Two-dimensional (2D) semiconductor heterostructures are key building blocks for many electronic and optoelectronic devices. Reconfiguring the band-edge states and modulating their interplay with charge carriers at the interface in a continuous manner have long been sought yet are challenging. Here, using organic semiconductor–incorporated 2D halide perovskites as the model system, we realize the manipulation of band-edge states and charge distribution via mechanical—rather than chemical or thermal—regulation. Compression induces band-alignment switching and charge redistribution due to the different pressure responses of organic and inorganic building blocks, giving controllable emission properties of 2D perovskites. We propose and demonstrate a “pressure gating” strategy that enables the control of multiple emission states within a single material. We also reveal that band-alignment transition at the organic-inorganic interface is intrinsically not well resolved at room temperature owing to the thermally activated transfer and shuffling of band-edge carriers. This work provides important fundamental insights into the energetics and carrier dynamics of hybrid semiconductor heterostructures.

Design and exploration of high-performance nonlinear optical (NLO) materials have long been sought with the goal of tunable local structures and NLO properties for advanced laser technology. Thus far, the design strategies for second-order NLO materials have been mainly focused on anionic groups that have made great progress in the development of new NLO compounds. However, few studies have focused on the effects of cationic components and their contributions to NLO properties have long been underappreciated and remain unclear. Here, by introducing pressure to continuously tune the Cu displacement, we demonstrate the significant role of the cationic configuration in NLO properties, and a remarkable enhancement by one order of magnitude in second-harmonic generation (SHG) has been achieved at 3.4 GPa in thiophosphate CuInP 2 S 6 (CIPS). In situ high-pressure structural characterization indicates that Cu cations move from the van der Waals edge to the cages of S 6 octahedra during compression and subsequently form highly distorted [CuS 6 ] octahedra at 3.2 GPa. We quantitively demonstrate the contributions of cationic displacement on the octahedral distortion and interband dipole moments, which dominate optical nonlinearity and determine the enhanced SHG. This work deepens the fundamental understanding of the relationship between cationic displacement and SHG properties, thus providing new paths to NLO material design by optimizing the cationic configurations.

Two-dimensional (2D) van der Waals (vdW) materials, featuring relaxed phase-matching conditions and highly tunable optical nonlinearity, endow them with potential applications in nanoscale nonlinear optical (NLO) devices. Despite significant progress, fundamental questions in 2D NLO materials remain, such as how structural distortion affects second-order NLO properties, which call for advanced regulation and in situ diagnostic tools. Here, by applying pressure to continuously tune the displacement of Nb atoms in 2D vdW NbOI 2 , we effectively modulate the polarization and achieve a 3-fold boost of the secondharmonic generation (SHG) at 2.5 GPa. By introducing a Peierls distortion parameter, λ, we establish a quantitative relationship between λ and SHG intensity. Importantly, we further demonstrate that the SHG enhancement can be achieved under ambient conditions by anionic substitution to tune the distortion in NbO(I 1−x Br x ) 2 (x = 0−1) compounds, where the chemical tailoring simulates the pressure effects on the structural optimization. Consequently, NbO(I 0.60 Br 0.40 ) 2 with λ = 0.17 exhibits a giant SHG of over 2 orders of magnitude higher than that in monolayer WSe 2 , reaching the record-high value among reported 2D vdW NLO materials. This work unambiguously demonstrates the correlation between Peierls distortion and SHG property and, more broadly, opens new paths for the development of advanced NLO materials by manipulating the structure distortions.

The unique intermolecular van der Waals force in emerging two-dimensional inorganic molecular crystals (2DIMCs) endows them with highly tunable structures and properties upon applying external stimuli. Using high pressure to modulate the intermolecular bonding, here we reveal the highly tunable charge transport behavior in 2DIMCs for the first time, from an insulator to a semiconductor. As pressure increases, 2D α-Sb 2 O 3 molecular crystal undergoes three isostructural transitions, and the intermolecular bonding enhances gradually, which results in a considerably decreased band gap by 25 % and a greatly enhanced charge transport. Impressively, the in situ resistivity measurement of the α-Sb 2 O 3 flake shows a sharp drop by 5 orders of magnitude in 0-3.2 GPa. This work sheds new light on the manipulation of charge transport in 2DIMCs and is of great significance for promoting the fundamental understanding and potential applications of 2DIMCs in advanced modern technologies.

Two-dimensional (2D) lead halide perovskites (LHPs) have shown great promises for light-emitting applications and excitonic devices. Fulfilling these promises demands an in-depth understanding on the relationships between the structural dynamics and excitonphonon interactions that govern the optical properties. Here, we unveil the structural dynamics of 2D lead iodide perovskites with different spacer cations. Loose packing of an undersized spacer cation leads to out-ofplane octahedral tilting, whereas compact packing of an oversized spacer cation stretches PbÀ I bond length, resulting in Pb 2 + off-center displacement driven by stereochemical expression of the Pb 2 + 6s 2 lone pair electrons. Density functional theory calculations indicate that the Pb 2 + cation is off-center displaced mainly along the direction where the octahedra are stretched the most by the spacer cation. We find dynamic structural distortions associated with either octahedral tilting or Pb 2 + off-centering lead to a broad Raman central peak background and phonon softening, which increase the non-radiative recombination loss via exciton-phonon interactions and quench the photoluminescence intensity. The correlations between the structural, phonon, and optical properties are further confirmed by the pressure tuning of the 2D LHPs. Our results demonstrate that minimizing the dynamic structural distortions via a judicious selection of the spacer cations is essential to realize high luminescence properties in 2D LHPs.