Elward Jennifer M, Chakraborty Arindam
Army Research Laboratory, Aberdeen Proving Ground, Aberdeen, Maryland 21005, United States.
Department of Chemistry, Syracuse University , Syracuse, New York 13244, United States.
J Chem Theory Comput. 2015 Feb 10;11(2):462-71. doi: 10.1021/ct500548x. Epub 2015 Jan 21.
Presence of heterojunctions is important for generation of free charge carriers and the dissociation of bound electron-hole pairs in semiconductor nanoparticles. This work presents a theoretical investigation of the effect of core/shell heterojunction on electron-hole interaction in CdSe/ZnS quantum dots. The excitonic wave function in the CdSe/ZnS dots was calculated using the electron-hole explicitly correlated Hartree-Fock (eh-XCHF) method and the effect of successive addition of the ZnS shell on exciton binding energy, electron-hole recombination probability, and the electron-hole separation distance was investigated. It was found that the scaling of all the three quantities as a function of dot diameter did not follow conventional volume scaling laws of core-only dots, and the scaling laws were significantly altered due to the presence of the heterojunction. The spatial localization of the quasiparticles in the core/shell quantum dot was analyzed by calculating the 1-particle reduced density from the eh-XCHF wave function and partitioning the density spatially into core and shell regions. It was found that in the 15 nm CdSe/ZnS dot, the relative probability of the electron localization in the shell region was higher than the hole by a factor of 3. The degree of spatial localization of the quasiparticles was found to depend strongly on the initial size of the CdSe core in the core/shell quantum dot. It was found that a reduction in the CdSe core diameter by a factor of 1.7 resulted in an enhancement of the preferential localization of the electron in the shell region by a factor of 11.3. The results demonstrate that large CdSe/ZnS quantum dots with a small CdSe core have the necessary characteristics for efficient exciton dissociation and generation of free charge carriers.
异质结的存在对于半导体纳米颗粒中自由电荷载流子的产生以及束缚电子 - 空穴对的解离至关重要。本文对核/壳异质结对CdSe/ZnS量子点中电子 - 空穴相互作用的影响进行了理论研究。使用电子 - 空穴显式相关哈特里 - 福克（eh - XCHF）方法计算了CdSe/ZnS量子点中的激子波函数，并研究了连续添加ZnS壳对激子结合能、电子 - 空穴复合概率以及电子 - 空穴分离距离的影响。研究发现，这三个量随量子点直径的变化规律并不遵循仅含核的量子点的传统体积缩放定律，并且由于异质结的存在，缩放定律发生了显著改变。通过从eh - XCHF波函数计算单粒子约化密度并将密度在空间上划分为核区和壳区，分析了核/壳量子点中准粒子的空间定位。研究发现，在15 nm的CdSe/ZnS量子点中，电子在壳区的定位相对概率比空穴高3倍。发现准粒子的空间定位程度强烈依赖于核/壳量子点中CdSe核的初始尺寸。研究发现，CdSe核直径减小1.7倍会导致电子在壳区的优先定位增强11.3倍。结果表明，具有小CdSe核的大尺寸CdSe/ZnS量子点具有有效激子解离和产生自由电荷载流子的必要特性。
