In this experimental work, plasma treatment of the active layer in the bulk heterojunction solar cells was studied. The active layers consisting of zinc oxide nanoparticles:polyaniline were spin-coated on indium tin oxide covered glasses then kept in the cold plasma medium for different treatment times. The J-V characteristics were considered under air mass 1.5G standard illumination, and variations of the open-circuit voltages and short circuit currents were studied under different treatment times. The results show that there is an optimum treatment time to improve the properties of the layers. In order to understand the origin of this effect, the Hall coefficient, along with ultraviolet-visible spectra were measured, and for studying the topological impact of plasma on the surface of the layers, atomic force microscopy and Fourier-transform infrared spectroscopy were considered. The measurements confirmed the time dependency of the open-circuit voltages and short circuit currents of the cells on the plasma treatment times. Atomic force microscopy of the layers shows the significant topological effects of the plasma treatments on the surface of the active layers for different treatment times.