Suppressing the Dark Current in Quantum Dot Infrared Photodetectors by Controlling Carrier Statistics

Lead sulfide colloidal quantum dot photodiodes (PbS QDPDs) exhibit a high energy conversion efficiency for infrared detection. Despite the high photoinduced current, the performance of PbS QDPDs is limited by the high dark current which is rarely investigated. Understanding the dark current in PbS QDPDs is critical to improving the detectivity of PbS QDPDs. Herein, it is demonstrated that minority carriers of I-passivated PbS films and trap sites of EDT-passivated PbS films are related to the dark current of PbS QDPD. Utilizing annealing and low-temperature ligand exchange processes, the dark current density can be decreased almost tenfold by suppressing the minority carrier diffusion in the PN junction and trap-assisted charge injection from the electrode. PN junction simulation, space charge limited current measurements, as well as structural, optical, and chemical characterizations are conducted to elucidate the origins of the dark current suppression. The authors achieve the lowest dark current density of 2.9 x 10(-5) mA cm(-2) at -1 V among PbS-based QDPDs and a high detectivity of 6.7 x 10(12) Jones at 980 nm. It is believed that this work provides fundamental understanding of carrier statistics in nanomaterials and device performance as well as a technological basis for realizing low-cost high-performance optoelectronic devices.