Interfacial coupling enables high carrier mobility in PbS colloidal quantum dot photodetectors

Carrier transport in colloidal quantum dot (CQD) films is strongly influenced by the interfacial coupling between CQDs. Currently, the shape of PbS CQDs synthesized using traditional methods results in random orientation relationships between the crystal facets in CQD films, limiting the coupling strength and the final performance of optoelectronic devices. In this study, post-synthesis surface treatment of PbS CQDs was employed to achieve facet control during secondary growth, manipulating the facets of PbS CQDs at the nanoscale to enhance interfacial coupling within CQD films. Additionally, mixed ligands of PbX₂ (X = Br, I) and anhydrous sodium acetate were used to passivate the PbS CQDs, ensuring sufficient passivation. This method combines facet passivation with strong coupling through the (100) facets of CQDs, thereby enhancing carrier mobility and improving device performance. Experimental results showed that, compared to standard PbS CQD films, the electron and hole mobilities of the PbS CQD films subjected to secondary growth were significantly improved, with hole mobility increased by 6 times. Photodetectors fabricated using these films achieved a quantum efficiency of 33% at 1500 nm under 0 V bias, a threefold improvement compared to standard devices.