Photoelectric properties of thin layers of Ag2S quantum dots passivated with thiol-containing molecules

Abstract

In this work, we studied the electrophysical properties of condensates of colloidal Ag2S quantum dots (QDs), passivated with thiol-containing molecules (thioglycolic acid and L-cysteine) (further, Ag2S/TGA QDs and Ag2S/L-Cys QDs) on indium tin oxide (ITO) substrates. The temperature dependences of the electrical characteristics (conductivity) are analyzed in the temperature range from 300 to 360 K. Facts of the formation of the Schottky barrier structures is obtained. Activation energies of 0.2 eV (Ag2S/L-Cys QDs) and 0.66 eV (Ag2S/TGA QDs) were obtained by the use of linear approximations of current–voltage (I–V) characteristics in Arrhenius coordinates. It is shown that the conductivity of ITO - Ag2S QDs film - Al structure is mainly determined by the Schottky barrier that is formed at the Al-Ag2S QDs film junction. The rectifying contact is formed at the Ag2S film -Al junction due to the lower work function of Al. The I–V characteristics under the optical radiation action were analyzed for the studied sandwich structures. They turned out to be similar for Ag2S/TGA and Ag2S/L-Cys QDs. When a reverse or forward bias voltage is applied to a sandwich structure, in the case of the optical radiation action with a wavelength starting from the its value, corresponding to the most probable exciton transition in the QDs absorption the photocurrent is observed. The found difference (by an order of magnitude) in the photocurrent values of the sandwich structure, based on Ag2S/TGA QDs and Ag2S/L-Cys QDs is related to the smaller thickness of the Ag2S/TGA QDs film.