Ultrafast Charge Separation in Two-Dimensional CsPbBr3 Perovskite Nanoplatelets

Two-dimensional (2D) cesium lead halide perovskite colloidal nanoplatelets show sharper excitonic absorption/emission peaks and larger absorption cross section in comparison to bulk materials and quantum dots. It remains unclear how 2D exciton and charge separation properties can be utilized to further enhance the performance of perovskite materials for optoelectrical applications. Herein, we report a study of exciton and interfacial charge-transfer dynamics of CsPbBr3 nanoplatelets via transient absorption spectroscopy. The exciton binding energy (similar to 260 meV) is determined via detailed spectral analysis. The exciton bleach is caused by band-edge exciton state-filling with negligible single carrier (electron or hole) contributions. Efficient charge separation can be achieved by selective electron and hole transfers to adsorbed molecular acceptors (benzoquinone and phenothiazine, respectively), and the half-life of the charge-separated state (>> 100 ns) in nanoplatelet-phenothiazine complexes is >100 fold longer than that in quantum dot-phenothiazine complexes. Our results suggest that CsPbBr3 nanoplatelets are promising materials for photocatalysis and photovoltaic applications.