The development of optoelectronic synapses can provide an important breakthrough toward creating a sophisticated and adaptable artificial visual system analogous to that of humans. However, it remains a great challenge to implement the various functions of the biological visual neuromorphic system at the single device level. Intriguingly, 2D van der Waals (vdW) heterostructure may offer a platform to address the issue. Here, a novel multifunctional synaptic device based on ferroelectric α-In 2 Se 3 /GaSe vdW heterojunction is proposed to emulate the entire biological visual system. Essential synaptic behaviors are observed in response to light and electrical stimuli; additionally, the retina-like selectivity for light wavelengths and the achievement of Pavlov's dog experiment demonstrate the device's capacity for processing complex electrical and optical inputs. Beyond the optoelectronic synaptic behaviors, the device incorporates memory and logic functions analogous to those in the brain's visual cortex. The results of artificial neural network simulations show that the vdW heterojunction-based device is completely capable of performing logic operations and recognizing images with a high degree of accuracy. The study indicates that versatile devices with a rationally designed construction have great potential for efficiently processing complex visual information and may simplify the design of artificial visual systems.

Memory transistors based on two-dimensional (2D) ferroelectric semiconductors are intriguing for next-generation in-memory computing, which may surpass the prevailing Von Neumann architecture. To date several 2D FE materials have been unveiled, among which 2D In2Se3 is the most promising, as all the paraelectric (PE) (β), ferroelectric (FE) (α) and antiferroelectric (AFE) (β′) phases can be attained in the 2D quintuple layers. However, the large-scale synthesis of 2D In2Se3 film with desired phase is still in absence, and the stability conditions for each phase remain obscure.Here, we show the successful growth of centimetre (cm)-scale 2D β-In2Se3 film by chemical vapor deposition (CVD). We also obtain distinct cm-scale 2D β′-In2Se3 film by InSe precursor addition during CVD. More importantly, we demonstrate that asgrown 2D β′-In2Se3 film on mica substrates can be delaminated or transferred onto flexible or uneven substrates which simultaneously yields cm-scale 2D α-In2Se3 film through complete phase transition. Thus, a full spectrum of PE, FE and AFE 2D films are readily obtained by means of the correlated polymorphism in 2D In2Se3, enabling 2D memory transistors with high electron mobility (29 and 53 cm 2 V -1 s -1 in reverse sweep for β′-and α-In2Se3, respectively), and polarizable β′-α In2Se3 hetero-phase junctions with improved non-volatile memory performance. Our work pioneers in tailoring the 2D FE structures by precise phase engineering, and unlocks their great potentials for logic-in-memory electronics.

2D hybrid perovskites are very attractive for optoelectronic applications because of their numerous exceptional properties. The emerging 2D perovskite ferroelectrics, in which are the coupling of spontaneous polarization and piezoelectric effects, as well as photoexcitation and semiconductor behaviors, have great appeal in the field of piezo‐phototronics that enable to effectively improve the performance of optoelectronic devices via modulating the electro‐optical processes. However, current studies on 2D perovskite ferroelectrics focus on bulk ceramics that cannot endure irregular mechanical deformation and limit their application in flexible optoelectronics and piezo‐phototronics. Herein, we synthesize ferroelectric EA4Pb3Br10 single‐crystalline thin‐films (SCFs) for integration into flexible photodetectors. The in‐plane multiaxial ferroelectricity is evident within the EA4Pb3Br10 SCFs through systematic characterizations. Flexible photodetectors based on EA4Pb3Br10 SCFs are achieved with an impressive photodetection performance. More importantly, optoelectronic EA4Pb3Br10 SCFs incorporated with in‐plane ferroelectric polarization and effective piezoelectric coefficient show great promise for the observation of piezo‐phototronic effect, which is capable of greatly enhancing the photodetector performance. Under external strains, the responsivity of the flexible photodetectors can be modulated by piezo‐phototronic effect with a remarkable enhancement up to 284%. Our findings shed light on the piezo‐phototronic devices and offer a promising avenue to broaden functionalities of hybrid perovskite ferroelectrics.

Hybrid perovskite single-crystalline thin films are promising for making high-performance perovskite optoelectronic devices due to their superior physical properties. However, it is still challenging to incorporate them into multilayer devices because of their on-substrate growth. Here, a wet transfer method is used in transferring perovskite single-crystalline films perfectly onto various target substrates. More importantly, large millimeter-scaled single-crystalline films can be obtained via a diffusion-facilitated space-confined growth method as thin as a few hundred nanometers, which are capable of sustaining excellent crystalline quality and morphology after the transferring process. The availability of these crystalline films offers us a convenient route to further investigate their intrinsic properties of hybrid perovskites. We also demonstrate that the wet transfer method can be used for scalable fabrication of perovskite single-crystalline film-based photodetectors exhibiting a remarkable photoresponsivity. It is expected that this transferring strategy would promise broad applications of perovskite single-crystalline films for more complex perovskite devices.

2D materials have drawn tremendous attention and extensive investigations for emerging applications in energy, electronics, and optoelectronics have been conducted. [1,2] In particular, 2D transition metal carbides and nitrides (MXenes) are considered as emerging energy materials. Enjoying their endowments in the high hydrophilic surface, porosity, and conductivity, MXenes possess widespread applications in battery, electrocatalyst, supercapacitor, and biochemistry. [3][4][5][6][7] MXenes are usually described by a chemical formula of M n+1 X n T x (n = 1, 2, and 3), where M represents an early transition metal (such as Ti, Nb, Cr, and V.), X stands for the C and/or N element, and T x is the