Perovskite photodetectors and their application in artificial photonic synapses

Multidimensional Deep Ultraviolet (DUV) Synapses Based on Organic/Perovskite Semiconductor Heterojunction Transistors for Antispoofing Facial Recognition Systems

Reliably discerning real human faces from fake ones, known as antispoofing, is crucial for facial recognition systems. While neuromorphic systems offer integrated sensing-memory-processing functions, they still struggle with efficient antispoofing techniques. Here we introduce a neuromorphic facial recognition system incorporating multidimensional deep ultraviolet (DUV) optoelectronic synapses to address these challenges. To overcome the complexity and high cost of producing DUV synapses using traditional wide-bandgap semiconductors, we developed a low-temperature (≤70 °C) solution process for fabricating DUV synapses based on PEA2PbBr4/C8-BTBT heterojunction field-effect transistors. This method enables the large-scale (4-in.), uniform, and transparent production of DUV synapses. These devices respond to both DUV and visible light, showing multidimensional features. Leveraging the unique ability of the multidimensional DUV synapse (MDUVS) to discriminate real human skin from artificial materials, we have achieved robust neuromorphic facial recognition with antispoofing capability, successfully identifying genuine human faces with an accuracy exceeding 92%.

Artificial Neuron Devices

Efforts to design devices emulating complex cognitive abilities and response processes of biological systems have long been a coveted goal. Recent advancements in flexible electronics, mirroring human tissue's mechanical properties, hold significant promise. Artificial neuron devices, hinging on flexible artificial synapses, bioinspired sensors, and actuators, are meticulously engineered to mimic the biological systems. However, this field is in its infancy, requiring substantial groundwork to achieve autonomous systems with intelligent feedback, adaptability, and tangible problem-solving capabilities. This review provides a comprehensive overview of recent advancements in artificial neuron devices. It starts with fundamental principles of artificial synaptic devices and explores artificial sensory systems, integrating artificial synapses and bioinspired sensors to replicate all five human senses. A systematic presentation of artificial nervous systems follows, designed to emulate fundamental human nervous system functions. The review also discusses potential applications and outlines existing challenges, offering insights into future prospects. We aim for this review to illuminate the burgeoning field of artificial neuron devices, inspiring further innovation in this captivating area of research.

Circular polarization-resolved ultraviolet photonic artificial synapse based on chiral perovskite

Circularly polarized light (CPL) adds a unique dimension to optical information processing and communication. Integrating CPL sensitivity with light learning and memory in a photonic artificial synapse (PAS) device holds significant value for advanced neuromorphic vision systems. However, the development of such systems has been impeded by the scarcity of suitable CPL active optoelectronic materials. In this work, we employ a helical chiral perovskite hybrid combined with single-wall carbon nanotubes to achieve circularly polarized ultraviolet neuromorphic vision sensing and imaging. The heterostructure demonstrates long-term charge storage as evidenced by multiple-pulsed transient absorption measurements and highly sensitive circular polarization-dependent photodetection, thereby enabling efficient CPL-resolved synaptic and neuromorphic behaviors. Significantly, our PAS sensor arrays adeptly visualize, discriminate, and memorize distinct circularly polarized images with up to 93% recognition accuracy in spiking neural network simulations. These findings underscore the pivotal role of chiral perovskites in advancing PAS technology and circular polarization-enhanced ultraviolet neuromorphic vision systems.

High-Entropy Perovskite Thin Film in the Gd-Nd-Sm-La-Y-Co System: Deposition, Structure and Optoelectronic Properties

Multicomponent equimolar perovskite oxides (ME-POs) have recently emerged as a highly promising class of materials with unique synergistic effects, making them well-suited for applications in such areas as photovoltaics and micro- and nanoelectronics. High-entropy perovskite oxide thin film in the (Gd_0.2Nd_0.2La_0.2Sm_0.2Y_0.2)CoO₃ (RECO, where RE = Gd_0.2Nd_0.2La_0.2Sm_0.2Y_0.2, C = Co, and O = O₃) system was synthesized via pulsed laser deposition. The crystalline growth in an amorphous fused quartz substrate and single-phase composition of the synthesized film was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Surface conductivity and activation energy were determined using a novel technique implementing atomic force microscopy (AFM) in combination with current mapping. The optoelectronic properties of the deposited RECO thin film were characterized using UV/VIS spectroscopy. The energy gap and nature of optical transitions were calculated using the Inverse Logarithmic Derivative (ILD) and four-point resistance method, suggesting direct allowed transitions with altered dispersions. The narrow energy gap of RECO, along with its relatively high absorption properties in the visible spectrum, positions it as a promising candidate for further exploration in the domains of low-energy infrared optics and electrocatalysis.

Retina-Inspired Organic Photonic Synapses for Selective Detection of SWIR Light

Photonic synapses with the dual function of optical signal detection and information processing can simulate human visual system. However, photonic synapses with selective detection of short-wavelength infrared (SWIR) light have never been reported, which can not only broaden the human vision region but also integrate neuromorphic computation and infrared optical communication. Here, organic photonic synapses based on a new donor-acceptor copolymer P1 are fabricated, which exhibit excellent synaptic characteristics with selective detection for SWIR and extremely low energy consumption (2.85 fJ). The working mechanism is rooted in energy level barriers and unbalanced charge transportation. Moreover, these photonic synapses demonstrate excellent performance in multi-signal logic editing, letter imaging and memory with noise reduction function. This contribution provides ideas of constructing selective-response synapses for artificial visual system and neuromorphic computing.

Artificial optical synaptic devices with ultra-low power consumption

A BP/CdS heterostructure-based artificial photonic synapse with an ultra-low power consumption is proposed, presenting great potential in high-performance neuromorphic vision systems.

Go beyond the limit: Rationally designed mixed-dimensional perovskite/semiconductor heterostructures and their applications

Halide perovskite heterojunctions rationally integrate the chemical and physical properties of multi-dimensional perovskites and judiciously chosen semiconductor materials, offering the promise of going beyond the limit of a single component. This emerging platform of materials innovation offers fresh opportunities to tune material properties, discover interesting phenomena, and enable novel applications. In this review, we first discuss the fundamentals of forming heterojunctions with perovskites and a wide range of semiconductors, and then we give an overview of the research progress of halide perovskite heterojunctions in terms of their optical, electrical, and mechanical properties, focusing on how the heterojunction tunes the energy band structure, electrical transport, and charge recombination behaviors. We further outline the progress of perovskite-based heterojunctions in optoelectronics. Finally, the challenges and future research directions for perovskite/semiconductor heterojunctions are discussed.

Sn-Based Perovskite Halides for Electronic Devices

Because of its less toxicity and electronic structure analogous to that of lead, tin halide perovskite (THP) is currently one of the most favorable candidates as an active layer for optoelectronic and electric devices such as solar cells, photodiodes, and field-effect transistors (FETs). Promising photovoltaics and FETs performances have been recently demonstrated because of their desirable electrical and optical properties. Nevertheless, THP's easy oxidation from Sn²⁺ to Sn⁴⁺ , easy formation of tin vacancy, uncontrollable film morphology and crystallinity, and interface instability severely impede its widespread application. This review paper aims to provide a basic understanding of THP as a semiconductor by highlighting the physical structure, energy band structure, electrical properties, and doping mechanisms. Additionally, the key chemical instability issues of THPs are discussed, which are identified as the potential bottleneck for further device development. Based on the understanding of the THPs properties, the key recent progress of THP-based solar cells and FETs is briefly discussed. To conclude, current challenges and perspective opportunities are highlighted.

Static Disorder in Lead Halide Perovskites

In crystalline and amorphous semiconductors, the temperature-dependent Urbach energy can be determined from the inverse slope of the logarithm of the absorption spectrum and reflects the static and dynamic energetic disorder. Using recent advances in the sensitivity of photocurrent spectroscopy methods, we elucidate the temperature-dependent Urbach energy in lead halide perovskites containing different numbers of cation components. We find Urbach energies at room temperature to be 13.0 ± 1.0, 13.2 ± 1.0, and 13.5 ± 1.0 meV for single, double, and triple cation perovskite. Static, temperature-independent contributions to the Urbach energy are found to be as low as 5.1 ± 0.5, 4.7 ± 0.3, and 3.3 ± 0.9 meV for the same systems. Our results suggest that, at a low temperature, the dominant static disorder in perovskites is derived from zero-point phonon energy rather than structural disorder. This is unusual for solution-processed semiconductors but broadens the potential application of perovskites further to quantum electronics and devices.

High-conductivity thiocyanate ionic liquid interface engineering for efficient and stable perovskite solar cells

A high-conductivity thiocyanate ionic liquid (EMIMSCN) was introduced into perovskite solar cells for the first time. The high conductivity of EMIMSCN ensures an adequate supply of free SCN^- anions and EMIM⁺ cations, so as to multifunctionally passivate the I vacancy and Pb-I antisite defects and realize an optimized interfacial energy level. Consequently, the devices with EMIMSCN treatment achieve a high PCE of 22.55% with substantial enhancement in stability. This simple and efficient strategy provides new insights into the selection of passivation agents for efficient and stable PSCs.

Two-dimensional N-doped Pd/carbon for highly efficient heterogeneous catalysis

A novel two-dimensional ZIF-derived Pd@CN material prepared via one-step calcination exhibits outstanding catalytic activity in heterogeneous hydrogenation. Its well-developed porous structure, low dimensions and low density make active sites more accessible. This facile and effective strategy can guide the synthesis of highly active and durable Pd@CN catalysts with specific morphologies.