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

Toward Antimony Selenide Sensitized Solar Cells: Efficient Charge Photogeneration at <i>spiro</i>-OMeTAD/Sb₂Se₃/Metal Oxide Heterojunctions

Photovoltaic devices comprising metal chalcogenide nanocrystals as light-harvesting components are emerging as a promising power-generation technology. Here, we report a strategy to evenly deposit Sb₂Se₃ nanoparticles on mesoporous TiO₂ as confirmed by Raman spectroscopy, energy-dispersive X-ray spectrometry, and transmission electron microscopy. Detailed study of the interfacial charge transfer dynamics by means of transient absorption spectroscopy provides evidence of electron injection across the Sb₂Se₃/TiO₂ interface upon illumination, which can be improved 3-fold by annealing at low temperatures. Following addition of the <i>spiro</i>-OMeTAD hole transporting material, regeneration yields exceeding 80% are achieved, and the lifetime of the charge separated species is found to be on the millisecond time scale (τ_50% ∼ 50 ms). These findings are discussed with respect to the design of solid-state Sb₂Se₃ sensitized solar cells