PbS Colloidal Quantum Dots For Next Generation Short-Wavelength Photodetectors

Short-wavelength infrared (SWIR) photodetectors are essential for applications including telecommunications, light detection and ranging, and biomedical sensing, yet conventional materials such as HgCdTe and InGaAs remain constrained by costly fabrication and integration challenges. This thesis investigates solution-processable PbS quantum dots (QDs) as a scalable platform for high-performance SWIR optoelectronics, focusing on surface chemistry, colloidal stability, charge transport, and scalable device fabrication. A major challenge is the colloidal instability of large PbS QDs, which expose poorly passivated {100} facets. Methylammonium lead iodide ligands combined with optimized solvents enable stable n-type PbS QD inks containing QDs up to 6.7 nm, with shelf lives exceeding 10 weeks. These inks yield photodiodes with an external quantum efficiency of 76% at 1300 nm and a specific detectivity of 1.8 × 10¹² Jones. The approach is extended to p-type PbS QD inks using sulfur-based ligands and tailored solvent systems, enabling fully blade-coated n–p and p–n photodiodes with improved detectivity and bandwidth. Further control of QD stoichiometry using organoselenide ligands produces selenium-passivated, p-type PbS QDs with a record hole mobility of 0.15 cm² V⁻¹ s⁻¹. The resulting devices achieve a bandwidth of 374 kHz and a detectivity of 7.1 × 10¹² Jones. Finally, hybrid Pb–Sn perovskite/organic semiconductor photodetectors demonstrate high SWIR response and intrinsic narrowband filtering near 1000 nm. Overall, this work establishes surface and solvent engineering as effective strategies toward stable, high-performance, and scalable solution-processed SWIR photodetectors.