Ultraviolet Photodetector With Solution-Cast Magic-Sized PbS Clusters

Colloidal PbS quantum dots (QDs) are increasingly recognized as a promising material for photodetectors, offering tunable spectral sensitivity and flexibility in device architecture. This study highlights the viability of using magic-sized PbS clusters, characterized by an excitonic absorption peak at 365 nm, as sensitizers in vertical photoconductors (vPCs). It also showcases their capability to form rectifying planar p-n heterojunctions with ZnO in photodiodes (PDs). The integration of these ultraviolet (UV)-sensitive PbS clusters with ZnO nanocrystals greatly improves the band-edge absorption of ZnO and improves the electrical properties, as is evident from the reduced dark current in the resultant vPC. These findings present both new opportunities and challenges in solution-based fabrication of photodetectors. Notably, uniformly sized PbS clusters are critical for the solution-casting of highly UV-responsive PDs with detectivities on the order of 10
$^{\text{14}}$
Jones. The synthesis of PbS clusters includes an intermediate ligand exchange step. During this stage, the PbS clusters are subjected to nanostrain, facilitated by the addition of 3-mercaptopropyltrimethoxysilane (MPTMS). This unique surface chemistry promotes the formation of magic-sized PbS clusters.