Bandgap grading in thin-film devices via solid group iiia particles

Abstract

Methods and devices are provided for forming thin-films from solid group IIIA-based particles. In one embodiment, a method is provided for bandgap grading in a thin-film device using such particles. The method may be comprised of providing a bandgap grading material comprising of an alloy having: a) a IIIA material and b) a group IA-based material, wherein the alloy has a higher melting temperature than a melting temperature of the IIIA material in elemental form. A precursor material may be deposited on a substrate to form a precursor layer. The precursor material comprising group IB, IIIA, and/or VIA based particles. The bandgap grading material of the alloy may be deposited after depositing the precursor material. The alloy in the grading material may react after the precursor layer has begun to sinter and thus maintains a higher concentration of IIIA material in a portion of the compound film that forms above a portion that sinters first.

1 . A process of forming a Group IBIIIAVIA solar cell absorber on a base, comprising: forming a film on the base, wherein the film is substantially metallic and comprises Cu and In; forming a separator layer over the film, wherein the separator layer substantially comprises a Group VIA material; forming a source layer over the separator layer, wherein the source layer substantially comprises Ga and it is substantially metallic; forming a cap layer over the source layer, wherein the cap layer substantially comprises Se; and reacting the film, the separator layer, the source layer and the cap layer with each other at a reaction temperature to form the Group IBIIIAVIA absorber layer, the absorber layer including a surface region of less than or equal to 300 nm thickness, wherein the Ga/(Ga+In) molar ratio within the surface region is in the range of 0.1-0.3. 
     
     
         2 . The process of  claim 1 , wherein the reaction temperature is in the range of 500-600.degree. C. 
     
     
         3 . The process of  claim 2 , wherein the film, the separator layer, the source layer and the cap layer are distinct layers with no substantial intermixing, and the step of reacting includes rapidly heating the film, the separator layer, the source layer and the cap layer to the reaction temperature with a heating rate of at least 50° C. per second. 
     
     
         4 . (canceled) 
     
     
         5 . The process of  claim 2 , wherein the film further includes Ga. 
     
     
         6 . The process of  claim 5 , wherein the film is in the form of a material stack made of distinct layers and the step of forming the film comprises: depositing a Cu layer over the base; and depositing at least two additional layers including Ga and In over the Cu layer, wherein the Ga/(Ga+In) ratio within the film is in the range of 0-0.7. 
     
     
         7 . The process of  claim 6 , wherein the steps of depositing the Cu layer and depositing at least two additional layers are carried out by electroplating. 
     
     
         8 . The process of  claim 7 , wherein the step of forming the separator layer comprises electroplating. 
     
     
         9 . The process of  claim 8 , wherein the step of forming the source layer comprises vapor deposition. 
     
     
         10 . The process of  claim 9 , wherein the step of forming the cap layer comprises vapor deposition. 
     
     
         11 . (canceled) 
     
     
         12 . The process of  claim 11 , wherein the fourth additive material includes at least one dopant material selected from the group of Na, K and Li. 
     
     
         13 . The process of  claim 12 , wherein the molar ratio of Cu/In+Ga in the film is in the range of 0.8-1.0 
     
     
         14 . The process of  claim 2 , wherein the separator layer further includes a first additive material, wherein a ratio of the molar amount of the Group VIA material to the total molar amounts of the Group VIA material and the first additive material is in the range of 0.95-1.0. 
     
     
         15 . The process of  claim 14 , wherein the Group VIA material includes at least one of Se and Te, and the first additive material includes at least one of Cu, In, Ga and a dopant material selected from the group of Na, K and Li. 
     
     
         16 . (canceled) 
     
     
         17 . The process of  claim 16 , wherein the second additive material includes at least one of Cu, In, and a dopant material selected from the group of Na, K and Li. 
     
     
         18 . (canceled) 
     
     
         19 . The process of  claim 18 , wherein the third additive material includes at least one of Te and a dopant material selected from the group of Na, K and Li. 
     
     
         20 . The process of  claim 2 , wherein at least one of the separator layer, the source layer and the cap layer includes a dopant film comprising one of Na, K and Li. 
     
     
         21 . (canceled) 
     
     
         22 . (canceled) 
     
     
         23 . The process of  claim 1 , wherein the step of forming the separator layer comprises electroplating. 
     
     
         24 . A multilayer structure to form Group IBIIIAVIA absorber layers for solar cells, comprising: a base; a substantially metallic film formed over the base, wherein the substantially metallic film includes Cu and In; a separator layer formed over the substantially metallic film, the separator layer substantially comprises a Group VIA material; a substantially metallic source layer formed over the separator layer, the source layer substantially comprises Ga; and a cap layer formed over the source layer, the cap layer substantially comprises Se. 
     
     
         25 . (canceled) 
     
     
         26 . (canceled) 
     
     
         27 . The multilayer structure of  claim 26 , wherein the Group VIA material comprises at least one of Se and Te, and the first additive material comprises at least one of Cu, In, Ga, and a dopant material selected from the group of Na, K and Li. 
     
     
         28 - 32 . (canceled) 
     
     
         33 . The multilayer structure of claim  32 , wherein the substrate comprises one of glass sheet, polyimide foil, stainless steel foil and aluminum alloy foil, and the contact layer comprises Mo. 
     
     
         34 - 39 . (canceled)