  Light-induced instabilities/degradation in Cu(In,Ga)Se2 (CIGS) solar cells
are a prevalent and urgent issue to resolve to improve performance, uniformity,
and reliability. Here, mechanisms contributing to light-induced instabilities
are identified focusing on an observed short circuit current (JSC) reduction.
External quantum efficiency measurements before and after light soaking
identified a reduction in long wavelength photon carrier collection efficiency
in the CIGS absorber layer. Using deep level optical spectroscopy (DLOS), the
concentration of CIGS EV+0.98 eV deep level is correlated with the amount of
JSC degradation, Finally, capacitance voltage (C-V) measurements reveal light
induces a large reduction in the depletion depth and reduction of carrier
collection and are all correlated with the JSC reduction. Finally, the EV+0.53
eV trap concentrations are shown to correlate with VOC instability but not the
JSC reduction confirming that multiple trap-induced mechanism are responsible
for the light-induced instabilities.
