CuGaSe2 thin films prepared by a novel CCSVT technique for photovoltaic application

In situ X-ray photoelectron spectroscopy study of the oxidation of CuGaSe2

“…All XPS data in table 2 are given relative to the Cu content (set to one) with a relative error of ~10%. The surface composition (XPS) of sample #1 and #2 strongly deviates from the bulk composition a The Na bulk concentration of 1at% [9] was related to the Cu content set to 1 b The Na bulk concentration of 0.06at% [15] was related to the Cu content set to 1 (XRF) thus showing a Cu depletion. The existence of a Cudepleted near surface region for stoichiometric and Ga-rich grown GuGaSe 2 films (see table 2, [9] and [15]) as well as stoichiometric and In-rich CuInSe 2 films [17] is well known from literature.…”

“…The bulk Na content of CCSVT thin films is far below the detection limit of XRF. It was determined by Heavy ion elastic recoil detection analysis (HI-ERDA) to an amount of 1at% [9], which corresponds to a value of 0.04 compared to Cu (see table 2). Thus, the surfaces of sample #1 and #2 are Cu-depleted and enriched in Ga, Se and Na.…”

“…Thin polycrystalline films of CuGaSe 2 were grown by chemical close-spaced vapor transport (CCSVT) [9]. The soda lime glass substrates were covered with a 750 nm thick Mo layer and a 250 nm thick Cu layer by electron beam evaporation.…”

“…Polycrystalline Ga 2 Se 3 -synthesized from the elements -was subjected to a continuous flow of H 2 /HCl and volatilized due to chemical reactions at a source temperature of 550°C. The resulting gases GaCl, GaCl 2 , GaCl 3 and H 2 Se then reacted on the substrate with the Cu precursor layer at a temperature of 450°C to CuGaSe 2 (for details see [9]). In a second annealing step the HCl flux was reduced to allow fine tuning of the thickness and the [Ga]/[Cu]-ratio of the resulting Cu x Ga y Se 2 films [9].…”

“…The resulting gases GaCl, GaCl 2 , GaCl 3 and H 2 Se then reacted on the substrate with the Cu precursor layer at a temperature of 450°C to CuGaSe 2 (for details see [9]). In a second annealing step the HCl flux was reduced to allow fine tuning of the thickness and the [Ga]/[Cu]-ratio of the resulting Cu x Ga y Se 2 films [9]. Alternatively CuGaSe 2 thin films were grown on Mo coated soda lime glass substrates by halogen supported chemical vapor deposition (CVD) in an open tube system.…”