the field of photovoltaic and wide-ranged optoelectronic devices. Among various perovskite materials, the lattices of 3D perovskite are easily decomposed into reactants under the conditions of ultraviolet irradiation, high temperature, or/and hydration environment, resulting in the rapid decline of device performance. [12,13] In comparison, 2D perovskites, with robust environmental stability, optoelectronic tunability, and unique quantum well structures, are becoming the rising choice of candidates for next-generation energy and optoelectronic applications. [14][15][16][17] The 2D perovskites composed by the organic cation layer and the inorganic unit layer show unique layer-by-layer structure, which are thus endowed with distinctive properties and notable merits. The large organic ligands in the 2D perovskite lattices provide the space barriers for the surface water penetration, which can effectively inhibit the invasion of water. [18][19][20] In addition, the large-sized organic ligands can confine the charge carrier transport within the 2D local scope, [21] thereby affecting the photoelectric conversion efficiency. Importantly, the organic spacers also act as the dielectric regulator, which determines the electrostatic force on the electron-hole pairs, promoting the exciton radiative recombination efficiency. [22] Furthermore, the unique layered structure of 2D perovskites makes the ion movements in the films are highly dependent on their growth orientations. [23,24] Despite 2D layered organic-inorganic perovskites have attracted substantial attention due to their high stability and promising optoelectronic properties. However, in-depth insights on the anisotropic carrier transport properties of these 2D perovskites are remaining challenging, while they are significant for further designing the high-performance device applications. Here, the carrier transport properties within 2D perovskite single crystals are investigated and a layered-carrier-transport model is developed through the non-invasive and non-destructive surface-enhanced Raman scattering techniques. The carrier transport features of 2D perovskites show clearly the thickness-, applied voltage-and anisotropy-dependent behaviors, which are demonstrated to origin from the quantum confinement effect. The findings elucidate the carrier transport mechanisms within 2D perovskites from their molecular level through Raman spectroscopy, thus providing a promising way for exploring the photo-physical properties in wide-ranged halide perovskites and designing highly efficient perovskite optoelectronic devices.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202103756.
