Photoinduced Transfer of Spin-Polarized Charges at Semiconductor Interfaces

Abstract

Charge transfer at the organic/inorganic semiconductor interfaces lies at the heart of interfacial photochemistry. While decades of research have shaped the current understanding that interfacial charge transfer depends crucially on energetic driving force and electronic coupling, much less is known about the role played by the spin degree of freedom. In particular, it is not clear how spin states evolve during the charge transfer process. With the advent of group 6 transition metal dichalcogenides (TMDC), a class of two-dimensional layered materials which permits the optical generation of spin-polarized electron-hole pairs in the monolayer limit, we now have the opportunity to investigate if charge transfer at an organic/inorganic interface could enable the transfer of spin polarization. Using time-resolved Faraday rotation and transient absorption spectroscopy, it is found in the MoSe₂/H₂Pc and C₆₀/WS₂ heterostructures that the photoinduced hole transfer from MoSe₂ to H₂Pc and electron transfer from WS₂ to C₆₀ results in spin polarization lifetimes one order of magnitude longer than that of a monolayer. In the WS₂/MoSe₂/H₂Pc heterostructure, the addition of a WS2 monolayer drives the dissociation of electron-hole pairs bound at the MoSe₂/H₂Pc interface and leads to the observation of nanosecond-long spin polarization at room temperature. These findings evidence the photoinduced transfer of spin polarization, a mechanism which could potentially be exploited to enhance the efficiency and selectivity of photochemical reactions involving angular momentum change, and may be generalized to other organic/inorganic interfaces composed of crystalline semiconductors with spin-momentum locking.