Broadband photodetectors based on PbS quantum dots synthesized using the multiple injection growth method

Abstract PbS colloidal quantum dot (CQD) photodiodes are becoming increasingly significant for their utility in short-wave infrared detection and imaging. Despite their promise, challenges persist in synthesizing large PbS quantum dots that extend their response wavelength beyond 1500 nm. The usual hot-injection method has problems because of changes in temperature, solution ratios, and the Ostwald ripening process, all of which make it harder to make large PbS quantum dots that are all the same size as the temperature rises. In this study, we introduced small-sized PbS quantum dots, which absorb light at approximately 600 nm, into a reaction system containing seed quantum dots that absorb light at approximately 1050 nm. This process was repeated on multiple occasions to facilitate the growth of the quantum dots, resulting in larger PbS quantum dots with an absorption peak at 1550 nm. By meticulously regulating parameters such as dosage, reaction time, and the number of injections, we successfully synthesized PbS quantum dots of varying sizes. This approach not only enables the production of PbS quantum dots with specific size requirements but also introduces novel insights into the synthesis mechanism of PbS. Furthermore, PbS CQD photodiodes were fabricated with reduced dark current densities by employing SnO 2 synthesized via the sol–gel method as an electron transport layer, which better matches the energy bands of the larger PbS quantum dots. At ambient temperature, the photodiode demonstrated a responsivity of 290 mA W −1 with a normalized detectivity of 1.16 × 10 11 Jones, thereby underscoring its promising potential for practical applications.