the Fermi energy η that gives the variation of the mobility with increasing carrier concentration: 

The constant β has been chosen such that /MMA i equal to 1 in the limit of a very large disorder parameter and a very small charge concentration (deep in the Boltzmann regime). Fig. 11 shows $_{,}$/MMA a function of the disorder parameter, in the zero-concentration limit. Eq. (S18), combined with Fig. 11, show that for strong disorder, 1 (/ MMA) varies to a good approximation linearly with to [ / ( ¾ Τ )] $^{2}$, with a slope equal to —1/4. 

Typically, A/a for small molecules is assumed to be in the 0.1 —0.3 range. As we focus in this work on transport due to NN-hops, the mobility enhancement factor / BNN does not enter our final expression for 7 , Eq. (Sll). Extending the model to include this effect would also require providing an analogous analysis of the mobil ity enhancement as a function of A/a from full 3D-ME or KMC simulations of the mobility. 

## C . NUMERICAL EVALUATION O F 

We see from Eq. (SI 1) that is a complex function of the carrier concentration and the disorder parameter. In this section, we provide a numerical evaluation of this dependence. The analysis suggests that within a fairly wide range of parameter values, 7 can be written in the form 

where and are independent of c and <7. The finding that 7 can be approximated as 

