Due to its superior carrier mobility and high air stability, the emerging two-dimensional (2D) layered bismuth oxyselenide (Bi 2 O 2 Se) nanosheets have attracted extensive attention, showing great potential for applications in the electronic and optoelectronic fields. However, a high mobility easily leads to a high dark current, seriously restricting optoelectronic applications, especially in the field of photodetectors. In this paper, we report a high-quality Van der Waals (vdWs) Bi 2 O 2 Se/Bi 2 Se 3 heterostructure on a fluorophlogopite substrate, exhibiting excellent photodiode characteristics. By means of the effective separation of photogenerated electrons and holes by a junction barrier at the interface, the current on/off ratio is up to about 3 × 10 3 under 532 nm laser illumination with zero bias. In addition, the photodetector not only achieves a fast response speed of 41 ms but also has a broadband photoresponse from 532 to 1450 nm (visible−NIR). Additionally, the responsivity can reach 0.29 A/W, and the external quantum efficiency exceeds 69% when the device operates in the reverse bias condition. The results indicate that the Bi 2 O 2 Se/Bi 2 Se 3 vdWs heterostructure has great potential for self-powered, broadband, and fast photodetection applications.
Abstract2D bismuth oxyselenide (Bi2O2Se) nanosheets have received increasing attention in the field of electronics and optoelectronics due to their high‐mobility, moderate energy bandgap, and air‐stability. However, due to the intrinsic high mobility, the photodetectors based on 2D Bi2O2Se have an inevitable high dark current, leading to high power consumption and limiting its potential application in photodetection. Herein, a novel highly sensitive WS2/Bi2O2Se van der Walls (vdWs) heterostructure with straddling band configuration is assembled on fluorophlogopite substrate. Owing to the effective separation of photogenerated electron–hole pairs and the quantum tunneling effect, the responsivity and external quantum efficiency of the WS2/Bi2O2Se heterostructure are 628 mA W−1 and 147.6% under 532 nm illumination, respectively. The Iphoto/Idark ratio with more than two orders of magnitude can be obtained, and the rise time is ≈33 ms, while the fall time is 38 ms. Furthermore, the heterostructure achieves a broadband photodetection capability from visible to near infrared (532–1450 nm). The results suggest that the WS2/Bi2O2Se vdWs heterostructure possesses a promising potential application prospect in high performance and broadband photodetectors.
Two‐dimensional Bi2O2Se is a newly developed 2D semiconductor material with air stability, moderate bandgap (0.8 eV), and high carrier mobility, which shows a bright prospect in optoelectronics. However, the reported photodetectors based on 2D Bi2O2Se suffer from the disadvantage of high dark current on account of the high carrier mobility and conductivity. Here, a Schottky photodiode based on 2D Bi2O2Se is constructed by employing an asymmetric electrodes technology. Due to the Schottky barrier, the dark current of the device is significantly suppressed. And the photodetector avoids the complex and precise preparation process of traditional heterojunction devices. The photodetector shows a broadband response from 450 to 1400 nm (Visible‐NIR), and the responsivity and detectivity reach 1.2 A W−1 and 7 × 1011 Jones under the irradiation of 500 nm light (6.4 mW cm−2), respectively. Moreover, the device achieved On/Off ratios of more than three orders of magnitude and fast response at zero bias (117 ms for rise time and 58.5 ms for fall time). What's more, the responsivity reaches 193 A W−1, and the external quantum efficiency exceeds 47 899% with external bias (−0.5 V). These results indicate the unlimited potential of 2D Bi2O2Se in highly sensitive, broadband, and low‐power optoelectronics devices.
An ultracapacitor State-of-Charge (SOC) fusion estimation method for electric vehicles under variable temperature environment is proposed in this paper. Firstly, Thevenin model is selected as the ultracapacitor model. Then, genetic algorithm (GA) is adopted to identify the ultracapacitor model parameters at different temperatures (−10 °C, 10 °C, 25 °C and 40 °C). Secondly, a variable temperature model is established by using polynomial fitting the temperatures and parameters, which is applied to promote the ultracapacitor model applicability. Next, the off-line experimental data is iterated by adaptive extended Kalman filter (AEKF) to train the Nonlinear Auto-Regressive Model with Exogenous Inputs (NARX) neural network. Thirdly, the output of the NARX is employed to compensate the AEKF estimation and thereby realize the ultracapacitor SOC fusion estimation. Finally, the variable temperature model and robustness of the proposed SOC fusion estimation method are verified by experiments. The analysis results show that the root mean square error (RMSE) of the variable temperature model is reduced by 90.187% compared with the non-variable temperature model. In addition, the SOC estimation error of the proposed NARX-AEKF fusion estimation method based on the variable temperature model remains within 2.055%. Even when the SOC initial error is 0.150, the NARX-AEKF fusion estimation method can quickly converge to the reference value within 5.000 s.
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