Devices are provided for inhibiting the electrical activity of an excitable cell through the application of a pulse of light which includes a substrate and a photoreactive film both of non-conducting material and laid directly on one another, in which the photoreactive film includes a layer of semiconductor polymer material and has an interface surface which can be placed in contact with an excitable cell and an electrolyte solution. After absorbing light, when placed in contact with the excitable cell and the electrolyte solution, the photoreactive film produces a potential difference across this interface surface which is capable of giving rise to hyperpolarization of the membrane of the excitable cell. Methods of inhibiting the electrical activity of excitable cells using such devices are also provided.