Polypyrrole (PPy) is a well-known conducting polymer with significant sensing capabilities for ammonia detection. In parallel, Ionic Liquids (ILs) have been developed as an alternative to water to absorb ammonia. Convinced that a combination of PPy and IL will allow to increase the sensors' sensibility, we developed in this study microconductometric ammonia sensors composed of PPy and ILs-functionalized PPy. These sensors were fabricated by electropolymerization on interdigitated electrodes. The resulting films incorporated various counterions, namely bis(trifluoromethylsulfonyl)imide (TFSI-), hexafluorophosphate (PF6-) and tetrafluoroborate (BF4-). Two series of sensors were prepared containing either pure PPy or copolymers functionalized with ILs. The sensing performances of these sensors towards ammonia were tested and compared. It is mesmerizing to realize that all the sensors containing ionic liquids demonstrated superior responses to NH3, experimentally detecting concentrations as low as 1 ppm under ambient conditions. Remarkably, the PPyIm-TFSI-based sensor exhibited the highest sensitivity and relative response of-4.72 %.ppm-1 and-65 %, respectively, with an impressive limit of detection of 63 ppb. Meanwhile, the PPyIm-BF4-based sensor displayed the fastest adsorption/desorption kinetics (t90) of 19 s/26 s, respectively. These characteristics makes these sensors some of the most effective organic chemoresistive sensors reported so far for real-environmental applications.

Ambipolar devices are a hot topic in research tables due to their unique advantage in reducing the size of the electrical system and enhancing its efficiency. Here, we report a bilayer heterojunction device constructed using octafluoro-vanadyl-phthalocyanine (VOF8Pc) and lutetium bisphthalocyanine (LuPc2), which exhibits both p- and n-type behaviors under oxidizing (NO2 and O3) and reducing gas (NH3) species depending on the humidity level and temperature variations. The initial polarity of the device is identified as n-type by measuring a current decrease under oxygen exposure. Most interestingly, we were capable of observing the zero state (no response) where both opposite charge carriers fight for the majority to dominate the electrical properties of the device when it goes from n- to p-type or vice versa. The inversion in the nature of the majority charge carriers in this ambipolar device was achieved by optimizing the external trigger. The unique property of controllable polarity inversion in a VOF8Pc/LuPc2-based bilayer heterojunction device makes it the most effective ambipolar device for real-world applications.

Gas sensors based on ambipolar materials offer significant advantages in reducing the size of the analytical system and enhancing its efficiency. Here, bilayer heterojunction devices are constructed using different octafluorinated phthalocyanine complexes, with Zn and Co as metal centers, combined with a lutetium bisphthalocyanine complex (LuPc2). Stable p-type behavior is observed for the ZnF8Pc/LuPc2 device under both electron-donating (NH3) and -oxidizing (NO2 and O3) gaseous species, while the CoF8Pc/LuPc2 device exhibits n-type behavior under reducing gases and p-type behavior under oxidizing gases. The nature of majority of the charge carriers of Co-based devices varies depending on the nature of target gases, displaying an ambipolar behavior. Both heterojunction devices demonstrate stable and observable response toward all three toxic gases in the sub-ppm range. Remarkably, the Co-based device is highly sensitive toward ammonia with a limit of detection (LOD) of 200 ppb, whereas the Zn-based device demonstrates exceptional sensitivity toward oxidizing gases, with excellent LOD values of 4.9 and 0.75 ppb toward NO2 and O3, respectively, which makes it one of the most effective organic heterojunction sensors reported so far for oxidizing gases.

In the last two decades, many research works have been focused on enhancing the properties of gas sensors by utilising external triggers like temperature and light. Most interestingly, the light-activated gas sensors show promising results, particularly using visible light as an external trigger that lowers the power consumption as well as improves the stability, sensitivity and safety of the sensors. It effectively eliminates the possible damage to sensing material caused by high operating temperature or high energy light. This review summarises the effect of visible light illumination on both chemoresistors and heterostructure gas sensors based on inorganic and organic materials and provides a clear understanding of the involved phenomena. Finally, the fascinating concept of ambipolar gas sensors is presented, which utilised visible light as an external trigger for inversion in the nature of majority charge carriers in devices. This review should offer insight into the current technologies and offer a new perspective towards future development utilising visible light in light-assisted gas sensors.

pi-Extended porphyrins represent an attractive class of organic compounds because of their unique photophysical, optoelectronic, and physicochemical properties. Herein, cross-conjugated (Ace-PQ-Ni) and linear-conjugated (AM6) porphyrins are used to build double-layer heterojunction devices by combining them with a lutetium bisphthalocyanine complex (LuPc2). The heterojunction effect at the porphyrin-phthalocyanine interface plays a key role in the charge transport properties. Both devices exhibit exceptionally high ammonia sensitivity at room temperature and under ambient relative humidity, with limit of detection values of 156 and 115 ppb for Ace-PQ-Ni/LuPc2 and AM6/LuPc2 sensors, respectively. Interestingly, the Ace-PQ-Ni/LuPc2 and AM6/LuPc2 sensors display opposite effects upon light illumination. While the former sensors show largely decreased ammonia sensitivity under light illumination, the current variation of the latter under ammonia is remarkably enhanced with a multiplication factor of 13 and a limit of detection (LOD) of 83 ppb. The striking difference in their sensing properties upon light illumination is attributed to their different pi-conjugation pathways (cross-conjugation versus linear conjugation).

The dependence of the nature of majority charge carriers on the fluorination degree of polymers in double lateral heterojunction devices.

Conjugated polymers have revolutionized the field of conductometric gas sensors for sensing toxic gases arising from the fast urbanization and industrialization. In this work, we report the synthesis of a series of 5,15-diaryl Ni(II) porphyrin-conjugated polymers (pNiD(Aryl)P) and their integration as the top layer on an octafluorinated copper phthalocyanine (CuF 8 Pc) sublayer to construct bilayer heterojunction (BLH) devices for ammonia sensing. For the first time, we report the pioneering demonstration of polarity engineering within a BLH device by manipulating the meso-substituent of the 5,15-diaryl Ni(II) porphyrin-conjugated polymer constituting the top layer of the CuF 8 Pc/pNiD(Aryl)P BLH device. The BLH devices prepared from the 5,15-diaryl Ni(II) porphyrin-conjugated polymer bearing electron-donating meso-substituents as the top layer exhibit a p-type behavior, whereas an n-type behavior is observed for the BLH devices prepared from the 5,15-diaryl Ni(II) porphyrin-conjugated polymer bearing electron-withdrawing meso-substituents. Laser desorption ionization high-resolution mass spectrometry, UV/vis/NIR, and X-ray photoelectron spectroscopy studies provide evidence of a decrease in intramolecular dehydrogenative coupling in pNiD(Aryl)P bearing electron-withdrawing meso-substituents, resulting in low electrical conductivity of the thin films. Density functional theory calculations reveal noninvolvement of electron-withdrawing meso-substituents toward pi-delocalization in the fused Ni(II) porphyrin tapes. Interestingly, all the CuF 8 Pc/pNiD(Aryl)P BLH devices exhibit remarkable sensing response toward NH3. Among all the devices, CuF 8 Pc/pNiDPP displays the highest sensitivity of -1.17% ppm-1 for NH3, whereas CuF 8 Pc/pNiDNapP and CuF 8 Pc/pNiDCNPP exhibit the best limit of detection for NH3, below 200 ppb. In addition, CuF 8 Pc/pNiDCNPP shows short response and recovery times of 13 and 255 s, respectively, making this device highly suitable for deployment in emergency services.

Silicon phthalocyanines (R2-SiPcs) are an emerging class of high-performance organic semiconductors which have recently found application in highly sensitive and selective bilayer organic heterojunction devices for ammonia (NH3) sensing. We report bilayer heterojunction devices based on axially-substituted bis(pentafluorophenoxy)silicon phthalocyanines of increasing peripheral fluorination ((F5PhO)2-FXSiPc) as a bottom layer and lutetium bis-phthalocyanine (LuPc2) and demonstrate how increased peripheral fluorination changes device operation from p-type to n-type in response to NH3. Sensors fabricated with (F5PhO)2-F16SiPc exhibits the smallest apparent energy barrier for interfacial charge transport by impedance spectroscopy due to better alignment of the semiconductor molecular orbitals with the semi-occupied molecular orbital of LuPc2. Bilayer heterojunction devices all demonstrated a limit of detection (LOD) below 1 ppm with (F5PhO)2-SiPc/LuPc2 yielding an LOD of 307 ppb and a sensitivity of - 0.72%& sdot;ppm- 1. Postdeposition thermal annealing of the (F5PhO)2-SiPc/LuPc2 device is shown to further enhance sensor performance with a 1.5-fold increase in sensitivity to - 1.15%& sdot;ppm- 1 and a LOD of 198 ppb.

Herein, we examined and optimized the influence of annealing temperature on microstructural and electrochemical charge storage properties of spinel NiFe2O4nanopowder synthesized from a simple one-pot sol-gel route. Microstructural techniques encompassing Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, x-ray diffractometry, and Fourier transform infra-red spectroscopy indicate the resulting powder are composed of spinel NiFe2O4 nanoparticle with metal oxygen vibration, crystal properties and lattice strain, all dependent on annealing temperature. Electrochemical charge storage performance of the electrode fabricated from the synthesized material were investigated with the aid of cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements. The obtained results showed that the charge storage performance and rate capability of NiFe2O4 electrode is dependent on the annealing temperature. The study also showed that the electrode from the material annealed at 400 degrees C demonstrated optimum electrochemical charge storage performance having exhibited optimum specific capacitance and capacity values of 1128 Fg-- 1 and 58 mAh g- 1 at 5 mVs-- 1 scan rate and 0.5 Ag- 1 current density, respectively. The electrode EIS fitted equivalent circuit values were also found dependent on annealing temperature indicating the charge transfer process and rate capability of spinel NiFe2O4 nano-powder can be tailored by simply varying the annealing temperature. The study demonstrates cheap route by which spinel NiFe2O4 powder can be prepared. It also unveils the effect annealing temperature on the microstructural build-up and electrochemical charge storage performance of the material.

Herein, we examined and optimized the influence of annealing temperature on microstructural and electrochemical charge storage properties of spinel NiFe2O4 nanopowder synthesized from a simple one-pot sol-gel route. Microstructural techniques encompassing Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, x-ray diffractometry, and Fourier transform infra-red spectroscopy indicate the resulting powder are composed of spinel NiFe2O4 nanoparticle with metal oxygen vibration, crystal properties and lattice strain, all dependent on annealing temperature. Electrochemical charge storage performance of the electrode fabricated from the synthesized material were investigated with the aid of cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy measurements. The obtained results showed that the charge storage performance and rate capability of NiFe2O4 electrode is dependent on the annealing temperature. The study also showed that the electrode from the material annealed at 400 °C demonstrated optimum electrochemical charge storage performance having exhibited optimum specific capacitance and capacity values of 1128 Fg−1 and 58 mAh g−1 at 5 mVs−1 scan rate and 0.5 Ag−1 current density, respectively. The electrode EIS fitted equivalent circuit values were also found dependent on annealing temperature indicating the charge transfer process and rate capability of spinel NiFe2O4 nano-powder can be tailored by simply varying the annealing temperature. The study demonstrates cheap route by which spinel NiFe2O4 powder can be prepared. It also unveils the effect annealing temperature on the microstructural build-up and electrochemical charge storage performance of the material.

We report a novel highly sensitive and pseudocapacitive transparent nickel oxide (NiO) thin film based electrode material fabricated on a conductive glass substrate using a facile binderless electrodeposition process. Effect of the incorporation of Mo-dopant ion on some surface structural and electrochemical properties of the electrode was examined for high performance optoelectronic and charge storage poten-tials. The material showed some uniqueness in some microstructural features and enhanced degree of crystallinity, suitable for charge extraction and transport with Mo doping. The deposited NiO film de-monstrated red shift in band structure by exhibiting optical band gap narrowing from 3.88 to 3.61 eV with increasing Mo content. The degree of disorder as revealed from Urbach response of NiO film was found varying with Mo-content. The material also exhibited enhanced Ni2+ electronic transition states with in-creasing Mo content which quenched at a critical dopant concentration of 2.4 %. The fabricated NiO thin film electrode showed increased supercapacitive specific capacitance and areal capacity up to a peak value of 1412 Fg-1 and 101 mAh m-2 for 3 % Mo dopant content at 5 mVs-1 scan rate and 0.5 mA cm-2, respectively, but returned diminished at higher dopant content. Excellent cycling stability at 85 % after 5000 cycles, was also exhibited. Impedance spectroscopic features of Mo-doped NiO electrode indicated fast electrolytic ion transfer response with high rate charge storage capability. The study presents successful fabrication of Mo-modified NiO nanostructured electrode film and demonstrated the influence of Mo impurity on tai-loring the properties of NiO host film as suitable electrode in high performance photocatalytic and su-percapacitor devices.(c) 2022 Elsevier B.V. All rights reserved.

Novel organic heterostructures fabricated with a bilayer consisting of an axially substituted silicon phthalocyanine (R 2 ‐SiPc) derivative and lutetium bis‐phthalocyanine (LuPc 2 ) are investigated for their ammonia sensing properties. Surface and microstructure characterization of the heterostructure films reveal either compact or highly porous surface topography in (345F) 2 ‐SiPc and Cl 2 ‐SiPc‐based heterostructures, while electrical characterization reveals a strong influence of the axial substituent in R 2 ‐SiPc on NH 3 sensing capabilities. Electrical characterization further demonstrates an apparent energy barrier for interfacial charge transport, which is higher in the (345F) 2 ‐SiPc/LuPc 2 heterojunction device. In‐depth charge transport studies by impedance spectroscopy further reveal a resistive interface in (345F) 2 ‐SiPc/LuPc 2 and faster bulk and interfacial charge transport in Cl 2 ‐SiPc/LuPc 2 heterojunction devices. Different interfacial charge transport capabilities and surface topographies affect NH 3 sensing properties of the two heterojunction devices, in which (345F) 2 ‐SiPc/LuPc 2 reveals a fast and non‐linear response with a limit of detection (LOD) of 310 ppb, while Cl 2 ‐SiPc/LuPc 2 exhibits a slow, and linear response to NH 3 with LOD of 100 ppb. Finally, different metrological parameters of the two sensors are correlated to the respective gas‐material interactions, in which adsorption and diffusion regimes are modulated by the surface topography and hydrophobicity of the sensing layer.

The versatility of metal complexes of corroles has raised interest in the use of these molecules as elements of chemical sensors. The tuning of the macrocycle properties via synthetic modification of the different components of the corrole ring, such as functional groups, the molecular skeleton, and coordinated metal, allows for the creation of a vast library of corrole-based sensors. However, the scarce conductivity of most of the aggregates of corroles limits the development of simple conductometric sensors and requires the use of optical or mass transducers that are rather more cumbersome and less prone to be integrated into microelectronics systems. To compensate for the scarce conductivity, corroles are often used to functionalize the surface of conductive materials such as graphene oxide, carbon nanotubes, or conductive polymers. Alternatively, they can be incorporated into heterojunction devices where they are interfaced with a conductive material such as a phthalocyanine. Herewith, we introduce two heterostructure sensors combining lutetium bisphthalocyanine (LuPc2) with either 5,10,15-tris(pentafluorophenyl) corrolato Cu (1) or 5,10,15-tris(4-methoxyphenyl)corrolato Cu (2). The optical spectra show that after deposition, corroles maintain their original structure. The conductivity of the devices reveals an energy barrier for interfacial charge transport for 1/LuPc2, which is a heterojunction device. On the contrary, only ohmic contacts are observed in the 2/LuPc2 device. These different electrical properties, which result from the different electron-withdrawing or -donating substituents on corrole rings, are also manifested by the opposite response with respect to ammonia (NH3), with 1/LuPc2 behaving as an n-type conductor and 2/LuPC2 behaving as a p-type conductor. Both devices are capable of detecting NH3 down to 10 ppm at room temperature. Furthermore, the sensors show high sensitivity with respect to relative humidity (RH) but with a reversible and fast response in the range of 30–60% RH.

Two-layer optoelectronic devices like p-n junction diode have attracted much attention due to their modern fast switching, optical detection, and sensing applications. In this work, we have fabricated a p-Si/n-SDC junction diode with higher photocurrent by preparing pure and Silver doped CeO2 (SDC) thin-film through facile spray pyrolysis. A monophase cubic fluorite crystal structure was confirmed by XRD analysis. FE-SEM micrographs showed noticeable grain growth after doping the Silver (Ag) in CeO2 film. UV-Vis. study revealed a sharp absorption peak at 340 nm for 6 wt. % of SDC film. The conductivity of SDC films was found to improve while increasing the doping level of Ag. The p-Si/n-SDC junction diode exhibited a higher photocurrent under an illumination environment, conforming to the fabricated diode's photo-conducting behavior. Compared with the p-Si/n-CeO2 diode, the SDC diode recorded a higher ON-OFF response as expected.

In this work, pure and Mn-doped nickel ferrite (Ni1-xMnxFe2O4, x = 0, 3, 6, 9, and 12 wt%) thin films were prepared using facile nebulizer spray pyrolysis technique. The effect of Mn concentration on the structural, optical, and magnetic properties was studied. The XRD pattern confirms the cubic spinel structure of Ni1-xMnxFe2O4 thin films and reveals the preferred orientation along the (311) direction for each film. Moreover, the average crystallite size (D) is found to increase from 13 to 30 nm with increasing Mn concentration. The FESEM micrographs exhibit randomly arranged plate-like and rice-like grains. The elements such as Mn, Ni, Fe, and O are confirmed by the EDX analysis. The optical band gap energy (Eg) varies between 2.90 and 3.60 eV. The Ni1-xMnxFe2O4 film prepared with 3 wt% of Mn exhibits superior ferrimagnetic behavior with the highest value of ηB (57.31) due to the high crystallinity, packing density, and smooth surface of the film. The present work shows that the facile nebulizer spray pyrolysis technique can produce high-quality Ni1-xMnxFe2O4 thin films with good magnetic properties.

In this work, we have prepared Co3O4 thin films for different doping level including 0, 2, 4, and 6 wt% by JNSP method and analyzed their structural, morphological, optical, and electrical properties by XRD, FESEM, EDX, UV-Vis, and current-voltage (I-V) characteristics. The XRD profiles confirm the cubic crystal structures of Sn doped Co3O4 films. Spherical-like grains are observed from the FE-SEM images and were suppressed due to Sn doping. Also, the elements like Sn, Co, and O were confirmed by EDX analysis. The optical band gap of Co3O4 film is noticed to be increased after adding Sn ions, which has been studied through UV-Vis spectroscopy. Most importantly, we have fabricated an undoped and Sn doped p-Co3O4/n-Si junction diode for various concentrations. The determined ideality factor of the p-Sn doped Co3O4/n-Si diodes were reduced for both under dark and light conditions. In addition, the calculated responsivity, quantum efficiency, and specific detectivity of the diodes were enhanced with forwarded voltage. The p-Sn@Co3O4/n-Si diode fabricated with 2 wt% was achieved maximum responsivity and quantum efficiency of R = 247.03 mA/W, QE = 95.7%, and D* = 2.84 x10(10) at 3 V. We observed that the p-Sn doped Co3O4/n-Si diodes are highly sensitive and appropriate for photo-detection applications. (C) 2021 Elsevier B.V. All rights reserved.