  We demonstrate the ability to reduce the carrier concentration of thin films
of the topological insulator (TI) Bi2Se3 by utilizing a novel approach, namely
non-volatile electrostatic gating via corona charging of electret polymers.
Sufficient electric field can be imparted to a polymer-TI bilayer to result in
significant electron density depletion, even without the continuous connection
of a gate electrode or the chemical modification of the TI. We show that the
Fermi level of Bi2Se3 is shifted towards the Dirac point with this method.
Using THz spectroscopy, we find that the surface chemical potential is lowered
into the bulk band gap (~ 50 meV above the Dirac point and 170 meV below the
conduction band minimum) and it is stabilized in the intrinsic regime while
enhancing electron mobility. This represents the first use of a charged polymer
gate for modulating TI charge density. The mobility of surface state electrons
is enhanced to a value as high as ~1600 cm^2/Vs at 5K.
