moderate UV light is beneficial for human health, however, excessive UV radiation can cause various human diseases as well as strong destruction to the output of crops and the lifespan of buildings. [1b,3a,4] Therefore, an efficient detection of UV radiation is of significant importance in widespread applications, for example, chemical, environmental, and biological analysis or warning, astronomical investigation, and optical communication. [1c,5] For forewarning UV radiation with high-efficiency, a wide variety of UV PDs such as photomultiplier and silicon diode, have been extensively investigated and applied in the past decades. Nevertheless, there are intrinsic imperfections for the present commercial PDs, such as fragile, large volume, and excessive cost, which are obstacles when meeting the growing requirement of miniaturized and reliable UV detection devices for portable or shipped applications. In recent years, the development of semiconductor-based PDs that work according to the photoelectric effect has received great research interest. [1b,3a,6] In this scenario, a delicate selection of suitable materials with efficient morphological, microstructural, and photoelectrical characteristics plays a key role in the construction of PDs with high-performance. Generally, the PDs work following several different physical mechanisms, that is, surface plasma-wave-assisted effect, photoconductive effect, photothermoelectric effect, and photovoltaic effect, which have been systematically demonstrated in the previous report. [7] More recently, a new generation of wide-bandgap semiconductors including the classification of nitrides (GaN, AlN, BN, etc.), carbides (SiC, diamond, etc.), sulfides (ZnS, etc.), oxides (ZnO, Ga 2 O 3 , TiO 2 , etc.), halide perovskites (e.g., CH 3 NH 3 PbCl 3 ), [8] and their combinations, is emerged as the most attractive material candidates for constructing high-performance UV PDs, owing to their unique advantages, for instance low permittivity, high breakdown electric-fields, good thermal conductivity, high electron saturation rates, excellent radiation resistance, and their appropriate spectral range for UV response. [1d] In addition, the photoelectric conversion processes of the semiconductorbased PDs can be generally described by the behaviors of charge carriers, such as their generation, separation, transportation, and extraction. [9] Therefore, any factor that influences the photon-generated carrier behaviors should be the key parameter for further tuning their photodetecting performances. It As a wide-bandgap semiconductor material, titanium dioxide (TiO 2 ), which possesses three crystal polymorphs (i.e., rutile, anatase, and brookite), has gained tremendous attention as a cutting-edge material for application in the environment and energy fields. Based on the strong attractiveness from its advantages such as high stability, excellent photoelectric properties, and lowcost fabrication, the construction of high-performance photodetectors (PDs) based on TiO 2 nanostructures is ...

higher carrier mobility and longer carrier lifetime, thanks to their fewer grain boundaries, enhanced crystallinity and reduced trap density. With such performance improvements, the lead-free halide perovskite single crystal is considered to be a promising photosensitive material in optoelectronic devices. [6] In order to effectively promote power conversion efficiency, the thickness of leadfree halide perovskite single crystal should be controlled at a suitable level, which is suggested to be greater than light-absorption length and less than carrier-diffusion length. [7] In the current semiconductor and photoelectronic industries, thin silicon wafers are fabricated mainly through top-down process, which requires high yields accompanied with large material loss, waste and subsequent complicated slicing process. Against this background, a facile and effective space-confined fabrication is adopted to produce large singlecrystalline thin film, through a bottom-up process. [8] Compared with vapor epitaxial growth and cavitation triggered asymmetrical crystallization, [9] space-confined methods possess moderate growth conditions to grow SCTF without rigorous restrictions. However, this method is limited to the growth of organic-inorganic lead halide perovskite SCTF, few studies focus on lead-free halide perovskite SCTF, such as Sn-based, Bi-based and Sb-based, etc. This is limited by the lack of understanding of the precursor solution chemistry in space-confined method. [10] Although previous work pointed out that the preheated-substrate and local heating are important in the space-confined growth, [11] there is a lack of investigation on the influence of the precursor solution temperature on the crystallization process. In general, the growth drive force of the space-confined growth is considered to be inverse-temperature crystallization or solvent evaporation, in which the supersaturation plays a key role in controlling size and quality. [12] An indepth insight of the relationship between the nucleation and crystallization process in the precursor solution is of significant importance. Therefore, it is necessary to clarify the effects of supersaturation in the space-confined growth.Furthermore, the space-confined method demonstrates the advantage of substrate-independent characteristics, which facilitate convenient integration of lead-free halide perovskite SCTF Monolithical integration of the promising optoelectronic material with mature and inexpensive silicon circuitry contributes to simplifying device geometry, enhancing performance, and expanding new functionalities. Herein, a leadfree halide perovskite Cs 3 Bi 2 I 9 single-crystalline thin film (SCTF), with thickness ranging from 900 nm to 4.1 µm and aspect ratio up to 1666, is directly integrated on various substrates including Si wafer, through a facile and lowtemperature solution-processing method. The growth kinetics of the lead-free halide perovskite SCTF are elucidated by in situ observation, and the solution supersaturation is controlled to reduce the ...

Photodetectors, which convert the light signal into other forms of signal, have been under the spotlight of research for many years because they are widely applied in monitoring, communication, and imaging. Most of the currently available photodetectors can output electrical signals to indicate the transient light intensity, while some display color change to reveal the absorbed light dosage. However, there is no device that can tell the transient light intensity and accumulated light dosage at the same time. Here, a paper‐based wearable photodetector that can simultaneously measure transient light intensity and accumulated light dosage is reported. The phosphomolybdic acid/citric acid system, whose color change can be observed by the naked eye, is designed as the photochromic material to combine with photodetective materials (using 2D Sr2Nb3O10 and ZnO nanoparticle as examples) on paper. Such paper‐based photodetector fully utilizes natural hygroscopicity and softness of paper, showing decent flexibility. Its optoelectronic signal remains stable even after 1000 cycles of bending. To the best of one's knowledge, this is the first photodetector that can tell light intensity and dosage simultaneously. This work introduces a new type of wearable photodetector by structure design and material selection, shedding light on more novel works for convenient and practical photodetection.

In article number 2103010, Xiaosheng Fang and report a supersaturationcontrolled growth method for growing lead-free halide perovskite single-crystalline thin film on target substrates to realize facile monolithical integration. The sufficient thinness and incommensurate lattice matching contribute to high-sensitivity silicon-compatible photodetectors, better than advanced lead-free halide perovskite optoelectronic devices.

Ultraviolet(UV) photodetectors(PDs) can monitor UV radiation, enabling it to be effective for many applications, such as communication, imaging and sensing. The rapid progress on portable and wearable optoelectronic devices places a great demand on self-powered PDs. However, high-performance self-powered PDs are still limited. Herein we display a transparent (a 74% average transparency) and self-powered PD based on a p-CuI/n-TiO2 heterojunction, which exhibits a high on-off ratio (~104 at 310 nm) and a fast response speed (rise time/decay time = 0.11 ms/0.72 ms) without bias. Moreover, the device shows an excellent UV-selective sensitivity as a solar-blind UV PD with a high UV/visible rejection ratio (R300 nm/R400 nm = 5.3×102), which can be ascribed to the wide bandgaps of CuI and TiO2. This work provides a feasible route for the construction of transparent, self-powered PDs based on p-n heterojunctions.