Breaking the Size Limit of Room-Temperature Prepared Lead Sulfide Colloidal Quantum Dots for High-Performance Short-Wave Infrared Optoelectronics

Lead sulfide (PbS) colloidal quantum dots (CQDs) are of great interest for short-wave infrared (SWIR) optoelectronic devices due to their tunable bandgaps across the whole SWIR spectra. PbS CQD inks synthesized directly at room temperature (RT) and ready for the fabrication of various SWIR devices are highly demanded. There are currently no available protocols for RT synthesis of PbS CQDs with absorption beyond 1200 nm. Here, we report on the first synthesis of PbS CQDs at RT with an absorption beyond 1800 nm. There is a delicate balance between nucleation of new seeds and growth of existing dots regulated by the lead-to-sulfur (Pb/S) precursor ratio in the reaction medium, and a proper Pb/S ratio ranging from 1.1 to 2 should be maintained to keep the continuous growth. Photodiodes based on PbS CQDs with a 1550 nm excitonic absorption are fabricated to demonstrate their suitability for device applications. The resulting devices achieve a high photo responsivity of 0.635 A/W, a specific detectivity of 1.01 x 1011 Jones, and a fast response with rise and fall times of 1.08 and 1.10 mu s, respectively.