Synergistic Charge Dynamics and Light Harvesting in TiO₂/MgO Composites for Efficiency Enhancement in CdS Quantum Dot-Sensitized Solar CellsSynergistic Charge Dynamics and Light Harvesting in TiO₂/MgO Composites for Efficiency Enhancement in CdS Quantum Dot-Sensitized Solar Cells

Abstract

Quantum dot-sensitized solar cells (QDSSCs) represent a promising advancement in renewable energy technologies, with recent improvements achieving power conversion efficiencies close to 6%. Structurally similar to dye-sensitized solar cells (DSSCs), QDSSCs employ quantum dots (QDs) as sensitizers that absorb photons and inject excited electrons into the conduction band of a wide-bandgap semiconductor electrode. while a redox electrolyte removes the generated holes, completing the circuit by regenerating them at the counter electrode. Quantum dots composed of materials such as CdS, CdSe, PbS, and InP are increasingly studied for use in QDSSCs, offering the advantage of tunable optical band gaps through particle size manipulation. This adaptability enhances QDSSCs’ design potential, enabling the integration of third-generation solar cell configurations, including multiple exciton generation (MEG), to further enhance energy conversion efficiency. Despite these advancements, QDSSC performance is currently limited by issues such as reduced photovoltage and recombination losses at the TiO₂-QD-electrolyte interface. This study explores the use of magnesium oxide (MgO) coatings on TiO₂ nanoparticles to address these limitations, focusing on improving the fill factor (FF) and overall cell efficiency. MgO serves as an electron-blocking layer, effectively reducing recombination and associated energy losses. Furthermore, MgO facilitates electron transport from QDs to the TiO₂ electrode, improving charge collection. The light-scattering properties of MgO also increase the photon's path length within the cell, enhancing light absorption and consequently boosting the short-circuit current. In this study, MgO powder was incorporated in specific mass ratios with TiO₂, followed by the application of CdS quantum dots (QDs) on the TiO₂/MgO composite layer using the SILAR method. Results indicated a significant improvement in the fill factor (FF) at an optimal MgO-to-TiO₂ ratio, attributed to synergistic effects of MgO on interface stabilization, reduced recombination, and enhanced charge transport. The optimized MgO-modified TiO₂ films achieved a current density of 1.946 mA, voltage of 437 V, and power of 0.121 W, reaching an efficiency of 0.311 (18.7% higher than TiO₂/CdS QDSCs), with improved interfacial impedance, Incident Photon to Current Efficiency (IPCE), and FF of 37.4%.