An energy conversion film and a quantum dot film which contain a quantum dot compound, an energy conversion layer including the quantum dot film, and a solar cell including the energy conversion layer. The films act as cut-off filters blocking light of a particular energy level using the light absorption and emission effects of quantum dots and can convert high energy light to low energy light. The efficiency of a solar cell may be improved by providing the cell with a film that converts light above the spectrum-responsive region to light in the cell's spectrum-responsive region. The absorption wavelength region of the films can be broadened by providing the quantum dot compound in a variety of average particle sizes, for example, by providing a mixture of a first quantum dot compound having a first average particle size and a first quantum dot compound having a second average particle size.