No abstract

2D halide perovskites feature solution processability and tunable optoelectronic properties for optoelectronic applications. However, the controllable fabrication of halide perovskite heterojunction still remains a challenge. Herein, through controlling surface tension and nucleation driving force, a fast and facile aqueous floating growth is demonstrated to obtain a series of large-area single-crystalline 2D perovskite microplates at room temperature. The optoelectronic performance of 2D perovskites can be tuned by composition engineering, and the best performance is realized for quantum well index n = 4, including a suppressed dark current with boosted photocurrent and an on/off ratio up to 3.5 orders of magnitude. Benefiting from a convenient transfer method onto arbitrary substrates, vertically oriented 2D perovskite hetero-/homo-junctions are gently stacked, which exhibit improved self-powered characteristics. This straightforward growth strategy is an universal solution-processed method for growing 2D perovskites, laying the foundation of the 2D perovskite hetero-/homo-junction for future miniaturization and functionalization of next-generation optoelectronics.

Fibrous photodetectors (FPDs) have attracted great interest in wearable and consumer electronics, which is a lightweight and flexible tools to achieve efficient light information transmission. However, there is a necessary compromise between high optoelectronic performance and high‐level integration. Herein, a woven optoelectronic keyboard consisting of 40 PD button units is extended and integrated from four individual FPDs, with the integration level expanding by 1000%. Each FPD is based on uniform type‐II TiO2/Cs3Cu2I5 heterojunction, which exhibits greatly reduced dark current by eight orders of magnitudes, large rectification ratio up to 33306@± 5V, high on–off ratio of 2.8 × 104@−1 V and self‐powered responsivity of 26.9 mA W−1. The vacuum‐deposited Cs3Cu2I5 nanoparticles finely passivate the massive defects and serve as a p‐type hole transport layer to improve hole transfer efficiency, which greatly promotes the radial transport and collection of photogenerated electrons. Moreover, the photocurrent remains highly stable after bending and twisting states. Intriguingly, the woven optoelectronic keyboards successfully realize logic AND/OR, further identifying the UV light signal as a keying text signal (“A–Z” letters, “0–9” numbers, and four punctuations). This work not only provides a scalable strategy to reduce device redundancy but also shows the great potential of fibrous photodetectors for wearable optical communication.

The imitation of human visual memory, which demands the multifunctional integration of light sensors similar to the eyes, and image memory, similar to the brain. Although humans have already implemented electronic devices with visual memory functions, these devices require a combination of various components and logical circuits. With the advancement of integrated circuits, the miniaturization and high integration of devices are an inevitable trend. Therefore, the combining of visual perception and high‐performance information storage capabilities into a single device to achieve visual memory remains a challenging. In this study, inspired by the function of human visual memory, we designed a dual‐functional perovskite‐based photodetector (PD) and memristor to realize visual perception and memory capacities. As a PD, it realized an ultra‐high self‐powered responsivity of 276 mAW−1, a high detectivity of 4.7×1011 Jones (530 nm; light intensities, 2.34 mWcm−2), and a high rectification ratio of ∼100 (± 2 V). As a memristor, an ultra‐high on/off ratio (∼105), an ultra‐low power consumption of 3×10−11 W, a low setting voltage (0.15 V), and a long retention time (>7000 s) were realized. Moreover, the dual‐functional device has the capacity to perceive and remember light paths and store data with good cyclic stability. Our device exhibits perceptual and cyclic erasable memory functions, which provide new opportunities for mimicking human visual memory in future multifunctional applications.This article is protected by copyright. All rights reserved

Photodetectors (PDs) composed of lead-free metal halide perovskites have been a shining topic in optoelectronics. However, it is debatable whether perovskites are an n-type or p-type semiconductor with a direct or indirect band gap. Furthermore, to date, little research has been conducted on lead-free metal halide perovskites with color-sensing abilities. Herein, for the first time, single-crystal MA 3 Bi 2 I 3x Br 9−3x (x = 0, 1, 2, and 3) perovskites were systematically studied, and the results showed that MA 3 Bi 2 I 9 is a p-type direct-band-gap semiconductor, whereas MA 3 Bi 2 Br 9 is an n-type indirect-band-gap semiconductor. Furthermore, the band gap of MA 3 Bi 2 I 3x Br 9−3x (x = 0, 1, 2, and 3) perovskites can be systematically tuned from 2.06 to 2.55 eV, affording it with color-sensing abilities from 450 to 580 nm, respectively. The representative Au-MA 3 Bi 2 I 9 -ITO (ITO = indium tin oxide) PD exhibits a superior self-powered photodetecting performance with a high responsivity (15.8 mA W −1 ; 580 nm, 1.0 mW cm −2 ), detectivity (8.1 × 10 11 Jones), an on/off ratio (4231), LDR (72.5 dB) and a fast response speed (rise time of 2 μs and decay time of 29 μs). This study not only facilitates the theoretical understanding of the band gap of perovskite materials but also sheds light on the application of lead-free perovskites in object interaction and color perception. KEYWORDS: photoimaging, color-sensing, band-gap-tunable, lead-free perovskite, MA 3 Bi 2 I 3x Br 9−3x (x = 0, 1, 2, and 3)