Characterization of cadmium sulfide buffer layers using electrolyte contacts

Electrolyte contacts were used to characterize cadmium sulfide (CdS) films grown by chemical bath deposition on fluorine-doped tin oxide glass (FTO). Capacitance measurements were made in a buffered electrolyte free of redox species, and cyclic sweep voltammetry was carried out using an electrolyte containing Fe(CN)64− ions. A theoretical model was developed to describe the influence of pinholes on Mott Schottky plots of CdS-coated FTO. The model allows estimation of the pinhole coverage by fitting the Mott Schottky plot over an extended voltage range. Cyclic voltammetry in a hexacyanoferrate(II) electrolyte also allows detection of pinholes, but quantitative estimation of pinhole coverage is complicated by the fact that diffusion of Fe(CN)64− to pinholes occurs by hemispherical diffusion, which can substantially enhance the current response. Comparison of the results of capacitance and voltammetry measurements provides insights into average pore size and number density. Results presented for CdS films grown using two different chemical bath compositions reveal substantial differences in pinhole numbers and doping density.