for a curve of this type I = mT + yT^k + C . i.e. the current may have a constant offset (C) and a component directly linked to T (mT) and an exponential component related to T (yT^k).
So replot I v T using logs, this gives you logI = (log m + logT) + {logy +( k LogT )} +log C. This will give you a linear "curve" whose slope is k. taking two extreme values you can work out the differences of the slope , hence giving you logm and logC.
Substitute these anti logged values into the original formula will give you the correct formula. I don't know how you are going to generate the exponential coefficient.
Frank