Charge carrier dynamics in colloidal quantum dots: Tracking the dance of electrons and holes by ultrashort laser pulses

Sammanfattning: Quantum dots (QDs) are semiconductor nanocrystals with quantum
confinement. This thesis uses various time-resolved spectroscopic
techniques to study ultrafast charge carrier dynamics in colloidal CdSe quantum dots that are important both from a theoretical point of view and for their relevance for solar cell applications. Using 2D electronic spectroscopy, we follow charge carrier relaxation and trapping, demonstrating the power and relevance of this technique to QDs. The 2D spectroscopy and other ultrafast techniques allow us to distinguish between trap states with different characteristics with respect to energy level, lifetime and localization. We characterize energy transfer in films of QDs of different sizes, using ultrafast experiments and a detailed theoretical description of the film and QD geometry. Electron and hole transfer is affected by trapping, by the shell in core–shell structures, and by charging of the QD during injection of several excited electrons. Finally, we study the formation and decay of multiple excitons in QDs. Together, the techniques reveal a rich picture of processes and show how these can be controlled for more efficient solar cells.