  Transition metal dichalcogenide (TMD) bilayers are a new class of tunable
moir\'e systems attracting interest as quantum simulators of
strongly-interacting electrons in two dimensions. In particular, recent theory
predicts that the correlated insulator observed in WSe$_2$/WS$_2$ at half
filling is a charge-transfer insulator similar to cuprates and, upon further
hole doping, exhibits a transfer of charge from anion-like to cation-like
orbitals at different locations in the moir\'e unit cell. In this work, we
demonstrate that in this doped charge-transfer insulator, tightly-bound
charge-2e excitations can form to lower the total electrostatic repulsion. This
composite excitation, which we dub a trimer, consists of a pair of holes bound
to a charge-transfer exciton. When the bandwidth of doped holes is small,
trimers crystallize into insulating pair density waves at a sequence of
commensurate doping levels. When the bandwidth becomes comparable to the pair
binding energy, itinerant holes and charge-2e trimers interact resonantly,
leading to unconventional superconductivity similar to superfluidity in an
ultracold Fermi gas near Feshbach resonance. Our theory is broadly applicable
to strongly-interacting charge-transfer insulators, such as WSe$_2$/WS$_2$ or
TMD homobilayers under an applied electric field.
