  The recent Xenon1T excess can be explained by solar neutrino scattering with
electron via a light mediator, either scalar or vector, in addition to many
other explanations from the dark sector. Since only the recoil electron is
observable, a keV sterile neutrino instead of an active neutrino can appear in
the final state. The sterile neutrino allows pseudoscalar mediator to explain
the Xenon1T excess which was thought impossible. In addition, nonzero recoil
energy lower bound arises from the sterile neutrino mass, which can be used to
testify if the sterile neutrino is massive or not. We also briefly discuss the
case of a sterile neutrino final state with light $Z'$ mediator.
