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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...

Recently, there has been significant interest in perovskite–polymer composite nanostructures due to their biological nontoxicity and excellent waterproof stability. However, the exploration of their potential in water erosion highly recoverable and flexible high-performance photodetectors remains limited. In this study, we propose a specific photodetector (PD) strategy based on the electrospun perovskite–polymer [polymethyl methacrylate (PMMA)] fiber membranes (PPFMs), where perovskite nanocrystals are uniformly embedded within the long PMMA microfibers. The Schottky contact PDs, formed by in situ growth of PPFMs on lateral electrodes, exhibit ∼97% recovery in performance after drying the devices from the water-induced short-circuit states. The capacitive contact PDs, achieved by dry transfer of PPFMs onto the electrodes, maintain stable photoresponse with less than 2-fold performance fluctuations upon exposure to water, thanks to the suppressed water infiltration effects. Furthermore, due to the strong self-adhesion and flexibility of electrospun PPFMs, which establish tight contact with the lateral electrodes without requiring additional treatments, the PDs retain almost 100% of their original performances even after undergoing 500 bending cycles to a folded state.