sessing the same electronic structure as Pb 2+ . Very recently, a few Bi-based substitutions have been successfully synthesized and applied to optoelectronics, [19][20][21][22][23][24][25] and the all-inorganic component design offers well material stability under higher temperatures and moisture conditions. [26] The latest research such as resistive switches, [27] achromatic quarter-waver plates [28] and high-performance X-ray detectors [19,20,22] have been reported.As well known, the Cs 3 Bi 2 I 9 is an isolated zero-dimensional molecular salt structure, wherein a pair of [BiI 6 ] 3− octahedra that share a common face form a [Bi 2 I 9 ] 3− dioctahedral cluster and their voids are filled with Cs + cations. While in this hexagonal structure, distinct dimer [Bi 2 I 9 ] 3− anions are placed in a layered arrangement along the cleavage plane (001). Therefore, it can be considered as a layered perovskite-like crystal structure according to the previous reports, [19,20] and the bi-layered [Bi 2 I 9 ] 3− are connected by the van der Waals forces. Up to now, the important influence of such anisotropic crystal structures on their photoelectric performance has not been widely recognized and investigated so far. [19] It should be noted that, in regular Ruddlesden-Popper phase perovskite, their adjacent perovskite octahedral layers are mutually connected by Coulombic-held organic chains (such as an aliphatic or aromatic alkylammonium), and corresponding anisotropy abruptly weakens with lessened intercalated organic layers. [10][11][12][13] As the He group demonstrated, the anisotropy of dark and photo-current dropped almost one-order magnitude when the sheet number of perovskite octahedral layers only increases from 1 to 3, [29] as well as their electric conductance and carriers mobility studied by the Priya group. [30] While in the layered perovskite-like phase, bi-layered close-packed octahedral frameworks are mutually connected by van der Waals forces instead of chemical bonds, [19,21] moreover, their crystal structure is a stationary type for the given elements. Thus, such a non-contact suspended spacer possesses much more significant anisotropy over the Ruddlesden-Popper phases.Very recently, only the Yang group observes the anisotropic X-ray photo-response based on a layered perovskite-like (NH 4 ) 3 Bi 2 I 9 single crystal, and its anisotropy is only measured at one-order magnitude. [19] Essentially speaking, its anisotropic photo-response originates from the photon-induced carriers' transmission differences along in-plane and cross-plane directions. [19,29,30] The investigation of anisotropy is conducive to the design of performance-improved devices, by contrasting the Lead-free all-inorganic perovskite single crystals are being pursued intensively because of their reduced biological toxicity and enhanced material stability, greatly relieving two major bottlenecks of practical device applications. However, the investigation of their predicted photoelectric anisotropy is still absent, especially under visible and nea...

Ruddlesden–Popper (RP) metal‐halide perovskites are attracting increasing attention due to their improved stability. The intercalated hydrophobic organic layer accounts for this improvement, however, it is detrimental to the out‐of‐plane optoelectronics. Here, the n‐involved performance optimization in RP (PEA)2(Cs)n−1PbnI3n+1 nanomaterials is reported. The exciton is confirmed as the majority of photo‐induced species, but it is more free carrier‐like in n‐larger samples due to the weakened quantum confinement effects. After 90‐day treatment in 65% humidity, it is found that only RP nanomaterials originally designed as n = 4 ((PEA)2(Cs)3Pb4I13) possess the best residual optoelectronic performances (photo‐responsivity and specific detectivity) at minimal drop proportions (≈20%). Particularly, the Coulombic screening effect triggers saturated optoelectronic performances at low driving voltage, due to the almost total depletion of responsive photo‐current even under enhanced external excitations. This work balances the optoelectronic performances and moisture resistance of PEA‐based RP nanomaterials, and is mainly aiming to alleviate the deterioration of optoelectronic performance in 90‐day moisture‐treated (65%) conditions.

High‐quality perovskite single crystals (SCs) are emerging as promising optoelectronic materials and extensive photodetectors have been reported based on their SC frameworks, however, they are all disabled without applied external bias, and this is an evident obstacle for practical applications. Here, self‐powered photodetection (SPD) of perovskite SCs based on capacitance effects is reported when the capacitor releases its previously stored electric power by discharging operations. The capacitive results are highly in accord with numerical simulations of dielectrics, rather than the common ion migration. The lateral structures show good selectivity for local illuminations and consequently the induced self‐driven photovoltaic effects, but such influences on the SPD can be ignored when the capacitors are charged with sufficient electric power. This work first shows an attempt at achieving SPD in the form of lateral capacitors and may provide another new strategy for self‐powered perovskite devices.

Time-domain study of coherent acoustic phonons in nanomaterials provides dynamic and unparalleled insight into their mechanical and structural features. Ruddlesden-Popper (RP) perovskite shows excellent acoustic behaviors due to the large impedance mismatch between its hard perovskite frameworks and soft organic chains. However, the optical probe-independent acoustic nano-mechanical resonance and its real application in this important class of semiconductors have not yet been achieved. Herein, the acoustic breathing mode of resonant coherent phonons (RCP) in nanoscale RP perovskite films is reported. In contrast to the previously reported Brillouin mode in thick materials, such resonant breathing mode is no longer interfered by the optical probe, but as a self-sustained acoustic oscillation source whose features are directly related to material geometry along the direction of phonon propagation. As a nano-mechanical resonance, RCP oscillation is applied as a novel and non-destructive approach for quantitatively evaluating the decomposition of moisture-exposed RP perovskite. These results reveal the decisive effect of structural geometry on acoustic performances in perovskite nanomaterials. The nanoscale counterparts show evident advantages in acoustic mode modulation and structure detection.