  This paper is focused on the the variable-range hopping of electrons in
semiconductor nanocrystal (NC) films below the critical doping concentration
$n_c$ at which it becomes metallic. The hopping conductivity is described by
the Efros-Shklovskii law which depends on the localization length of electrons.
We study how the localization length grows with the doping concentration $n$ in
the film of touching NCs. For that we calculate the electron transfer matrix
element $t(n)$ between neighboring NCs for two models when NCs touch by small
facets or just one point. We study two sources of disorder: variations of NC
diameters and random Coulomb potentials originating from random numbers of
donors in NCs. We use the ratio of $t(n)$ to the disorder-induced NC level
dispersion to find the localization length of electrons due to the multi-step
elastic co-tunneling process. We found three different phases at $n<n_c$
depending on the strength of disorder, the material, sizes of NCs and their
facets: 1) "insulator" where the localization length of electrons increases
monotonically with $n$ and 2) "oscillating insulator" when the localization
length (and the conductivity) oscillates with $n$ from the insulator base and
3) "blinking metal" where the localization length periodically diverges. The
first two phases were seen experimentally and we discuss how one can see the
more exotic third one. In all three the localization length diverges at
$n=n_c$. This allows us to find $n_c$.
