NOVELTY - The energy recovery device comprises a space-charge region and a device for frequency conversion of irradiated light with quantum dots. The space-charge region comprises an absorption spectrum with an absorption maximum with a quantum efficiency of over 90%, is allocated for the conversion device, where 50% of an emission spectrum of space-charge region lies in a frequency range in which the space-charge region has the absorption efficiency of 60%. The device further comprises a device for frequency conversion of non-linear optical, luminescent, phosphorescent and/or fluorescent materials.    USE - The energy recovery device is useful as a single, multi or hetero junction organic solar cell (all claimed).    ADVANTAGE - The energy recovery device exhibits high quantum and conversion efficiencies.    DETAILED DESCRIPTION - The energy recovery device comprises a space-charge region and a device for frequency conversion of irradiated light with quantum dots. The space-charge region comprises an absorption spectrum with an absorption maximum with a quantum efficiency of over 90%, is allocated for the frequency conversion device, where 50% of an emission spectrum of space-charge region lies in a frequency range in which the space-charge region has the absorption efficiency of over 60%. The device further comprises a device for frequency conversion of non-linear optical, luminescent, phosphorescent and/or fluorescent materials. The frequency conversion device comprises arrays in which quantum dots are arranged. The quantum dots are equipped with shells. The frequency conversion device is arranged direction of incidence in before and/or behind the space-charge region of the energy recovery device. The device is formed at the back, and faces away from the direction of incidence of a sunlight side mirror. A layer of frequency conversion material has a light transmission under a binding layer thickness, and reflects after the frequency conversion. The space charge zone and the device for frequency conversion are arranged in a photon trap, which prevents the escape of photons of different wavelengths. The absorption spectrum has a full width at a half maximum of up to 200 nm. The space-charge region has a size of 20 mu m in a spatial direction, and includes three-dimensional structures with a size of 5 nm. The frequency conversion device comprises layers, and nanotubes, nanowires, nanocrystals or nano-ring with a size of less than 5 nm in the spatial direction, and is spaced-apart from the space-charge region. The frequency conversion device and/or the space-charge region includes a collecting unit such as a prism, a lens and/or an optically-conductive and/or concentrating device. The frequency conversion device is spatially arranged in the space-charge region. In the operation, photos are emitted from the space charge region. The frequency conversion device absorbs and emits an unequal number of photons such as a smaller number of photons. The frequency conversion device in an area of the space charge region has a quantum efficiency of more than 60% in a first wavelength range. The first wavelength range: is reduced by a wavelength whose energy corresponds to a band gap energy of the device in the area of the space charge region; and is less than 20%. The frequency conversion device is adapted to generate multi-photons and/or for to concert the photons whose wavelength is outside the first wavelength range. The device is configured for frequency conversion so that a frequency, which is an integer multiple or quotient of a frequency of the first wavelength range, has an absorption of 50%. The frequency conversion device has the band gap of 0.5-0.85 eV in a wavelength of 1459-2480 nm and band gap of 2-4.5 eV in a wavelength of 275-620 nm. The space charge region and/or frequency conversion device is designed as the photon trap or associated with the photon trap. The frequency conversion device converts 90% of the emitted photons, is disposed before or in or near the space charge region, and has emission peaks. The space charge region is disposed on a side of a light source of the energy recovery device for the power production. The frequency conversion material in the space charge region has a quantum efficiency of 10%. The energy recovery device has a quantum efficiency of lower than 20%. The frequency conversion device is disposed in the area of the space charge region such that the absorption efficiency of the frequency conversion device is less than 20% and at the space charge region has the absorption efficiency of greater than 20%.