In -situ Microscopy Characterization of Cu(In,Ga)Se2 Potential -Induced Degradation

We report on the role of sodium in potentialinduced degradation (PID) of Cu(In, Ga)Se2 (CIGS) solar cells. In-situ microscopy characterizations on AFM platform were performed on two stressed CIGS device under room temperature (RT) and high temperature (HT) at 85 C. During PID stressing we observed depletion region gets wider as Na migrates, p -n junction becomes leaky at RT for over a month; and similar junction evolution was observed for HT -stressed sample, eventually the junction collapsed after 18 hours. The diode behaviors were confirmed by dark I-V measurement. Time-ofFlight secondary-ion mass spectrometry reveals that the Na accumulates on ZnO and CdS side, as well as the upper layer of CIGS layer. The results indicate that Na drifted by the voltage applied on the soda-lime glass, then diffuse through the whole device. And the sodium profiles have different points of evolution due to the temperature differences between the two stressed samples. The consistent results unambiguously show how Na from substrate glass causes PID in CIGS solar cells.