Plasmonic phenomenon inside the materials composing an organic solar cell based on a photoactive poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene):(6,6)-phenyl-C(61)-butyric-acid-methyl ester (MEH-PPV:PCBM) bulk heterojunction is studied using Finite Difference Time Domain (FDTD) method calculations and the modeling results are compared with experimental results. Enhanced absorptance of light up to 50% is experimentally obtained in a 50-nm-thick blend layer including spin-coated silver nanospheres with a diameter of 40 nm. FDTD calculations based on the design of 2D-grating of nanoparticles confirm the high values of absorptance. Spatial distributions of electromagnetic field power density in the structures show confinement of the power at the interface or in the vicinity of the nanoparticles depending on the wavelength and on the preferential directions. (C) 2009 Elsevier B.V. All rights reserved.