CHARACTERIZATION OF THIN-FILM N-CDS/P-CUGA0.5IN0.5SE2 HETEROJUNCTIONS

CuGaxIn1-xSe2 is a potential absorber material for the fabrication of heterojunction solar cells. CuGa0.5In0.5Se2 films (0.5-3-mu-m) grown at T(s) = 598-648 K on Corning 7059 glass substrates using the flash evaporation technique were nearly stoichiometric and polycrystalline with a chalcopyrite structure (a = 5.689 angstrom and c = 11.343 angstrom). Thermoelectric power and Hall effect measurements indicated p-type conduction in the films. The resistivity and Hall mobility of the films were in the range 50-350 ohm-cm and 2-20 cm2 V-1 s-1, respectively. The optical absorption studies revealed a direct fundamental band gap of 1.29 eV. Band splitting by crystal-field and spin-orbit effects were observed, respectively, at 1.39 and 1.58 eV. n-CdS/p-CuGa0.5In0.5Se2 thin film heterojunctions were fabricated and current density-voltage, capacitance-voltage and spectral response of the junctions were studied. The heterojunction was illuminated in the back-wall configuration and an open-circuit voltage of 575 mV, a short-circuit current density of 20 mA cm-2 and an electrical conversion efficiency of 6.7% have been obtained for a 1 cm2 area cell under a solar input of 85 mW cm-2.