Characterization of thin film CuGa 0.5In 0.5Se 2 heterojunctions

Abstract

CuGa x In 1− x Se 2 is a potential absorber material for the fabrication of heterojunction solar cells. CuGa 0.5In 0.5Se 2 films (0.5–3 μm) growns 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 A ̊ , c = 11.343 A ̊ ). 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 50–350ωcm and 2–20 cm 2V −1s −1 respectively. Optical absorption studies revealed a direct fundamental band gap of 1.29 eV. Band splitting by crystal field and spin-orbit effects was observed at 1.39 and 1.58 eV respectively. n-CdS/p-CuGa 0.5In 0.5Se 2 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 20mA cm −2 and an electrical conversion efficiency of 6.7% have been obtained for a cell 1 cm 2 in area under a solar input of 85 mW cm −2.