Crystallographic and electrical properties of wide gap Ag(In1−x,Gax)Se2 thin films and solar cells

Ag(In1−x,Gax)Se2 (AIGS) thin films have been deposited on Corning 1737 and Mo-coated soda lime glass substrates by three-stage process using a molecular beam epitaxy (MBE) system. The crystallographic properties of AIGS thin film have been investigated using X-ray diffraction and scanning electron microscope (SEM). Near-stoichiometric AIGS thin films possessed a tetragonal Ag(In,Ga)Se2 phase with a small amount of tetragonal Ag(In,Ga)5Se8 phase. A tetragonal Ag(In,Ga)Se2 phase became predominant as Ga/(In+Ga) atomic ratio increased. Hall measurements and thermo probe analysis revealed that AgInSe2 films showed n-type conduction with high electron mobility. A wide gap Ag(In0.2,Ga0.8)Se2 thin film solar cell with a band gap energy of 1.7 eV showed a total-area efficiency of 7.3% (8.0% active area efficiency) with open-circuit voltage Voc=866 mV, short-circuit current Jsc=14.5 mA/cm2, fill factor FF=0.584, and total area=0.42 cm2.