Investigation of the effect of Sr-doped in ZnSe layers to improve photovoltaic characteristics of ZnSe/CdS/CdSe/ZnSe quantum dot sensitized solar cells

Abstract

In this work, QDSSCs were synthesized based on CdS/CdSe QDs with two ZnSe layers and we investigated the effect of alkaline earth metal ions (such as: Mg2+, Ca2+, Sr2+, Ba2+) dopants in outer ZnSe passivation layer to improve the photovoltaic performance in QDSSCs. Amongst different metal ions, Sr2+ doped ZnSe passivation layer obtained the best PCE comparing to plain ZnSe passivation layer. Then, at the following, we investigated the effect of Sr2+ ions doped in two ZnSe layers: the inner, the outer and each two layers simultaneously. The cell devices were prepared using photoanodes with different configurations, polysulfide electrolyte and Cu2S/Brass foil counter electrode. Photovoltaic measurement results represent that Sr2+ ions doped in two ZnSe layers assist to a notable improvement in the photocurrent, photovoltage and power conversion efficiency of the resultant cell device in comparison with a plain ZnSe layers and show the best performance between all studied cell devices with a solar PCE of 4.10% under one full sun illumination. The results of impedance spectroscopy (IS) show that doping of Sr2+ ions in both of the ZnSe layers increase the photogenerated electron lifetime and better transport electron and hole in the photoanode comparing to plain ZnSe treated photoanode.