SOLUTION-BASED FABRICATION OF PHOTOVOLTAIC CELL
An ink for forming CIGS photovoltaic cell active layers is disclosed along with methods for making the ink, methods for making the active layers and a solar cell made with the active layer. The ink contains a mixture of nanoparticles of elements of groups IB, IIIA and (optionally) VIA. The particles are in a desired particle size range of between about 1 nm and about 500 nm in diameter, where a majority of the mass of the particles comprises particles ranging 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. The use of such ink avoids the need to expose the material to an H 2 Se gas during the construction of a photovoltaic cell and allows more uniform melting during film annealing, more uniform intermixing of nanoparticles, and allows higher quality absorber films to be formed.
1 . A method comprising:
providing a liquid ink comprising a) particles containing one or more elements from group IB and b) one or more liquid metals containing one or more elements from group IIIA;
depositing the liquid ink on a substrate; and
heating the liquid ink in one or more steps to form a photovoltaic absorber layer.
2 . The method of claim 1 further comprising adding group VIA material during the heating step.
3 . The method of claim 1 wherein the heating step comprises of heating the liquid ink to in an H 2 or N 2 atmosphere and then heating in a Group VIA atmosphere.
4 . The method of claim 1 wherein the heating step comprises of heating the liquid ink to anneal the particles together in a non-Group VIA atmosphere and then heating in a Group VIA atmosphere.
5 . The method of claim 1 , wherein a Group VIA element is introduced by heating the ink in a Group VIA vapor.
6 . The method of claim 1 , wherein a Group VIA element is introduced by heating the ink in a sulfur vapor.
7 . The method of claim 1 , wherein a Group VIA element is introduced by heating the ink in a selenium vapor.
8 . The method of claim 1 , wherein a Group VIA element is introduced into the liquid ink by adding particles containing one or more Group VIA element.
9 . The method of claim 1 wherein the particles are combined with an organic solvent to form the liquid ink.
10 . The method of claim 1 wherein the particles are combined with an inorganic solvent to form the liquid ink.
11 . The method of claim 1 wherein the particles are combined with water to form the liquid ink.
12 . The method of claim 1 further comprising adding a dispersant to the liquid ink.
13 . The method of claim 1 , further comprising adding one or more surfactants, polymers, dispersants, binders, modifiers, detergents or additives to the liquid ink.
14 . The method of claim 1 wherein the non-oxide nanoparticles are added to a solvent to form a suspension.
15 . The method of claim 1 wherein the non-oxide nanoparticles are added to a solvent to form a colloidal suspension.
16 . The method of claim 1 , wherein the substrate comprises a metal foil.
17 . The method of claim 1 , wherein the substrate comprises a metal foil up to 2 meters wide.
18 . The method of claim 1 , wherein the substrate comprises of at least one material from the group consisting of: stainless steel, molybdenum, and aluminum.
19 . The method of claim 1 , wherein the substrate comprises a metallized film.
20 . The method of claim 1 , wherein applying the liquid ink comprises spreading a thin film of the liquid ink over the substrate using solution based coating techniques selected from the group consisting of: web coating, spray coating, spin coating, doctor blade coating, printing techniques including contact printing, gravure printing, microgravure printing, ink-jet printing, jet deposition, and combinations thereof.
21 . The method of claim 1 , wherein applying the liquid ink comprises spreading a thin film of the liquid ink over the substrate in a roll-to-roll manner using a web coating system.
22 . The method of claim 1 , wherein the particles containing the containing one or more elements of group IB are alloy particles.
23 . The method of claim 1 further comprising removing solvents from the ink by heating the ink and substrate.
24 . The method of claim 1 wherein heating occurs in a non-vacuum environment.
25 . A processing assembly for use with a flexible substrate, the assembly comprising:
a roll-to-roll processing tool transporting a substrate through an annealing zone for heating a precursor layer on the substrate and then through heating zone in a group VIA vapor tool, wherein the heating occurs in a non-vacuum environment.
26 . A photovoltaic device precursor material comprising:
a liquid ink comprising:
a) particles containing one or more elements from group IB and b) one or more liquid metals containing one or more elements from group IIIA
a dispersant; and
a solvent.