なかのにっき

Solid state devices based on copper indium diselenide, (CIS), have produced world record efficiencies for polycrystalline photovoltaic solar cells. In order to understand thin film phase transformations that are relevant to the production of CIS, multilayer thin films of copper and indium have been analyzed. Using differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, the reaction pathways for equal atomic concentration, copper rich, and indium rich films were established. Indium was found to react during deposition, so that the as-deposited films consisted of CuIn2 and copper. During constant heat rate experiments, the excess concentration of copper within the film provided the driving force in the formation of phases richer in copper. The Cu11In9 phase was observed to form from CuIn2 and Cu at 130 °C, and Cu7In3 formed from Cu11In9 and Cu at 310 °C. In the indium rich samples, a given phase was found to be stable until melting. In films with an overall indium concentration exceeding the concentration of Cu11In9, the excess indium was shown to move primarily to the film surface, and in indium rich films, to grain boundaries between the Cu11In9 phase.

The details of the sulfurization reaction of Cu/In metallic precursor layers for the preparation of CuInS2 photovoltaic absorbers have been investigated. For this, an experiment has been designed in order to establish the main mechanisms that govern the sulfurization reaction. A metallic layer containing Cu and In (Cu/In = 1.8) has been processed using a combined sequence of sulfurization and selenization steps. Afterwards, this sample was investigated by Auger electron spectroscopy, Raman spectroscopy, and transmission electron microscopy in order to study its microstructure and chemical composition. The results show that the sulfurization reaction of these films is dominated by the out-diffusion of the metallic atoms through the chalcogen layer. Moreover, taking into account our previous investigations we have developed a consistent model for the formation of these absorber layers.

We investigate Cu-In thin films used as precursors for the production of CuInS2 and Se2 solar-cell absorber material via reactive annealing. The films are produced by coevaporation of Cu and In onto glass substrates and are characterized by means of Rutherford backscattering and x-ray diffraction (XRD). The interplay of phase composition, morphology, and surface topography is studied as a function of chemical composition, substrate temperature, and annealing processes. The analysis of the XRD data is based on known crystallographic data for the phases Cu7In3 (δ-phase), Cu16In9 (η'-phase), Cu11In9, and In. Refined crystallographic data for CuIn2 are presented, and the low-temperature modification of Cu16In9 (η-phase) is investigated by means of bulk powder samples. These data and the inclusion of texture effects allow us to perform a complete RIETVELD type analysis of the Cu-In precursors. It is shown that, in contrast to sequentially evaporated films, all known Cu-In equilibrium phases can be formed during film deposition. These are Cu7In3, Cu16In9, Cu11In9, and CuIn2. Moreover, it is found that single-phase films of all these phases can be produced. Film roughness is shown to increase with deposition temperature and In content. The results presented offer new prospects for sulfurization and selenization processes in solar-cell production.