Publication date: 27th June 2014
Semiconductor Quantum Dots (QDs) are of great potential for optoelectronics applications like light-emitting devices, photovoltaic and photoelectrochemical cells. Charge transfer processes are ubiquitous in all these applications and their understanding is paramount for advancing in the construction of these devices. Despite these promising features, charge transfer between a QD and an acceptor, such as a metal oxide substrate like TiO2 or another QD in QD solids, is in competition with deleterious processes like electron and/or hole trapping.In a recent work, we showed that fast electron trapping obstructs charge transport between CdTe and CdSe QD films. A similar behavior occurs in colloidal dispersion of CdTe QDs, in which the rate of electron trapping increases with increased number of washing steps.
In this work, we perform atomistic simulations based on density functional theory (DFT) to unravel the origin of these trap states. In conjunction with a number of experiments on CdTe and CdSe QDs in which we control electrochemically the Fermi level, we are able to present a theoretical model that explains how the chemical processes occurring at the interface of these QDs is key in generating both electron and hole traps. Thanks to this new knowledge, we finally suggest a systematic way to remove trap states in an efficient way.
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