Enhancing the stability of the electron density in electrochemically doped ZnO quantum dots

Electronic doping of semiconductor nanomaterials can be efficiently achieved using electrochemistry. However, the injected charge carriers are usually not very stable. After disconnecting the cell that is used for electrochemical doping, the carrier density drops, typically in several minutes. While there are multiple possible causes for this, we demonstrate here using n-doped ZnO quantum-dot (QD) films of variable thickness that the dominant mechanism is reduction of solvent impurities by the injected electrons. We subsequently investigate two different ways to enhance the doping stability of ZnO QD films. The first method uses preemptive reduction of the solvent impurities; the second method involves a solid covering the QD film, which hinders impurity diffusion to the film. Both methods enhance the doping stability of the QD films greatly.