  Using graphene as a tuneable optical material enables a series of optical
devices such as switchable radar absorbers, variable infrared emissivity
surfaces, or visible electrochromic devices. These devices rely on controlling
the charge density on graphene with electrostatic gating or intercalation. In
this paper, we studied the effect of ionic liquid intercalation on the
long-term performance of optoelectronic devices operating within a broad
infrared wavelength range. Our spectroscopic and thermal characterization
results reveal the key limiting factors for the intercalation process and the
performance of the infrared devices, such as the electrolyte ion-size asymmetry
and charge distribution scheme and the effects of oxygen. Our results provide
insight for the limiting mechanism for graphene applications in infrared
thermal management and tunable heat signature control.
