A device for converting electromagnetic radiation into electricity comprises an expander that includes a conical shape having an axis and a curved surface that is configured to reflect electromagnetic radiation away from the axis to expand a beam of the electromagnetic radiation; and one or more energy conversion components configured to receive a beam of electromagnetic radiation expanded by the expander, and to generate electricity from the expanded beam of electromagnetic radiation. With the expander's curved surface, a beam of electromagnetic radiation that is highly concentrated—has a large radiation flux—may be converted into a beam that has a larger cross-sectional area. Moreover, one can configure, if desired, the curved surface to provide a substantially uniform distribution of radiation across the expanded cross-sectional area. With such an expanded beam the one or more energy conversion components can efficiently convert some of the electromagnetic radiation into electricity.