Hot carrier extraction from 2D semiconductor photoelectrodes

Hot carrier-based energy conversion systems could double the efficiency of
conventional solar energy technology or drive photochemical reactions that
would not be possible using fully thermalized, “cool” carriers, but
current strategies require expensive multi-junction architectures. Using
an unprecedented combination of photoelectrochemical and in situ transient
absorption spectroscopy measurements, we demonstrate ultrafast (<50
fs) hot exciton and free carrier extraction under applied bias in a
proof-of-concept photoelectrochemical solar cell made from earth-abundant
and potentially inexpensive monolayer (ML) MoS2. Our approach facilitates
ultrathin 7 Å charge transport distances over 1 cm2 areas by
intimately coupling ML-MoS2 to an electron-selective solid contact and a
hole-selective electrolyte contact. Our theoretical investigations of the
spatial distribution of exciton states suggest greater electronic coupling
between hot exciton states located on peripheral S atoms and neighboring
contacts likely facilitates ultrafast charge transfer. Our work delineates
future 2D semiconductor design strategies for practical implementation in
ultrathin photovoltaic and solar fuels applications.