NOVELTY - Energy conversion device for converting light into electricity comprises: (a) a first dielectric medium for enabling input light propagation; (b) a first metallic medium in physical contact with the first dielectric medium; (c) a dielectric-metal interface; (d) an array of surface-plasmon-polariton (SPP) resonator cavities formed at a nano-scale; (e) a second metallic medium coupled with the anodes of the SPP resonator cavities; and (g) a second dielectric medium.    USE - The energy conversion device is used for converting light into electricity (claimed).    ADVANTAGE - The energy conversion device obtains high energy conversion efficiencies of up to a theoretical maximum of 84%.    DETAILED DESCRIPTION - Energy conversion device for converting light into electricity comprises: (a) a first dielectric medium for enabling input light propagation; (b) a first metallic medium in physical contact with the first dielectric medium; (c) a dielectric-metal interface common to the first dielectric medium and the first metallic medium; (d) an array of surface-plasmon-polariton (SPP) resonator cavities formed at a nano-scale and distributed in the first metallic medium below the dielectric-metal interface, where each resonator cavity has a hollow interior to form a metal cathode in the first metallic medium, and a metal anode disposed within the hollow interior which is electrically isolated from the metal cathode and the first metallic medium; (e) a second metallic medium coupled in electrical contact with the anodes of the SPP resonator cavities; and (f) a second dielectric medium forming electrical insulation between the first metallic medium and the second metallic medium, where each the cathode is spaced by a nano-scale gap from its respective anode so that input light propagating in the first dielectric medium is converted into standing waves of SPP excitations within the SPP resonator cavities below the dielectric-metal interface, and where the SPP resonator cavities are configured to enhance electric field interactions of standing waves of SPP excitations within the SPP resonator cavities to exceed a threshold needed for quantum field emission so that electrons are driven out of the cathode by the standing waves of SPP excitations into ballistic electrons that escape from the cathode and pass across the nano-scale gap to the anode which is coupled by the second metallic medium to an electrical output circuit.