We have set up infrastructure to determine the in situ changes in the optical absorption and photoluminescence of thin films of semiconductor nanocrystal, polymers, fullerenes etc. while changing the electrochemical potential and, hence, while controlling the doping density.
With the combination of these techniques we have been able to investigate a wide range of materials (CIS nanocrystal, CdTe nanocrystal, CdSe/CdS core/shell nanocrystals, polythiophene conducting polymers, films of C60 and PCBM) and we have been able to study the existence of electron and hole traps in these materials.
The work has been very successful overall.
We have shown the successful control over the doping density in films of semiconductor nanocrystals, conducting polymers and fullerenes. Moreover, we have shown that this charge density can be stabilized at room temperature in two different ways: 1) by using nitrile base high melting point solvents and performing the electrochemical charging at elevated temperatures. At RT the solvents are froze and the charge density is stable. 2) By using photopolymerizable solvents and electrolyte ions. After doping, exposure to UV light stabilizes the charge density. We have also shown for method 1, that it can be used to make pn junctions.
Finally we showed that electrochemical doping can indeed be used to lower, even remove, the threshold for optical gain in semiconductor nanocrystals, bringing the realization of solution process low-threshold nanocrystal lasers much closer.
The results show that electrochemical doping is a promising and viable way to control the charge density in films of semiconductor nanocrystals, enabling the design of semiconductor devices such as LEDs, lasers, photodiodes and solar cells based on these materials.
The work has resulted in over 20 journal publications and a patent. Is has also formed teh basis of an ERC proof-of-concept to explore the valorisation potential of the methods developed to stabilize the charge density after electrochemical doping.
