Berlin 2015 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 5: Photovoltaics: CIGS and related compounds

HL 5.4: Talk

Monday, March 16, 2015, 10:15–10:30, EW 202

A Real-Time XRD Investigation of Cu(In,Ga)Se₂ by Three-Stage Thermal Co-Evaporation — •Setareh Zahedi-Azad, Paul Pistor, Enrico Jarzembowski, Stefan Hartnauer, Leonard Wägele, Wolfgang Fränzel, and Roland Scheer — Institute of Physics, Martin-Luther-University Halle-Wittenberg

Solar cells based on Cu(In,Ga)Se₂ (CIGS) thin films have achieved efficiencies of up to 21.7%, which makes this technology comparable to Si-based Solar cells. Further improvement requires a detailed understanding of the crystal phase evolution during preparation. Therefore, the phase evolution of Cu(In_1−x,Ga_x)Se₂ thin films prepared by multi-stage co-evaporation and with x (= Ga/Ga+In) ranging from 0 to 1, was investigated during the deposition process via time resolved in situ X-ray diffractometry (in situ XRD). Dependent on x, films exhibit different crystalline phases during the different stages of the growth. The phases monitored during the growth of CuInSe₂ (x=0) are in agreement with the In₂Se₃−Cu₂Se pseudo-binary phase diagram. In this case and in the case of x = 0.33, ordered vacancy phases of Cu(In,Ga)₅Se₈ and Cu(In,Ga)₃Se₅ are observed, while for higher Gallium contents (x>=0.55), no such phases were detected. The formation of Cu₂Se phases was observed at the beginning of the Cu-rich growth regime for all processes. The Cu₂Se diffraction peaks disappear again in the third stage when the samples become Cu-poor again. The XRD peak width is analyzed quantitatively and interpreted in terms of crystallite size, crystalline quality and compositional gradients within the layer.