A photoelectric conversion device includes a first electrode and a second electrode facing each other, a photoelectric conversion layer between the first electrode and the second electrode and configured to absorb light in at least one part of a wavelength spectrum of light and to convert it into an electric signal, and an inorganic nanolayer between the first electrode and the photoelectric conversion layer and including a lanthanide element, calcium (Ca), potassium (K), aluminum (Al), or an alloy thereof. An organic CMOS image sensor may include the photoelectric conversion device. An electronic device may include the organic CMOS image sensor.