Temperature-Dependent Optical Properties of PbS/CdS Core/Shell Quantum Dot Thin Films:Probing the Wave Function Delocalization

Colloidal semiconductor quantum dots (QDs) are extraordinarily appealing for the development of cheap and large area solar cells due to high absorption efficiency; tunable bandgap energies; and solution processability. Understanding:and controlling electronic wave function delocalitation in QD thin films is therefore pivotal for realizing efficient optoelectronic devices: Here, a detailed study of the exciton recombination dynamics in PbS/CdS core/shell films as a function of temperature and surface chemistry is reported: By decreasing the temperature from 295 to 5.4 K, electronic wave function delocalization from the PbS core to the monolayer CdS shell is observed, demonstrating a reduction of the conduction band offset at low temperature and the formation of a quasi-type II band alignment: Interestingly, films made with core shell particles, where the shell is thicker than a monolayer, display type I alignment also at low temperature.