Properties of CuIn1-xGaxSe2 films prepared by the rapid thermal annealing of spray-deposited CuIn1-xGaxS2 and Se

Abstract

ABSTRACTMany reported CuIn1-xGaxSe2 (CIGS) thin films for high-efficiency solar cells have been prepared via a two-stage process that consists of a high-vacuum film deposition step followed by selenization with excess H2Se gas or Se vapor. Removing toxic gas and high-vacuum requirements from this process would greatly simplify it and make it less hazardous. We report the formation of CuIn1-xGaxSe2 (x = 0, 0.25, 0.50, 0.75, 1.0) thin films achieved by rapid thermal annealing of spray-deposited CuIn1-xGaxS2 and Se in the absence of an additional selenium source. To prepare the Se layer, commercial Se powder was dissolved by refluxing in ethylenediamine/2,2-dimethylimidizolidine. After cooling to room temperature, this mixture was combined with 2-propanol and the resulting colloidal Se suspension was sprayed by airbrush onto a heated glass substrate. The resulting film was coated with nanocrystalline CuIn1-xGaxS2 via spray deposition of a toluene-based “nanoink” suspension. The two-layer sample was annealed at 550 oC in an argon atmosphere for 60 minutes to form the final CIGS product. Scanning electron microscopy images reveal that film grains are 200-300 nm in diameter and comparable to sizes of the reactant CuIn1-xGaxS2 nanoparticles. XRD patterns are consistent with the chalcopyrite unit cell and calculated lattice parameters and A1 phonon frequencies change nearly linearly between those for CuInSe2 and CuGaSe2.