Charge dynamics in CuInS2 photovoltaic devices with In2S3 as buffer layer

The charge carrier dynamics of photovoltaic devices composed of FTO/TiO2/In2S3/CuInS2/graphite (FTO=Fluorine doped Tin Oxide) is investigated by Intensity Modulated Photocurrent Spectroscopy (IMPS) and Intensity Modulated Photovoltage Spectroscopy (IMVS). Characteristic lifetimes and transport times are obtained. The dependence of the lifetime with light intensity can be explained by multitrapping processes, which justify the rather long lifetimes. Moreover, typical spectral features in the Nyquist plots are obtained by a model based on the continuity equation where diffusion is the major transport process, as confirmed by the dependence of the transport times on the externally applied potential. Changes from a kinetically limited process to a diffusion limited process are observed by modifying the excitation wavelength. Moreover, the existence of a potential barrier or a similar limitation process at the In2S3/CuInS2 interface could be inferred by comparing of the experimental IMPS measurements with data derived from. The existence of defect states at the In2S3 can be deduced from the IMVS dependence with wavelength. Also, different capacitive effects in the samples can be discriminated due to the spectroscopic nature of the techniques here employed.