The paper investigates the bosonic aspects of exciton statistics in non-equilibrium situations. A kinetic model is formulated treating the excitons in different states as chemical species, using a master equation consistent with Bose-Einstein statistics. The model reveals that in two-state model for singlet-triplet generation-recombination, the chemical potential of the lower state becomes pinned at high concentration. Analysis of exciton diffusion shows that the chemical diffusion coefficient is independent of the concentration, while the single particle ( tracer) diffusion coefficient increases strongly due to the attractive statistical force. (c) 2008 Elsevier B. V. All rights reserved.