Photo current metastability in Cu(In,Ga)Se2 solar cells with controlled conduction band alignment

A metastability of current density–voltage characteristics, so called a light soaking (LS) effect, in (Zn,Mg)O (ZMO)/Cu(In,Ga)Se2 (CIGS) solar cells with the controlled conduction band offset (CBO) between window and CIGS layers was measured. The strong LS effect was observed with increasing the CBO value from +0.03 eV to +0.35 eV. Here, plus sign of CBO indicate the conduction band minimums of the window layers above that of the CIGS layers. When the CBO is positive, the CBO acts as a barrier for photo-generated electrons in the CIGS layer. On the other hand, the CIGS solar cells with Cd partial electrolyte treatment for the CIGS surface before the ZMO deposition showed the negligible LS effect. These results indicate that the LS effect would relate to the photo current which is affected by CBO and surface condition of the CIGS film, and the external quantum efficiency measurements support this hypothesis.