A large-scale flexible X-ray detector based on a perovskite p–n homojunction is reported in this work. The addition of a Bi 3+ -doped MAPbI 3 layer would effectively suppress the dark current and noise while maintaining high sensitivity.
Narrowband photodetectors have wide application potential in high-resolution imaging and encrypted communication, due to their high-precision spectral resolution capability. In this work, we report a fast response, high spectral rejection ratio, and self-filtered ultranarrowband photodetector with a new mechanism, which introduces bulk recombination by doping Bi3+ and cooperates with surface recombination for further quenching photogenerated charges generated by short-wavelength-light excitation in perovskite single-crystal. A perovskite film focused on collecting charges is fabricated on the single crystal by a lattice-matched solution-processed epitaxial growth method. Due to the formation of PN heterojunctions, a narrowband photodetector in this mechanism has remarkable spectral selectivity and detection performance with an ultranarrow full width at half-maximum (FWHM) of 7.7 nm and a high spectral rejection ratio of 790, as well as a high specific detectivity up to 1.5 × 1010 Jones, a fast response speed with a rise time and fall time of ∼8 and 137 μs. The ultrafast and ultranarrow spectra response of self-filtered narrowband photodetector provides a new strategy in high-precision and high-resolution photoelectric detection.
Abstract Substance discrimination beyond the shape feature is urgently desired for x‐ray imaging for enhancing target identification. With two x‐ray sources or stacked two detectors, the two‐energy‐channel x‐ray detection can discriminate substance density by normalizing the target thickness. Nevertheless, the artifacts, high radiation dose and difficulty in image alignment due to two sources or two detectors impede their widespread application. In this work, we report a single direct x‐ray detector with MAPbI 3 /MAPbBr 3 heterojunction for switchable soft x‐ray (<20 keV) and hard x‐ray (>20 keV) detection under one x‐ray source. Systematic characterizations confirm soft and hard x‐ray deposit their energy in MAPbI 3 and MAPbBr 3 layer, respectively, while working voltages can control the collection of generated charge carriers in each layer for selective soft/hard x‐ray detection. The switching rate between soft and hard x‐ray detection mode reaches 100 Hz. Moreover, the detector possesses a moderate performance with ~50 nGy s −1 in limit‐of‐detection, ~8000 μC Gy −1 cm −2 in sensitivity and ~7 lp/mm in imaging resolution. By defining the attenuation coefficient ratio ( 𝜇 L /𝜇 H ) as substance label, we effectively mitigate the influence of target thickness and successfully discriminate substances in the acquired x‐ray images. image
Abstract Low-cost, handily prepared, and efficient large-scale triboelectric nanogenerator (TENG) is considered as the new scheme for distributed mechanical conversion or renewable blue energy utilization. Semiconductors with high carrier mobility introduction potency overcome pure polymer restriction for uncompetitive short current density. An extremely popular all-inorganic lead-free double perovskite Cs 2 AgBiBr 6 (CABB) has emerged as extraordinary potential material in the substitution of semiconductor triboelectric material, which overcomes the limitations of high impedance associated with organic polymer insulator-based materials. In this current study, assembled by CABB which was certified as an available positive frictional material, TENG with a sandwiched structure of ITO/c-TiO 2 (compact TiO 2 )/m-TiO 2 (mesoporous TiO 2 )/CABB - the poly tetra fluoroethylene (PTFE)/Al exhibits appropriate performance on environmental stability and output capacity. A comparison of the fabrication process showed that spraying is an inexpensive method to prepare large-scale functional films of CABB TENG with brilliant relative dielectric constant and work function (W f ) difference that possess more distinguished output characteristics. This was confirmed by the appearance of higher open-circuit voltage of 105 V, larger short-current density of 2.45 mA/m 2 at 0.25 Hz motion parameter, and more abundant power density output of 0.76 W/m 2 under a higher frequency of 10 Hz. Further study clearly confirmed that both higher frequency and larger contact area are conducive to the total output power, while terminal charging speed is inversely or positively proportional with capacitance or mechanical frequency. The final physical display effect showed that spraying with CABB TENG could light up at least 53 commercial yellow LEDs, holding decent energy conversion ability. This confirms its efficiency, high throughput, and cost efficiency.
X-ray detection and imaging are widely used in medical diagnosis, product inspection, security monitoring, etc. Large-scale polycrystalline perovskite thick films possess high potential for direct X-ray imaging. However, the notorious problems of baseline drift and high detection limit caused by ions migration are still remained. Here, ion migration is reduced by incorporating 2D perovskite into 3D perovskite, thereby increasing the ion activation energy. This approach hinders ion migration within the perovskite film, consequently suppressing baseline drift and reducing the lowest detection limit(LOD) of the device. As a result, the baseline drifting declines by 20 times and the LOD reduces to 21.1 nGy s
All-inorganic halide semiconductors with perovskite or perovskite-like structure have aroused a widespread concern recently for its environmental friendliness and stabilities while possessing excellent optoelectronic properties. Double perovskite Cs2AgBiBr6 single crystal (SC) is one of the most representative materials in the latest research area. To further improve the device response range and decrease its dark current density effectively, functional layers based on the solution-processed epitaxial method are normally fabricated as heterojunctions. Herein, a novel idea of a broadband heterojunction MAPbI3 (MA = CH3NH3)/Cs2AgBiBr6 is proposed in this work to achieve this goal. A MAPbI3 layer is fabricated on Cs2AgBiBr6 SC substrates through immersing Cs2AgBiBr6 SC into MAPbI3 solution at a MAPbI3 crystallization temperature. Ultimately, this heterojunction device expands the absorption limit from 618 to 838 nm, makes responsivity range redshift from 629 to 860 nm, and achieves a responsivity of 16.8 mA W−1 while the detectivity of 1.33 × 1011 Jones under 622 nm 0.55 mW cm−2 illumination at −20 V bias, maintaining excellent optoelectronic properties.
Compared with the pure lead-based MAPbBr3 (MA = CH3NH3) perovskite single crystals (PSCs), tin–lead alloy (MAPbxSn1−xBr3) PSCs with higher carrier mobility and longer carrier lifetime are expected to perform as better-quality ionization radiation detectors. In this work, we design MAPbBr3–MAPb0.9Sn0.1Br3–MAPb0.8Sn0.2Br3 structure detectors by employing solution-process epitaxial growth. Because of the gradient change in tin element proportion, the relatively low mismatch rates between different PSC layers can effectively reduce defects generated at the interface, which improves charge collection efficiency. Moreover, band barriers between different PSC layers form depletion layers due to the differences in band structure, and the high resistivity and built-in electric field of depletion layers can suppress dark current under high voltages. The optimized detector exhibits a high x-ray detection sensitivity of 6.76 × 104μC Gy−1 cm−2 and the lowest detectable dose rate of 7.4 nGy s−1 under 40 kVp x-ray radiation. Based on 241Am (5.95 MeV) α particle irradiation, tin–lead HD has lower detection noise and more obvious response compared to MAPbBr3 PSCs. The electron mobility was indicated as high as 612 cm2 s−1 V−1, and the mobility-lifetime (μτ) products were measured to be 3.5 × 10−3 cm2 V−1 using the Hecht equation, demonstrating superior transport properties.
Solution-processed lead halide perovskite single crystals (LHPSCs) are believed to have great potential in gamma-ray spectroscopy. However, obtaining low-defect LHPSCs from a solution at low temperatures is difficult compared to obtaining Bridgman single crystals such as CdTe and Si. Herein, noise from the intrinsic defects of LHPSCs is considered as the main problem hindering their gamma-ray detection performance. By isolating the defect-induced holes in LHPSCs via energy barriers, we show that NIN photodiodes based on three types of LHPSCs, i.e., MAPbBr3 (MA = CH3NH3), MAPbBr2.5Cl0.5, and cascade LHPSCs, have demonstrated good energy resolution in the range of 6.7–10.3% for 662 keV 137Cs gamma-ray photons. The noise for >10 mm3 devices is low, in the order of 340–860 electrons, and the electron collection efficiency reaches 23–43%. These results pave the way for obtaining low-cost, large, high energy-resolution gamma-ray detectors at room temperature (300 K).
Recent years, organic-inorganic hybrid perovskites (OIHPs) have been widely used in applications, such as solar cells, lasers, light-emission diodes, and photodetectors due to their outstanding optoelectronic properties. Nowadays photodetectors based on perovskite films (PFs) suffer from surface and interface traps, which result from low crystalline quality of perovskite films and lattice mismatch between perovskite films and substrates. Herein, we fabricate MAPbI 3 -(MA = CH 3 NH 3 ) single-crystal films (SCFs) on MAPbBr 3 single crystal substrates in MAPbI 3 precursor solution during crystallization process via solution-processed epitaxy. Benefit from the good lattice matching, epitaxial MAPbI 3 SCFs with high crystallinity and smooth morphology are of comparable quality to MAPbI 3 PSCs and are of better quality than MAPbI 3 polycrystalline films. Here we report that epitaxial MAPbI 3 SCFs have a low trap density of 5.64×10 11 cm –3 and a long carrier lifetime of 11.86 μs. In this work, photodetector based on epitaxial MAPbI 3 single-crystal film (SCF) exhibits an excellent stability of a long-term stable response after 120 days, a fast response time of 2.21 μs, a high responsivity of 1.2 A W –1 and a high detectivity of 3.07 ×10 12 jones.
Abstract Narrowband photodetection provides important information in a specific wavelength range. Specially, the use of nonoptical‐filter narrowband photodetectors based on MAPbX 3 (MA = CH 3 NH 3 ; X = Cl, Br, I) perovskites is reported of great potential. However, current MAPbX 3 ‐based narrowband photodetectors have to sacrifice their photocurrent and response speed to achieve an acceptable spectral rejection ratio. In this work, a new type of heterojunction photodetector (hetero‐PD) with a structure of (n‐type doped MAPbCl 3 )/(intrinsic MAPbBr 2.5 Cl 0.5 )/(n‐type doped MAPbBr 3 ) via epitaxial growth is demonstrated as a narrowband photodetector. Through optical bandgap engineering, photons with different wavelength can be absorbed in different layers. Owing to the n–i–n energy band structure, most external bias would apply on a tiny region near the n–i heterojunction. Besides, the energy barriers in the heterojunctions can block holes from injection and collection, resulting in low‐noise electron‐only hetero‐PDs. By sufficiently suppressing the background noise from short‐wavelength photons, hetero‐PDs are capable of achieving a high spectral rejection ratio of 98.1% under an electrical field of 8 V cm −1 . Moreover, hetero‐PDs exhibit a high external quantum efficiency value of 45%, a narrow full width at half‐maximum of 13 nm, and a response time of 1.35 µs.
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