Electrical characterization of defects in Cu(In,Ga)Se 2 solar cells containing a ZnSe or a CdS buffer layer

Abstract

Cu(In,Ga)Se 2 based solar cells with a ZnSe buffer layer deposited by metal-organic vapor deposition are compared to reference cells with a usual CdS buffer. Current–voltage characteristics were measured at different intensities of illumination (up to 100 mW/cm 2) in the temperature range between 80 and 300 K. We observe a current roll-over for cells with ZnSe buffer at much higher temperatures than for cells with CdS buffer, which seems to originate from defects either in the buffer volume, or at the buffer/absorber interface. Also wavelength-dependent I( V) measurements were performed before and after annealing at 380 K. A distortion of the I( V) curve measured under red illumination occurs for most of the cells with CdS buffer, but cannot be observed in cells with ZnSe buffer. This effect can be attributed to deep levels in the CdS volume.