In the last years, organic materials attract more and more attention for thermoelectric applications as materials with more diverse properties, accessible row components and obtained by cost- effective environmentally friendly production technology.  For the rmoelectric converters materials of both  p - and  n-type are necessary. Usually, the materials of ntype have lower values of the thermoelectric figure of merit  ZT, then those of p-type. Therefore, it is important to search materials of ntype with improved thermoelectric performance. In this paper, the thermoelectric properties of  ntype organic crystals of tetrathiotetracene – tetracyanoquinodimethane, TTT(TCNQ)2, are modeled  and optimal parameters in order to increase  ZT are determined. It is obtained that, if the carrier concentration is increased by 2.3  times with respect to  stoichiometric one and the crystals are further purified, values of ZT ~ 1.2are expected, higher than reported until now  in  organic crystals of n-type.