  Fano noise, readout noise, and the partial charge collection (PCC) effect
collectively contribute to the degradation of energy spectra in Charge Coupled
Devices (CCD) measurements, especially at low energies. In this work, the X-ray
produced by the fluorescence of fluorine (677 eV) and aluminum (1486 eV) were
recorded using a Skipper-CCD, which enabled the reading noise to be reduced to
0.2 e-. Based on an analytical description of photopeak shapes resulting from
the convolution of the PCC effect and Fano noise, we achieved a precise
characterization of the energy spectra. This description enabled us to
disentangle and quantify the contributions from both Fano noise and the PCC
effect. As a result, we determined the Fano factor and the electron-hole pair
creation energy. Additionally, we estimated the PCC-region of the sensor and,
for the first time, experimentally observed the expected skewness of photopeaks
at low energies.
