Fabrication of Cu(In, Ga)Se2 thin film solar cell absorbers from electrodeposited bilayers

CuInSe2 (CIS) and Cu(In, Ga)Se2 (CIGS) films as solar cell absorbers have been fabricated from electrodeposited (ED) In–Se/CIS and CIS/CuGaSe2 (CGS) bilayers, respectively. Firstly, In–Se/CIS bilayers were intermixed by annealing at 600 °C for 10 min and it followed that CIS films with large grains and controlled compositional ratios were realized. CIS solar cells using these films showed around 2.2% efficiency. Next, CIS/CGS bilayers were annealed at 600 °C for 60 min for intermixing. Here, oxygen-free CGS films prepared from Cu–Ga–Se solution added Li2SO4 as the supporting electrolyte were used because Ga–O compound formed in ED-CGS films worked as the defects. As the results, around 2.9% efficiency CIGS solar cell using the films was realized. Especially, 29.7 mA/cm2 and 36.1 mA/cm2 high short-circuit current density were obtained in the CIS and CIGS solar cells, respectively. These results indicate that ED-bilayers technique is useful to realize low-cost and high efficiency solar cell.