Ionic liquid enables high-performance, self-powered CsPbBr3 perovskite nanonet photodetector.

We fabricated high-quality CsPbBr3 perovskite nanonet films with the assistance of polystyrene spheres, and constructed self-powered photodetectors (PDs) with an ITO/SnO2/CsPbBr3/carbon structure. By passivating the nanonet with different concentrations of 1-butyl-3-methylimidazolium bromide (BMIMBr) ionic liquid, we found that as the concentration of BMIMBr increases, the dark current of the device first decreases and then gradually increases, while the photocurrent remains essentially unchanged. Finally, the PD with 1 mg mL-1 BMIMBr ionic liquid exhibited the best performance with a switch ratio of about 1.35 × 106, a linear dynamic range extending to 140 dB, and responsivity and detectivity values of 0.19 A W-1 and 4.31 × 1012 Jones, respectively. These results provide an important reference for fabricating perovskite PDs.

A-Site Substitute for Fabricating All-Inorganic Perovskite CsPbCl3 with Application in Self-Powered Ultraviolet Photodetectors.

Because of its stable chemical properties and wide band gap, CsPbCl3 perovskite has shown great application prospects in ultraviolet photodetectors (UPDs). However, the poor solubility of CsCl in organic solvents impedes the fabrication of high-quality CsPbCl3 films. Herein, we introduced an A-site substitute route for fabricating a high-quality CsPbCl3 microcrystalline (MC) film by spin-coating cesium acetate on a MAPbCl3 MC film followed by a high-temperature annealing process. To enhance the device performance of the FTO/SnO2/CsPbCl3 MCs/carbon structure UPD, a pressure-assisted annealing strategy was carried out, which reduced the void density and surface roughness of the microcrystal film. Finally, our optimized PDs showed high device performances with an on/off ratio of 6 × 104, a responsivity of 0.13 A W-1, a detectivity of as high as 1.07 × 1012 Jones, and a rise/fall time of 10/24 µs. Moreover, our unpacked PDs showed good storage and light stability. Our results lay a foundation for the application of all inorganic perovskite in the ultraviolet region.

Self-Powered CsPbBr3 Perovskite Nanonet Photodetector with a Hollow Vertical Structure.

For most commercial photodetectors (PDs), incident light is illuminated from the top or side of the device, but the opaque electrode (gold, copper, or aluminum, etc.) on the top will block part of the light from entering, wasting the efficiency of light utilization. Herein, to solve this issue, we introduced perovskite nanonet PDs with a hollow vertical structure by using a polystyrene microsphere template. Compared with ordinary thin film devices, our reticulated hollow vertical structure devices not only can enable easy entrance of the light from the reticulated hollow surface of the devices but also can reduce the reflection of light, resulting in better device performance. For our optimal CsPbBr3 perovskite PDs, high photoelectric performances were achieved with the switching ratio up to 4.17 × 104, a detectivity of 7.44 × 1011 Jones, a linear dynamic range of 108 dB, and the rise/fall time of 0.1/0.16 ms. More importantly, because of the reticulated hollow structure, our device performance showed less reduction when the incident light was illuminated from the top than from the bottom. These results may be of great reference value for improving the photoelectric performance of silicon-based devices or deep ultraviolet PDs.

Single-Layer ZnO Hollow Hemispheres Enable High-Performance Self-Powered Perovskite Photodetector for Optical Communication.

The carrier transport layer with reflection reduction morphology has attracted extensive attention for improving the utilization of light. Herein, we introduced single-layer hollow ZnO hemisphere arrays (ZHAs) behaving light trapping effect as the electron transport layer in perovskite photodetectors (PDs). The single-layer hollow ZHAs can not only reduce the reflection, but also widen the angle of the effective incident light and especially transfer the distribution of the optical field from the ZnO/FTO interface to the perovskite active layer confirmed by the 3D finite-difference time-domain simulation. These merits benefit for the generation, transport and separation of carriers, improving the light utilization efficiency. Finally, our optimized FTO/ZHA/CsPbBr3/carbon structure PDs showed high self-powered performance with a linear dynamic range of 120.3 dB, a detectivity of 4.2 × 1012 Jones, rise/fall time of 13/28 µs and the f-3 dB of up to 28 kHz. Benefiting from the high device performance, the PD was demonstrated to the application in the directional transmission of encrypted files as the signal receiving port with super high accuracy. This work uniquely utilizes the features of high-performance self-powered perovskite PDs in optical communication, paving the path to wide applications of all-inorganic perovskite PDs.

Welding Perovskite Nanowires for Stable, Sensitive, Flexible Photodetectors.

Compared with a single nanowire (NW) or NW array, the simpler preparation process of an NW network (NWN) enables it to be fabricated in large-scale, flexible, and wearable applications of photodetectors (PDs). However, the NWN behaves many microinterfaces (MIs) between NWs, seriously limiting the device performance and stability. Here, we demonstrate a welding strategy for an MAPbI3 NWN, which enhances the crystallinity of the NWN and enhances the radial transmission of photogenerated carriers, leading to a better device performance with ultrahigh stability. Our NWN PDs fabricated by using the welding strategy showed ultrahigh performance with an on/off ratio and detectivity of 2.8 × 104 and 4.16 × 1012 Jones, respectively, which are the best performance for reported metal-semiconductor-metal (MSM) perovskite NWN PDs and are comparable to those of single-NW or NW array PDs. More importantly, our unpackaged NWN PDs show ultrahigh storage stability in air with a humidity of 55-65%, and the flexible NWN PDs can enable 250 bending cycles at different bending radii and 1000 bending cycles at fixed bending radii with no performance degradation being observed. These results indicate our welding strategy is very powerful for improving the performance of the NW device with applications in the wearable field.

All-Inorganic Halide Perovskite Alloy Nanowire Network Photodetectors with High Performance.

Organic-inorganic hybrid lead halide perovskites have attracted much attention in the photoelectric field due to their excellent characteristics, such as a tunable band gap, simple fabrication process, and high photoelectric conversion efficiency. However, the commercialization of the perovskite-based devices still faces many challenges, one of which is the inclusion of the toxic lead. Herein, we demonstrated a two-step solution method for synthesizing tin-based perovskite nanowires (NWs) with their application in photodetectors (PDs). By changing the halide exchange time and the Sn content in the precursor, the dark current of the CsPbxSn1-x(BryI1-y)3 perovskite NW PDs increased with increasing content of tin and decreased with increasing Br concentration, and the lowest dark current with a value of 0.672 nA at 1 V was achieved for the perovskite alloy NW PDs synthesized with 0.5 mg mL-1 SnI2. Our optimized perovskite alloy NW PDs showed high performance with a linear dynamic range of up to 120 dB, a rising/falling time of 4.25/4.82 ms, and a detectivity of 2 × 1010 Jones. In addition, our Sn-based perovskite NW devices could maintain good performance after storing in air for 30 days. These results demonstrated good practical application for the Sn-based perovskite NW devices.

Low-reflection, (110)-orientation-preferred CsPbBr3 nanonet films for application in high-performance perovskite photodetectors.

All-inorganic metal halide perovskites have attracted great interest in recent years due to their good device performance with higher thermal stability than that of their organic-inorganic perovskite counterparts. However, the all-inorganic perovskite polycrystalline films prepared by the conventional spin-coating method possess many pinholes, nonuniform surface with many small crystals, and irregular agglomerates, limiting their device performance. Herein, we introduced a monolayer nano-polystyrene (PS) sphere confined growth method for obtaining CsPbBr3 nanonet films (NFs) with ordered nanostructures grown in the preferred (110) orientation, which is beneficial for the charge carrier transport and the light-harvesting efficiency. The (110) peak intensity of CsPbBr3 NFs increased with the increase of the diameter of the monolayer sphere, while the (001) peak intensity was suppressed greatly, indicating the more preferred (110) oriented growth. The PDs based on (110)-orientation-preferred CsPbBr3 NFs prepared by using 850 nm PS spheres showed the best performance. The best performing device displayed the biggest linear dynamic range of up to 120 dB. In addition, a responsivity of 2.84 A W-1 and a detectivity of 5.47 × 1012 Jones were also achieved.

A 2.5-dimensional method for the prediction of structure-borne low-frequency noise from concrete rail transit bridges.

Predicting structure-borne noise from bridges subjected to moving trains using the three-dimensional (3D) boundary element method (BEM) is a time consuming process. This paper presents a two-and-a-half dimensional (2.5D) BEM-based procedure for simulating bridge-borne low-frequency noise with higher efficiency, yet no loss of accuracy. The two-dimensional (2D) BEM of a bridge with a constant cross section along the track direction is adopted to calculate the spatial modal acoustic transfer vectors (MATVs) of the bridge using the space-wave number transforms of its 3D modal shapes. The MATVs calculated using the 2.5D method are then validated by those computed using the 3D BEM. The bridge-borne noise is finally obtained through the MATVs and modal coordinate responses of the bridge, considering time-varying vehicle-track-bridge dynamic interaction. The presented procedure is applied to predict the sound pressure radiating from a U-shaped concrete bridge, and the computed results are compared with those obtained from field tests on Shanghai rail transit line 8. The numerical results match well with the measured results in both time and frequency domains at near-field points. Nevertheless, the computed results are smaller than the measured ones for far-field points, mainly due to the sound radiation from adjacent spans neglected in the current model.