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 solar cell formed using a liquid containing intermixed elements of groups IB, IIIA, and VIA, comprising the steps of:
a) forming by sonochemical method non-oxide nanoparticles;
b) providing a suspension comprised of one or more liquid metals, wherein the one or more liquid metals comprises at least one group IIIA based material;
c) mixing the non-oxide nanoparticles of step a) and the suspension of one or more liquid metals of step b) to form an ink containing both the non-oxide nanoparticles and the one or more liquid metals;
wherein the nanoparticles 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.
2. The method of claim 1 wherein the ink comprises non-oxide nanoparticles of step a) formed from Cu(Ac) 2 and/or In(Ac) 3 and selenourea dissolved in water and sonicated for about 1 hour or more under an atmosphere of inert gas.
3. The method of claim 1 wherein a round-bottom vessel is used for the sonochemical method of step a).
4. The method of claim 1 wherein the temperature of the mixture rises gradually to about 80° C. during ultrasonic irradiation in sonochemical method of step a).
5. The method of claim 1 wherein after about 1 hour or more of sonication in sonochemical method of step a), the solution is centrifuged, and the precipitate washed with water and then with absolute ethanol.
6. The method of claim 1 further comprising depositing the liquid ink on a substrate; and
heating the liquid ink in one or more steps to form a photovoltaic absorber layer.
7. The method of claim 6 , wherein the substrate comprises a metal foil up to 2 meters wide.
8. The method of claim 6 , wherein the substrate comprises of at least one material from the group consisting of: stainless steel, molybdenum, and aluminum.
9. The method of claim 6 , wherein the substrate comprises a metallized film.
10. The method of claim 6 , 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.
11. The method of claim 6 , 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.
12. The method of claim 1 wherein the ink includes a solvent.