  Optical absorption plays a central role in optoelectronic and photonic
technologies. Strongly absorbing materials are thus needed for efficient and
miniaturized devices. There exists, however, a fundamental limit of 50%
absorptance for any ultrathin film in a symmetric environment. Although
deviating from these conditions allows higher absorption, finding the thinnest
possible material with the highest intrinsic absorption is still desirable.
Here, we demonstrate strong absorption approaching the fundamental limit by
artificially stacking WS$_2$ monolayers into superlattices. We compare three
simple approaches based on different spacer materials to surpass the record
peak absorptance of WS2 monolayers, which stands at 16% on ideal substrates.
Through direct monolayer stacking without an intentional spacer, we reach a
transmittance contrast of 30% for an artificial bilayer, although with limited
control over interlayer distance. Using a molecular spacer via spin coating, we
demonstrate controllable spacer thickness in a bilayer, reaching 28%
transmittance contrast while increasing photoluminescence thanks to doping.
Finally, we exploit atomic layer deposition of alumina spacers to boost the
transmittance contrast to 36% for a 4-monolayer superlattice. Our results
demonstrate that monolayer superlattices are a powerful platform directly
applicable to improve exciton-polariton phenomena such as strong light-matter
coupling and nanophotonic devices such as modulators and photodetectors.
