Ohmic-like contact formation at the rear interface between Cu(In,Ga)Se2 and ZnO:Al in a lift-off Cu(In,Ga)Se2 solar cell

Abstract

A lift-off Cu(In,Ga)Se2 (CIGS) solar cell, which could serve as the top solar cell in a tandem-type solar cell, was fabricated with a superstrate-type structure consisting of soda-lime glass (SLG)/epoxy/Al/n-type ZnO:Al (AZO)/ZnO/CdS/p-type CIGS/n-type AZO (back electrode)/Al. This study proposes a method of realizing the ohmic-like contact between p-type CIGS and n-type AZO in a lift-off CIGS solar cell to improve the conversion efficiency (η). The sputtering conditions under which the n-type AZO layer was deposited, specifically the sample position and radio frequency (RF) power density, were optimized to form ohmic-like contact through trap-assisted tunneling recombination. The sputtering damage near the CIGS surface that induced the trap-assisted tunneling recombination was evaluated by examining the photoluminescence peak intensity. Ultimately, ohmic-like characteristics were attained for the p-type CIGS/n-type AZO interface under optimal AZO deposition conditions, with the sample positioned 0cm from the AZO target center and an RF power density of 2.4W/cm2. The proposed method was successfully applied to the fabrication of a lift-off CIGS solar cell. Consequently, an η value of 9.2% was obtained for the lift-off CIGS solar cell, which is 70% that of a substrate-type CIGS solar cell.