Formation of compound film for photovoltaic device

Abstract

A compound film for an active layer of a photovoltaic device may be formed in two or more sub-layers. A first sub-layer having a first component of the active layer may be formed on a substrate with a first process. A second sub-layer including a second component of the active layer may then be formed using a second process such that the first sub-layer is disposed between the second sub-layer and the substrate. The second component has a different chemical composition than the first component. The first and/or second sub-layer may comprise one or more components in the form of particles and/or globules. This procedure may be repeated any number of times for any number of sub-layers so that active layer can be built up sequentially. The different chemical compositions of the components in the sub-layers can provide the active layer with a graded bandgap. The components of the sub-layers may include elements of group IB, and/or group IIIA. One or more elements of group VIA can be incorporated into the components of the sub-layers before, during or after formation of the layers.

1 . A method of forming a compound film for an active layer of a photovoltaic device comprising the steps of: 
 forming a first sub-layer including a first component of the active layer on a substrate with a first process;    forming a second sub-layer including a second component of the active layer using a second process, wherein the second component has a different chemical composition than the first component and wherein the first sub-layer is disposed between the second sub-layer and the substrate    wherein the first and/or second component includes particles.    
   
   
       2 . The method of  claim 1 , further comprising, forming one or more additional sub-layers including one or more additional components of the active layer.  
   
   
       3 . The method of  claim 1  wherein the particles include nanoparticles and/or nanoglobules.  
   
   
       4 . The method of  claim 1  wherein the first and/or second process is a printing process.  
   
   
       5 . The method of  claim 1 , further comprising depositing a one or more addition sub-layers by a vapor deposition technique.  
   
   
       6 . The method of  claim 5  wherein the vapor deposition technique is selected from the group of ALD, evaporation, sputtering, CVD, PVD, electroplating and the like.  
   
   
       7 . The method of  claim 1  wherein the different chemical compositions of the first and second components in the first and second sub-layers provide the active layer with a graded bandgap.  
   
   
       8 . The method of  claim 1  wherein the first and/or second components include elements of group IB, and/or group IIIA.  
   
   
       9 . The method of  claim 8 , further comprising the step of incorporating an element of group VIA into the first and/or second component.  
   
   
       10 . The method of  claim 1  wherein forming the first and/or second sub-layer includes making one or more phase-stabilized precursors in the form of fine particles, particles comprising at least one metal oxide and reducing the metal oxides in a reducing atmosphere.  
   
   
       11 . The method of  claim 1  wherein forming the first and/or second sub-layer includes making single-phase mixed-metal oxide particles with an average diameter of less than about 1 micron by preparing a solution comprising Cu and In and/or Ga as metal-containing compounds; forming droplets of the solution; and heating the droplets in an oxidizing atmosphere to pyrolyze the contents of the droplets to form single-phase copper indium oxide, copper gallium oxide or copper indium gallium oxide particles.  
   
   
       12 . The method of  claim 1  wherein forming the first and/or second sub-layer includes preparing a source material, depositing the source material on the substrate to form a precursor, and heating the precursor to form a film, wherein the source material includes Group IB-IIIA containing particles having at least one Group IB-IIIA phase, with Group IB-IIIA constituents present at greater than about 50 molar percent of the Group IB elements and greater than about 50 molar percent of the Group IIIA elements in the source material.  
   
   
       13 . The method of  claim 1  wherein forming the first and/or second sub-layer includes formulating a nano-powder material with a controlled overall composition and having particles of one solid solution, depositing the nano-powder material to form the first or second sub-layer, and reacting in at least one suitable atmosphere to form the first or second component.  
   
   
       14 . The method of  claim 1  wherein forming the first and/or second sub-layer includes forming a liquid ink containing elements from groups IB, IIIA and optionally VIA, spreading a film of the liquid onto the substrate, and annealing the film to form the first or second sub-layer.  
   
   
       15 . The method of  claim 14  wherein forming the liquid ink includes 
 forming non-oxide quantum nanoparticles containing elements from group IB; and forming non-oxide quantum nanoparticles containing elements from group IIIA; and optionally forming non-oxide quantum nanoparticles containing elements from group VIA;    intermixing the non-oxide quantum nanoparticles from groups IB and IIIA and optionally VIA wherein the non-oxide quantum nanoparticles are in a desired particle size range of between about 0.1 nm and about 10 nm in diameter, wherein, for each element, a majority of the mass of the non-oxide quantum nanoparticles range in size from no more than about 40% above or below an average particle size, or, if the average particle size is less than about 5 nanometers, from no more than about 2 nanometers above or below the average particle size, and    mixing the non-oxide nanoparticles to form a liquid that serves as the ink    
   
   
       16 . The method of  claim 14  wherein forming the liquid ink includes: 
 forming nanoparticles from group IB; and    intermixing the nanoparticles from group IB with elements from group IIIA, wherein the elements from group IIIA are in molten form, wherein the nanoparticles from group IB comprise particles in a desired particle size range of between about 0.1 nm and about 500 nm in diameter, wherein a majority of the mass of the nanoparticles range in size from no more than about 40% above or below an average particle size, or, if the average particle size is less than about 5 nanometers, from no more than about 2 nanometers above or below the average particle size; and    mixing the nanoparticles with the molten elements to form a liquid that serves as the ink.    
   
   
       17 . The method of  claim 14  wherein forming the liquid ink includes: 
 forming nanoparticles containing elements from groups IB, and IIIA and optionally VIA, wherein the particles are in a desired particle size range of between about 0.1 nm and about 500 nm in diameter, wherein a majority of the mass of the nanoparticles range in size from no more than about 40% above or below an average particle size, or, if the average particle size is less than about 5 nanometers, from no more than about 2 nanometers above or below the average particle size; and    mixing the nanoparticles to form a liquid that serves as the ink.    
   
   
       18 . The method of  claim 1  wherein forming the first or second sub-layers includes: 
 forming a molten mixture of one or more metals of group IIIA and metallic nanoparticles containing elements of group IB; and    coating a substrate with a film formed from the molten mixture.    
   
   
       19 . The method of  claim 1  wherein forming the first or second sub-layers includes: 
 obtaining core nanoparticles containing one or more elements from group IB and/or IIIA; and    coating the core nanoparticles with one or more layers of metal from group IB, IIIA or an element from group VIA in a controlled fashion such that the resulting film of coated nanoparticles have a desired stoichiometric ratio of elements    forming an ink, paste, or paint containing the nanoparticles;    forming a thin film of the ink, paste or paint on the substrate; and    annealing the thin film.    
   
   
       20 . The method of  claim 1  wherein the substrate is an aluminum foil substrate.  
   
   
       21 . The method of  claim 1 , further comprising rapidly heating the first and/second sub-layer and/or substrate from an ambient temperature to a plateau temperature range of between about 200° C. and about 600° C.;  
     maintaining the first and/or second sub-layer and/or substrate in the plateau temperature range for between about a fraction of a second and about 60 minutes; and  
     reducing the temperature of the first and/or second sub-layer and/or substrate.  
   
   
       22 . The method of  claim 1 , further comprising:  
     performing atomic layer deposition of a group IB element and/or a group IIIA element and/or a group VIA element onto the substrate, the first sub-layer or the second sub-layer.  
   
   
       23 . The method of  claim 1 , wherein forming the first and/or second sub-layer includes formulating a dispersion of IB and IIIA elemental nanoparticles, wherein a group IIIA element is incorporated into the dispersion in the form of a suspension of nanoglobules; depositing said dispersion onto a substrate to form a film on the substrate; and reacting the film in a suitable atmosphere.  
   
   
       24 . The method of  claim 23 , further comprising iteratively repeating said formulating, depositing and reacting steps two or more times to form said compound film.  
   
   
       25 . The method of  claim 24  wherein, for at least one iteration, the formulating step includes changing a relative concentration of the IB, IIIA or VIA elemental nanoparticles such that a concentration of the IB, IIIA or VIA elements within the compound film varies as a function of depth.  
   
   
       26 . The method of  claim 24  wherein iteratively repeating said formulating, depositing and reacting steps produces a concentration of group IIIA elements that is relatively higher at and near a front region and a back region of the compound film, and relatively lower in a central region of the compound film, resulting in a “saddle” profile for the concentration of the one or more group IIIA elements as a function of depth within the compound film.  
   
   
       27 . The method of  claim 26  wherein the group IIIA elemental nanoparticles include Gallium and/or Indium.  
   
   
       28 . The method of  claim 27  wherein iteratively repeating said formulating, depositing and reacting steps produces a Gallium concentration that is relatively high at or near the back region.  
   
   
       29 . The method of  claim 26  wherein a Gallium concentration is relatively lesser in the central region.  
   
   
       30 . The method of  claim 26  wherein the group IB element is copper (Cu).  
   
   
       31 . The method of  claim 23 , wherein the IIIA elemental nanoparticles include Gallium  
   
   
       32 . The method of  claim 23  wherein the IIIA elemental nanoparticles include Indium.  
   
   
       33 . The method of  claim 23  wherein the IIIA elemental nanoparticles include Aluminum.  
   
   
       34 . The method of  claim 23  wherein the group IB elemental nanoparticles include Copper.  
   
   
       35 . The method of  claim 23  further comprising, incorporating a group VIA elemental material into the compound film.  
   
   
       36 . The method of  claim 35  wherein incorporating a group VIA elemental material into the compound film includes exposing the compound film to vapor and/or gas containing the group VIA elemental material in conjunction with annealing.  
   
   
       37 . The method of  claim 35  wherein incorporating the group VIA elemental material into the compound film includes the use of nanoparticles containing a VIA group element in step of formulating the dispersion.  
   
   
       38 . The method of  claim 35  wherein the group VIA elemental material includes Selenium.  
   
   
       39 . The method of  claim 35  wherein the group VIA elemental material includes Sulfur  
   
   
       40 . The method of  claim 35  wherein the group VIA elemental material includes Tellurium.  
   
   
       41 . The method of  claim 1  wherein the compound film includes an alloy of Copper and Gallium, wherein a ratio of Gallium to Copper varies as a function of depth within the compound film.  
   
   
       42 . The method of  claim 1  wherein the compound film includes an alloy of Copper and Indium wherein a ratio of Indium to Copper varies as a function of depth within the compound film.  
   
   
       43 . The method of  claim 1  wherein the substrate is a flexible substrate and printing the first and/or second sub-layers includes the use of roll-to-roll manufacturing on the flexible substrate.  
   
   
       44 . A photovoltaic device having a light-absorbing layer, wherein the light-absorbing layer is a compound film formed by the method of  claim 1 .  
   
   
       45 . The device of  claim 44  wherein the light-absorbing layer contains elements of groups IB, IIIA and VIA.  
   
   
       46 . The device of  claim 44  wherein a concentration of the IB, IIIA or VIA elements within the light-absorbing layer varies as a function of depth  
   
   
       47 . The device of  claim 44  wherein the light-absorbing layer is disposed between a base electrode and a transparent electrode.  
   
   
       48 . The device of  claim 47 , further comprising a junction partner layer between the active layer and the transparent electrode.  
   
   
       49 . The device of  claim 48  wherein the junction partner layer includes cadmium sulfide (CdS), zinc sulfide (ZnS), or zinc selenide (ZnS) or some combination of two or more of these.  
   
   
       50 . The device of  claim 48  wherein the junction partner layer includes an organic n-type polymer or small molecule.  
   
   
       51 . The device of  claim 48  wherein the base electrode includes a layer of molybdenum proximate the junction partner layer.  
   
   
       52 . The device of  claim 47  wherein the transparent electrode includes a layer of a transparent conductive oxide.  
   
   
       53 . The device of  claim 52  wherein the transparent conductive oxide is indium tin oxide, fluorinated indium tin oxide, zinc oxide or aluminum doped zinc oxide or a related material.  
   
   
       54 . A method of forming a compound film comprising the steps of: 
 formulating a dispersion of IB and IIIA elemental nanoparticles, wherein a group IIIA element is incorporated into the dispersion in the form of a suspension of nanoglobules; depositing said dispersion onto a substrate to form a layer on the substrate; and reacting the layer in a suitable atmosphere; and iteratively repeating said formulating, depositing and reacting steps two or more times to form said compound film, wherein, for at least one iteration, the formulating step includes changing a relative concentration of the IB, IIIA or VIA elemental nanoparticles such that a concentration of the IB, IIIA or VIA elements within the compound film varies as a function of depth.