  Recent approaches to develop infrared photodetectors characterized by high
sensitivities, broadband spectral coverage, easy integration with silicon
electronics and low cost have been based on hybrid structures of transition
metal dichalcogenides (TMDCs) and PbS colloidal quantum dots (CQDs). However,
to date, such photodetectors have been reported with high sensitivity up to 1.5
$\mu$m. Here we extend the spectral coverage of this technology towards 2
$\mu$m demonstrating for the first time compelling performance with
responsivities 1400 A/W at 1.8 $\mu$m with 1V bias and detectivities as high as
$10^{12}$ Jones at room temperature. To do this we studied two TMDC materials
as a carrier transport layer, tungsten disulfide (WS$_2$) and molybdenum
disulfide (MoS$_2$) and demonstrate that WS$_2$ based hybrid photodetectors
outperform those of MoS$_2$ due to a more adequate band alignment that favors
carrier transfer from the CQDs.
