title: Interplay between structure, stoichiometry, and electron transfer dynamics in SILAR-based quantum dot-sensitized oxides.
abstract: We quantify the rate and efficiency of picosecond electron transfer (ET) from PbS nanocrystals, grown by successive ionic layer adsorption and reaction (SILAR), into a mesoporous SnO2 support. Successive SILAR deposition steps allow for stoichiometry- and size-variation of the QDs, characterized using transmission electron microscopy. Whereas for sulfur-rich (p-type) QD surfaces substantial electron trapping at the QD surface occurs, for lead-rich (n-type) QD surfaces, the QD trapping channel is suppressed and the ET efficiency is boosted. The ET efficiency increase achieved by lead-rich QD surfaces is found to be QD-size dependent, increasing linearly with QD surface area. On the other hand, ET rates are found to be independent of both QD size and surface stoichiometry, suggesting that the donor-acceptor energetics (constituting the driving force for ET) are fixed due to Fermi level pinning at the QD/oxide interface. Implications of our results for QD-sensitized solar cell design are discussed.
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Hai
authors.initials: H
authors.lastname: Wang
authors.forename: Irene
authors.initials: I
authors.lastname: Barceló
authors.forename: Teresa
authors.initials: T
authors.lastname: Lana-Villarreal
authors.forename: Roberto
authors.initials: R
authors.lastname: Gómez
authors.forename: Mischa
authors.initials: M
authors.lastname: Bonn
authors.forename: Enrique
authors.initials: E
authors.lastname: Cánovas
keywords: PbS quantum dots; Quantum dot stoichiometry; SILAR; THz spectroscopy; electron transfer; epitaxial growth; quantum dot-sensitized solar cells