Enhanced light absorption and charge recombination control in quantum dot sensitized solar cells using tin doped cadmium sulfide quantum dots

Abstract

The photovoltaic performance of quantum dot sensitized solar cells (QDSSCs) is limited due to charge recombination processes at the photoelectrode/electrolyte interfaces. We analyzed the effect of Sn4+ ion incorporation into CdS quantum dots (QDs) deposited onto TiO2 substrates in terms of enhancing light absorption and retarding electron-hole recombination at the TiO2/QDs/electrolyte interfaces. Sensitization involved depositing CdS QDs with different Sn4+ concentrations on the surface of TiO2 using a facile and cost-effective successive ionic layer adsorption and reaction (SILAR) method. Optimized photovoltaic performance of Sn-CdS sensitized QDSSCs was explored using CuS counter electrodes (CEs) and a polysulfide electrolyte. Structural and optical studies of the photoanodes revealed that the gaps between CdS nanoparticles were partially filled by Sn4+ ions, which enhanced the light absorption of the solar cell device. Electrochemical impedance spectroscopy (EIS) and open circuit voltage decay (OCVD) tests suggested that Sn4+ ions can remarkably retard electron-hole recombination at the interfaces, stimulate electron injection into semiconductor QD layers, and provide long-term electron lifetime to the cells. We found that solar cells based on CdS photoanodes doped with 10% Sn4+ ions exhibited a superior power conversion efficiency (PCE) of 3.22%, open circuit voltage (Voc) of 0.593 V, fill factor (FF) of 0.561, and short-circuit current density (Jsc) of 9.68 mA cm−2 under an air mass coefficient (AM) 1.5 G full sun illumination. These values were much higher than those of QDSSCs based on bare CdS photoanodes (PCE = 2.16%, Voc = 0.552 V, FF = 0.471, and Jsc = 8.31 mA cm−2).