NOVELTY - A radiation conversion device comprises at least one radiation conversion cell, the radiation conversion cell comprising: a photo-absorber unit having a predetermined absorption spectrum for absorbing radiation of a certain wavelength range thus converting the absorbed radiation into charge carriers, and at least partially reflective layer structure configured to be substantially reflective for the certain wavelength range.    USE - The radiation conversion device is useful for converting solar energy into useful electric energy.    ADVANTAGE - The radiation conversion device is stable, has improved performance, and cost effective.    DETAILED DESCRIPTION - A radiation conversion device comprises at least one radiation conversion cell, the radiation conversion cell comprising: a photo-absorber unit having a predetermined absorption spectrum for absorbing radiation of a certain wavelength range thus converting the absorbed radiation into charge carriers, and at least partially reflective layer structure configured to be substantially reflective for the certain wavelength range, the photo-absorber unit and the at least partially reflective structure being configured to provide a desired refractive index profile across the radiation conversion cell with respect to the certain wavelength range and to define an optical cavity with respect to the certain wavelength range within the photo-absorber unit, thus providing a desired interference condition for the certain wavelength range, thus causing the radiation, absorbed by and propagating through the photo-absorber unit while being reflected from the at least partially reflective structure, to be effectively trapped within the photo-absorber unit. An INDEPENDENT CLAIM is a method for forming a radiation conversion device, comprising: applying an at least partially reflective coating layer structure on a substrate; applying a photo-absorber structure comprising an optically active semiconductor of a predetermined thickness and a predetermined absorption spectrum on top of the at least partially reflective coating, the predetermined thickness being selected in accordance with refractive index profile along the device to thus provide an optical cavity providing a desired interference condition for the certain wavelength range within the photo-absorber structure thus causing light of a wavelength range within the predetermined absorption spectrum impinging onto the photo-absorber structure to be trapped within the optically active semiconductor.