  The recently emerged organohalide perovskites (e.g., CH3NH3PbI3) have drawn
intense attention for high efficiency solar cells. However, with a considerable
solubility in many solvents, these perovskites are not typically compatible
with conventional lithography processes for more complicated device
fabrications that are important for both fundamental studies and technological
applications. Here we report the creation of novel heterojunction devices based
on perovskites and two-dimensional (2D) crystals by taking advantage of the
layered characteristic of lead iodide (PbI2) and vapor phase intercalation. We
show a graphene/perovskite/graphene vertical stack can deliver a highest
photoresponsivity of ~950 A/W and photoconductive gain of ~2200, and a
graphene/WSe2/perovskite/graphene heterojunction can display a high on/off
ratio (~10^6) transistor behavior with distinct gate-tunable diode
characteristics and open-circuit voltages. Such unique perovskite-2D
heterostructures have significant potential for future optoelectronic research
and can enable broad possibilities with compositional tunability of
organohalide perovskites and the versatility offered by diverse 2D materials.
