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 for fabricating a liquid containing intermixed elements of groups IB and IIIA, and optionally VIA, comprising the steps of:
forming nanoparticles containing elements from group IB; and
forming nanoparticles containing elements from group IIIA; and optionally forming non-oxide nanoparticles containing elements from group VIA;
combining the nanoparticles with a liquid to form an ink;
wherein the nanoparticles for the ink may be prepared from a mixture of metal nanoparticles and a vapor or powder containing either Se or S.
2 . The method of claim 1 wherein forming non-oxide quantum nanoparticles includes preparing metal nanoparticles containing elements of groups IB, IIIA, VIA or a IB-IIIA-VIA alloy, by laser ablation, nucleation from vapor, exploding wires by electrical current surge, thermal decomposition of organometallic compounds, sonolysis, pulse radiolysis, electrochemical reduction or chemical reduction.
3 . The method of claim 1 wherein the ink is formed by mixture with water.
4 . The method of claim 1 wherein the ink is formed by mixture with organic solvent.
5 . The method of claim 1 , further comprising adding a capping agent to the non-oxide nanoparticles.
6 . The method of claim 1 , further comprising adding a binder to the non-oxide quantum nanoparticles.
7 . The method of claim 1 , further comprising adding a fluxing agent to the non-oxide quantum nanoparticles.
8 . The method of claim 1 , further comprising adding one or more surfactants, polymers, dispersants, binders, modifiers, detergents or additives to the non-oxide quantum nanoparticles.
9 . The method of claim 1 wherein the group IB element is copper (Cu), the group IIIA element is indium and optionally includes gallium) and the group VIA element is selenium (Se) or sulfur (S) and a stoichiometric ratio of the Cu, In and Se or S in the liquid is approximately CuIn1-xGax(S or Se) 2 , where x is between 0 and 1.
10 . The method of claim 9 wherein a majority of the group IB nanoparticles range in size from no more than about 40% above or below an average nanoparticle size, or, if the average nanoparticle size is less than about 5 nanometers, from no more than about 2 nanometers above or below the average nanoparticle size.
11 . The method of claim 9 , further comprising adjusting the temperature of the Cu—In—Ga mixture until a solid forms and then grinding the solid to form nanoparticles.
12 . The method of claim 1 further comprising the step of capping the nanoparticles with an organic material.
13 . The method of claim 12 wherein the organic material is a small molecule with low boiling point.
14 . The method of claim 13 wherein the organic material is selected from the group of trioctylphosphine oxide, trioctylphosphine, triphenylphosphine, pyridine, alcohols (methanol, ethanol, propanol, butanol), ethane thiol, tetrahydrofuran, ethers, ammonia, amines (methyl amine, ethylamine, ethylenediamine) and acetonitrile.
15 . The method of claims 14 wherein the organic material is pyridine.
16 . The method of claim 1 wherein forming a mixture of non-oxide nanoparticles includes selecting particles in the desired particle size range.
17 . The method of claim 16 , wherein selecting nanoparticles in the desired size range includes adjusting one or more parameters of a reaction that forms the nanoparticles, size-selective precipitation, or ultrafiltration.
18 . The method of claims 1 further comprising adding a water-compatible dispersant to the liquid.
19 . The method of claims 1 wherein forming the non-oxide nanoparticles includes preparing particles in a non-oxygen atmosphere.
20 . The method of claim 1 wherein the size distributions of the CuInS 2 or CuIn(Se) 2 nanoparticulates may be adjusted by size-selective precipitation, ultrafiltration and the like.
21 . A photovoltaic device precursor material comprising:
a liquid ink comprising:
non-oxide metal nanoparticles containing elements from group IB, non-oxide metal nanoparticles from group IIIA; and adding one or more liquid metals containing one or more elements of group IIIA, wherein forming a mixture of non-oxide quantum nanoparticles includes reacting a single-source precursor to form particles of IB-IIIA-VIA material;
a dispersant; and
a solvent.