  We investigate the global 21-cm brightness temperature in the context of
viscous dark energy (VDE) models. The bulk viscosity of dark energy perturbs
the Hubble evolution of the Universe which could cool baryons faster, and
hence, alter the 21-cm brightness temperature. An additional amount of entropy
is also produced as an outcome of the viscous flow. We study the combined
contribution of Hawking radiation from primordial black holes, decay and
annihilation of particle dark matter and baryon-dark matter scattering in the
backdrop of VDE models towards modification of the 21-cm temperature. We obtain
bounds on the VDE model parameters which can account for the observational
excess of the EDGES experiment ($-500^{+200}_{-500}$ mK at redshift $14<z<20$)
due to the interplay of the above effects. Moreover, our analysis yields
modified constraints on the dark matter mass and scattering cross-section
compared to the case of the $\Lambda$CDM model.
