  Recently, signatures of nonlinear Hall effects induced by Berry-curvature
dipoles have been found in atomically thin 1T'/Td-WTe$_2$. In this work, we
show that in strained polar transition-metal dichalcogenides(TMDs) with
2H-structures, Berry-curvature dipoles created by spin degrees of freedom lead
to strong nonlinear Hall effects. Under an easily accessible uniaxial strain of
order 0.2%, strong nonlinear Hall signals, characterized by a Berry-curvature
dipole on the order of 1{\AA}, arise in electron-doped polar TMDs such as
MoSSe, and this is easily detectable experimentally. Moreover, the magnitude
and sign of the nonlinear Hall current can be easily tuned by electric gating
and strain. These properties can be used to distinguish nonlinear Hall effects
from classical mechanisms such as ratchet effects. Importantly, our system
provides a potential scheme for building electrically switchable
energy-harvesting rectifiers.
