Perovskite-quantum dots interface: Deciphering its ultrafast charge carrier dynamics

Understanding electron and hole (e,h) transport at semiconductor interfaces is paramount to developing efficient optoelectronic devices. Halide perovskite/semiconductor quantum dots (QDs) have emerged as smart hybrid systems with a huge potential for light emission and energy conversion. However, the dynamics of generated e-h pairs are not fully understood. Ultrafast UV–VIS transient absorption and THz spectroscopies have enabled us to unravel the processes of the e-h recombination within a hybrid film of methylammonium lead triiodide (MAPbI3) interacting with different amount of PbS/CdS core/shell QDs. To accurately analyze the complex behavior, we applied a new model for e-h events in this hybrid material. The results obtained with sample having a high concentration of QDs (7.3 mass percentage) indicate: (i) a large population (92%) of the photogenerated charge carriers are affected by QDs presence. The main part of these carriers (85% of the total) in perovskite domain diffuse towards QDs, where they transfer to the interface (electrons) and QD´s valence bands (holes) with rate constants of 1.2 × 1010 s−1 and 4.6 × 1010 s−1, respectively. 7% of these affected charged entities are excitons in the perovskite domain in close vicinity of the interface, and show a recombination rate constant of 3.7 × 1010 s−1. (ii) The carriers not affected by QDs presence (8%) recombine through known perovskite deactivation channels. Lowering the QDs mass percentage to 0.24 causes a decrease of electron and hole effective transfer rate constants, and disappearance of excitons. These results provide clues to improve the performance of perovskite/QD based devices.