受益于独特的物理、化学和结构特性，二维材料在光电器件中具有广泛的应用前景。由于层间是较弱的范德华相互作用，界面工程在二维同质/异质结中扮演重要角色，调控层间耦合会对其性能产生显著影响。半导体中的电荷载流子动力学对光电器件的性能具有决定性作用，尤其是非辐射过程，因为该过程是能量损失的主要途径。随着光谱检测技术的发展，时间分辨光谱可以用来研究光生载流子的各种动力学行为，但是难以对实验结果提供原子级理解，并且实验试错法也容易造成资源浪费。本文以层间耦合为核心，利用第一性原理方法研究了扭转角和铁电衬底对二维材料中光生载流子动力学的调控作用，对实验现象提供深层次理解并对光电器件提出理性设计原则。具体研究了扭转角对双层黑磷（BP）光生载流子寿命和扩散距离的调控、h-BN铁电衬底对单层BP（MBP）电子-空穴复合动力学的影响以及扭转角对WS₂/MoS₂和双层WS₂载流子超快转移和复合动力学的调控作用，我们的工作解释了实验现象，加深了层间耦合对二维同质/异质结载流子动力学调控的理解，主要结果如下：

（1）适当的扭转角可以延长双层BP中载流子非辐射复合寿命和扩散距离从而改善光电器件性能。首先，层间耦合由层间距离主导，与波函数在层间区域的重叠无关；与AB堆垛相比，扭转系统中较大的层间距离和软化的层间呼吸模式表明扭转角削弱了层间耦合，抑制了P原子的面外运动。其次，11.54°系统会形成清晰的莫尔条纹，与高对称结构价带顶（VBM）和导带底（CBM）电位错排的共同作用导致了电荷密度的自发分离。最后，38.94°和11.54°体系的电子-空穴复合时间分别是776和1223 ps，后者与AB堆垛相比延长近一个数量级。考虑载流子迁移率后，38.94°体系的电子和空穴扩散距离分别是AB堆垛的4.7和1.5倍；在11.54°体系中，该提升分别为4.2和3.7倍。我们的工作提供了关于扭转角依赖的载流子动力学的原子见解，包括载流子复合和输运性质。

（2）h-BN铁电衬底会通过层间弱相互作用显著影响BP电子-空穴复合动力学。AB堆垛的两层h-BN之间由于存在电荷转移导致铁电极化，AA堆垛不存在该极化。相对于顺电相衬底上的单层BP，铁电相结构会使载流子非辐射寿命缩短2-3倍。在独立单层BP中高频面内振动（Ag2 ）主导载流子复合过程。然而衬底的作用导致该过程主要由面外振动决定，这与两个界面（MBP/h-BN和h-BN/h-BN）的层间呼吸振动有关。在MBP/h-BN界面中，由于电荷转移导致的强静电相互作用会直接诱导低频的呼吸振动（LBM）和高频P原子的面外振动（Ag1 ）。在h-BN/h-BN界面中，更强烈的层间耦合导致铁电堆垛的呼吸振动强度比顺电堆垛强一个数量级，这使该呼吸模式与BP的低频面外振动模式（B1u ）强烈共振，增加了电子-空穴复合通道从而加速复合。因此，在实验中应注意h-BN的堆垛方式和避免小扭转角的引入。

（3）扭转角对WS₂/MoS₂异质结中的空穴转移影响较弱，但可以显著延长层间载流子寿命。较大的层间距离和红移的层间呼吸模式表明扭转角削弱了层间耦合，这倾向于延缓层间载流子动力学。然而，对称性降低诱导的受体态密度升高会加速空穴转移速率，两者的共同作用导致层间空穴转移时间尺度（235-253 fs）对扭转角依赖性较弱。0°系统的层间复合时间尺度达到2 ns，而扭转系统的层间复合时间尺度延长至4.0-8.9倍，具有较强的扭转角依赖性，这是由非绝热耦合主导的。载流子的层间动力学主要与化学键的高频面外振动模式耦合。该工作为实验中观测到的现象提供了原子级理解。

（4）扭转角会加快双层WS₂中空穴从K能谷向Γ能谷的转移，并且会延长载流子的谷间复合。Γ和Q能谷比K能谷对层间耦合更敏感。扭转角削弱了层间耦合，也增强了K能谷的光吸收能力。在K能谷的初始激发后，空穴在400-600 fs内转移到Γ能谷，减弱的层间耦合会导致空穴转移的能隙减小进而加快空穴转移；电子在50 fs内转移到Q能谷，层间耦合的减弱和对称性的减低使CBM从Q能谷变为K能谷，因此电子转移只发生在高对称结构中，同时这也会降低复合过程中电子-空穴波函数的重叠。在自然堆垛中，电子-空穴复合时间为434 ps，扭转角使复合时间延长至2.6和4.6倍。该工作解释了扭转角对双层TMDs光吸收能力和载流子谷间动力学的影响。

       Benefitting from the unique physical, chemical, and geometrical properties, two-dimensional (2D) materials have promissing applications in photoelectric devices. Because of the weak van der Waals (vdWs) interactions between two layers, interface engineering plays an important role in 2D homo-hetero junctions, which are significantly affected by interlayer coupling. The performance of photoelectric device is determined by charge carrier dynamics in semiconductors. Particularly, nonradiative recombination is a major pathway lossing energy. With the development of spectroscopic technologies, time-resolved spectroscopy has been used to study the various dynamics of photoinduced carriers. However, experimental trial-and-error method is not only prone to waste of resources, but also makes it difficult to provide an atomic understanding of results. Therefore, taking the interlayer coupling as the core, we used first-principles method to study the regulation of twist angle and ferroelectric substrate on photoexcited carrier dynamics in 2D materials, so as to provide atomic insights of experimental phenomena and put forward rational design principles. We studied the regulation of twist angle on carrier lifetime and diffusion length in bilayer black phosphorus (BP), the influence of ferroelectricity in h-BN on electron-hole recombination in monolayer BP (MBP), and the regulation of twist angle on the ultrafast carrier transfer and recombination in WS₂/MoS₂ and bilayer WS₂. Our works rationalize the experimental phenomenon, deepen the understanding about the regulation of weak interactions between layers. The results are as follows:

(1) The appropriate twist angle can improve the carrier nonradiative lifetime and diffusion length in the bilayer BP, thereby improving the performance of optoelectronic devices. Interlayer coupling is determined by the interlayer distance rather than wavefunctions overlap between the two-layer BP. Compared to AB stacking, the weakend interlayer coupligns, presented in the twisted systems, soften interlayer breathing modes and inhibit the out-of-plane motions of P atoms by increasing distances. Spontaneous charge separation happens in the 11.54° system attributed to mismatched potentials of electrons and holes in high-symmetry stackings-induced Moiré patterns. Overall, the carrier lifetimes are extended to 776 ps in the 38.94° and 1223 ps in the 11.54° system, which is one order of magnitude longer than that in the AB stacking. Correlated with the modulated charge carrier mobilities, the electron and hole diffusion lengths are extended by factors of 4.2 and 3.6 in 11.54° system and 4.7 and 1.5 in 38.94° system, compared with the AB stacking. Our work provides atomic insights on twist angle dependent carrier dynamics, including recombination and transport.

(2) The h-BN ferroelectric substrates significantly affect electron-hole recombination dynamics in MBP by weak interactions between layers. AB stacking shows the ferroelectric polarization due to charge transfer, while AA stakcing does not have this polarization. Compared to the MBP on the paraelectric substrate, the ferroelectric stackings shorten the carrier nonradiative lifetimes by factors of 2 to 3. In the free-standing MBP, high-frequency in-plane vibrations (Ag2 ) dominate carrier recombination. However, the out-of-plane motions of P atoms caused by the h-BN determine the carrier recombination in the MBP@BN. The two interfaces (MBP/h-BN and h-BN/h-BN) are responsible for the pathways of carrier recombination. In the MBP/h-BN interface, strong electrostatic interactions due to charge transfer directly induce low-frequency layered breathing modes (LBMs) and high-frequency out-of-plane vibrations (Ag1 ) of P atoms. In the h-BN/h-BN interface, stronger interlayer coupling results in an order of magnitude stronger intensity of interlayer breathing vibration in the ferroelectric stacking, which makes the LBMs strongly resonate with the low-frequency out-of-plane vibration mode (B1u ) of MBP, opening new channels to accelerate recombination. Therefore, experimenters should pay attention to the h-BN stackings and the small twist angles in multilayers h-BN.

(3) The twist angles have weak effect on hole transfer in WS₂/MoS₂ heterojunctions, but they can significantly prolong interlyaer carrier lifetimes. The larger interlayer distance and red-shift of interlayer breathing mode indicate weakened interlayer coupling, which tends to delay interlayer carrier dynamics. However, the increase of acceptor-state densities induced by symmetry reduction accelerate the hole transfer rates. The combined effect of the two factors result in the weak angle-dependent hole transfer (235-253 fs). Compared to 0° system, the electron-hole recombination timescales of the twisted systems are extended to 4.0-8.9 times, which show strong dependence of angles. The results are dominated by nonadiabatic couplings. This work provides an atomic-scale understanding of experimental phenomena.

(4) The twist angles can accelerate the hole transfer from K valley to Γ valley in the bilayer WS₂ and prolong the intervalley recombination of carriers. Γ and Q valleys are more sensitive to interlayer coupling than K valleys. The twist angles weaken the interlayer couplings and also enhance the light absorption at K valleys. After the initial excitation at K valleys, the holes transfer to the Γ valleys within 400-600 fs, and the weakened interlayer couplings cause the decrease of energy gaps, thereby accelerating the transfer. Electrons transfer to the Q valleys within 50 fs only in high-symmetry stackings. The weakened interlayer coupling and the reduction of symmetry change CBM from Q to K valleys, and in the meantime the twist angles also reduce the overlaps of the electron-hole wavefunctions during recombination. In natural stacking, the electron-hole recombination time is 434 ps, and the twist angles extend the lifetime by factors of 2.6 and 4.6. This work rationalizes the effect of twist angles on the light absorptions and carrier intervalley dynamics in bilayer TMDs.