Synthesis and characterization of CuInSe2 thin films from Cu, In and Se stacked layers using a closed graphite box

Various techniques have been used to produce CuInSe2, but the problem of producing films with the desired properties for efficient device fabrication over large areas has always persisted. The Stacked Elemental Layer (SEL) technique has been demonstrated as a method for producing films over a large area, but the films normally annealed in vacuum or in Se ambient, mostly exhibited poor morphology with small grain sizes which result in poor devices. A method of synthesizing CuInSe2 films by annealing or selenization of the Cu, In and Se elemental layers using a closed graphite box was developed. SEM, EDX, XRD, spectrophotometric and Hall measurements were used to characterize all annealed films. Results have shown single phase chalcopyrite films with improved crystal sizes of about 4 mu m. The film composition varied from Cu-rich to In-rich with electrical resistivities of 10(-3) to 10(4) Omega cm, carrier concentrations of 5 x 10(15) to 10(17) cm(-3) and mobilities of 0.6 to 7.8 cm(2) V-1 s(-1). An energy band gap of 0.99 eV and 1.02 eV was obtained for a Cu-rich and near stoichiometric In-rich films respectively. Heterojunction devices using the structure ZnO/CdS/CuInSe2 were fabricated with electrical conversion efficiencies of 6.5%.