Quasi one dimensional organic crystals of tetrathiotetracene-iodide TTT2I3 are promising materials for thermoelectric applications. A theoretical study of thermoelectric properties of these crystals was initially performed in terms of a one-dimensional (1D) model. In this paper, the effect of interaction between molecular chains on the electrical conductivity and thermopower (Seebeck coefficient) is investigated. For simplicity, a 2D model is applied. The criteria where the weak interaction between 1D molecular chains can be neglected are also determined.