Noncadmium ZnO/CIS and ZnSe/CIS solar cells

This paper concerns studies of CIS solar cells based on ZnSe and ZnO buffer layers. ZnSe and ZnO films are grown by MOCVD. These investigations have been primarily carried out with CIS substrates from Siemens Solar. CIS substrates have been characterized with photoluminescence and thermoelectric probe measurements. In particular, PL studies established that the Siemens standard CIS material has a segregated phase(s) on the surface, and thermoelectric probe measurements have established that this surface is n-type. Test cells formed on ZnSe/CIS film structures indicate that the ZnSe/CIS cell structure has a potential efficiency > than 14%. Open circuit voltages are typically larger than 500 mV and the optimum range of ZnSe film thickness for maximum efficiency is between 100 Å and 250 Å. Deposition of ZnO onto a ZnSe/CIS structure typically leads to poor cell performance. Using a layer of MOCVD ZnO as a protective layer, a total area efficiency of 8.74% was achieved for a ZnSe/CIS cell. Direct ZnO/CIS cells were fabricated with MOCVD ZnO buffer layers. A total area efficiency of 11.1% has been achieved