Fabrication of Double Graded Bandgap CuInGaSe/sub 2/ Thin Film Solar Cells by Electrodeposition

How to increase the conversion efficiency is a key technology in solar cells. Bandgap engineering in Cu(In, Ga)Se2 thin film solar cells is an efficient method to improve its conversion efficiency. The method is to add Ga element into the CuInSe2 thin film. Changing the ratio of Ga/(In+Ga) in Cu(In, Ga)Se2 thin film solar cells can result in the variation of bandgap and then improve the conversion efficiency. In addition, it is well known that thin film solar cells will be grown by a little of material and have potentials in low cost, mass production and flexible substrate applications. The most interesting substrates are steel foils, since they can be coated in a roll-to-roll process at high temperatures of up to 600°C in a Se atmosphere. Two important works are studied in this project. One is the fabrication of double Ga-grading Cu(In, Ga)Se2 solar cells by electrodeposition and the other is the deposition of Cu(In, Ga)Se2 solar cells on steel foils. In the first work, double Ga-grading Cu(In, Ga)Se2 solar cells are fabricated by electrodeposition. In the initial growth, the Ga/(In+Ga) ratio in electrolyte solution is fixed. As the deposition time passed, the electrolyte solution containing the Ga ratio will be diluted gradually and then be gradually increased again. An increased Ga/(In+Ga) ratio toward the back contact and the front end will be formed. The variation of the Ga/(In+Ga) ratio will affect the bandgap of Cu(In, Ga)Se2 films. A good design in bandgap variation will be helpful for open circuit voltage, short circuit voltage and conversion efficiency. The optimized parameters of double Ga-graded bandgap will be obtained by computer simulation and verified by experimentally. The electrodeposition parameters, such as electrolyte solution concentration, pH value, potential, deposition time and anneal temperature, etc., will be carefully investigated to find a good fabrication process. In the second work, to fabricate the Cu(In, Ga)Se2 solar cell on steel foils will be examined. The preparation of highly efficient solar cells requires the deposition of a barrier layer to reduce the diffusion of impurities from the metal substrate into the solar cells. Various metals and oxides of Cr, Ta, Al2O3 and SiO2 will be used as diffusion barrier to prevent the metal ion outdiffusion.

Project ID:PB9709-3579
External Project ID:NSC97-2221-E182-010