Passivation-induced improvement of electron transport in PbS CQDs for enhanced photodetector responsivity and detectivity

Solution-processed semiconductors have emerged as a promising platform for next-generation optoelectronic technologies. Colloidal quantum dots (CQDs) are widely applied in light-emitting diodes, photodetectors, and solar cells, where their performance is often enhanced through effective surface passivation. In this study, phenethylammonium iodide (PEAI) ligands were employed to passivate the surface of lead sulfide (PbS) CQDs and form a PbS/PEAI interface in PbS-based photodetectors. This strategy improved iodine-ion passivation on the PbS surface, enhanced carrier extraction, and increased the optical response of the device. Additionally, Phenyl-C61-butyric-acid methyl ester (PCBM) was incorporated into the electron transport layer (ETL) to reduce defect density and further improve charge transport. The initial device structure prior to surface passivation (ITO/ZnO/PbS/MoO3/Ag) exhibited an external quantum efficiency (EQE) of 3.06%. After applying PEAI surface passivation and introducing PCBM into the ETL, the optimized device (ITO/ZnO/PCBM/PbS/PbS–PEAI/MoO3/Ag) achieved a maximum EQE of 17.24%, corresponding to an approximately 5-fold enhancement compared with the unpassivated device. Moreover, the photodetector device exhibited a frequency cut-off of 101 kHz, and the transient photovoltage measurements showed rise and fall times of 4.8[Formula: see text]s and 4.2[Formula: see text]s, respectively. These findings suggest that the developed device could be suitable for future medical image recognition applications, owing to its high detectivity in the infrared region.