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% (J_SC = 8.91 mA cm^-2, V_OC = 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.