Insight Into Metastable Defects in Flexible $\text{Cu}(\text{In}_{1-x}\text{Ga}_{x})\text{Se}_{2}$ Modules via X-ray Microscopy

The origin of metastability in Cu(In
_1-x
Ga
_x
)Se
₂
solar cells has long be a topic of study and debate. The drop in device performance after light soaking has been attributed to changes in the V
_Se
-V
_Cu
defect pair and to the electromigration of Cu. In this work, we use a suite of X-ray microscopy tools to study the nanoscale distribution of Cu and Se in industrially-relevant CIGS modules on stainless steel before and after accelerated stress testing from dark heat and light soaking. Changes in chemical inhomogeneity are studied through nano-scale X-ray fluorescence and correlated to electrical performance through Xray beam induced current and voltage. We observe no meaningful variation in the Cu distribution before and after light soaking but a sensible difference in the Se distribution. Average XBIC values at the nano-scale trend directly with changes in full device Jsc both of which see a reduction after light soaking. We note that low performing areas of XBIC in both the initial and dark heat samples perform significantly worse after light soaking when compared to changes in the good performing areas.