Disclosed are a photoelectric conversion device and an organic sensor and an electronic device including the same. The photoelectric conversion device includes a first and a second electrode, a photoelectric conversion layer between the first and the second electrode and configured to absorb light in at least one portion of a wavelength spectrum and to convert the absorbed light into an electric signal, and a buffer layer between the second electrode and the photoelectric conversion layer and including a mixture of at least two materials. The mixture includes a first and a second material. The first material has an energy bandgap of at least about 3.2 eV and a HOMO energy level of at least about 6.0 eV. The second material has an energy bandgap of less than or equal to about 2.8 eV and a HOMO energy level of at least about 6.0 eV.