High efficiency CdTe solar cells by close spaced sublimation

High efficiency CdTe/CdS solar cells have been prepared on glass substrates. The CdS films are deposited on SnO₂ coated 7059 glass substrates by the chemical bath deposition process (CBD) to a thickness of 500-1200 Å. The CdTe films are deposited by the close-spaced sublimation (CSS) technique to a thickness of 4-8 μm. Doped-graphite paste is used as the ohmic contact to the CdTe. The substrate temperature used for the deposition of the CdTe films appears to be an important parameter for the junction formation process. It is believed to be critical in the formation of an interface Cd_xS _1-xTe mixed crystal layer. The heat treatment of the CdS films in hydrogen is also an important processing step, and it must be modified as the thickness of the CdS films is decreased in order to maintain high fill factors. High photocurrents in conjunction with high open-circuit voltages and fill factors are achieved by properly adjusting the annealing conditions of thin CdS films. The open-circuit voltage, short-circuit current, and fill factor of the best device were 843 mV, 25.1 mA/cm², and 74.5% respectively, corresponding to a conversion efficiency of 15.8% as measured under AM1.5 conditions at the National Renewable Energy Laboratory