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The scientific community is very interested in artificial visual perception systems because of their neuromorphological capabilities, such as image recognition, learning, and memory. This study reports on an organic heterojunction ambipolar transistor with PTCDI‐C8/C8‐BTBT/PTCDI‐C8 sandwich structure. The proposed transistor efficiently transports both holes and electrons, with a current‐on‐switch ratio of ≈106. Furthermore, hole or electron carrier transmission mechanisms are constructed to achieve the controllable adjustment of bi‐directional photoresponse under identical light illumination conditions by adjusting the gate voltage (positive photoresponse for Vg = 30 V and negative photoresponse for Vg = −30 V). The basic synaptic behaviors are simulated under light illumination, and the power consumption of the device is 18.51 fJ per synaptic event, which is comparable to the energy required for biological synapses. Finally, the simulation of human visual adaptation is completed using the bi‐directional photoresponse effects of the organic heterojunction phototransistor array, which provides a novel idea for neuromorphic visual simulation. [ABSTRACT FROM AUTHOR]

Nonlinear optical (NLO) materials are of great importance for applications in lasers, atomic clocks, free-space communication, etc. Herein, inspired by the recent prediction of excellent second harmonic generation (SHG) performance in van der Waals (vdW) materials with 1D building blocks, 14 new NLO materials are found from 244 bulk crystals constructed with 1D polymers using high-throughput first-principles calculations. Nearly half of the new NLO materials exhibit superior NLO performance with SHG susceptibilities approaching the theoretical upper limit. The 2D form of 11 candidates inherits the NLO property covering UV, visible, and infrared regions. Bader charge analysis reveals that the SHG susceptibility is determined by the charge difference of ions on the chains. Finally, it is proposed that superior NLO materials can be found in materials with proper bandgaps and large charge differences on the chains. This work not only screens out candidates with outstanding NLO performance in vdW materials with 1D building blocks but also provides a guideline for the search and design of NLO vdW 1D polymer patterns with excellent NLO properties. [ABSTRACT FROM AUTHOR]

The visual system, one of the most crucial units of the human perception system, combines the functions of multi‐wavelength signal detection and data processing. Herein, the large‐scale artificial synaptic device arrays based on the organic molecule‐nanowire heterojunctions with tunable photoconductivity are proposed and demonstrated. The organic thin films of p‐type 2,7‐dioctyl[1]benzothieno[3,2‐b][1] benzothiophene (C8‐BTBT) or n‐type phenyl‐C61‐butyric acid methyl ester (PC61BM) are used to wrap the InGaAs nanowire parallel arrays to configure two different type‐I heterojunctions, respectively. Due to the difference in carrier injection, persistent negative photoconductivity (NPC) or positive photoconductivity (PPC) are achieved in these heterojunctions. The irradiation with different wavelengths (solar‐blind to visible ranges) can stimulate the heterojunction devices, effectively mimicking the synaptic behaviors with two different photoconductivities. The long‐term and multi‐state light memory are also realized through synergistic photoelectric modulation. Notably, the arrays with different photoconductivities are adopted to build the hardware kernel for the visual system. Due to the tunable photoconductivity and response to multiple wavelengths, the recognition rate of neural networks can reach 100% with lower complexity and power consumption. Evidently, these photosynaptic devices are illustrated with retina‐like behaviors and capabilities for large‐area integration, which reveals their promising potential for artificial visual systems. [ABSTRACT FROM AUTHOR]

Recently developed CsPbX3 (X = Cl, Br, and I) perovskite quantum dots (QDs) hold great potential for various applications owing to their superior optical properties, such as tunable emissions, high quantum efficiency, and narrow linewidths. However, poor stability under ambient conditions and spontaneous ion exchange among QDs hinder their application, for example, as phosphors in white-light-emitting diodes (WLEDs). Here, a facile two-step synthesis procedure is reported for luminescent and color-tunable CsPbX3-zeolite-Y composite phosphors, where perovskite QDs are encapsulated in the porous zeolite matrix. First zeolite-Y is infused with Cs+ ions by ion exchange from an aqueous solution and then forms CsPbX3 QDs by diffusion and reaction with an organic solution of PbX2. The zeolite encapsulation reduces degradation and improves the stability of the QDs under strong illumination. A WLED is fabricated using the resulting microscale composites, with Commission Internationale de I'Eclairage (CIE) color coordinates (0.38, 0.37) and achieving 114% of National Television Standards Committee (NTSC) and 85% of the ITU-R Recommendation BT.2020 (Rec.2020) coverage. [ABSTRACT FROM AUTHOR]

High-performance organic heterojunction phototransistors are fabricated using highly ordered copper phthalocyanine (CuPc) and para-sexiphenyl ( p-6P) thin films. The p-6P thin film plays an important role on the performance of CuPc/ p-6P heterojunction phototransistors. It acts as a molecular template layer to induce the growth of highly ordered CuPc thin film, which dramatically improves the charge transport and decreases the grain boundaries. On the other hand, the p-6P thin film can form an effective heterojunction with CuPc thin film, which is greatly helpful to enhance the light absorption and photogenerated carriers. Under 365 nm ultraviolet light irradiation, the ratio of photocurrent and dark current and photoresponsivity of CuPc/ p-6P heterojunction phototransistors reaches to about 2.2 × 104 and 4.3 × 102 A W−1, respectively, which are much larger than that of CuPc phototransistors of about 2.7 × 102 and 7.3 A W−1, respectively. A detailed study carried out with current sensing atomic force microscopy proves that the photocurrent is predominately produced inside the highly ordered CuPc/ p-6P heterojunction grains, while the photocurrent produced at the boundaries between grains can be neglected. The research provides a good method for fabricating high-performance organic phototransistors using a combination of molecular template growth and organic heterojunction. [ABSTRACT FROM AUTHOR]

A low-voltage operable, highly sensitive, and selectively responsive polymer for the detection of nitroaromatic explosives is investigated. Resistive devices are fabricated by simple spin-coating on flexible and transparent substrates in addition to silicon substrates and are stable under ambient temperature and oxygen levels before exposure to the nitroaromatics. After exposure to 2,4,6-trinitrotoluene (TNT), the devices show increased conductance, even with picogram (pg) quantities of TNT, accompanied by a confirming color change from colorless to deep red. The relative conductance increase per unit exposure is the highest yet reported for TNT. Aromatic anion salts, on the other hand, do not induce any electronic responses. 1H NMR and microscopic analyses show chemical interactions and morphological changes correlated with the electronic responses, some of which are specific to TNT in relation to other nitroaromatics. The binding constant for the imidazole rings and TNT is on the order of tens of M−1. The materials are promising for rapid indication of exposure to nitroaromatic compounds. [ABSTRACT FROM AUTHOR]

High‐performance organic phototransistors are fabricated by Jia Sun, Junliang Yang, and co‐workers in article number 1604933, by using a combination of organic heterojunction and molecular template growth. The phototransistors based on highly ordered copper phthalocyanine thin film grown on para‐sexiphenyl template layer produce a high photoresponsivity up to 4.3 × 102 AW−1, as well as a high ratio of photocurrent and dark current up to 2.2 × 104. [ABSTRACT FROM AUTHOR]