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. Here, we investigate methods to increase the stability of electrochemically
injected charges in thin films of a wide variety of semiconductor
materials, namely inorganic semiconductors (ZnO NCs, CdSe NCs, and
CdSe/CdS core/shell NCs) and organic semiconductors (P3DT, PCBM, and
C
60
). We show that by charging the semiconductors at elevated
temperatures in solvents with melting points above room temperature,
the charge stability at room temperature increases greatly, from seconds
to days. At reduced temperature (−75 °C when using succinonitrile
as electrolyte solvent) the injected charge becomes entirely stable
on the time scale of our experiments (up to several days). Other high
melting point solvents such as dimethyl sulfone, ethylene carbonate,
and poly(ethylene glycol) (PEG) also offer increased charge stability
at room temperature. Especially the use of PEG increases the room
temperature charge stability by several orders of magnitude compared
to using acetonitrile. We discuss how this improvement of the charge
stability is related to the immobilization of electrolyte ions and
impurities. While the electrolyte ions are immobilized, conductivity
measurements show that electrons in the semiconductor films remain
mobile. 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 thin films.