Sensitization of TiO₂ with PbSe Quantum Dots by SILAR: How Mercaptophenol Improves Charge Separation

The use of PbSe quantum dots (QDs) as sensitizers for TiO₂ samples has been primarily hampered by limitations on charge injection. Herein, a novel successive ionic layer adsorption and reaction (SILAR) method, allowing for an intimate TiO₂/PbSe contact and a strong quantum confinement, is described. Photoelectrochemical experiments and transient absorption measurements reveal that charge separation indeed occurs when using either aqueous sulfite or <i>spiro</i>-OMeTAD as a hole conductor and that it can be further enhanced by attaching <i>p</i>-mercaptophenol (MPH) to the QD surface. These results suggest that MPH can promote an efficient funneling of the photogenerated holes from the PbSe to the hole scavenging medium, thereby increasing the yield of electron injection into TiO₂. In a more general vein, this work paves the way for the fabrication of PbSe-sensitized solar cells, emphasizing the importance of controlling the QD/hole scavenger interface to further boost their conversion efficiency