Improving the performance of quantum dot sensitized solar cells through CdNiS quantum dots with reduced recombination and enhanced electron lifetime†
To make quantum dot-sensitized solar cells (QDSSCs) competitive, we investigated the effect of Ni2+ ion incorporation into a CdS layer to create long-lived charge carriers and reduce the electron–hole recombination. The Ni2+-doped CdS (simplified as CdNiS) QD layer was introduced to a TiO2 surface via the simple successive ionic layer adsorption and reaction (SILAR) method in order to introduce intermediate-energy levels in the QDs. The effects of different Ni2+ concentrations (5, 10, 15, and 20 mM) on the physical, chemical, and photovoltaic properties of the QDSSCs were investigated. The Ni2+ dopant improves the light absorption of the device, accelerates the electron injection kinetics, and reduces the charge recombination, which results in improved charge transfer and collection. The 15% CdNiS cell exhibits the best photovoltaic performance with a power conversion efficiency (η) of 3.11% (JSC = 8.91 mA cm−2, VOC = 0.643 V, FF = 0.543) under one full sun illumination (AM 1.5 G). These results are among the best achieved for CdS-based QDSSCs. Electrochemical impedance spectroscopy (EIS) and open circuit voltage decay (OCVD) measurements confirm that the Ni2+ dopant can suppress charge recombination, prolong the electron lifetime, and improve the power conversion efficiency of the cells.