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Recently, stretchable and wearable health monitoring equipment has greatly improved human’s daily life, which sets higher demands for portable power source in stretchability, sustainability, and biocompatibility. In this work, we proposed a stretchable triboelectric nanogenerator (TENG) based on stretchable poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/porous carbon hybrid for oxyhemoglobin saturation (SpO2) monitoring. To combine advantages of carbon material for its high conductivity and organic electrode for its high stretchability, we spin-coated a solution of PEDOT:PSS/porous carbon onto a plasma-treated pre-stretched Ecoflex film to fabricate a stretchable electrode with rough surface. Due to its roughness and high potential difference with the dielectric material, the stretchable-electrode-based TENG exhibited better performance compared to the pristine TENG based on carbon or PEDOT:PSS material. The output voltage and current reached up to 51.5 V and 13.2 µA as the carbon concentration increased. More importantly, the performance further increased under large strain (100%) which is suitable for wearable systems. Finally, the device demonstrated its application potential for powering a flexible blood oxygen monitor. This simple and cost-effective method can enhance the stretchability and stability of organic/inorganic electrode-based TENG, which paves the development of high-performance stretchable TENG.

A stable terahertz (THz) photo-writable electrical-erasable memory from a CsPbI3:Ag (Ag-nanoparticle-added CsPbI3)/SnO2/PEDOT:PSS hybrid sample was investigated. A significant THz modulation depth ...

A large bandwidth and high-efficiency subwavelength quarter-wave plate (QWP) is an indispensable component of an integrated miniaturized optical system. The bandwidth of existing plasmonic quarter-wave plates with a transmission efficiency of more than 50% is less than 320 nm in the near-infrared band. In this paper, a metallic quarter-wave plate with a bandwidth of 600 nm (0.95–1.55 µm) and an average transmittance of more than 70% has been designed and shows excellent potential to be used in miniaturized optical polarization detection systems and as an optical data storage device. For TE mode incident waves, this miniaturized optical element can be equivalent to a Fabry-Pérot (FP) resonator. Meanwhile, for the TM mode incident wave, the transmission characteristics of this structure are controlled by gap surface plasmon polaritons (G-SPPs) existing in the symmetric metal/insulator/metal (MIM) configuration.

The organic photodetectors (OPDs) can be proposed in two different ways: a photodiode system or a photoconductor type, where the external quantum efficiency (EQE) cannot exceed 100% in the former one but it can in the latter one. Whether the electrode-active layer contacts can inject at least one kind of carriers is the critical factor to determine the specific photodetector type. Therefore, the role of electrode/semiconductor contacts in the OPDs needs to be fully understood. In this work, we demonstrate the high performance OPDs based on PTB7:PC71BM bulk heterojunction with the different top metal electrodes (Ag, Au, Al) by incorporating the PFN modified ITO electrode. Ultraviolet photoelectron spectroscopy shows that the work function of ITO is effectively reduced from 4.7 eV to 4.1 eV due to the PFN dipole layer. Combined with current density-voltage characteristics and the EQE, the results indicate the devices show different working modes: a photodiode or photoconductor type OPDs. For the Ag or Au electrode device, the photogenerated charges can rapidly transport to the corresponding electrodes and then to be collected under reverse bias, which meets the photodiode type. However, the Al electrode device with more than 100% EQE presents the photoconductor mode, which is contributed to that the photogenerated charges accumulate around the interface between the PFN layer and the active layer, and then create a tunneling charge injection under reverse bias. Although both the proposed photodiode and photoconductor devices exhibit large signal-to-noise ratio (104∼105), fast response (∼μs), and low working voltage (−0.5 V), these two type devices show their unique strengths due to the different working modes. The photodiode devices have higher detectivity (more than 1013 Jones) and broader linear dynamic range (over 120 dB), while the photoconductor ones possess more than 100% EQE and the better responsivity (0.56 A/W). This work may pave a way to obtain the desirable working mode of the photodetectors by simply tuning the electrode work function.

Infrared cameras with narrow-band detection capability are widely used for SF6 gas detection, which is an essential part of power equipment inspection. Narrow-band detection is usually achieved by a combination of quantum well infrared photodetectors (QWIPs) and narrow-band filters. Improving the quantum efficiency of QWIPs and reducing the detection bandwidth are important ways to improve camera performance. In this study, a back-incident-type device of quantum well micropillar array targeting at a 10.5 μm central wavelength is designed and studied by three-dimensional simulation. The operating mechanism of the device was determined by investigating the effect of the device geometry on the quantum efficiency. The enhanced absorption capability of the device mainly comes from the Fabry–Pérot resonance and the antireflection effect. The final device exhibits a remarkable peak quantum efficiency of 83% at 10.5 μm and an ultra-narrow spectral bandwidth of 0.2 μm. These excellent properties are achieved without an antireflective film and narrow-band filter, which can significantly improve the narrow-band capability and integration of the system; the dark current reduces to be 0.2762 times due to the low-duty cycle. These properties indicate that the structure of the quantum well micropillar array is of great significance to the development of QWIPs used in gas detection.

A terahertz read-only in situ electrically-erasable rewritable photo-memory device based on a perovskite:Ag (perovskite with Ag nanoparticles added)/SnO2/PEDOT:PSS hetero-junction structure is reported. Under low optical excitation, considerable terahertz amplitude modulation in a perovskite:Ag/PEDOT:PSS hybrid structure was achieved. When a SnO2 nanoparticle film was inserted between the perovskite and PEDOT:PSS layer, the attenuation of the terahertz signal was weaker than that of the perovskite:Ag/PEDOT:PSS hybrid structure; however, the SnO2 nanoparticle film considerably prolonged the recovery time of the modulated terahertz wave in air after photo-excitation was stopped. In addition, when bias voltages were applied to the perovskite:Ag/PEDOT:PSS and perovskite:Ag/SnO2/PEDOT:PSS hybrid structures, respectively, the terahertz signals recovered rapidly for both structures. Consequently, the photo-memory functionality was achieved based on a perovskite:Ag/SnO2/PEDOT:PSS hybrid structure with an in situ method for erasing stored information.

Stretchable and wearable opto-electronics have attracted worldwide attention due to their broad prospects in health monitoring and epidermal applications. Resistive strain sensors, as one of the most typical and important device, have been the subject of great improvements in sensitivity and stretchability. Nevertheless, it is hard to take both sensitivity and stretchability into consideration for practical applications. Herein, we demonstrated a simple strategy to construct a highly sensitive and stretchable graphene-based strain sensor. According to the strain distribution in the simulation result, highly sensitive planar graphene and highly stretchable crumpled graphene (CG) were rationally connected to effectively modulate the sensitivity and stretchability of the device. For the stretching mode, the device showed a gauge factor (GF) of 20.1 with 105% tensile strain. The sensitivity of the device was relatively high in this large working range, and the device could endure a maximum tensile strain of 135% with a GF of 337.8. In addition, in the bending mode, the device could work in outward and inward modes. This work introduced a novel and simple method with which to effectively monitor sensitivity and stretchability at the same time. More importantly, the method could be applied to other material categories to further improve the performance.

In this work, we demonstrate high sensitive organic photodetectors (OPDs) by incorporating the common sol-gel processed ZnO film between the ITO electrode and the polymer:fullerene active layer. The device requires a low negative working voltage to exhibit fast response and broad linear dynamic range (LDR), and the external quantum efficiency (EQE) of the devices can exceed 100%. The sol-gel ZnO layer can efficiently block the external charge injection from the ITO electrode to the active layer, which dramatically reduces the dark current density. Two kind devices (ITO/ZnO/P3HT:PC61BM/Al and ITO/ZnO/PTB7:PC71BM/Ag) are demonstrated and their dark current densities are effectively reduced from 0.07 mA/cm2 to 8.16 × 10−5 mA/cm2 and from 0.75 mA/cm2 to 6.50 × 10−5 mA/cm2 at −0.5 V, respectively. Although the two kind devices show the comparable characteristics, the transient photocurrent and capacitance–voltage (C-V) measurements indicate the two different working mechanisms related. Under illumination, in the P3HT:PC61BM based devices, some surface defect states of ZnO can be occupied and the photogenerated charges accumulate around the interface between the ZnO layer and the active layer, which contribute a tunneling injection under the applied reverse bias. While in the PTB7:PC71BM based devices, the photogenerated charges rapidly transport to the corresponding electrodes and then be collected under reverse bias. The different working mechanisms lead to the various device performances. The OPDs based on P3HT:PC61BM exhibit a higher EQE of more than 200% (460 nm - 600 nm) at −0.5 V, while the PTB7:PC71BM based devices show a more than 1.0 × 1015 Jones detectivity (390 nm - 730 nm) and achieve the over 110 dB linear dynamic range (LDR) under the different monochromatic illuminations at −0.5 V.

Bias-driven terahertz (THz) negative conductivity and transmission enhancement based on structures composed of monolayer graphene, MXene (Ti3C2Tx) and poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate):dimethyl sulfoxide (PEDOT:PSS:DMSO) caused by photo-excited or bias-driven are investigated. The THz signals that pass through the monolayer graphene/quartz, MXene/quartz, thinner and thicker PEDOT:PSS:DMSO/quartz structures are enhanced effectively under photo excitation or application of an external bias voltage in a THz time-domain spectroscopy (THz-TDS) system. This enhancement of THz transmission indicates that negative conductivity occurs, which is consistent with the results based on the monolayer graphene, thinner PEDOT:PSS:DMSO samples detected using an optical pump-THz probe (OPTP) system. The conductivity reduction mechanism is explained using an established Drude model. After photo excitation, this results in the generation of photo-induced carriers and an increase in the average scattering rate of the carriers. And as a consequence of the energy injection into the carrier system of the sample after applying a bias, the carrier temperature increases rapidly; this results in the generation of carriers and an increase in the average scattering rate of the carriers. However, the increase in the average scattering rate of the carriers is much higher than the increase in the average carrier density, which leads to the negative conductivity and the increased THz transmission.

Ultrafast carrier response of perovskite/MoO3/graphene heterostructure was investigated by optical-pump terahertz (THz) probe spectroscopy. The high work function of MoO3 changes the tunable graphene Fermi level via hole doping. Compared with monolayer graphene, it generates a more negative photoconductivity and enables ultra-fast THz functional manipulation. The subsequent THz signal decrease is related to hot-carrier cooling and the carrier concentration contributed by the CH3NH3PbI3 layer. The charge transfer and recombination reduce the positive conductance of the hybrid structure relative to that of neat CH3NH3PbI3.

In this work, we propose a facile microwave-assisted approach for annealing sol-gel derived ZnO films to serve as electron transport layers (ETLs) for inverted bulk heterojunction polymer solar cells. We have demonstrated an impressive enhancement in performance for devices based on a poly (3-hexylthiophene) (P3HT): (6,6)-phenyl-C 61 -butyric acid methyl ester (PC 61 BM) system employing the microwave-annealed ZnO (ZnO (MW)) ETLs in comparison to the cases using the conventional hotplate-annealed ZnO (ZnO (HP)) ones. The better electron transport in the device with the ZnO (MW) ETL is mainly ascribed to the preferable interfacial contact as evidenced by the morphology characteristics. Furthermore, the comprehensive analyses conducted from the light intensity dependent photocurrent and photovoltage measurements, the capacitance-voltage characteristics, and the alternating current impedance spectra suggest that the utilization of the ZnO (MW) ETLs can effectively suppress trap-assisted recombination as well as charge accumulation at the interface between P3HT: PC 61 BM layers and ZnO layers, which is responsible for the enhanced device performance.

Ligand-free rutile and anatase TiO2 nanocrystals have been synthesized through a hydrolytic sol–gel reaction. The morphology, crystal structure, elemental composition and band structure of the obtained nanocrystals are characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and UV-visible absorption spectroscopy. These two kinds of nanocrystals could serve as electron extraction layers for improving the performance in inverted polymer solar cells. Compared with the device fabricated by using amorphous TiO2 (6.11%) and rutile TiO2 (6.93%), the device based on anatase TiO2 shows a significant enhancement in power conversion efficiency (7.85%). Meanwhile, the ideal current–voltage model for a single heterojunction solar cell is applied to clarify the junction property of the cell. The model demonstrates that the device based on anatase TiO2 has effective electron extraction and hole-blocking properties.

Low dark current density plays a key role in determining the overall performance of organic photodetectors (OPDs). However, both the donor domains and acceptor domains in the bulk heterojunction, which has high exciton dissociation efficiency, are in contact with the two electrodes. Therefore, the undesirable charge injection from the electrodes to the active layer is hard to avoid, leading to a high dark current density in most OPDs. In this work, we fabricate the OPDs based on a conventional poly(3-hexylthiophene) (P3HT)/(phenyl-C61-butyric-acid-methyl-ester) (PC61BM) bulk heterojunction. By incorporating a water/alcohol soluble conjugated polymer (WSCP), poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN), interlayer between the anode and the active layer, the dark current density is effectively reduced from 0.07 mA cm−2 to 1.92 × 10−5 mA cm−2 under a −0.5 V bias. The resulting OPDs show a 1.93 × 105 signal-to-noise ratio (SNR), a 10 MHz bandwidth, and a 9.10 × 1012 Jones detectivity at a low reverse bias of −0.5 V (at 550 nm). Our research provides a promising way for high performance OPDs.

Hybrid organic–inorganic halide perovskite crystals exhibit potential applications in amplified spontaneous emission (ASE) devices. The enhancement of the photoluminescence (PL) and full width at half maximum (FWHM) with the temperature dependent phase transition are beneficial to investigate the low threshold of ASE devices. However, the ASE performance and temperature dependent transition characteristics of perovskite films critically depend on morphology and crystallinity. In this paper, we propose vacuum-assisted thermal treatment to effectively prepare smooth, condense and well-crystalline MAPbI3 perovskite films. An obvious temperature dependent phase transition occurs in the vacuum annealed MAPbI3 perovskite films, leading to an increase in PL intensity, which could non-monotonically lower the threshold for ASE. Investigating the transient performance at the temperature dependent phase transition underlines an important step in optimizing these novel materials.

Active ultraviolet light-induced terahertz modulation of an indium oxide film is investigated. A large absorption modulation of ~66% is achieved upon illumination with a low intensity UV laser (11 mW/cm2). The interaction between indium oxide and a flexible metamaterial structure is investigated owing to the large UV-induced enhancement of photo carriers observed in an indium oxide film. We are able to realize absorption peak shifts of 37 GHz by changing the UV excitation light intensity. We also propose a multi-frequency switch by building a circular metallic split ring resonator whose gaps are filled with silicon, germanium, and indium oxide. In future, a photo-excited tunable multi-frequency metamaterial switch can be realized by irradiating the structure with multi-wavelength laser beam.

In this work, the effects of solvent additives on the trapping and recombination of carriers in polymer solar cells based on the blend of poly(3-hexylthiophene) (P3HT) and indene-C60-bisadduct (ICBA) are investigated by measuring the ideality factor and transient photocurrent. The addition of a few percent of 4-bromoanisole (BrAni) and 1-chloronaphthalene (CN) can give rise to the preferable morphology with well-ordered interpenetrating networks, which is beneficial for charge transport. Efficiency enhancement of polymer solar cells with solvent additives originates from the decreased defects and suppressed trap-assisted recombination at the interface between the donor and acceptor materials.

In this work, the effects of photo-induced defects on polymer solar cells (PSCs) based on the blends of poly (4,8-bis-alkyloxybenzo (1,2-b:4,5-b′) dithiophene-2,6-diyl-alt-(alkyl thieno(3,4-b) thiophene-2-carboxylate)-2,6-diyl) (PBDTTT-C) and [6,6]-phenyl C70-butyric acid methyl ester (PC70BM) are investigated. In addition to conventional PSC characterization approaches, the capacitance–voltage (C–V) response and the ideality factor are used to analyze the changes in the built-in potential and defect-induced recombination at the internal donor/acceptor interface and the electrode interfaces in illuminated PSCs. The results show that the dominant trap states increase with increasing illumination time, which indicates that photo-induced defects play an important role in the photodegradation of inverted PSCs. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Organic–inorganic tri-halide perovskites (MAPbX3, where MA = CH3NH3, and X = Cl, Br, I) have shown promise as laser gain media. The laser characteristics of perovskite films are susceptible to their crystallinity and morphology. Herein, we demonstrate the morphology and crystallinity of perovskite films could be well-controlled in a modified sequential deposition process by using binary solvent mixtures involving N,N-dimethylmethanamide (DMF) and dimethylsulfoxide (DMSO). The highly crystalline and notably smooth MAPbI3 films on glass substrates yield outstanding amplified spontaneous emission (ASE) performance. The binary solvent engineering approach opens up new opportunities for the development of low-cost and high-efficient ASE devices based on perovskite materials.

We demonstrate the use of TiO2 nanorods with well-controlled lengths as excellent electron extraction materials for significantly improving the performance of inverted polymer solar cells. The cells containing long nanorods outperform the devices using amorphous TiO2 particles as the electron extraction layer, mainly by a 2-fold increase in short-circuit current and fill factor. The enhanced charge extraction is attributed to the high electron mobility in crystalline nanorods and their preferential alignment during film formation. Furthermore, transient photocurrent studies suggest the presence of fewer interfacial and internal defects in the nanorod interlayers, which can effectively decrease carrier recombination and suppress electron trapping.

The post-annealing effects on the performance of poly (3-hexylthiophene) (P3HT)/(6,6)-phenyl C61 butyric acid methyl ester (PCBM) solar cells with conventional bulk heterojunction (CBHJ) and layer-evolved bulk heterojunction (LBHJ) have been compared. It is found that contrary to the much better performance obtained from CBHJ cells, the post-annealing deteriorates the performance of LBHJ devices. Aqueous contact angle and X-ray photoelectron spectroscopy measurements show that P3HT is dominant at the top surface of CBHJ film, while PCBM is dominant at the top surface of LBHJ film. The micron-scale morphology evolution of the active layer/Al interface upon post-annealing reveals that the PCBM-rich surface is beneficial for the nucleation and growth of PCBM crystal, which does harm to the contact between the active layer and the electrode and results in the decrease of the fill factor. However, the original P3HT-rich surface prevents the formation of large surface-segregated PCBM clusters upon post-annealing, which is highly desirable for the efficient polymer/fullerene solar cells.

The effects of thermal treatment on the photovoltaic performance of conventional and inverted polymer solar cells (PSCs) based on the combination of poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b;4,5-b′]dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thie-no[3,4-b]thiophene))-2,6-diyl] (PBDTTT-C) and [6,6]-phenyl C70-butyric acid methyl ester (PC70BM) are investigated. The transient photoconductivity, the absorption spectra, and the transmission electron microscopy (TEM) images have been employed to study the thermal degradation of the inverted PSCs. The degradation is attributed to the inefficient charge generation and imbalance in charge-carrier transport, which is closely associated with the morphological evolution of the active layer with prolonged heating time.

With Ar plasma treatment of the indium tin oxide (ITO) cathode, we achieve efficient inverted bulk heterojunction solar cells based on poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester, which do not require electron selective layer. The plasma treatment improves the power conversion efficiency of the device from 1.07% to 3.57% with a fill factor of 66%, open-circuit voltage of 0.60 V, and short-circuit current of 9.03 mA cm−2. This result is comparable to the regular inverted devices with an additional electron selective layer. The Kelvin probe detects a reduction in the ITO work function of ∼0.45 eV after plasma treatment, which finally leads to an increase in the built-in potential and faster carrier extraction. As a result, good device performance is achieved. Because the electron selective layer becomes unnecessary, our strategy suggests a simple way to achieve efficient inverted organic solar cells.

An active all-optical high-efficiency broadband terahertz device based on an organometal halide perovskite (CH 3 NH 3 PM 3 , MAPbI 3 )/inorganic (Si) structure is investigated. Spectrally broadband modulation of the THz transmission is obtained in the frequency range from 0.2 to 2.6 THz, and a modulation depth of nearly 100% can be achieved with a low-level photoexcitation power (∼0.4 W/cm2). Both THz transmission and reflection were suppressed in the MAPbI 3 /Si structure by an external continuous-wave (CW) laser. Enhancement of the charge carrier density at the MAPbI 3 /Si interface is crucial for photo-induced absorption. The results show that the proposed high-efficiency broadband optically-controlled terahertz device based on the MAPbI 3 /Si structure has been realized.

We investigate terahertz (THz) read-only multi-order nonvolatile rewritable photo-memory based on indium oxide (In2O3) nanoparticles. Optical excitation of an In2O3/quartz sample increases its conductivity, which attenuates its THz transmission. When the optical excitation is terminated, the modulated THz transmission can recover back to its original value in air. However, the THz transmission shows no obvious change over a long-term when In2O3/quartz is encapsulated in an inert gas (nitrogen). Multi-order nonvolatile digital information storage is obtained at different light intensities, and the photo-memory can be rewritten after thermal annealing. Different THz transmissions are used as coded signal units, which are programmed to store information. These results show that THz read-only multi-level nonvolatile rewritable photo-memory can be realized.

Although the performance of hybrid organic-inorganic perovskite solar cells (PSCs) is encouraging, the detailed working principles and mechanisms of PSCs remain to be further studied. In this work, an overshoot phenomenon of open-circuit voltage (Voc) was observed when the illumination light pulse was switched off. The evolution of the Voc overshoot was systematically investigated along with the intensity and the width of the light pulse, the background illumination, and pretreatment by different bias. Based on the experimental results, we could conclude that the Voc overshoot originated from carrier motion against carrier collection direction, which happened at the ionic-accumulation-induced band bending areas near the interfaces between the perovskite active layer and the two carrier transport layers. The investigation on the Voc overshoot can help us to better understand ionic migration, carrier accumulation, and recombination of PSCs under open-circuit conditions.

We investigate a high-efficiency broadband terahertz wave modulator with structures made from the conjugated polymer [2-methoxy-5-(2′-ethylhexyloxy)-1, 4-phenylennevinylene], graphene, and Si, irradiated with an external excitation laser. We demonstrate a strategy that can alleviate the tradeoff between the requirements of modulation depth and modulation speed in polymer/silicon terahertz wave modulators. Using terahertz time-domain and continuous-wave systems, we measured both the terahertz transmission modulation properties and the time responses of the modulator structures. The conjugated polymer/graphene/silicon structure achieved a high modulation factor of 93% for transmission as well as improved the modulation speed of the devices based on polymer/silicon. The high modulation efficiency of the polymer/graphene/silicon structure was induced by the enhancement in carrier density and the extremely high carrier mobility of graphene, respectively.

The sodium chloride methanol solution process is conducted on the conventional poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) polymer bulk heterojunction solar cells. The device exhibits a power conversion efficiency of up to 3.36%, 18% higher than that of the device without the solution process. The measurements of the active layer by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and ultraviolet photoelectron spectroscopy (UPS) indicate a slight phase separation in the vertical direction and a sodium chloride distributed island-like interface between the active layer and the cathode. The capacitance–voltage (C–V) and impedance spectroscopy measurements prove that the sodium chloride methanol process can reduce the electron injection barrier and improve the interfacial contact of polymer solar cells. Therefore, this one-step solution process not only optimizes the phase separation in the active layers but also forms a cathode buffer layer, which can enhance the generation, transport, and collection of photogenerated charge carriers in the device simultaneously. This work indicates that the inexpensive and non-toxic sodium chloride methanol solution process is an efficient one-step method for the low cost manufacturing of polymer solar cells.

An active all-optical high-efficiency broadband terahertz device based on an organometal halide perovskite (CH3NH3PbI3, MAPbI3)/inorganic (Si) structure is investigated. Spectrally broadband modulation of the THz transmission is obtained in the frequency range from 0.2 to 2.6 THz, and a modulation depth of nearly 100% can be achieved with a low-level photoexcitation power (∼0.4 W/cm2). Both THz transmission and reflection were suppressed in the MAPbI3/Si structure by an external continuous-wave (CW) laser. Enhancement of the charge carrier density at the MAPbI3/Si interface is crucial for photo-induced absorption. The results show that the proposed high-efficiency broadband optically controlled terahertz device based on the MAPbI3/Si structure has been realized.

Er3+ and Yb3+ co-doped Y2O3 nanoparticles have been prepared by using a coprecipitation method followed by a post-thermal-treatment, in which a surfactant (cetyltrimethylammonium bromide, CTAB) plays an important role in the size-controlling and upconversion luminescence tuning. The green (2H11/2, 4S3/2 → 4I15/2) and red emission (4F9/2 → 4I15/2) intensity can be effectively tuned by varying the surfactant concentration, which can induce the defects in the as-obtained products. The probability of quenching and nonradiative relaxation from 4F7/2, 2H11/2, and 4S3/2 to 4F9/2 could be increased as the number of defects introduced by the surfactant increases, and thus the ratio of red to green emission is also changed. The upconversion mechanism has been analyzed and discussed, which may be a new complement for upconversion luminescence.

An electrically bistable device has been fabricated based on poly(N-vinylcarbazole) (PVK)-silver sulfide (Ag2S) composite films using a simple spin-coating method. Current–voltage (I-V) characteristics of the as-fabricated devices exhibit a typical electrical bistability and negative differential resistance (NDR) effect. The NDR effect can be tuned by varying the positive charging voltage and the charging time. The maximum current ratio between the high-conducting state (ON state) and low-conducting state (OFF state) can reach up to 104. The carrier transport mechanisms in the OFF and ON states are described by using different models on the basis of the experimental result.