Transition metal doping for enhancing quantum dot sensitized solar cells performance

Abstract

In this paper we show that efficiency of quantum dot sensitized solar cells (QDSCs) can be systematically enhanced by simply doping the semiconductor quantum dots with various transition metals. A general study is conducted on the effect of various doping materials like Zn, Co, and Mn on the performance of QDSCs. For the first reported CdS:Zn/CdSe, and CdS:Co/CdSe sensitized cells, the cell performance with 2.82% and 3.42 % (Voc = 609 mV, Jsc = 11.25 mA cm−2, FF = 0.5) efficiency is obtained respectively which is enhanced compared with the photovoltaic properties of the cells with conventional CdS/CdSe sensitized cells (η = 2.24%, Voc = 545 mV, Jsc = 9.12 mA cm−2, FF = 0.45). Impedance spectroscopy (IS) and open circuit voltage decay is performed on the doped QDSCs in order to understand the origin of the performance increment. Results indicate that the electron recombination loss is reduced in the case of doped QDs, while reduced electron conductivity in the cells is a limiting factor that should be considered for further efficiency improvements. Mechanism of charge transport in the doped cells is explained based on electron trapping/detrapping through midgap trap states in the doped QDs. This general study indicates that QDs doping could be introduced as a simple effective method for increasing the performance of QDSCs.