We introduce diagrammatic technique for Hubbard nonequilibrium Green
functions (NEGF). The formulation is an extension of equilibrium considerations
for strongly correlated lattice models to description of current carrying
molecular junctions. Within the technique intra-system interactions are taken
into account exactly, while molecular coupling to contacts is used as a small
parameter in perturbative expansion. We demonstrate the viability of the
approach with numerical simulations for a generic junction model of quantum dot
coupled to two electron reservoirs.