Jin Ho, Livache Clément, Kim Whi Dong, Diroll Benjamin T, Schaller Richard D, Klimov Victor I
Nanotechnology and Advanced Spectroscopy Team, C-PCS, Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM, USA.
Center for High Technology Materials, University of New Mexico, Albuquerque, NM, USA.
Nat Mater. 2023 Aug;22(8):1013-1021. doi: 10.1038/s41563-023-01598-x. Epub 2023 Jul 13.
Carrier multiplication is a process whereby a kinetic energy of a carrier relaxes via generation of additional electron-hole pairs (excitons). This effect has been extensively studied in the context of advanced photoconversion as it could boost the yield of generated excitons. Carrier multiplication is driven by carrier-carrier interactions that lead to excitation of a valence-band electron to the conduction band. Normally, the rate of phonon-assisted relaxation exceeds that of Coulombic collisions, which limits the carrier multiplication yield. Here we show that this limitation can be overcome by exploiting not 'direct' but 'spin-exchange' Coulomb interactions in manganese-doped core/shell PbSe/CdSe quantum dots. In these structures, carrier multiplication occurs via two spin-exchange steps. First, an exciton generated in the CdSe shell is rapidly transferred to a Mn dopant. Then, the excited Mn ion undergoes spin-flip relaxation via a spin-conserving pathway, which creates two excitons in the PbSe core. Due to the extremely fast, subpicosecond timescales of spin-exchange interactions, the Mn-doped quantum dots exhibit an up-to-threefold enhancement of the multiexciton yield versus the undoped samples, which points towards the considerable potential of spin-exchange carrier multiplication in advanced photoconversion.
载流子倍增是一个过程，通过该过程，载流子的动能通过产生额外的电子 - 空穴对（激子）而弛豫。在先进的光转换背景下，这种效应已得到广泛研究，因为它可以提高激子的产生率。载流子倍增由载流子 - 载流子相互作用驱动，这种相互作用导致价带电子激发到导带。通常，声子辅助弛豫速率超过库仑碰撞速率，这限制了载流子倍增产率。在这里，我们表明，通过利用锰掺杂的核/壳PbSe/CdSe量子点中的“自旋交换”而非“直接”库仑相互作用，可以克服这一限制。在这些结构中，载流子倍增通过两个自旋交换步骤发生。首先，在CdSe壳层中产生的激子迅速转移到锰掺杂剂上。然后，被激发的锰离子通过自旋守恒途径经历自旋翻转弛豫，这在PbSe核中产生两个激子。由于自旋交换相互作用的极快亚皮秒时间尺度，与未掺杂样品相比，锰掺杂量子点的多激子产率提高了多达三倍，这表明自旋交换载流子倍增在先进光转换中具有巨大潜力。
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