Abstract: An efficient nanoscale semiconducting optoelectronic system, containing a P/N acceptor donor organic hetrojunction which is optimized for neuronal stimulation—an organic electrolytic photocapacitor. The devices comprise a thin (80 nm) trilayer of metal and p-n semiconducting organic nanocrystals. When illuminated in physiological solution, these metal-semiconductor devices charge up, transducing light pulses into localized displacement currents that are strong enough to electrically stimulate neurons with safe light intensities.