Simultaneous Incorporation of CsI in the Two-step Deposition Process Boosts the Power Conversion Efficiency and Stability of Perovskite Solar Cells.

Two-step deposition method has been widely exploited to fabricate FA1-x Csx PbI3 perovskite solar cells. However, in previous studies, CsI is mainly added into the PbI2 precursor with DMF/DMSO as solvent. Here in this study, a novel method to fabricate FA1-x Csx PbI3 perovskite has been proposed. The CsI is simultaneously added into the PbI2 precursor and the organic FAI/MACl salts solution in our modified two-step deposition process. The resulting FA1-x Csx PbI3 film exhibits larger perovskite crystals and suppressed defect density (4.05×1015  cm-3 ) compared with the reference perovskite film (9.23×1015  cm-3 ) without CsI. Therefore, the obtained FA1-x Csx PbI3 perovskite solar cells have demonstrated superior power conversion efficiencies (PCE=21.96 %) together with better long-term device stability.

Fast near-infrared photodetectors from p-type SnSe nanoribbons.

Low-dimensional tin selenide nanoribbons (SnSe NRs) show a wide range of applications in optoelectronics fields such as optical switches, photodetectors, and photovoltaic devices due to the suitable band gap, strong light-matter interaction, and high carrier mobility. However, it is still challenging to grow high-quality SnSe NRs for high-performance photodetectors so far. In this work, we successfully synthesized high-quality p-type SnSe NRs by chemical vapor deposition and then fabricated near-infrared photodetectors. The SnSe NR photodetectors show a high responsivity of 376.71 A W-1, external quantum efficiency of 5.65 × 104%, and detectivity of 8.66 × 1011Jones. In addition, the devices show a fast response time with rise and fall time of up to 43µs and 57µs, respectively. Furthermore, the spatially resolved scanning photocurrent mapping shows very strong photocurrent at the metal-semiconductor contact regions, as well as fast generation-recombination photocurrent signals. This work demonstrated that p-type SnSe NRs are promising material candidates for broad-spectrum and fast-response optoelectronic devices.

Small-diameter p-type SnS nanowire photodetectors and phototransistors with low-noise and high-performance.

P-type nanostructured photodetectors and phototransistors have been widely used in the field of photodetection due to their excellent electrical and optoelectronic characteristics. However, the large dark current of p-type photodetectors will limit the detectivity. Herein, we synthesized small-diameter single-crystalline p-type SnS nanowires (NWs) and then fabricated single SnS NW photodetectors and phototransistors. The device exhibits low noise and low dark current, and its noise current power is as low as 2.4 × 10-28A2. Under 830 nm illumination and low power density of 0.12 mW cm-2, the photoconductive gain, responsivity and detectivity of the photodetector are as high as 3.9 × 102, 2.6 × 102A W-1and 1.8 × 1013Jones, respectively, at zero gate voltage. The rise and fall time of response are about 9.6 and 14 ms. The experimental results show that the small-diameter p-type SnS NWs have broad application prospects in high-performance and low-power photodetectors with high sensitivity, fast response speed and wide spectrum detection in the future.

Piezoelectric potential enhanced photocatalytic performance based on ZnO with different nanostructures.

In this paper, two novel nanostructures with ZnO nanowire and nanosheet arrays vertically growing on the FTO and Al foil have been synthesized by a hydrothermal method, which exhibit both the piezoelectric and photocatalytic properties. These nanostructures have typical wurtzite structures based on the XRD results. From the SEM results, the average diameter and length of nanowire have been measured to be about 150 nm and 4.5 µm, the thickness of ZnO nanosheet is about 50 nm and the width is about 5 µm. In the photocatalytic test, the photodegradation of RhB under 365 nm illumination for nanowire and nanosheet is about 25% and 37% in 80 min reaction. With stirring, the degradation rate is increased to 61% and 85%. Finally, the photocurrent test and finite element method were used to analyze the piezo-photodegradation mechanism.

Room-Temperature Single-Photon Detector Based on Single Nanowire.

Single-photon detectors that can resolve photon number play a key role in advanced quantum information technologies. Despite significant progress in improving conventional photon-counting detectors and developing novel device concepts, single-photon detectors that are capable of distinguishing incident photon number at room temperature are still very limited. We demonstrate a room-temperature photon-number-resolving detector by integrating a field-effect transistor configuration with core/shell-like nanowires. The shell serves as a photosensitive gate, shielding negative back-gated voltage, and leads to a persistent photocurrent. At room temperature, our detector is demonstrated to identify 1, 2, and 3 photon-number states with a confidence of >82%. The detection efficiency is determined to be 23%, and the dark count rate is 1.87 × 10-3 Hz. Importantly, benefiting from the anisotropic nature of 1D nanowires, the detector shows an intrinsic photon-polarization selection, which distinguishes itself from existing intensity single-photon detectors. The unique performance for the single-photon detectors based on single nanowire demonstrates the great potential for future single-photon detection applications.

When Nanowires Meet Ultrahigh Ferroelectric Field-High-Performance Full-Depleted Nanowire Photodetectors.

One-dimensional semiconductor nanowires (NWs) have been widely applied in photodetector due to their excellent optoelectronic characteristics. However, intrinsic carrier concentration at certain level results in appreciable dark current, which limits the detectivity of the devices. Here, we fabricated a novel type of ferroelectric-enhanced side-gated NW photodetectors. The intrinsic carriers in the NW channel can be fully depleted by the ultrahigh electrostatic field from polarization of P(VDF-TrFE) ferroelectric polymer. In this scenario, the dark current is significantly reduced and thus the sensitivity of the photodetector is increased even when the gate voltage is removed. Particularly, a single InP NW photodetector exhibits high-photoconductive gain of 4.2 × 10(5), responsivity of 2.8 × 10(5) A W(-1), and specific detectivity (D*) of 9.1 × 10(15) Jones at λ = 830 nm. To further demonstrate the universality of the configuration we also demonstrate ferroelectric polymer side-gated single CdS NW photodetectors with ultrahigh photoconductive gain of 1.2 × 10(7), responsivity of 5.2 × 10(6) A W(-1) and D* up to 1.7 × 10(18) Jones at λ = 520 nm. Overall, our work demonstrates a new approach to fabricate a controllable, full-depleted, and high-performance NW photodetector. This can inspire novel device structure design of high-performance optoelectronic devices based on semiconductor NWs.

Visible Light-Assisted High-Performance Mid-Infrared Photodetectors Based on Single InAs Nanowire.

One-dimensional InAs nanowires (NWs) have been widely researched in recent years. Features of high mobility and narrow bandgap reveal its great potential of optoelectronic applications. However, most reported work about InAs NW-based photodetectors is limited to the visible waveband. Although some work shows certain response for near-infrared light, the problems of large dark current and small light on/off ratio are unsolved, thus significantly restricting the detectivity. Here in this work, a novel "visible light-assisted dark-current suppressing method" is proposed for the first time to reduce the dark current and enhance the infrared photodetection of single InAs NW photodetectors. This method effectively increases the barrier height of the metal-semiconductor contact, thus significantly making the device a metal-semiconductor-metal (MSM) photodiode. These MSM photodiodes demonstrate broadband detection from less than 1 µm to more than 3 µm and a fast response of tens of microseconds. A high detectivity of ∼1012 Jones has been achieved for the wavelength of 2000 nm at a low bias voltage of 0.1 V with corresponding responsivity of as much as 40 A/W. Even for the incident wavelength of 3113 nm, a detectivity of ∼1010 Jones and a responsivity of 0.6 A/W have been obtained. Our work has achieved an extended detection waveband for single InAs NW photodetector from visible and near-infrared to mid-infrared. The excellent performance for infrared detection demonstrated the great potential of narrow bandgap NWs for future infrared optoelectronic applications.

Surface Passivation of Perovskite Solar Cells with Oxalic Acid: Increased Efficiency and Device Stability.

Solution processed perovskite films usually exhibit numerous defect states on the surfaces of the films. Here in this work, oxalic acid (H2 C2 O4 ), which has two C=O groups, is selected and used to passivate the surface defects of the two-step deposited perovskite films via post-treatment. Strong interaction between H2 C2 O4 molecule and the Pb2+ ions located on the surface of perovskite film has been confirmed via Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, which can result in an effective suppress of the surface defects. Furthermore, time-resolved PL spectrum indicates that carrier lifetime is prolonged in the H2 C2 O4 passivated perovskite film. After optimizing the H2 C2 O4 concentration, the target perovskite solar cells can demonstrate superior power conversion efficiencies (21.67 % from reverse measurement and 21.54 % from forward measurement) and superior device-stability.

DFT-Based Study of the Structure, Stability, and Spectral and Optical Properties of Gas-Phase NbMgn (n = 2-12) Clusters.

Gas-phase NbMgn (n = 2-12) clusters were fully searched by CALYPSO software, and then the low-energy isomers were further optimized and calculated under DFT. It is shown that the three lowest energy isomers of NbMgn (n = 3-12) at each size are grown from two seed structures, i.e., tetrahedral and pentahedral structures, and the transition size occurs at the NbMg8 cluster. Interestingly, the relative stability calculations of the NbMg8 cluster ground-state isomer stand out under the examination of several parameters' calculations. The charge-transfer properties of the clusters of the ground-state isomers of various sizes had been comprehensively investigated. In order to be able to provide data guidance for future experimental probing of these ground-state clusters, this work also predicted infrared and Raman spectra at the same level of theoretical calculations. The results show that the multipeak nature of the IR and Raman spectra predicts that it is difficult to distinguish them directly. Finally, the optical properties of these clusters were investigated by calculating the static linear, second-order nonlinear, and third-order nonlinear coefficients. Importantly and interestingly, the NbMg8 cluster was shown to have superior nonlinear optical characteristics to all other clusters; thus, it is a powerful candidate for a potentially ultrasensitive nonlinear optical response device for some special purpose.

Pyro-phototronic effect enhanced broadband photodetection based on CdS nanorod arrays by magnetron sputtering.

In this work, self-powered photodetectors (PDs) based on RF magnetron sputtering-fabricated CdS nanorod arrays and polished Si substrates were prepared for the first time. By introducing the pyro-phototronic effect of wurtzite CdS, the self-powered PDs exhibit a broadband response range from UV (365 nm) to IR (1310 nm) at zero bias, even beyond the bandgap limit of the material. Both the photoresponsivity and specific detectivity are also enhanced by 23.3 times compared with those only based on the photovoltaic effect. In addition, the rise and fall times of self-powered PDs are 70 µs and 90 µs under 980 nm laser illumination. This research not only expands the application of CdS nanostructures in the field of pyro-phototronics, but also greatly enriches the preparation methods of CdS based pyro-phototronics materials.

An investigation of the effects of ZnO inverse opal pore size in the composite of ZnO nanorods/ZnO inverse opal on the performance of quantum dot-sensitized solar cells.

A semiconductor oxide composite consisting of ZnO nanorods (NRs) and ZnO inverse opal (IO) was fabricated and used in the photoanode of quantum dot-sensitized solar cells (QDSSCs). Using polystyrene spheres 500, 800, 1000, and 1500 nm in diameter as the IO template, ZnO composites and corresponding QDSSCs with ZnO IOs of different pore sizes were fabricated. The oxide composite prepared with ZnO IOs of different pore sizes showed similar micro-morphologies; however, the photovoltaic performance of the QDSSCs based on these composites varied greatly. The QDSSCs based on the ZnO composite achieved high power conversion efficiencies (PCEs) of more than 6%, and the maximum PCE was 7.26% when the ZnO IO pore diameter in the composite was 800 nm. This resulted in very high PCE values for the QDSSCs using CdS/CdSe quantum dot sensitizers. With further interface modifications of NH4F and ZnS, the QDSSC achieved an even higher PCE value of 11.38%. Subsequently, the effects of ZnO IO pore size in the composite on QDSSC performance were investigated.

High-Performance Near-Infrared Photodetectors Based on p-Type SnX (X = S, Se) Nanowires Grown via Chemical Vapor Deposition.

Because of the distinct electronic properties and strong interaction with light, quasi-one-dimensional nanowires (NWs) with semiconducting property have been demonstrated with tremendous potential for various technological applications, especially electronics and optoelectronics. However, until now, most of the state-of-the-art NW photodetectors are predominantly based on the n-type NW channel. Here, we successfully synthesized p-type SnSe and SnS NWs via the chemical vapor deposition method and fabricated high-performance single SnSe and SnS NW photodetectors. Importantly, these two NW devices exhibit an impressive photodetection performance with a high photoconductive gain of 1.5 × 104 (2.8 × 104), good responsivity of 1.0 × 104 A W-1 (1.6 × 104 A W-1), and excellent detectivity of 3.3 × 1012 Jones (2.4 × 1012 Jones) under near-infrared illumination at a bias of 3 V for the SnSe NW (SnS NW) channel. The rise and fall times can be as efficient as 460 and 520 µs (1.2 and 15.1 ms), respectively, for the SnSe NW (SnS NW) device. Moreover, the spatially resolved photocurrent mapping of the devices further reveals the bias-dependent photocurrent generation. All these results evidently demonstrate that the p-type SnSe and SnS NWs have great potential to be applied in next-generation high-performance optoelectronic devices.