Elucidating the Mechanisms of the Large Stokes Shift in Isolated and Coupled PbS Quantum Dots

Despite much effort being made, the origin of Stokes shift in colloidal quantum dot (CQD) solutions is still debatable to date, particularly in the case of QD films, which are typically used as active layers in the optoelectronic devices but have been rarely explored. Herein, we demonstrate that for QD solutions, the main origin contribution to the Stokes shift is the confined electron state (CES). In the case of QD films, in addition to the aforementioned CES, for the first time, we found that the Stokes shift is also affected by the electronic coupling strength between adjacent QDs. Overall, an improved understanding of the origin of the Stokes shift in lead sulfide (PbS) QD solutions and films can provide the key fundamental knowledge for realizing efficient optoelectronic devices.