Thiol-Free p-Type Colloidal Quantum Dot for Efficient Broadband Optoelectronics

Colloidal quantum dots (CQDs) are promising semiconductors for optoelectronic applications owing to their bandgap tunability and solution processability. Historically, ethanedithiol has been widely employed as a surface ligand to form a p-type CQD layer via a layer-by-layer process. However, the limited control of p-type characteristics reduces the device performance, and the high reactivity of ligand and processing solvents degrade the underlying layer. In this study, a thiol-free p-type CQD is demonstrated by creating native p-type CQDs during the synthesis process. Sulfurization of PbS CQD results in p-type properties that enable the avoidance of any further thiol-ligand treatment process. Further, alternative surface passivation of the sulfurized CQD using halide ligand yields a robust, p-type, morphologically uniform, and trap-suppressed film. The developed CQD film is then employed as a hole-transporting layer (HTL) for both broadband solar cells and photodetectors. The resulting CQD devices exhibit improved performance with a 65.7% increase in photovoltaic efficiency and a 1.7-fold improvement in responsivity for infrared photodetection. The devices also demonstrate higher ambient stability, retaining 85% of the initial performance after 1,000 hr owing to the uniform top HTL morphology, indicating the potential of the new p-type layer to be utilized in various emerging optoelectronics.