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

Cu(In,Ga)Se, based solar cells with a ZnSe buffer layer deposited by metal- organic vapor deposition are compared to reference cells with a usual CdS b uffer. Current-voltage characteristics were measured at different intensiti es 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 mu ch higher temperatures than for cells with CdS buffer, which seems to origi nate from defects either in the buffer volume, or at the buffer/absorber in terface. 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 dee p levels in the CdS volume. (C) 2001 Elsevier Science B.V. All rights reser ved.