Tuning the Photoresponse Mode of PbS Quantum Dot Homojunction Photodetectors

Colloidal quantum dots (QDs), particularly lead sulfide (PbS) QDs, are attractive for optoelectronic applications due to their tunable bandgap and outstanding photoelectric properties. However, conventional PbS QD photodetectors are often limited to a single photoconductivity mode. In this work, we fabricate photodiode-type devices based on PbS QD homojunctions and demonstrate bias tunability across multiple photoresponse modes─especially from negative to positive photoconductivity. Systematic analysis reveals that the operating mode transitions from drift- to diffusion-dominated photoresponses as the bias increases. Field-effect transistor measurements further show that illumination not only enhances carrier concentration but also significantly boosts carrier mobility. QD size and surface ligands serve as additional control variables. These findings on photoresponse regulation provide a mechanistic foundation for designing multimodal photodetectors and advancing QD-based optoelectronic logic devices.