Printable Nanocomposite FeS₂-PbS Nanocrystals/Graphene Heterojunction Photodetectors for Broadband Photodetection

Colloidal nanocrystals are attractive materials for optoelectronics applications because they offer a compelling combination of low-cost solution processing, printability, and spectral tunability through the quantum dot size effect. Here we explore a novel nanocomposite photosensitizer consisting of colloidal nanocrystals of FeS₂ and PbS with complementary optical and microstructural properties for broadband photodetection. Using a newly developed ligand exchange to achieve high-efficiency charge transfer across the nanocomposite FeS₂-PbS sensitizer and graphene on the FeS₂-PbS/graphene photoconductors, an extraordinary photoresponsivity in exceeding ∼10⁶ A/W was obtained in an ultrabroad spectrum of ultraviolet (UV)-visible-near-infrared (NIR). This is in contrast to the nearly 3 orders of magnitude reduction of the photoresponsivity from ∼10⁶ A/W at UV to 10³ A/W at NIR on their counterpart of FeS₂/graphene detectors. This illustrates the combined advantages of the nanocomposite sensitizers and the high charge mobility in FeS₂-PbS/graphene van der Waals heterostructures for nanohybrid optoelectronics with high performance, low cost, and scalability for commercialization.