Ex Situ CdSe Quantum Dot-Sensitized Solar Cells Employing Inorganic Ligand Exchange To Boost Efficiency

We present an effective way to boost the as-synthesized CdSe quantum dot-sensitized solar cells (QDSSCs) performance by introducing an inorganic ligand exchange strategy into this traditional system. Inorganic ligand exchange, to the best of our knowledge, is designed for the first time for CdSe-based QDSSCs, and it features low-cost, easy operation, and repeatable process. The route involves the direct deposition of the CdSe quantum dots (QDs), which were initially capped with trioctylphosphine (TOP) ligands onto mesoporous TiO<sub>2</sub> nanocrystalline electrodes and followed by a post-treatment of the sensitized photoanode films with sulfur ions (S<sup>2–</sup>) solution. Here, changes in surface chemical status of CdSe QDs during the inorganic ligand exchange process and the influence of ligand exchange on the electron’s ultralfast transfer between nanoparticles were investigated through XPS and femtosecond transient grating techniques, respectively. With the inorganic ligand passivated CdSe QDs, the QDSSCs exhibited a power conversion efficiency of 3.17% (AM1.5G, 100 mW/cm<sup>2</sup>), 65% higher than that of the organic ligands capped QDSSCs.