Improving the Infrared Photodetector Performance of PbS Nanocrystal Superlattice through Ligand Optimization

Benefiting from the enhanced electronic coupling of the long-range-order quantum dot (QD) superlattice, the PbS QD superlattice is expected to be a promising candidate in optoelectronic devices. However, the presence of long organic ligands dramatically hinders charge carrier transfer in the QD-based devices and results in a lower photocurrent than anticipated. Here, three distinct PbS QD superlattices were meticulously prepared through solid-phase interface self-assembly and subsequent ligand exchange. The results reveal that the exchange of ligands with ethylenediamine (EDA) leads to a high degree of crystallinity and orientational alignment of PbS QDs and demonstrates that the amine groups can promote the formation of a more compact superlattice on the premise of not destroying the degree of order. Compared to the pristine superlattice photodetector, responsivity and detectivity were enhanced in the ligand-exchanged EDA-superlattice device. The improved performance is attributed to the reduced interdot distance between QDs, which enhances the charge transport properties within the superlattice. These findings significantly contribute to our understanding of ligand exchange in solid superlattices and indicate that ligand-exchanged EDA-superlattices are desirable building blocks for fabricating high-performance photodetectors.