Metasurface-controlled high-speed tunable external cavity lasers.

After reshaping the field of photovoltaics, halide perovskites are now impacting other areas of optoelectronic research, catalysing advances in light emission [, ], photodetection [], X‐ray detection [], and are emerging as highly promising platforms for neuromorphic electronics [, ]. In fact, their intrinsic mixed ionic‐electronic transport, long considered a challenge for device performance and stability, is increasingly recognized as a powerful functional asset for emulating synaptic dynamics [, ]. In particular, the exceptional photoresponse accompanied by pronounced dynamical phenomena, such as current‐voltage hysteresis, slow transients and persistent photocurrent [], related to the coupling between electronic and ionic transport, trap dynamics and interfacial electrostatics, enable conductance modulation, switching behaviors and plasticity, that can be tuned electrically and optically, making these materials very interesting for novel neuromorphic devices such as memristors. Moreover, stochasticity and noise‐related effects are increasingly recognized as relevant ingredients in memristive dynamics and can strongly influence hysteresis and state stability, motivating dedicated investigations in a variety of material platforms [, , ]. Most studies have so far focused on thin polycrystalline films, where grain boundaries and defects in the surface and in the bulk dominate charge transport, creating poorly controlled channels for ion migration and obscuring the intrinsic properties of the material. Single‐crystals (SC), on the contrary, are particularly powerful platforms to investigate intrinsic‐transport and defect‐mediated processes because they minimize microstructural disorder and grain‐boundary effects that complicate the study of these materials. At the same time, SC based devices still display substantial history‑dependent electrical behavior because ionic redistribution and interfacial charging can occur even in the absence of grain boundaries []. Despite the progress in recent years, the synthesis of solution‐based high quality single‐crystal perovskites, especially in the thin film form (thickness below a few micrometers), which is the only suitable form for device integration and scalability, is still not a very mature and controlled process [, ]. In this work, we grow methylammonium lead iodide (CHNHPbI‐MAPbI) single‐crystals using a space‐confined inverse temperature approach and integrate them into planar, optically accessible, two terminal devices using an easy and low‐cost fabrication approach based on the direct deposition of conductive silver electrodes. We show that these devices under illumination show strong photoconductivity, pronounced polarity‐dependent hysteresis, and a threshold‐like transition between two conductance states that can be tuned by the incident optical power. To rationalize this behavior, we analyse the transport within a back‐to‐back Schottky barrier framework, which captures the contact‐limited character of the devices and the dominant role of the Ag/MAPbI. In addition to the light‐induced effects, temperature‐dependent measurements in the 300–400 K range confirm thermally activated transport and contact‐modulated transport. These results highlight the importance of the study of light stimuli in tuning memristive‐like behaviors in halide perovskites and show that Ag electrodes can act as active electrochemical interfaces enabling light‐assisted barrier modulation and threshold‐like switching. This view is consistent with recent reports emphasizing the role of Ag‐based electrode engineering in halide‐perovskite devices [, ]. MAPbI is a three‐dimensional (3D) organic‐inorganic hybrid perovskite material composed of a network of corner‐sharing halide octahedra with a metal cation at the centre and organic cations occupying the spaces between the octahedra [, ]. Their characteristic crystal structure is described by ABX, where A is a small‐sized monovalent organic or inorganic cation, B is a divalent metal cation (Pb or Sn), X is a halide anion. SCs‐MAPbI were grown by utilizing the method as shown in Figure . A precursor solution of MAPbI 1.3 M in γ‐butyrolactone (GBL) was prepared by dissolving lead iodide (PbI) (from Sigma Aldrich) and methylammonium iodide (MAI) (from Greatcellsolar) in a 1:1 molar ratio and maintaining the mixture in a hot plate at 65°C under continuous stirring for 2 h.