Preparation of copper indium diselenide by selenization of copper indium oxide

Abstract

A process is reported for preparation of thin films of copper indium diselenide (CIS). This process involves two steps: (a) formation of Cu2In2O5 by spray pyrolysis and (b) reaction of Cu2In2O5 with selenium vapor to form CIS. The purity of the CIS prepared by this method can approach that of the material prepared by vacuum deposition methods because highly purified water and nitrate salts can be used in the spray pyrolysis step, and the purity of the selenium used in the second step can be identical to that used in any of the vacuum processes. This two-step process appears to have general applicability; we have been able to prepare a variety of sulfides and tellurides in addition to selenides. The advantage of this process is that any metal ion added to the spray solution is incorporated in the oxide and remains in the selenide after the selenization. Comparison of the Cu/In ratios of the selenide films with those of the precursor oxide films shows that there was a slight decrease in the copper content when the oxide was converted to the selenide. The consistency of the composition of the films prepared at 400 °C is comparable to that of films prepared by the other methods such as thermal processing of elemental layers and reactive sputtering of Cu and In with selenium vapor. Auger composition studies indicated that selenium substitution occurred stepwise. The x-ray-diffraction data for CIS were consistent with a chalcopyrite phase. The data for the resistivity and Hall-effect measurements at room temperature indicated a marked dependence of the resistivity and the hole density on the Cu/In atomic ratio. When this ratio was around 1.45, the resistivity had low values around 30 Ω cm, and the hole density was in the 1017 cm−3 range. A direct band gap of 0.95 eV was determined from the optical-absorption spectrum of this material.

CuInS2 Films for Photovoltaic Applications Deposited by a Low-Cost Method

“…Except for sample E (not shown), in which the sulfurization process was applied after each coating cycle, no delamination upon fracturing can be detected by SEM. This, considering also the surface free of cracks and pinholes, is an indication of sufficient adherence to the substrate 4 Micrographs of the cross-sections of samples A3 (a) and D (b) and morphology of film B1 (c) and B2 (d) surfaces. …”

“…The color change to transparent with a very slight brownish hue suggests that the Cu(0) is oxidized to Cu(I) . Hence it can be concluded that prior to sulfurization the films are composed mainly of Cu(I) and In(III) amorphous oxides, although the presence of a small amount of Cu(II) cannot be excluded …”

“…Although low-cost methods for chalcopyrite films deposition have been reported, they yield inferior film quality and cell performance. These methods include spray pyrolysis, − electrodeposition, , and nanoparticle precursors. − Compact films have been obtained from ethylcellulose paste containing metal salts treated with elemental selenium vapor, in this case forming an amorphous carbon underlayer. Relatively high efficiency (13.6%) has been obtained by printing suspensions of oxide nanoparticles followed by consecutive reduction and selenization with H 2 and H 2 Se …”

“…Although low-cost methods for chalcopyrite films deposition have been reported, 9 they yield inferior film quality and cell performance. These methods include spray pyrolysis, [10][11][12][13] electrodeposition, 14,15 and nanoparticle precursors. [16][17][18] Compact films have been obtained from ethylcellulose paste containing metal salts treated with elemental selenium vapor, 16 in this case forming an amorphous carbon underlayer.…”

Direct Liquid Coating of Chalcopyrite Light‐Absorbing Layers for Photovoltaic Devices

“…[68,69] Power conversion efficiencies of up to 5 % have been reported using this approach. [70] The main impediment to higher efficiency in devices prepared using these approaches appears to be achieving adequate phase and compositional purity (e.g., inclusion of impurities from the solvent, precursor or atmosphere).…”