Shang Qiongyi, Kaledin Alexey L, Li Qiuyang, Lian Tianquan
Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, USA.
J Chem Phys. 2019 Aug 21;151(7):074705. doi: 10.1063/1.5109894.
CsPbI perovskite quantum dots (QDs) have shown great potential in light-harvesting and light-emitting applications, which often involve the transfer of charge carriers in and out of these materials. Here, we studied size-dependent charge separation (CS) and charge recombination (CR) between CsPbI QDs and rhodamine B (RhB) molecules, using transient absorption spectroscopy. When the average size decreases from 11.8 nm to 6.5 nm, the average intrinsic CS time constant decreases from 872 ± 52 ps to 40.6 ± 4.3 ps and the corresponding charge recombination time constant decreases from 3829 ± 51 ns to 1384 ± 54 ns. The observed trend of size-dependent CS and CR rates can be well explained by Marcus theory using the theoretically calculated CS and CR driving forces (ΔG and ΔG), molecular reorganization energy (λ), and electronic coupling strength between QD and RhB (H and H). Unlike the extensively studied more strongly quantum confined Cd chalcogenide QDs, the CsPbI QDs are in a weak quantum confinement regime in which size-dependent coupling strength plays a dominant role in the size-dependent charge transfer properties.
CsPbI钙钛矿量子点（QDs）在光捕获和发光应用中显示出巨大潜力，这些应用通常涉及电荷载流子进出这些材料的转移。在此，我们使用瞬态吸收光谱研究了CsPbI量子点与罗丹明B（RhB）分子之间的尺寸依赖性电荷分离（CS）和电荷复合（CR）。当平均尺寸从11.8 nm减小到6.5 nm时，平均本征CS时间常数从872±52 ps减小到40.6±4.3 ps，相应的电荷复合时间常数从3829±51 ns减小到1384±54 ns。使用理论计算的CS和CR驱动力（ΔG和ΔG）、分子重组能（λ）以及量子点与RhB之间的电子耦合强度（H和H），通过马库斯理论可以很好地解释观察到的尺寸依赖性CS和CR速率趋势。与广泛研究的量子限制更强 的Cd硫族化物量子点不同，CsPbI量子点处于弱量子限制 regime，其中尺寸依赖性耦合强度在尺寸依赖性电荷转移特性中起主导作用。
