•Flower-like Co3O4 have been fabricated by a solvothermal method.•The flower-like structure was composed of single-crystalline porous nanosheets.•The flower-like Co3O4 showed a high response to xylene at 175 °C.•The gas sensors of the nanostructure showed low optimum working temperature.Co3O4 with hierarchical nanostructure was prepared by a low-cost and environmentally friendly one-step solvothermal method. In the process of material synthesis, ethanolamine (EA) was used to assemble nanosheets in a way to have flower-like hierarchical morphology. The crystallinity and valence state of the prepared materials were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) was also used to demonstrate the extraordinary 3D nanostructures characteristic of the materials. The gas sensing properties of the as-prepared pure Co3O4 and Fe-doped Co3O4 were tested toward various gases. The results showed that the sensor based on 6.0 at% Fe-doped Co3O4 exhibited the optimum performance, with the highest response of 18.2–100 ppm xylene, a fast response time (40 s) and recovery time (35 s) at a low optimum operating temperature of 175 °C. It's worthy to mention that for a Co3O4-based material, the optimum operating temperature of the nanomaterials prepared in our study is much lower than those reported in previous literature.

•SnO2 dodecahedrons were successfully synthesized by one-step solvothermal method.•The high-energy facets of dodecahedron were observed through the characters.•The response to SO2 can reach 1.92–10 ppm, and the limit detection can reach 400 ppb.Dodecahedron-like SnO2 nanomaterial was synthesized via a solvothermal method under mild reaction condition. The morphological and structural characterization results indicated that the as-prepare dodecahedral SnO2 nanocrystallines with the average length of 130 nm and width of 45 nm were partially surrounded by high surface-energy {221} facets. The gas-sensing performance of the sample was investigated and the experiment results showed that the sensor had a good sensitivity to sulfur dioxide (SO2) at 183 °C. To 800 ppb SO2, the response could reach 1.32 and the response time was about 10 s. The good SO2-sensing performance of SnO2 nanocrystallines was closely related to the high surface-energy {221} facets whose surface possessed more dangling bonds and the corresponding SO2-sensing mechanism was discussed.

Tetrafluoro-tetracyanoquinodimethane (F4-TCNQ), a strong molecular acceptor, has been proved to be an excellent candidate to achieve the p-type doping effect. When F4-TCNQ is incorporated into a poly(3-hexylthiophene) (P3HT): indene-C60 bisadduct (ICBA) active layer, superior behavior upon inducing polymer donor excited electron transport is demonstrated due to the addition of a deep-lying lowest unoccupied molecular orbital (LUMO) from F4-TCNQ, leading to the realization of organic solar cells (OSCs) with an improved power conversion efficiency (PCE) of 5.83%, accounting for 29.6% enhancement. In the system of active layer, the low LUMO of F4-TCNQ can easily accept electrons, remarkably reducing electron/hole recombination, which contributes to the enhancement of the photoconductivity and charge carrier mobility, resulting in higher short-circuit current density (Jsc), and achieving a more balanced charge carrier transport, as well as an ideal fill factor (FF).

A heterojunction photo-conductive ultraviolet (UV) detector was developed based on TiO2 nanowires array (NWA) surrounded by N,N′-bis-(1-naphthalenyl)-N,N′-bis-phenyl-(1,1′-biphenyl)-4,4′-diamine (NPB). The novel and effective two-step method of static infusion and dynamic solution-cleaning was employed to fill NPB into TiO2 NWA gaps and simultaneously remove the unwelcomed top NPB layer. The device fabricated via the two-step method exhibited optimal performance compared to TiO2/NPB device with top NPB layer and TiO2 NWA device. In dark conditions, the TiO2/NPB heterojunction device without top NPB was found to possess the capacity of depleting majority carriers, thereby providing improved dark-resistivity to limit the dark current (Id). Under UV illumination, the depleting effect could be eliminated by the dissociation and accumulation of photo-generated carriers between pn heterojunction, leading to increased carrier density and photo-conductivity. It cleared up the high barrier due to the removal of top NPB layer, which was beneficial for hot electron transport than the device with top NPB layer under illumination, thereby achieving an enhanced light current (Il) to Id ratio of 1.67 × 104. A simple technology is provided to prepare organic–inorganic hybrid one-dimensional array heterostructure, which plays a remarkable role in the working of the UV detector, enhancing photo-conductivity and dark-resistivity of the device.

In this work, Au was employed as an ideal dopant to obtain enhanced sensing performance of xylene gas sensor. Firstly, the as-perpared Au-doped WO3·H2O powder was synthesized by a facile and efficient hydrothermal method. Then various techniques including X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectrometer (EDX) were employed to investigate the morphology, microstructure, crystalline nature and chemical compositions of the as-prepared Au-doped WO3·H2O nanomaterials. The morphologies of the nanomaterials could be easily controlled by changing the atomic percentage (at%) of Au (0.15 at%, 0.30 at%, 0.45 at%) in the precursor solutions. And it have been attested that the 0.30 at% Au-doped WO3·H2O-based sensor realized higher gas response of 26.4–5 ppm xylene at 255 °C, faster response/recovery speed and stronger selectivity to target gas compared with the unloaded one. Furthermore, the detection limit could be as low as 200 ppb level. Hence, Au-loaded WO3·H2O nanomaterial could be a promising material applied in xylene gas sensor.Also, the mechanism involved in the improving xylene sensing properties of Au/WO3·H2O was discussed.

•Ni-doped α-MoO3 nanolamella with different Ni concentrations was synthesized.•Influence on formaldehyde sensing properties caused by Ni doping was studied.•Ni-doped α-MoO3 highly improved formaldehyde sensing properties.In this work, α-MoO3 and Ni-doped α-MoO3 were synthesized through a facile solvothermal method and various techniques were employed to study the phase and morphological properties. The gas sensing measurements showed that 5 mol% Ni-doped α-MoO3 had superior formaldehyde sensing capability compared with pure α-MoO3. The maximum response value approached 41–100 ppm formaldehyde at 255 °C, which was about 4.1 times bigger than that of pure α-MoO3. In addition, the 5 mol% Ni-doped α-MoO3 gas sensor was also found to have lower detection limit and better selectivity to formaldehyde. The mechanism involved in gas sensing performance of Ni-doped α-MoO3 was also discussed.

The reproducible silylation of titanium oxide (TiO2) with small molecular (dichloromethyl) dimethylchlorosilane (DCS) as the cathode buffer layer was developed to improve electron extraction. Through incorporating the DCS capping layer into polymer solar cells (PSCs), the interfacial coherence of devices could be enhanced, leading to a shift in nanocrystallite size and a smaller internal charge transport resistance. Furthermore, a TiO2/DCS combined interfacial layer could serve as both an exciton dissociation center and a charge transfer channel, which results in a reduction in the energy barrier and electron loss, improving hole-blocking and surface-state passivation in the TiO2 interfacial layer. The Kelvin probe measurements demonstrate that the employment of the DCS nanolayer decreases conduction band energy of TiO2via forming a dipole layer at the interface of TiO2 and the DCS nanolayer, which tunes the work-function of the device and ulteriorly enhances charge carrier transfer between the electrode and the active layer. As a result, the photocurrent and the fill factor of the PSCs are both increased, resulting in an increased power conversion efficiency (PCE) of 6.959%.

Pompon-like Co3O4 and Cr-doped Co3O4 hierarchical nanostructures were synthesized via a hydrothermal reaction, and a series of different proportions of Cr were doped to investigate the effect of Cr-doping on the gas sensing performance. All the prepared materials were used to fabricate gas sensors, and the result of the gas sensing measurements indicated that the optimum proportion of Cr/Co was 5 at%, whose response (6.38) to xylene (5 ppm) was higher than the others. Further, with increasing Cr ratio, the response to xylene (5 ppm) tended to decline after ascending, with 5 at% (Cr/Co) as the cut-off point, but all sensors made from Cr-doped Co3O4 hierarchical nanostructures showed a higher response to xylene than the pure Co3O4 hierarchical nanostructures, which improved the selectivity of sensors. In addition, it is worth mentioning that all the sensors’ optimum working temperatures were low, requiring a smaller heating current and low power consumption.

Au nanoparticle-functionalized composites have been proven to be promising materials for gas sensing applications. We successfully synthesized tungsten oxide (WO3·H2O) nanosheets by a facile and effective hydrothermal process and decorated Au nanoparticles on their surface for ultra-high sensitivity levels to toluene gas. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), Energy Dispersive X-ray Spectrometer (EDX), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Gas-sensing measurements revealed superior toluene sensing properties of Au nanoparticle-functionalized WO3·H2O nanosheets (Au-WO3·H2O) compared with bare WO3·H2O. The maximum response value of Au-WO3 reached 50–100 ppm toluene at 300 °C, which was nearly four times as high as that of bare WO3. Meanwhile, Au-WO3·H2O exhibited the shorter response/recovery time, better selectivity and lower operating temperature to toluene gas than those of bare WO3·H2O. Also, the mechanism involved in improving the toluene sensing properties of WO3·H2O by Au nanoparticle-functionalization was discussed.

Cu@SnO2 spherical nanoreactor with hierarchical structure was prepared through a simple solvothermal method, the structure and morphology were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) showing the materials with extraordinary 3D nanoarchitectures. The gas sensing properties of the as-prepared pure SnO2 and Cu-doped SnO2 were tested toward various gases. The results showed that Cu-doped SnO2 sensor displayed an excellent selectivity toward formaldehyde at the operating temperature 230 °C, which was much lower than most formaldehyde sensor in heater type among previous reports. The τrec and the τrec values of the Cu-doped SnO2 to 1000 ppm formaldehyde were 2 s and 2 s, respectively, demonstrating extraordinary gas sensing properties, while those of the pure SnO2 sensor were relatively long. The enhancement might be attributed to increased oxygen vacancy due to formation of active centers around doped elements and broad surface of unique mesoporous structure.

A remarkable performance ultraviolet (UV) photodetector was demonstrated by introducing a poly(9,9-dihexylfluorene) (PDHF) interlayer with the roles of barrier-blocking electron transport and light-inducing hole injection, leading to enhanced properties of the device both in dark and under UV illumination. The PDHF interlayer can efficiently block the electrons, which provides low dark current as well as the reduced noise for devices. Furthermore, the accumulation of photogenerated electrons causes the energy-band bending, leading to promoted gain of holes under UV illumination. The specific detectivity of the device with the PDHF interlayer reaches 1.86 × 1013 cm Hz1/2 W–1. Moreover, the response and recovery speed have been upgraded due to the improvement of the carrier transport mechanism.

In this article, the heterostructure of ZnO particles on single-crystal CdS nanowires (ZnO@CdS) has been successfully synthesized via a facile two-step solvothermal process. The appealing application of the ZnO@CdS heterostructure as visible-light photodetector (PD) is presented. Photocurrent illuminated with light (shorter than 510 nm) to dark-current ratio of structurally-optimized ZnO@CdS nanomaterials based photon detector was enhanced significantly compared to the value of the pristine CdS nanowires based one. The corresponding mechanism for the phenomenon was discussed. Additionally, measurements of time resolved responses were conducted. The ZnO@CdS heterostructure based device kept a fast rise (5 ms) and decay (10 ms) speed to irradiation. This work demonstrates a promising application of ZnO@CdS heterostructure based visible-light detectors with high photocurrent/dark-current ratio, ultrafast time response and very good stability.

Metal sulfide Zn1–xCdxS nanowires (NWs) covering the entire compositional range prepared by one step solvothermal method were used to fabricate gas sensors. This is the first time for ternary metal sulfide nanostructures to be used in the field of gas sensing. Surprisingly, the sensors based on Zn1–xCdxS nanowires were found to exhibit enhanced response to ethanol compared to those of binary CdS and ZnS NWs. Especially for the sensor based on the Zn1–xCdxS (x = 0.4) NWs, a large sensor response (s = 12.8) and a quick rise time (2 s) and recovery time (1 s) were observed at 206 °C toward 20 ppm ethanol, showing preferred selectivity. A dynamic equilibrium mechanism of oxygen molecules absorption process and carrier intensity change in the NWs was used to explain the higher response of Zn1–xCdxS. The reason for the much quicker response and recovery speed of the Zn1–xCdxS NWs than those of the binary ZnS NWs was also discussed. These results demonstrated that the growth of metal sulfide Zn1–xCdxS nanostructures can be utilized to develop gas sensors with high performance.Keywords: gas sensing; high response; metal sulfide; quick rise and recovery time; solvothermal; Zn1−xCdxS

We demonstrate a novel solution-processed method to fabricate a stable anode buffer layer without any annealing process. As we know, buffer layers in polymer solar cells (PSCs) are always prepared by the traditional high-vacuum thermal evaporation or annealing-treated spin-coating methods, but the fabricating processes are complicated and time-consuming. Here, a solution method without any annealing to fabricate phosphomolybdic acid (PMA) as anode buffers is presented, which brings an obvious improvement of power conversion efficiency (PCE) from 1.75% to 6.57% by optimizing the PMA concentrations and interface pretreatment with device structure shown as ITO/TiO2/PCDTBT:PC70BM/PMA/Ag. The improvement is ascribed to the fine energy-level matching and perfect surface modification. This annealing-free method greatly simplifies the device fabrication process and supplies a wide way to achieve a large area fabrication for PSCs.Keywords: isopropyl alcohol; PCDTBT; phosphomolybdic acid; polymer solar cell

Hexagonal ZnO nanorings were synthesized using a one-step hydrothermal method and Au nanoparticles were decorated on the surface of the ZnO nanorings through a facile deposition process. The as-prepared ZnO nanorings showed a well-defined hexagonal shape with a width of 0.75–1.4 μm, a thickness of 0.17–0.33 μm and a hollow size of 0.2–1 μm. For the Au nanoparticle-decorated hexagonal ZnO nanorings (Au–ZnO nanorings), Au nanoparticles with a size of 3–10 nm were distributed discretely on the surface of the ZnO nanorings. The acetylene sensing performance was tested for the ZnO nanorings and Au–ZnO nanorings. The results indicated that the Au–ZnO nanorings showed a higher response (28 to 100 ppm acetylene), lower operating temperature (255 °C), faster response/recovery speed (less than 9 s and 5 s, respectively), and lower minimum detectable acetylene concentration (about 1 ppm). In addition, the mechanism for the enhanced acetylene-sensing performance of the Au–ZnO nanorings was discussed.

MoO3-NiO composites were prepared by a simple one-step electrospinning method and were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and nitrogen adsorption-desorption test. Humidity sensing properties of MoO3-NiO composites with different mass ratios were studied, the best result was obtained for the sample with MoO3-NiO mass ratio of 0.5 (S1) under the same preparation condition. The impedance of the sensor changed more than three orders of magnitude when relative humidity ranged from 11% to 95%. The response and recovery time were about 2 s and 10 s respectively with maximum hysteresis of <2%RH (relative humidity). The above findings suggest potential applications of the MoO3-NiO composite (S1) in high performance humidity sensors.

TiO2 nanowires array is synthesized on the FTO via hydrothermal method, which is modified with ZnO prepared by using the crystallization method. The fabricated ultraviolet detector based on TiO2/ZnO heterojunction possesses high photoelectric performance evaluated by the photo-to-dark current ratio, which has been demonstrated to reach 4 orders of magnitude. The separation of electron–hole pairs is facilitated by the built-in electric field in heterojunction, resulting in a large photocurrent as well as a high responsivity, which can attain 150 A/W. Compared with the pure TiO2 device, The red shift in both absorption spectrum and photo response provides a potential application for the TiO2/ZnO device.

Tungsten trioxides (WO3) are an important class of n-type semiconductor oxide materials with a wide band-gap. In this work, nanolamella of tungsten oxides have been successfully synthesized by a simple, facile and cost-effective route starting from Na2WO4 and subsequent calcination at 300 °C. The structure and morphology of the nanolamella were characterized by X-ray diffraction (XRD) scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and photoluminescence (PL), respectively. The morphologies of the prepared products can be tailored by changing the calcination temperature. The obtained WO3 products were investigated as sensitive materials for the detection of xylene. On the basis of gas sensing tests, the sensor using WO3 nanolamella after annealing at 300 °C for 2 h exhibited better gas sensing properties. The maximum response reached 47 to 100 ppm of xylene at 280 °C. These results indicated that the gas sensors based on WO3 nanolamella express high and fast response and recovery characteristics to xylene, and the WO3 nanolamella are promising sensitive materials for xylene detecting.

The performance of a Schottky metal–semiconductor–metal (MSM) ultraviolet (UV) photodetector is limited by the insufficient gain and the uncontrollable noise current. A remarkable detectivity UV detector is demonstrated based on graphene oxide (GO) modified TiO2 with high gain and low noise. The GO layer completely prevents the flow of electrons forming a hole-only device thus decreasing the dark current and noise current. Furthermore, gain of the holes is promoted under UV illumination. Moreover, the GO layer efficiently extracts the holes therefore reducing the fall time. Under a bias of 6 V, the responsivity value reaches 826.8 A W−1 and the noise current is only 1.8 pA, thereby, our device provides a detectivity of 2.82 × 1013 cm Hz1/2 W−1 at 280 nm. The results offer an effective approach to enhance the performance of a UV detector.

A one-step hydrothermal method assisted by polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA) was developed to synthesize hexagonal ZnO nanorings. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were used to characterize the as as-prepared ZnO nanorings and deduce the possible formation mechanism. The as-prepared ZnO nanorings showed the well-defined hexagonal shape with a width of 0.75–1.4 μm, a thickness of 0.17–0.33 μm and a hollow size of 0.2–1 μm. The trimethylamine (TMA) sensing performance of the hexagonal ZnO nanorings was tested. The results indicated that the hexagonal ZnO nanorings showed a high response (47 to 100 ppm TMA), fast response/recovery rate (less than 23 s and 37 s, respectively), wide linearity in a relatively wide range (1–200 ppm TMA), low detectable TMA minimum concentration (less than 5 ppm) and good selectivity to TMA. In addition, the TMA-sensing mechanism of the hexagonal ZnO nanorings was also discussed.

Cr2O3@WO3 and WO3 hierarchical nanostructures are prepared using a two-step water bath method, which just needs mild conditions and takes little time. The response to xylene of the Cr2O3@WO3-based sensor is much higher (about 4 times) than that of a WO3-based sensor, and both of the response and recovery processes are quick. As for the selectivity, the Cr2O3@WO3-based sensor shows a better response to xylene, while the WO3-based sensor shows a better response to ethanol. The reason for the response and selectivity change is considered to be that a heterostructure is formed between Cr2O3 (a P-type semiconductor) and WO3 (an N-type semiconductor). Moreover, Cr2O3 is reported to show catalytic oxidation of methyl groups.

A new type of acetylene gas sensor based on the hollow NiO/SnO2 heterostructure synthesized by a two-step hydrothermal method followed by calcination was fabricated. The properties of the sensing material were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer–Emmett–Teller (BET) and transmission electron microscopy (TEM). The acetylene gas-sensing performances were investigated. Compared with the pure SnO2 gas sensor, the response of the hollow NiO/SnO2 heterostructure gas sensor to 100 ppm acetylene (C2H2) was raised to 13.8 from 5.4 at the optimum operating temperature of 206 °C. A wide detection range from 1 to 1000 ppm and a low minimum detection limit of 1 ppm were obtained. In addition, the hollow NiO/SnO2 heterostructure gas sensor had a good repeatability, selectivity, stability and rapid response–recovery characteristics.

Neutral color semi-transparent polymer solar cells (STPSCs) have attracted a lot of attention due to their unique application in building integrated photovoltaic (BIPV) in recent years. Herein, we report a type of low band gap STPSCs with high color rendering index (CRI), which can be modulated by one-dimensional photonic crystals (1DPCs). To flatten transmitted light and eliminate chromatic aberration, the 1DPCs were integrated on top of the STPSCs as a wavelength-dependent filter. We have designed the centre wavelength of 1DPC at 520 nm to level the concavo-convex transmittance spectrum induced by the absorption of PSBTBT:PC60BM. By turning the pairs of 1DPCs, the optimal STPSCs with 3 pairs of 1DPC achieved an increased CRI from 77 to 91 under an AM 1.5G illumination light source, a suppressed chromaticity difference (DC) from 0.0308 to 0.0045 and a enhanced power conversion efficiency (PCE) from 3.43% to 4.01% compared to devices without 1DPC. Furthermore, we believe that this new method for STPSCs incorporating 1DPCs filters to balance the total transmittance spectrum and enhance the CRI will play a important role in future BIPV applications.

Zn@SnO2 microspheres with hierarchical structure were prepared through a simple solvothermal method; the structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM) showing the materials with extraordinary 3D nanoarchitectures. The gas sensing properties of the as-prepared pure SnO2 and Zn-doped SnO2 were tested toward various gases. The results showed that the SnO2 sensor with 6.67 wt% Zn-doping displayed an excellent selectivity toward formaldehyde at the operating temperature 160 °C, which was considerably lower than most formaldehyde sensors in heater type among previous reports, in addition to giving a response of about 15.2 to 100 ppm, which is about 2.1 times higher than that of sensors based on pure SnO2. The τres and the τrec values of the 6.67 wt% Zn-doped SnO2 sensor to 100 ppm formaldehyde were 2 s and 2 s respectively, demonstrating extraordinary gas sensing properties, whereas those of the pure SnO2 sensor were relatively long. The enhancement might be attributed to the unique morphology and increased oxygen vacancy due to the Zn doping.

In this work, novel bowl-like TiO2 submicron scale particles were prepared via a simple electrospray technique combined with high-temperature calcination. The morphologies of the particles are easily controlled by changing the TBT content (16 wt%, 23 wt%, 30 wt%, 37 wt%) in the precursor solutions. To improve the xylene sensing properties of the TiO2, appropriate Ni amounts (0, 2, 4, and 6 mol% doping) were doped into the bowl-like particles. Among them, the 2 mol% Ni doped TiO2 bowl-like particles show the lowest optimum working temperature and highest response while demonstrating a fast response (9 s) and recovery speed (1.2 s) to 100 ppm xylene gas.

SrTiO3 nanospheres were synthesized by a hydrothermal method and characterized by X-ray diffraction and scanning electron microscopy. Then, the material was coated on an Al2O3 ceramic substrate to fabricate humidity sensors using Ag–Pd interdigitated electrodes. The sensor shows high humidity sensitivity and fast response and recovery. The impedance changes by four orders of magnitude over a relative humidity (RH) range from 11% to 95%. At the frequency of 100 Hz, response and recovery times are both 2 s, and the maximum hysteresis is <1% RH. In addition, the complex impedance at different RH was investigated to understand the sensing mechanism. The results indicate potential applications of SrTiO3 for fabricating high-performance humidity sensors.

A unique Au@In2O3 core–shell nanostructure was firstly prepared through a simple sol–gel method, the structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). The results showed that unique architectures were core–shell nanostructure assembled from an Au core and an In2O3 shell. The gas sensing properties of the as-prepared pure In2O3 and Au@In2O3 core–shell samples were tested toward various gases. The sensor based on a Au@In2O3 core–shell nanostructure showed excellent selectivity toward ethanol at the operating temperature of 160 °C, giving a response of about 36.14 to 100 ppm, which was about 1.5 times higher than that of the sensor based on pure In2O3. The τres and the τrec values of the Au@In2O3 sensor to 100 ppm ethanol were 4 s and 2 s respectively, while those of the pure In2O3 sensor were relatively long. The enhancement might be attributed to the unique core–shell structure and existence of a Schottky junction between Au/In2O3.

In/Pd co-doped SnO2, Pd-doped SnO2, In-doped SnO2 and pure SnO2 microspheres with a diameter of 500–600 nm were prepared by the one-pot hydrothermal method. Their structures and morphological characteristics were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). Their formaldehyde (HCHO) sensing properties were investigated in detail. Compared with the In-doped SnO2, Pd-doped SnO2 and pure SnO2 microspheres sensors, the In/Pd–SnO2 microspheres sensor exhibited excellent gas-sensing properties to HCHO gas and the operating temperature was relatively low. At the optimal operating temperature of 160 °C, the response of the sensor based on In/Pd–SnO2 microspheres to 100 ppm HCHO was 24.6 and the detectable HCHO minimum was effectively reduced to 5 ppm. In addition, due to In and Pd co-doping, the response and recovery time of the sensors to 100 ppm HCHO gas were diminished to 3 s and 6 s, respectively.

Efficient semitransparent polymer solar cells (ST-PSCs) have been fabricated with one-dimensional photonic crystals (1DPCs) as a high reflector. The 1DPCs are composed of several pairs of WO3 (65.8 nm)/LiF (95.5 nm). By optimizing the pairs of WO3/LiF, 1DPCs can reflect the light back into the ST-PSCs due to the photonic band gap, when the high reflectance range of 1DPCs is matched with absorption spectrum of the active layer. ST-PSCs with 8 pairs of 1DPC exhibit an attractive performance. The short-circuit current density (Jsc) and power conversion efficiency (PCE), respectively, reach to 9.76 mA/cm2 and 5.16% compared to 8.12 mA/cm2 and 4.24% of the reference ST-PSCs without 1DPCs. A maximum enhancement of 20.2% in Jsc is obtained and the PCE increases by ∼21.7%. This approach provides a simple, fascinating and promising method to realize the highly efficient ST-PSCs toward applications.Keywords: distributed Bragg reflector; low-bandgap polymer solar cells; one-dimensional photonic crystals; reflectance; semitransparent; transmittance;

In this letter, a metal–semiconductor–metal ultraviolet photodetector based on NH4+ modified TiO2 film was fabricated. The barrier height between TiO2 and Au electrode was lowered due to the self-assembled NH4+ on TiO2 surface, leading to a significant improvement in the device performance. At 5 V bias, a photocurrent of 84.93 μA and a responsivity of 361.07 A/W were obtained under the irradiation of 300 nm UV light. The dark current was merely 88.8 pA, two orders of magnitude lower than that of the TiO2 device (2.85 nA). The rise time was sharply shortened from 2.735 s to 366.9 ms. The ratio of photocurrent to dark current was nearly 6 orders of magnitude.

Cu2O–Co3O4 core–shell composites were prepared via a hydrothermal method. The influences of the molar ratio of Cu/Co and reaction time on the morphology of Cu2O–Co3O4 core–shell composites were studied in detail. A possible mechanism was proposed on the basis of a series of experiments. Furthermore, these core–shell composites were integrated into a sensorial structure, which exhibited excellent ethanol sensing properties. These properties make the Cu2O–Co3O4 core–shell composites good candidates for ethanol detection.

•WO3 (40 nm)/Au (10 nm)/WO3 (20 nm) have fine optical and electric performance.•A high efficiency of 4.55% is obtained for ITO-free device.•Microcavity effect is investigated with 70 nm and 130 nm active layers.Indium tin oxide (ITO)-free polymer solar cells (PSCs) with the structure of Glass/tungsten trioxide (WO3)/Au/WO3/PCDTBT: PC70BM/LiF/Al was fabricated and studied. The multilayer structure of WO3/Au/WO3 is used as the potential transparent electrode to replace ITO. Metal resonant microcavity, which can enhance light harvesting of active layers, was constructed between Au and Al electrodes. According to the J–V and IPCE characterization with 70 nm active layer, power conversion efficiency (PCE) of the ITO-free microcavity device is approaching 4.55%, which is higher than that of the ITO-based device. However, PCE of the ITO-free device is much lower than that of the ITO-based device when the thickness of active layer increases to 130 nm. The opposite experimental tendency leads to theoretical research toward the simulation of light absorption and optical electric field and the calculation of maximum short circuit current density (Jsc max) as a function of active layer thickness based on ITO-free and ITO-based devices. The research results show that microcavity effect is closely linked to intrinsic absorption of active layers.Graphical abstract

•1D DBR overcomes the contradiction between efficiency and transparency.•A maximum efficiency of 4.12% with an enhancement of 24.1% is obtained.•The average transmittance is 55.6% in 600–800 nm based on 1D DBR.We demonstrate that one-dimensional photonic crystals as distributed Bragg reflectors can effectively improve the performance of semitransparent polymer solar cells (PSCs) based on the blend of P3HT:ICBA. The one dimensional distributed Bragg reflectors (1D DBRs) are composed of N pairs of WO3/LiF which are thermally evaporated on Ag anode. Due to its photonic bandgap, 1D DBRs can reflect the light totally back into the PSCs when the high reflectance range of 1D DBRs is well matched with absorption spectrum of the active layer. A maximum power conversion efficiency (PCE) of 4.12%, a highest transmittance of 80.4% at 660 nm and an average transmittance of 55.6% in the wavelength range of 600–800 nm are obtained in the case of N = 8, corresponding enhancement of 24.1% in PCE when compared with the device without the 1D DBRs.Graphical abstract

•Fe3O4-NiO core-shell composites were synthesized via a facile hydrothermal method.•The synthesis was conducted in water-ethanol-butanol solvent without any templates.•Sensor based on Fe3O4-NiO composites exhibits excellent toluene sensing performances.Fe3O4–NiO core–shell composites were prepared via a simple one-step hydrothermal method. The synthesis was conducted in water–ethanol–butanol mixed solvent without any templates. The structure and morphology of the composites were characterized by X-Ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). The results showed that these porous architectures were assembled from Fe3O4 sphere core and NiO flower-like shells. To demonstrate the use of the composites, a chemical gas sensor has been fabricated and investigated for toluene detection. The sensor exhibits excellent toluene sensing performances in terms of high response, superior selectivity, and rapid response-recovery.

Tetrafluoro-tetracyanoquinodimethane (F4-TCNQ), a strong molecular acceptor, has been proved to be an excellent candidate to achieve the p-type doping effect. When F4-TCNQ is incorporated into a poly(3-hexylthiophene) (P3HT): indene-C60 bisadduct (ICBA) active layer, superior behavior upon inducing polymer donor excited electron transport is demonstrated due to the addition of a deep-lying lowest unoccupied molecular orbital (LUMO) from F4-TCNQ, leading to the realization of organic solar cells (OSCs) with an improved power conversion efficiency (PCE) of 5.83%, accounting for 29.6% enhancement. In the system of active layer, the low LUMO of F4-TCNQ can easily accept electrons, remarkably reducing electron/hole recombination, which contributes to the enhancement of the photoconductivity and charge carrier mobility, resulting in higher short-circuit current density (Jsc), and achieving a more balanced charge carrier transport, as well as an ideal fill factor (FF).

The reproducible silylation of titanium oxide (TiO2) with small molecular (dichloromethyl) dimethylchlorosilane (DCS) as the cathode buffer layer was developed to improve electron extraction. Through incorporating the DCS capping layer into polymer solar cells (PSCs), the interfacial coherence of devices could be enhanced, leading to a shift in nanocrystallite size and a smaller internal charge transport resistance. Furthermore, a TiO2/DCS combined interfacial layer could serve as both an exciton dissociation center and a charge transfer channel, which results in a reduction in the energy barrier and electron loss, improving hole-blocking and surface-state passivation in the TiO2 interfacial layer. The Kelvin probe measurements demonstrate that the employment of the DCS nanolayer decreases conduction band energy of TiO2via forming a dipole layer at the interface of TiO2 and the DCS nanolayer, which tunes the work-function of the device and ulteriorly enhances charge carrier transfer between the electrode and the active layer. As a result, the photocurrent and the fill factor of the PSCs are both increased, resulting in an increased power conversion efficiency (PCE) of 6.959%.

In this article, the heterostructure of ZnO particles on single-crystal CdS nanowires (ZnO@CdS) has been successfully synthesized via a facile two-step solvothermal process. The appealing application of the ZnO@CdS heterostructure as visible-light photodetector (PD) is presented. Photocurrent illuminated with light (shorter than 510 nm) to dark-current ratio of structurally-optimized ZnO@CdS nanomaterials based photon detector was enhanced significantly compared to the value of the pristine CdS nanowires based one. The corresponding mechanism for the phenomenon was discussed. Additionally, measurements of time resolved responses were conducted. The ZnO@CdS heterostructure based device kept a fast rise (5 ms) and decay (10 ms) speed to irradiation. This work demonstrates a promising application of ZnO@CdS heterostructure based visible-light detectors with high photocurrent/dark-current ratio, ultrafast time response and very good stability.