  1304 ) of the flexible thin-film based thermoelectric module directly in contact with the layer of heat absorber material or the layer of photovoltaic material and a second surface (e.g., surface  1254 , metallic layer  1306 ) away therefrom to generate increased solar thermal power and/or electrical power output through the solar device compared to an otherwise equivalent solar device without the formed thin-film based thermoelectric module. 
     Although the present embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the various embodiments. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.