In this work, it is reported for the first time the synthesis of high-purity Lead Sulfide (PbS) quantum dot (QD) using the nano-emulsion method assisted by an ultrasonic bath, which was tested as a hole transporting material (HTM) in perovskite devices. Further, these PbS QDs were introduced in CH3NH3PbI3 based perovskite device, between the perovskite layer and the HTM to enhance its stability against humidity. The hydrophobic nature of the PbS protects the perovskite by preventing the diffusion of water into the device. To compare the effect, the perovskite devices with and without the layer of PbS QDs were tested under high humidity conditions (similar to 70%) without encapsulation. The pristine perovskite devices completely degraded after a span of 10 days, whereas the devices with PbS QDs showed huge resistance to humidity by retaining 76% of its initial efficiency after a span of 60 days. Such enhanced stability under adverse environmental conditions has never been reported. Also, these results would open up a new insight of PbS QDs being utilized as a barrier against high humid conditions for making air-stable devices.