There isn't really anything magical about sweeping the voltage. The script showed in the post you refer to can by tweaked extremely easily to support a different kind of sweeping. All you need to do, basically, is modify the "voltages" list. For instance, to run from 0 V to -3 V in steps of 0.5 V, use
voltages = [0.,-0.5,-1.,-1.5,-2.,-2.5,-3.]*Volt
or for more flexibility, use NumPy:
import numpy
voltages = numpy.linspace(0.,-3.,7)*Volt
and so on. You can just as well sweep backwards,
voltages = [3,2,1,0]*Volt
but note that it can be hard to converge the high-bias calculation without initializing it from a lower-bias self-consistent density.
The updated version of the ivcurve script in
this post should also be of relevance, esp. for the case of starting from a high bias, which perhaps is converged by climbing up from zero bias.