Organic Ligand Engineering for Tailoring Electron-Phonon Coupling in 2D Hybrid Perovskites.

In the emerging two-dimensional organic-inorganic hybrid perovskites, the electronic structures and carrier behaviors are strongly impacted by intrinsic electron-phonon interactions, which have received inadequate attention. In this study, we report an intriguing phenomenon of negative carrier diffusion induced by electron-phonon coupling in (2T)2PbI4. Theoretical calculations reveal that the electron-phonon coupling drives the band alignment in (2T)2PbI4 to alternate between type I and type II heterostructures. As a consequence, photoexcited holes undergo transitions between the organic ligands and inorganic layers, resulting in abnormal carrier transport behavior compared to other two-dimensional hybrid perovskites. These findings provide valuable insights into the role of electron-phonon coupling in shaping the band alignments and carrier behaviors in two-dimensional hybrid perovskites. They also open up exciting avenues for designing and fabricating functional semiconductor heterostructures with tailored properties.

Tunable Ultrafast Charge Transfer across Homojunction Interface.

Charge transfer at heterojunction interfaces is a fundamental process that plays a crucial role in modern electronic and photonic devices. The essence of such charge transfer lies in the band offset, making charge transfer uncommon in a homojunction. Recently, sliding ferroelectricity has been proposed and confirmed in two-dimensional van der Waals stacked materials such as bilayer boron nitride. During the sliding of these layers, the band alignment shifts, creating conditions for charge separation at the interface. We employ ab initio nonadiabatic molecular dynamics simulations to elucidate the excited state carrier dynamics in bilayer boron pnictides. We propose that, akin to ferroelectric polarization flipping, the precise modulation of the distribution of excited state carriers can also be reached by sliding. Our results demonstrate that sliding induces a reversal of the frontier orbital distribution on the upper and lower layers, facilitating a robust interlayer carrier transfer. Notably, the interlayer carrier transfer is more pronounced in boron phosphide than in boron nitride, attributed to strong electron scattering in momentum space in boron nitride. We propose this novel method to manipulate carrier distribution and dynamics in a homojunction exhibiting sliding ferroelectricity, in general, paving a new way for developing advanced electronic and photonic devices.