Proceedings of nanoGe Fall Meeting19 (NFM19)
DOI: https://doi.org/10.29363/nanoge.nfm.2019.145
Publication date: 18th July 2019
Semiconductor films that allow facile ion transport can be electronically doped via electrochemistry, where the amount of injected charge can be controlled by the potential applied. To apply electrochemical doping to the design of semiconductor devices the injected charge has to be stabilized to avoid unintentional relaxation back to the intrinsic state. Until now, complete doping stability has only been gained at cryogenic temperatures. At this temperature, the electrolyte solvent is frozen and both external dopants and impurities are immobilized. In addition, electrochemical side reactions of the semiconductor material itself are slowed down. However, freezing of the electrolyte does not need to occur at cryogenic temperatures.
Here we investigate the possibility of stabilizing electrochemically doped semiconductor films at room temperature using a large variety of electrolyte solvents with melting points above room temperature (RT). We show electrochemical doping for three different QD materials (ZnO, CdSe and CdSe/CdS QDs), two fullerenes (C60 and PCBM) and two conductive polymers (P3DT and P3HT). By using room temperature freezing, we show that the doping stability can be increased immensely, in some cases from few seconds to over an hour. By using PEG as the electrolyte solvent, ZnO QD samples are still degenerately doped after few days (compared to around half an hour in common electrolyte solvents). However, even at a low rate, injected electrons do leave the QDs. On the other hand by using succinonitrile at reduced temperatures (-75 °C), complete doping stability has been achieved.
At last by combining the results from many different solvents, we have found a solvent which is completely frozen at room temperature. That is, injected charges can’t be removed from a ZnO QD film, even if an external bias is applied over the film. These results highlight the potential of using solidified electrolytes to stabilize injected charges, which is a promising step toward making semiconductor devices based on electrochemically doped semiconductor films.
European Research Council Horizon 2020 ERC Grant Agreement No. 678004 (Doping on Demand).
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