Publication date: 27th June 2014
Effective passivation schemes for solution processed quantum dots (QDs) are essential for the successful implementation of QDs in optoelectronic devices. In this contribution, we explore the interplay between electron transfer (ET) efficiency and surface passivation (atomic vs molecular) for QDs grown by the successive ionic layer adsorption and reaction (SILAR) method onto a mesoporous oxide phase. Complete- and half- SILAR cycles provide QDs which are defined by anion and cation rich surfaces, respectively. Atomic and molecular passivation can be achieved by simple post-growth treatments. Optical pump-THz probe (OPTP) spectroscopy reveals that the electron transfer efficiency from PbS QDs to SnO2 is maximized in QDs with lead-rich surfaces (terminated by half SILAR cycle). This effect is can be explained by the atomic surface passivation of QDs provided by lead cations - in perfect agreement with theoretical calculations1. The cation passivation efficiency is found to be QD size dependent, and increases linearly with QD surface area. This surface area-dependence points to a kinetic competition between electron trapping at the QD surface and ET to the oxide. Finally, we demonstrate that the improvement in ET efficiency obtained for atomically passivated QDs is in quantitative agreement with results achieved with thiol-based passivating molecules.
[1]Donghun Kim et al. PRL 110, 196802 (2013)
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