Theoretical Study on the Contacting Interface-Dependent Band Alignments of CsPbBr₃@MoS₂ van der Waals Heterojunctions: Spin–Orbit Coupling Does Matter

Abstract

Van der Waals heterojunctions formed by all-inorganic cesium lead halide perovskites and two-dimensional transition-metal dichalcogenides (TMDs) have received much attention in recent years due to their outstanding optoelectronic properties. However, several fundamental issues such as band alignments and carrier dynamics in these novel heterojunctions remain unclear. Herein, we have first exploited static electronic structure calculations in combination with non-adiabatic dynamics simulations to investigate the interfacial properties of the heterojunctions formed by monolayer MoS2 and CsPbBr3 nanosheets. Our results indicate that the interfacial properties are closely related to the contacting interfaces during the formation of the heterojunctions. First, the planar-average charge-density difference and charge-density difference analyses indicate that the charge-transfer properties during the formation of heterojunctions are different with different contacting interfaces. Second, the band alignment alters from type-I to type-II, while the contacting facet of CsPbBr3 changes from PbBr2- to CsBr-terminated one. Moreover, the spin–orbit coupling effects are indispensable for correctly predicting such contacting interface-dependent band alignments of CsPbBr3@MoS2 heterojunctions. Finally, the non-adiabatic dynamics simulations reveal that the electron transfer from CsPbBr3 to MoS2 takes place within 100 fs in type-II CsPbBr3–CsPb@MoS2 due to the small adjacent energy differences. Based on these results, we propose that such contacting interface-dependent band alignments might be responsible for the experimentally observed weakened instead of totally vanished photoluminescence. Our present work not only provides a reasonable microscopic mechanism for interpreting previous experimental results but can also be helpful for the future design of novel devices based on two-dimensional TMD and perovskite heterojunctions with better optoelectronic performance.

Generalized Ab Initio Nonadiabatic Dynamics Simulation Methods from Molecular to Extended Systems

“…Time-dependent electron amounts remaining on CsPbBr 3 of CsPbBr 3 –PbCs@MoS 2 (b) and CsPbBr 3 –CsPb@MoS 2 (c) and the adjacent energy differences of the 1–150 conduction band minimum states in CsPbBr 3 –CsPb@MoS 2 (d). Reprinted with permission from ref . Copyright 2021 American Chemical Society.…”

“…Our recently developed GTSH approach at the time-domain TDDFT with collinear and noncollinear DFT methods are suitable for simulating much bigger systems, such as materials under the periodic boundary condition. Herein, we will discuss our latest progress on several important systems including transition-metal dichalcogenides (TMDs), perovskites, carbon nanotubes, etc. ,− In these complex systems, the photoinduced interfacial carrier dynamics are usually very important, which become a challenging task for both experimental and theoretical scientists.…”

“…). − Herein, we constructed two CsPbBr 3 @MoS 2 heterostructures, namely, PbBr 2 -terminated CsPbBr 3 –PbCs@MoS 2 and CsBr-terminated CsPbBr 3 –CsPb@MoS 2 (Figure ). Then, the GTSH nonadiabatic dynamics simulations with spin–orbit couplings were carried out to study the interfacial properties of these systems. According to the electron-transfer analysis, we found that different contacting interfaces would lead to different charge-transfer properties; the PbBr 2 - and CsBr-terminated systems can be assigned as the type-I and type-II heterostructures in terms of band alignment.…”

Nonadiabatic Dynamics Simulations for Photoinduced Processes in Molecules and Semiconductors: Methodologies and Applications

“…As mentioned before, the TSH methods are most widely used in MQC-based NAMD simulations due to their straightforward implementation, clear physical picture, and easy coding. Among various TSH algorithms, the FSSH method proposed by Tully et al , and its variants such as the GTSH method proposed by us are ones of the most typical methods, and they are also prevailingly used in our NAMD simulations for various molecules − and semiconductor materials. ,− Therefore, herein, we present the related algorithms and discuss some important aspects.…”

Enhanced Electron Transfer and Spin Flip through Spin–Orbital Couplings in Organic/Inorganic Heterojunctions: A Nonadiabatic Surface Hopping Simulation

“…NA-MD methods implementing the surface hopping (SH) scheme in the framework of time-dependent Kohn–Sham (TDKS) equation (in brief, TDKS-based NA-MD) − provide a detailed description of spin-free electronic state transitions resulting from electron–phonon couplings (EPCs), such as the charge transfer, hot carriers relaxation, and nonradiative recombination in condensed matter systems. ,,,− More recently, NA-MD has started to report SOC effects on these nonadiabatic processes, ,− yet SOC-induced spin dynamics is unreported to the best of our knowledge. Consequently, the fundamental knowledge of the fate of electron spin during the interlayer charge transfer and relaxation in solids, which is important for light harvesting, efficiency promotion of organic solar cells, and applicable high-IQE luminescent devices, , continues to be a missing piece of information because of the absence of suitable theoretical tools. ,, Therefore, there is an urgent need to investigate SOC-induced spin-related electron dynamics at organic/inorganic interfaces.…”