Wafer-Scale Photolithography-Pixeled Pb-Free Perovskite X-ray Detectors.

Pb-free perovskite material is considered to be a promising material utilized in next-generation X-ray detectors due to its high X-ray absorption coefficient, decent carrier transport properties, and relatively low toxicity. However, the pixelation of the perovskite material with an industry-level photolithography processing method remains challenging due to its poor structural stability. Herein, we use Cs2AgBiBr6 perovskite material as the prototype and investigate its interaction with photolithographic polar solvents. Inspired by that, we propose a wafer-scale photolithography patterning method, where the pixeled perovskite array devices for X-ray detection are successfully prepared. The devices based on pixeled Pb-free perovskite material show a high detection sensitivity up to 19118 ± 763 µC Gyair-1 cm-2, which is comparable to devices with Pb-based perovskite materials and superior to the detection sensitivity (∼20 µC Gyair-1 cm-2) of the commercial a-Se detector. After pixelation, the devices achieve an improved spatial resolution capacity with the spatial frequency from 2.7 to 7.8 lp mm-1 at modulation-transfer-function (MTF) = 0.2. Thus, this work may contribute to the development of high-performance array X-ray detectors based on Cs2AgBiBr6 perovskite material.

Two-stage amplification of an ultrasensitive MXene-based intelligent artificial eardrum.

We report an artificial eardrum using an acoustic sensor based on two-dimensional MXene (Ti3C2Tx), which mimics the function of a human eardrum for realizing voice detection and recognition. Using MXene with a large interlayer distance and micropyramid polydimethylsiloxane arrays can enable a two-stage amplification of pressure and acoustic sensing. The MXene artificial eardrum shows an extremely high sensitivity of 62 kPa-1 and a very low detection limit of 0.1 Pa. Notably, benefiting from the ultrasensitive MXene eardrum, the machine-learning algorithm for real-time voice classification can be realized with high accuracy. The 280 voice signals are successfully classified for seven categories, and a high accuracy of 96.4 and 95% can be achieved by the training dataset and the test dataset, respectively. The current results indicate that the MXene artificial intelligent eardrum shows great potential for applications in wearable acoustical health care devices.

Flexible Two-Dimensional Ti3C2 MXene Films as Thermoacoustic Devices.

MXenes have attracted great attention for their potential applications in electrochemical and electronic devices due to their excellent characteristics. Traditional sound sources based on the thermoacoustic effect demonstrated that a conductor needs to have an extremely low heat capacity and high thermal conductivity. Hence, a thin MXene film with a low heat capacity per unit area (HCPUA) and special layered structure is emerging as a promising candidate to build loudspeakers. However, the use of MXenes in a sound source device has not been explored. Herein, we have successfully prepared sound source devices on an anodic aluminum oxide (AAO) and a flexible polyimide (PI) substrates by using the prepared Ti3C2 MXene nanoflakes. Due to the larger interlayer distance of MXene, the MXene-based sound source device has a higher sound pressure level (SPL) than that of graphene of the same thickness. High-quality Ti3C2 MXene nanoflakes were fabricated by selectively etching the Ti3AlC2 powder. The as-fabricated MXene sound source device on an AAO substrate exhibits a higher SPL of 68.2 dB (f = 15 kHz) and has a very stable sound spectrum output with frequency varying from 100 Hz to 20 kHz. A theoretical model has been built to explain the mechanism of the sound source device on an AAO substrate, matching well with the experimental results. Furthermore, the MXene sound source device based on a flexible PI substrate has been attached to the arms, back of the hand, and fingers, indicating an excellent acoustic wearability. Then, the MXene film is packaged successfully into a commercial earphone case and shows an excellent performance at high frequencies, which is very suitable for human audio equipment.

Millimeter-Scale Nonlocal Photo-Sensing Based on Single-Crystal Perovskite Photodetector.

Organometal trihalide perovskites (OTPs) are promising optoelectronic materials for high-performance photodetectors. However, up to now, traditional polycrystal OTP-based photodetectors have demonstrated limited effective photo-sensing range. Recently, bulk perovskite single crystals have been seen to have the potential for position-sensitive photodetection. Herein, for the first time, we demonstrate a position-dependent photodetector based on perovskite single crystals by scanning a focused laser beam over the device perpendicular to the channel. The photodetector shows the best-ever effective photo-sensing distance up to the millimeter range. The photoresponsivity and photocurrent decrease by nearly an order of magnitude when the beam position varies from 0 to 950 µm and the tunability of carrier diffusion length in CH3NH2PbBr3 with the variation of the exciting laser intensity is demonstrated. Furthermore, a numerical model based on transport of photoexcited carriers is proposed to explain the position dependence. This photodetector shows excellent potential for application in future nanoelectronics and optoelectronics systems.