In Situ Spectroelectrochemical Determination of Energy Levels and Energy Level Offsets in Quantum-Dot Heterojunctions

In Situ Spectroelectrochemical Determination of Energy Levels and Energy Level Offsets in Quantum-Dot Heterojunctions

Boehme, S.C. (TU Delft ChemE/Opto-electronic Materials)
Vanmaekelbergh, Daniël (Universiteit Utrecht)
Evers, W.H. (TU Delft ChemE/Afdelingsbureau; Kavli institute of nanoscience Delft)
Siebbeles, L.D.A. (TU Delft ChemE/Opto-electronic Materials)
Houtepen, A.J. (TU Delft ChemE/Opto-electronic Materials)

2016-03-17

Charge transfer in semiconductor heterojunctions is largely governed by the offset in the energy levels of the constituent materials. Unfortunately, literature values for such energy level offsets vary widely and are usually based on energy levels of the individual materials rather than of actual heterojunctions. Here we present a new method to determine absolute energy levels and energy level offsets in situ for films containing CdSe and PbSe quantum dots. Using spectroelectrochemistry, we find a type I offset at the CdSe-PbSe heterojunction. Whereas the energy level offset follows the expected size-dependent trend, the absolute positions of the 1S_e level in the individual CdSe or PbSe quantum dots does not. This level varies by more than 0.5 eV, depending on film composition and surface defect concentration. Rather than extrapolating energy level offsets from measurements on pure CdSe or PbSe quantum-dot films, we suggest measuring energy level offsets in heterojunctions in situ.

http://resolver.tudelft.nl/uuid:eb97947f-95b1-402a-ba3f-ac965f693135

https://doi.org/10.1021/acs.jpcc.5b12016

1932-7447

The Journal of Physical Chemistry C, 120 (9), 5164-5173

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journal article

© 2016 S.C. Boehme, Daniël Vanmaekelbergh, W.H. Evers, L.D.A. Siebbeles, A.J. Houtepen