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Self‐powered ultraviolet (UV) photodetectors, which have vast applications in the military and for civilian purposes, have become particularly attractive in recent years due to their advantages of high sensitivity, ultrasmall size, and low power consumption. In particular, self‐powered UV photodetectors driven by a built‐in electric field cannot only detect UV signals but also be powered by the incident signals instead of external power. In this concept, the key issues and most recent developments on photovoltaic type UV photodetectors driven by p–n homojunction, heterojunction, and Schottky junction are surveyed. This should generate extensive interest in this field and encourage more researchers to engage in and tackle the scientific challenges.

Multiband detection has always been a challenge and has drawn much attention in the development of photodetectors (PDs). Herein, we present controllable synthesis of SnO 2 wires with different sizes via chemical vapor deposition and formed composites with CsPbBr 3 particles to realize dual spectral response. We constructed PDs based on a single SnO 2 millimeter wire decorated with CsPbBr 3 particles (SnO 2 MMW/CsPbBr 3 ), which showed a stepped spectrum, fast response speed, and self-powered function. Meanwhile, SnO 2 microwires/CsPbBr 3 composites (SnO 2 MWs/CsPbBr 3 ) were also utilized to fabricate PDs. It is noteworthy that detection occurred in two different wavelength bands (320 and 520 nm) with equivalent intensity at a bias of 0 V. The self-powered feature of this device comes from the built-in electric field at the interface of SnO 2 /CsPbBr 3 , and the dual-color response originates from asymmetric junction barriers between conduction bands of SnO 2 and CsPbBr 3 . This work demonstrated promising self-powered PDs that are capable of multiband detection.

Transparent ultraviolet (UV) photodetectors are an essential component of nextgeneration "see-through" electronics. However, the current photodetectors often suffer from relatively slow response speeds and high driving voltages. Here, all-solution-processed UV photodetectors are reported that are facilely prepared from environmentally friendly and abundant materials. The UV photodetectors are composed of a titanium dioxide thin film as the photosensitive layer sandwiched between two different transparent electrodes to form asymmetric Schottky junctions. The photodetector with high optical transparency can operate at zero bias because of spontaneous separation of photogenerated electron-hole pairs by the built-in electric field. The resulting self-powered photodetector displays high sensitivity to broadband UV light (200-400 nm). In particular, an ultrafast response speed up to 44 ns is obtained, representing a significant improvement over those of the conventional transparent photodetectors. Moreover, the photodetector has been successfully applied, for the first time, in a UV communication system as the self-powered signal receiver. This work uniquely combines the features of high optical transparency and self-power ability into UV photodetectors and would enable a broad range of optoelectronic applications.

to the long chemical readsorption process (oxygen molecules readsorption) occurred at the surface. [10,11] In contrast, the photo voltaic PDs including p-n homojunctions, p-n heterojunctions, and Schottky barrier diodes show a fast response speed and a possible selfpowered function due to the photovoltaic effect. Furthermore, as there is an increasing emphasis on low energy consumption, selfpowered PDs which can operate without an external power source are particularly appealing in applications like submarine oil leakage monitoring and forest fires prevention. [12] Thus, researchers are highly motivated to develop highperformance UV PDs with selfpowered characteristics.Thanks to the continuous innovations in semiconductor technology, various widebandgap materials such as diamond, ZnO, TiO 2 , ZnS, etc., have drawn great attention in the field of UV PDs. [13][14][15][16] Among them, SnO 2 , a conventional metal oxide with a direct bandgap, is generally regarded as a ntype material in its undoped form because of the intrinsic defects. It possesses unique chemical, electrical, and optoelectronic properties, thus having vast applications in gas sensors, transparent conductors, and optoelectronic devices. [17][18][19] In particular, with a wide bandgap of ≈3.6 eV (at 300 K), SnO 2 exhibits good UV light absorption characteristics and high vis ible light transparency, making it an ideal candidate for UV PD, especially under acidic or alkalic circumstances in comparison with ZnO. [20] Up to now, various efforts have been devoted to demonstrate the excellent UV photosensitivity of SnO 2 . Previ ously, our group presented thin SnO 2 nanowire UV PDs with a high external quantum efficiency. [21] Chen et al. [22] fabricated monolayer SnO 2 nanonets with a high UV photocurrent. Tian et al. [23] reported ZnOSnO 2 heterojunction nanofibers with a high UV photodark current ratio. However, the response time of the works mentioned above is still dissatisfactory, of which the decay time is >50 s, [22] ≈50 s, [21] and 7.8 s, [23] respectively. Recently, Ling et al. [24] constructed a SnO 2 nanoparticle thin film/ SiO 2 /pSi heterojunction, which exhibited a short response time (<0.1 s) and a high UV photocurrent (≈4.0 × 10 −5 A), however, it suffered from a low photosensitivity (≈40) due to the high dark current. Thus, a combination of a high photosensitivity and a fast response speed has not been realized in SnO 2 PDs, not to men tion additional functions including selfpowered property and flexibility.Herein, a single-crystal SnO 2 microwire photodetector (PD) is demonstrated with a fast response speed owing to a low concentration of point defects. However, the presence of surface defects (e.g., oxygen vacancies) still limits its optoelectronic performance. To further improve the photoresponse of such device, a core-shell p-n junction is constructed by simply coating a new p-type transparent conductive (CuS) 0.35 :(ZnS) 0.65 nanocomposite film (CuZnS) on n-type SnO 2 microwire. As a result, not only the surface of SnO 2 is modified...

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In article number https://doi.org/10.1002/adfm.201809013, Xiaosheng Fang, Hong Wang, and co‐workers develop a self‐powered ultraviolet (UV) photodetector with high optical transparency by using asymmetric Schottky junctions. The photodetector features high responsivity and an ultrafast response speed, making it a promising candidate for the “see‐through” signal receiver in UV communication systems.