  Methylammonium lead iodide perovskite has revolutionized the field of third
generation solid-state solar cells leading to simple solar cell structures1 and
certified efficiencies up to 20.1%. Recently the peculiar light harvesting
properties of organometal halide perovskites have been exploited in
photodetectors where responsivities of ~3.5 A/W and 180 A/W have been
respectively achieved for pure perovskite-based devices and hybrid
nanostructures. Here, we report on the first hybrid phototransistors where the
performance of a network of photoactive Methylammonium Lead Iodide nanowires
(hereafter MAPbI$_3$NW) are enhanced by CVD-grown monolayer graphene. These
devices show responsivities as high as ~2.6x10$^6$ A/W in the visible range
showing potential as room-temperature single-electron detector.
