Investigation of polycrystalline thin film CuInSe2 cells based on ZnSe windows

This paper describes investigations of CIS solar cells based on ZnSe window layers deposited by MOCVD. Investigations of ZnSe/CIS solar cells are being carried out in an effort to improve the efficiencies of CIS cells and to determine if ZnSe is a viable alternative to CdS as a window material. MOCVD growth of ZnSe is accomplished in a SPIRE 500XT reactor housed in the Electronic Materials Laboratory at WSU Tri-Cities by reacting a zinc adduct with H₂Se. Conductive n-type ZnSe is grown by using iodine as a dopant. Ethyliodide was mixed with helium and installed on one of the gas lines to the system. ZnSe films have been grown on CIS substrates at 200°C to 250°C. ZnO is also being deposited by MOCVD by reacting tetrahydrofuran (THF) with a zinc adduct. ZnSe/CIS heterojunctions have been studied by growing n-ZnSe films onto 2 cm×2 cm CIS substrates diced from materials supplied by Siemens and then depositing an array of aluminum circular areas 2.8 mm in diameter on top of the ZnSe to serve as contacts. Al films are deposited with a thickness of 80 to 100 Å so that light can pass through the film, thus allowing the illuminated characteristics of the ZnSe/CIS junction to be tested. Accounting for the 20 to 25% transmittance through the Al film into the ZnSe/CIS structure, current devices have estimated, active-area AM1.5 efficiencies of 14%. Open circuit voltages >500 mV are often attained