Phase constitution and element distribution in Cu-In-S based absorber layers grown by the CISCuT-process

Abstract

Solar cells based on CISCuT grown Cu-In-S absorber layers obtained efficiencies of about 6% in small areas. The CISCuT process for Cu-In-S absorber layer preparation starts from an metallurgical grade Cu tape. On this tape a thin In layer is electrochemically deposited in a continuous roll to roll process. The following sulphurisation step - also in a continuous roll to roll process - is characterised by a short reaction time of a few seconds and a relatively high process temperature of about 600°C under normal pressure in N2 atmosphere. Special conditions in the sulphurisation process lead to a well defined layer sequence of different Cu-In-S phases inside the grown layer. X-ray diffraction (XRD) based quantitative phase analysis of KCN etched CISCuT absorber layers shows the phases CuInS2, CuIn5S8 and Cu/In δ-phase. The measurements correspond to transmission electronic microscopy (TEM) and energy dispersive analysis of X-rays (EDX) determined phase constitutions and sublayer thickness. Additional investigations with RAMAN-spectroscopy as well as secondary ion mass spectrometry (SIMS) and secondary neutrals mass spectrometry (SNMS) give a consistent idea of the layer sequences and the impurity distribution inside the film system. As far as we know we describe here, for the first time, such an absorber structure possibly with advantages for further solar cell developments.