Copper(indium,gallium)selenide film formation from selenization of mixed metal/metal-selenide precursors

Cu(In,Ga)Se2 film fabrication by the selenization of the mixed metal/metal-selenide precursors was investigated. For the precursor preparation, the combination of electro deposition, annealing, co-evaporation and pre-selenization methods were employed with sequential sputtering as a control. The precursor structures studied were CuSe/Ga/In, Cu2-xSe/Ga/In, (Ga, In)-Se/Cu and metallic Cu-Ga/In as a control. Cu2-xSe/Ga/In precursors were prepared from both electro deposition and co-evaporation. These precursors were selenized in H2Se at at 450°C for 5, 15, and 90min. The structures of the precursors and reacted films were examined in terms of the crystalline phases, compositions and morphologies by scanning electron microscopy, energy dispersive spectroscopy, symmetric and asymmetric X-ray diffraction, and Auger electron spectroscopy. The similar selenization reaction rates were obtained for the precursors with copper selenide/Ga/In structures as that for the control precursor while that for the (Ga,In)-Se/Cu seems to be slower than the control. Ga accumulation at the backside of the selenized film was universally observed for the precursors including the control Cu-Ga/In precursor, with the exception of one precursor with the structure of CuSe/Ga/In made from electro deposition. For the CuSe/Ga/In precursor, a hill-like Ga profile with the maximum Ga concentration at the middle of the film was obtained. In addition, increased Ga composition at the front side of the selenized film was obtained for the Cu2-xSe/Ga/In precursor made from electro deposition compared to the control.;The device performance of the solar cells made of these selenized films were also investigated and related to the film properties. The comparable conversion efficiencies were obtained from the three precursors with copper selenide/Ga/In structures as the control. The long wavelength edge of external quantum efficiency curve indicates larger bandgap than the control for the films made from the two precursors including the CuSe/Ga/In and Cu2-x Se/Ga/In, both started with electron deposition. The enhanced Ga incorporation into Cu(In,Ga)Se2 structure corresponds to the larger bandgap for these precursors.