Electrical neurostimulation is the targeted excitation of neurons or parts of the central nervous system by an electric current. Organic electrolytic photocapacitors (OEPC) are recently developed opto-bioelectronic devices, based on the p-n bilayer of organic semiconductors, with the purpose of capacitive neurostimulation. It ensures the absence of electrochemical Faradaic reactions on the electrodes and avoids the generation of free radicals and metal ions in the vicinity of the bioelectronic implant. For safe and effective capacitive neurostimulation, it is desirable to spatially limit its effect to the target area, and to limit the unwanted current flow through sensitive areas of tissue. When choosing the geometry of a photocapacitor, it is necessary to understand the 3D propagation of the electric field around it. As part of this thesis, an experimental setup for direct measurement of the propagation of transient electric potential in the 3D space of the electrolyte around a photocapacitor of arbitrary geometry was assembled. Simple circular geometries of the photocapacitor were measured and the measurement results were compared with the results of the numerical model of the photocapacitor developed within the ”COMSOL Multiphysics” software package. The aim of the thesis is to check and validate the used model, so that it can be used in the future to optimize the geometry of the excitation and return electrodes for different desired implant application scenarios.