We report constraints on light dark matter ( DM ) models using ionization signals in the XENON1T experiment .
We mitigate backgrounds with strong event selections , rather than requiring a scintillation signal , leaving an effective exposure of ( 22 \pm 3 ) tonne-days .
Above \sim \SI { 0.4 } { keV _ { ee } } , we observe < 1 \text { event } / ( \text { tonne } \times \text { day } \times \text { keV } _ { \text { ee } } ) , which is more than one thousand times lower than in similar searches with other detectors .
Despite observing a higher rate at lower energies , no DM or CEvNS detection may be claimed because we can not model all of our backgrounds .
We thus exclude new regions in the parameter spaces for DM-nucleus scattering for DM masses m _ { \chi } within 3 - \SI { 6 } { GeV / c ^ { 2 } } , DM-electron scattering for m _ { \chi } > \SI { 30 } { MeV / c ^ { 2 } } , and absorption of dark photons and axion-like particles for m _ { \chi } within 0.186 - \SI { 1 } { keV / c ^ { 2 } } .