Ultrafast Carrier Dynamics in 2D CdSe Nanoplatelets-CsPbX3 Composites: Influence of the Halide Composition

Two-dimensional (2D) material-based composites are considered to be an important class of materials for light-harvesting applications because of their efficient charge separation. In this article, we have designed composites of 2D CdSe nanoplatelets (NPLs) and CsPbX3 (X = mixture of Br and I or I) perovskite nanocrystals and investigated their ultrafast carrier dynamics using ultrafast spectroscopy. A time-resolved fluorescence upconversion study reveals that the electron transfer from CdSe NPLs to CsPbX3 varies with changing the composition of perovskite from CsPbBr1.5I1.5 to CsPbI3. From the transient absorption spectroscopic study, the shortening of the faster component of bleach recovery kinetics of CdSe NPLs along with the enhancement of growth time of CsPbX3 NCs in composites indicates the ultrafast electron transfer from CdSe NPLs to CsPbX3 NCs. The ultrafast electron transfer from 2D CdSe NPLs to CsPbX3 NCs enhances in the following order: CsPbI3 > CsPbBrI2 > CsPbBr1.5I1.5. The dark current and photocurrent are 0.04 and 62.4 mu A in the CdSe-CsPbI3 composite. The dramatically improved photocurrent response in the CdSe-CsPbI3 composite confirms the enhancement of their efficient charge separation because of the ultrafast electron transfer from CdSe NPLs to pervoskite NCs. Our finding reveals that the integration of 2D CdSe NPLs with perovskite NCs offers a great opportunity for the improvement of the efficiency of perovskite solar cells by engineering the interfacial chargetransfer dynamics.