Ultralow Dark Current and Broadband PbS Colloidal Quantum Dot Photodetectors

PbS colloidal quantum dots (CQDs) hold great promise in the next generation of low-cost, high-performance short-wave infrared (SWIR) photodetectors. Both the dark current and the spectral response, however, have been hampered by the preparation of semiconductor-grade PbS CQDs. Here, we report high-performance PbS CQD photodetectors by leveraging a monomer-assisted ligand exchange strategy. The resultant PbS CQD films show enhanced defect passivation evidenced by more than 1 order of magnitude increase in their exciton lifetime, which translated into photodetectors with record low dark current and high specific detectivity (D*). For a cutoff wavelength ∼1700 nm, ultralow dark current (21 nA/cm2 at −0.5 V) and a peak specific detectivity (D*) of 8.73 × 1012 Jones were achieved at 1650 nm, which are comparable to commercial InGaAs photodetectors. In addition, the implementation of this approach to large-sized PbS CQDs leads to broadband photodetectors with a cutoff wavelength of ∼2330 nm, a regime previously inaccessible to PbS CQDs. The monolithic integration of PbS CQD photodetectors with a 256 × 256 pixel thin-film transistor readout circuit enables infrared imaging through Si and Ge filters, validating the technology’s potential for broadband imaging applications.