Controllable Growth of Ga Film Electrodeposited from Aqueous Solution and Cu(In,Ga)Se2 Solar Cells.

Electrodepositon of Ga film is very challenging due to the high standard reduction potential (-0.53 V vs SHE for Ga3+). In this study, Ga film with compact structure was successfully deposited on the Mo/Cu/In substrate by the pulse current electrodeposition (PCE) method using GaCl3 aqueous solution. A high deposition rate of Ga3+ and H+ can be achieved by applying a large overpotential induced by high pulse current. In the meanwhile, the concentration polarization induced by cation depletion can be minimized by changing the pulse frequency and duty cycle. Uniform and smooth Ga film was fabricated at high deposition rate with pulse current density 125 mA/cm2, pulse frequency 5 Hz, and duty cycle 0.25. Ga film was then selenized together with electrodeposited Cu and In films to make a CIGSe absorber film for solar cells. The solar cell based on the Ga film presents conversion efficiency of 11.04%, fill factor of 63.40%, and Voc of 505 mV, which is much better than those based on the inhomogeneous and rough Ga film prepared by the DCE method, indicating the pulse current electrodeposition process is promising for the fabrication of CIGSe solar cell.