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In this work, white light emission from the blend of a hole transport material, 4,4′-cyclohexylidene bis[N,N-bis(4-methylphenyl)benzenamine] (TAPC), and an electron transport material, 2,2′,2″-(1,3...

We have already demonstrated a facile strategy for improving light scattering in bifacial dye sensitized solar cells (DSSCs) through fugitive inclusions of ZnO micro-flowers leading to enhanced photovoltaic performance without adversely affecting the transparency (Sasidharan et al., 2020). In the present work, we were able to further ameliorate the light scattering properties by employing micron sized ZnO hierarchical structures (fibril and sheet like aggregates) as sacrificial inclusions. ZnO hierarchical structures being deposited over TiO2 active layer were selectively etched off, leaving behind imprints over the TiO2 layer, which act as scattering centers to enhance the photocurrent of DSSCs owing to the increased light absorption. The present strategy extends the possibility to improve the performance of DSSCs under both one sun (100 mW/cm2) as well as indoor/ambient light conditions without compromising transparency to larger extend. By employing this strategy on a 6 µm thick TiO2 photoanode and implementing it in a DSSC using N719 sensitizer and iodide/triiodie electrolyte, power conversion efficiency of 15.5% could be achieved under indoor illumination (1000 lx) from a compact fluorescent lamp. A detailed study of the charge transfer dynamics at various interfaces were carried out using a range of electrical and optical perturbation techniques.

We successfully fabricated dye sensitized solar cells (DSSCs) employing a quasi-solid state electrolyte based on pristine insulator natural rubber latex from Hevea brasiliensis and iodide electrolyte. Optimized devices exhibited a maximum power conversion efficiency (PCE) of 1.14% under simulated sunlight with 90 mW/cm2 illumination, 0.46% under 100 mW/cm2 and 7.85% under low intensity illumination of 1000 lx (Daylight LED). This gives a new perspective for the introduction of natural rubber latex abundant in nature as an additive to the water based redox mediator in order to improve the PCE in DSSC. A detailed study on the interfacial charge transfer in fabricated devices revealed that the introduction of rubber helped in arresting the back electron transfer, which was predominant in aqueous electrolyte based dye sensitized solar cell. This opens up opportunities for water-based electrolyte based on natural raw materials to be used in nature inspired DSSC technology.

Dye-sensitized solar cells (DSCs) have proven to be one of the best photovoltaic approaches for harnessing indoor/artificial light. Herein, we report two new molecularly engineered, cost-effective, metal-free, carbazole-based D–π–A sensitizers (YK 8 and YK 9) by judiciously varying their π-spacers, which are suitable for indoor photovoltaic applications. Using YK 8, we achieved an efficiency of 28.7% under standard 1000 lux Osram 14 W T2 cool day light fluorescent tube illumination with a power output of 68.88 μW cm−2 and 30.24% with a power output of 108.85 μW cm−2 under a higher illumination intensity of 1500 lux without co-sensitizers using iodide/triiodide electrolyte. With a small footprint/active area of 1.24 cm2, we could power a temperature sensor completely autonomously at a low light intensity of 500 lux, displaying the potential of these indoor photovoltaic devices to serve as energy sources for low-power sensors and actuators on the Internet of Things (IoT) network, reducing the dependence on batteries and leading to a smaller carbon footprint. The role of the π-spacer and its influence on recombination and device performance were explored via extensive interfacial studies.

A set of four symmetric, butterfly-shaped 4-(4-(decyloxy)phenyl)-2,6-di(thiophen-2-yl)pyridine (TPY) derivatives 2TPA-TPY (TPY center and triphenylamine end groups), 2CBZ-TPY (TPY center and N-ethyl carbazole end groups), 2TPY-TPA (triphenylamine center and TPY at the periphery) and 2TPY-CBZ (N-ethyl carbazole center and TPY at the periphery) was synthesized. The molecules show reverse saturable absorption (RSA) which is consistent with two-photon absorption (2PA) associated with excited-state absorption (ESA) when excited using a 532 nm laser beam. The molecules 2TPA-TPY and 2TPY-TPA possess extremely low limiting thresholds of 1.73 and 2.68 J cm-2 , respectively. An organic light-emitting diode (OLED) fabricated from 2TPA-TPY exhibits green emission with a maximum luminance of 207 cd m-2 , a current efficiency (ηCE ) of 1.51cd A-1 , a maximum power efficiency (ηPmax ) of 0.46 lm W-1 and an external quantum efficiency (ηEQE ) of 0.48 % at 100 cd m-2 .

Undoped zinc oxide (ZnO) and nitrogen-doped zinc oxide (NZO) thin films were prepared on transparent conducting oxide-coated glass substrates by employing sol–gel technique. The effect of different solvents and nitrogen doping on the optical, structural, and electrical properties was investigated by UV–visible absorption spectroscopy, atomic force microscopy (AFM), X-ray diffraction (XRD), profilometry, and Hall effect studies. ZnO films yielded transmittance above 85% and the bandgap of ZnO thin films decreased with doping. XRD pattern confirmed hexagonal wurtzite structure of ZnO. NZO thin films were found to be in the nano-thin film phase with thickness of 40 nm. Hall effect studies yielded carrier concentration of 1.2 × 1015 cm−3 and 2.03 × 1014 cm−3, respectively, for undoped and doped ZnO thin films. The changes in vibrational modes of ZnO due to nitrogen doping were detected using Fourier transform infrared (FTIR) analysis. It was found that p-type doping, leading to an improved surface morphology, led to a reduction in optical bandgap and an increased charge carrier mobility. The choice of the solvent was found to have a profound influence on the surface morphology, optical bandgap, tail states distribution, and charge carrier mobility.

Organic light-emitting diodes (OLEDs), in general, require multilayer devices and microcavity structures for emission tuning, which increases the complexity and cost of production. Hence, it is imperative to develop techniques for spectral tuning, which employ simplified device structures. In this study, we have selected a tris(8-hydroxyquinolinato)aluminum (Alq3): 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)benzopyropyrano (6,7-8-i,j)quinolizin-11-one (C545T)-based OLED and investigated the dependence of the OLED emission on various deposition parameters and the electrical bias. The concentration of the dopant in the emissive layer (EML) was varied from 3 to 50%, and the single dopant emitter as a limiting case was also studied along with studies on the varied deposition rates and EML thickness. By varying the deposition parameters, the emission was observed to change from excitonic green to excimeric yellow. With increased doping concentration, reduction in pure exciton emission with an increase in excimer emission was observed, resulting in electroluminescent spectral red shift. Similarly, electroluminescence spectra have shown different levels of broadening, depending on the deposition rate and thickness of the EML. These effects could be reversed with increasing applied electric field. Thus, it is indicated that, by suitably optimizing the deposition parameters of the dopant material, spectral tuning can easily be obtained, which may form the basis of simplified and cost-effective device structures.

2D layered graphene and inorganic graphene analogue structures are attracting considerable research interest as electrode materials of energy storage devices due to their intrinsic electronic properties. Herein, we report the preparation of few-layered MoS2 nanosheets by exfoliation from bulk for electrochemical application. A nanocomposite containing MoS2 and reduced graphene oxide (rGO) has been prepared by simple physical mixing. The as-prepared MoS2 nanosheets and the MoS2-rGO nanocomposite have been characterized by powder X-ray diffraction, Transmission Electron microscopy, Scanning Electron microscopy, FTIR and Raman spectroscopy analyses. The electrochemical properties of the MoS2 nanosheets and MoS2-rGO nanocomposite have been analyzed in 3-electrode configuration. At a scan rate of 10 mV s−1, the MoS2 nanosheets and the MoS2-rGO nanocomposite exhibit specific capacitance values of 375 Fg-1, and 739 Fg-1 respectively. MoS2-rGO nanocomposite electrode retains a stability of 96% ven after 5000 cycles of continuous charge-discharge at a current density of 6 A g−1.

The hierarchical self-assembly of the charge-transfer (CT) complexes in the solid state is of paramount importance to dictate the performance of electronic devices. In this work, we describe a three-component hierarchical self-assembly approach to generate stable alternate donor–acceptor (D–A) assemblies within block copolymer microdomains by involving the supramolecular approach in self-assembly of block copolymers. So far, the assembly between a single small molecule and block copolymer was explored to obtain block copolymer supramolecules. Here we report block copolymer supramolecules composed of two small molecules (donor and acceptor) and polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP). 1-Pyrenebutyric acid (PBA, donor) forms hydrogen bonding with P4VP and aromatic interactions with naphthalene diimide (NDI, acceptor) to generate CT complexes within the block copolymer domains in the solid state. Using FTIR, SAXS, WAXS, TEM, UV/vis spectroscopy, and photoluminescence spectroscopy measurements, we...

Dye solar cells (DSCs) are gaining increasing interest since the recent realization of their high-performance potential in low/indoor light environments. Fused conjugated metal-free organic dyes have become a prominent class of dyes used in DSC in recent times by virtue of their better backbone rigidity, efficient charge transport properties, and the opportunity they provide for further structural modifications. Herein, we report the synthesis and characterization of three metal-free D–π–A organic dyes employing indolo[3,2-b]indole as the donor unit. The optical, electrochemical and photovoltaic properties have been analyzed in detail as a function of π-spacers, namely, benzene (IID-1), thiophene (IID-2) and furan (IID-3). Eventually, the best performance was demonstrated by the dye bearing benzene as the π-spacer. The role of recombination in determining the photovoltaic performance as a function of the nature of π-spacers was explored in detail, using various perturbation techniques on the fabricated devices, and compared with the results obtained from molecular orbital calculations.

The synthesis, characterization, and spectroscopic investigations of a new solution‐processable N‐styrylcarbazole‐linked tetraphenylethylene (TPE) derivative (TPE‐BCzS) are reported, exhibiting green–orange emission. While the material displays weak photoluminescence (PL) in solution with a low PL quantum yield (PLQY of 4 ± 0.2%), significant PL enhancement in neat‐film PLQY (55 ± 8%) is observed. Studies using steady‐state spectroscopy, and femtosecond and nanosecond transient absorption spectroscopy reveal details of the excited‐state dynamics, consisting of the Franck–Condon (FC) state, nonradiative conformational relaxation, and formation and decay of the triplet excited state generated via intersystem crossing (ISC) upon ultrafast photoexcitation. Solution‐processed organic light‐emitting diodes (OLEDs) based on TPE‐BCzS display maximum external quantum efficiencies of 1.8% and 1.7% for neat and blend films (20 wt% in a 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl host), approaching the theoretical efficiency limit for the determined PLQYs of the films. While TPE materials are typically associated with aggregation‐induced emission, it is reported that the enhanced PLQYs in the solid state are due to restriction of structural relaxations in the solid state and not due to the commonly misunderstood aggregation effect.

Efficient optical outcoupling from organic light emitting diodes (OLEDs) is an important challenge in solid state lighting technology. In this work, the effect of an external light extraction layer, prepared using polydimethylsiloxane (PDMS) and zinc oxide (ZnO) nanoparticles, was studied on the performance of red, green, blue and white OLEDs. The self-standing flexible film can effectively address the loss modes at the substrate-air interface. With the application of the layer, a maximum enhancement of about 80% in light outcoupling was observed in white OLEDs. Monochrome OLEDs also showed appreciable enhancement in emission with green having the highest improvement (102%), followed by red (56%) and blue (35%). Finite-difference time-domain (FDTD) simulations were performed for elucidating the mechanism behind the improvement in light extraction due to nanoparticle scattering layer. Total-Field Scattered-Field (TFSF) source was used to simulate the scattering cross-section for different wavelengths. Reduced Fresnel reflections at the air-glass interface and advantageous Mie scattering by ZnO nanoparticles seem to increase the optical outcoupling. This film could be a potential candidate for light extraction in OLEDs because of its facile fabrication, economical precursors, and adaptability to flexible substrates and absence of any possible optical artefacts to the emission.

Pentacene based organic field-effect transistors (OFETs) were fabricated, with both cross-linked poly vinyl phenol (CL-PVP) and a bilayer of poly(α-methylstyrene) (PαMS)/ CL-PVP as gate dielectric. The PαMS layer decreases the surface energy of the gate dielectric and increases the hydrophobic nature, which leads to favorable growth of pentacene and the corresponding field-effect mobility, though at a higher gate voltage span, increases three times compared to that of the device with only CL-PVP as the gate dielectric. OFET with bilayer polymer gate dielectric exhibited non-volatile memory behavior with an on-off ratio 103, retention time >103 s and a large memory window of −25 V. The memory effect observed in the device was due to the charge trapping in the PαMS layer, with CL-PVP acting as a blocking dielectric. Our studies indicate that the bilayer dielectric, comprising of solution-processable PαMS/CL-PVP is a good choice for obtaining non-volatile electret memory on an OFET platform.

We have developed a regioregular poly (3-hexylthiophene) (rr-P3HT) based organic field-effect transistor (OFET) for the detection of low concentration of ammonia (NH3) gas. The ammonia sensing mechanism of OFET based sensor device can be described in terms of the chemical interaction between NH3 and P3HT. Upon exposing the conducting channel to various concentrations of ammonia, a reduction in source-drain current/mobility, and an increase in threshold voltage were observed. This deterioration of the performance parameters of the OFET while exposing to different concentrations of ammonia was attributed to the dedoping effect. Our OFET based ammonia sensor could detect ammonia gas concentrations in the range 20 ppm–100 ppm. Moreover, the device showed excellent recovery to the initial state within a few minutes.

Novel class of metal free organic dyes (CCTh and CCBz) with D-A-π-A configuration, having carbazole as donor and 3-cyanopyridine as auxiliary acceptor replacing conventional benzannulated heterocycles along with variable π-linkers were synthesized and used in dye-sensitized solar cells (DSSCs). Both the dyes are having cyanoacrylic acid as the anchoring group with thiophene (CCTh) and phenylene (CCBz) as π-linkers. The photophysical, electrochemical, theoretical and photovoltaic properties of the dyes were investigated in detail. The absorption spectra of dyes on TiO2 showed broader absorption band for CCTh in comparison to the solution spectra indicating aggregation in solid state. The aggregation studies in varied THF/water fraction indicates J-aggregation for both the dyes. CCTh with thiophene linker showed broader absorption compared to CCBz, and the photovoltaic performance recorded for CCTh directly indicates better light harvesting ability corresponding to the red shifted J-aggregated states. Hence, solar cells fabricated with CCTh gave a power conversion efficiency of 3.39% and CCBz delivered an efficiency of 2.03% under full sun condition. A detailed investigation of device dynamics have been carried out employing charge extraction (CE), intensity-modulated photovoltage spectroscopy (IMVS) and open-circuit voltage decay (OCVD) measurements.

White electroluminescence from a single molecule is a challenging topic in organic light emitting diode (OLED) research. Herein, we report the white light emission from a carbazole derivative, 9-ethyl-3,6-bis(4-(trifluoromethyl)phenyl)-carbazole (Cz(PhCF3)2), by harvesting both singlet and triplet emissions. The blue fluorescence and a broad emission from room temperature phosphorescence resulted in white light electroluminescence (EL) with a colour coordinate of (0.31, 0.44). We successfully synthesized another molecule namely 1,1'-(4,4'-(9-ethyl-9H-carbazole-3,6-diyl)bis(4,1-phenylene))diethanone Cz(PhBz)2 and achieved a four-fold increase in the efficiency of the EL with a substitution change from −Ph-CF3 to −Ph-CO-Ph with a colour coordinate of (0.29.0.35). The present route for the generation of white light emission from a solution processable single organic molecule utilizing both singlet and triplet excitons offers a promising way to improve the efficiency of future white OLEDs.

Organic light emitting diodes (OLEDs) often face the issue of decreasing power efficiency with increasing brightness. Loss of charge carrier balance is one of the factors contributing to the efficiency roll-off. We demonstrate that by using a combination of doped electron transport layer (ETL) and a specially chosen electron blocking layer (EBL) having high hole mobility, this efficiency roll-off can be effectively suppressed. A tris-(8-hydroxyquinoline) aluminium (Alq3) based OLED has been fabricated with 2,3,6,7-Tetrahydro-1,1,7,7,-tetramethyl-1H, 5H,11H-10-(2-benzothiazolyl) quinolizino-[9,9a, 1n gh]coumarin (C545T) as the emissive dopant. Bulk doping of the ETL with lithium fluoride (LiF) was optimized to increase the luminous intensity as well as the current efficiency. An EBL with high hole mobility introduced between the EML and the hole transport layer (HTL) improved the performance drastically, and the device brightness at 9 V got improved by a factor of 2.5 compared to that of the control device. While increasing the brightness from 100 cd/m2 to 1000 cd/m2, the power efficiency drop was 47% for the control device whereas only a drop of 15% was observed for the modified device. The possible mechanisms for the enhanced performance are discussed.

Development of new efficient luminescent materials is one of the active research areas of interest due to its promising optoelectronic applications including in organic light emitting devices (OLEDs). Among the various luminescent systems, emitters of deep blue electroluminescence with excellent color purity have great deal of importance as these are one of the important components for fabricating white OLEDs. In this context, we have designed and synthesized novel solution processable organic donor-acceptor dyads 1 and 2 having electron donating carbazole and accepting oxadiazole groups. The substitution pattern at the phenylene linker has been changed to understand the intramolecular electron communication between the donor and acceptor moieties of these dyads. The photophysical properties of these dyads were studied in both solution and film state. The emission maxima of the dyads red shifted with the increase in solvent polarity, which could be attributed to the intramolecular charge transfer (ICT) process. In the film state, dyads 1 and 2 showed deep blue emission having λmax at 415 nm and 409 nm, respectively. To understand the structure and band gap of these dyads, density functional theory (DFT) calculations have been performed. In line with the design strategy adopted, high thermal stability and formation of solution processed homogeneous film were obtained. Furthermore, we have fabricated the solution processed un-doped devices based on these dyads 1 and 2, which exhibited deep blue electroluminescence in near ultraviolet (NUV) region having λmax at 410 and 408 nm with a narrow full width at half maximum (FWHM) of 54 and 49 nm and CIE coordinates of (0.16, 0.07) and (0.16, 0.05), respectively, indicating thereby their potential in possible optoelectronic applications.

New solution processable organic donor–π–acceptor dyads 1 and 2 having electron donating phenoxazine and electron accepting oxadiazole groups have been synthesized. Intramolecular electron communication between the donor and acceptor moieties of these dyads was tuned through changing the substitution pattern at the phenylene linker. The photophysical properties of these dyads have been studied in the solution and film states. These dyads showed green fluorescence and exhibited a positive solvatochromism in the emission spectra, which indicates more polar excited states owing to an efficient charge migration from the donor phenoxazine to the acceptor oxadiazole moiety. The electrochemical, morphological and thermal properties were investigated through cyclic voltammetry, thermogravimetric and atomic force microscopy (AFM) analyses. To understand the electronic structure and band gap of these dyads, density functional theory (DFT) calculations have been performed. Furthermore, we have fabricated the solution processed un-doped electroluminescence devices based on these dyads, which exhibited efficient green emission with Commission Internationale de l’Eclairage (CIE) coordinates of (0.26, 0.49) and (0.27, 0.47) for 1 and 2, respectively, with a luminance maximum of ca. 1751 cd m−2 for the dyad 1, thereby demonstrating its use in organic light emitting diodes (OLEDS).

The semiconductor/dielectric interface controls the performance of organic field-effect transistors (OFETs). Herein, the influence of both the molecular weight and the polarity of the solvent of a poly(methyl methacrylate) (PMMA)-based gate dielectric on the performance of pentacene OFETs is systematically investigated, by studying surface energy, surface roughness, morphology, leakage current, and capacitance of the dielectric. Various existing views on the role of the surface energy are considered while deriving a correlation. Larger pentacene grains are observed when the film is grown on high molecular weight-PMMA films cast from high dipole moment-solvent. The electrical properties of the corresponding OFETs show great improvement compared to those of OFETs fabricated with low molecular weight-PMMA film as the gate dielectric, irrespective of the solvent. The authors attribute this enhanced performance to the increased surface energy of the polymeric dielectric which turns out to be a strong function of its molecular weight and the dipole moment of the solvent. Bias-stress measurements on the OFETs confirm this correlation.

Developing electronic sensors for ammonia (NH3) is very useful for environmental monitoring and diagnostic purposes. In this work, a highly sensitive, organic field-effect transistor (OFET) based, room temperature sensor for NH3 has been fabricated using dinaphtho [2,3-b:2′,3′-f]thieno [3,2-b]thiophene (DNTT), which showed a fast response to low concentration of the analyte down to 100 ppb. A thin film of solution-processed polymethyl methacrylate (PMMA) has been used as the gate dielectric material and its hydrophobic surface promoted structured growth of organic semiconductor, DNTT, by inducing mass transfer. By controlling the thickness and thereby exploiting the growth dynamics of the semiconductor film, the sensor performance was improved. The sensitivity of the device towards 1 ppm of NH3 was almost doubled with a thinner and porous film of DNTT as compared to that with a thick film. Morphological studies of the sensing layers, using atomic force microscopy (AFM), have established this structure-property relation. The variations in different transistor parameters have been studied with respect to different analyte concentrations. The p-channel devices in the enhancement mode showed depletion upon exposure to NH3. The devices exhibited a fast response and good recovery to the initial state within 2 min.

The electron–hole recombination and back electron flow at the conducting oxide–mesoporous film interface in dye-sensitized solar cells (DSSCs) are addressed primarily by the use of pre-blocking layers. Herein, the effects of zinc oxide (ZnO) blocking layers (BLs) on the photovoltaic performance of ZnO based DSSCs are investigated in detail using electrochemical impedance spectroscopy (EIS), open circuit voltage decay (OCVD) and intensity modulated photovoltage spectroscopic (IMVS) techniques. BLs of varying thicknesses obtained by a low temperature solution process provided uniform surface coverage of nanosized ZnO particles over FTO. Devices with optimized ZnO blocking layer thickness (12 nm) lead to improved performance (efficiency 2.57%) in comparison to the devices fabricated using bare FTO (1.27%) by suppressing interfacial recombination at the FTO/ZnO interface thereby improving the lifetime leading to better performance.

Two metal free organic dyes (TPCTh and TPCRh) with D-A-pi-A configuration, having 3-cyanopyridine as an auxiliary acceptor and thiophene pi-linkers along with a triphenylamine donor and cyanoacetic acid/rhodanine-3-acetic acid anchoring groups, were successfully synthesized and utilized as sensitizers in the fabrication of dye-sensitized solar cells (DSSCs). The opto-electronic properties of TPCTh and TPCRh were compared with the model sensitizer CCTh having carbazole as the donor and cyanoacetic acid as the anchoring group. Both the dyes showed red shifted absorption spectra compared to the standard CCTh dye. Also, TPCRh showed a broader absorption spectrum with a reduced band gap compared to TPCTh. However, theoretical studies indicate that the unavailability of excited state conjugation over the anchoring group could lead to restricted charge injection for the TPCRh dye, whereas the TPCTh dye exhibits complete conjugation over the entire molecule. The photovoltaic performance of the TPCTh dye was found to be better compared with the standard CCTh sensitizer as a result of better absorption contributed by the lower band gap in TPCTh leading to improved photon-light conversion and thus an improved J(sc) of 11 mA cm(-2) over the 7.12 mA cm(-2) of CCTh. In addition, lifetime measurements corroborated a lower electron lifetime for TPCRh compared to TPCTh and CCTh.

Organic light emitting diodes (OLEDs) have captured the attention of the flat-panel display market owing to their high luminescence and versatile properties. However, substrate processing plays a critical part in the fabrication of OLED displays, demonstrated here as a passive matrix display, where plenty of defects, which appear during the processing stage, result in poor display quality and yield. Photolithography is the most common technique used to develop the electrode pattern on a transparent glass substrate. Nevertheless, poor lithography leads to display defects such as dead pixels, dark columns and bright horizontal rows. Moreover, shorts between anodes due to partial etching of the transparent conducting material or cathode lines are also common problems. Herein, we discuss a technique which drastically reduces the number of electrode shorts. Selective etching of the cathode in this technique makes the optical inspection of electrode shorts far easier due to the higher contrast ratio between Cr/glass compared to indium tin oxide/glass. Further, a focused laser beam is employed to ablate the identified shorts between two or more anode/cathode lines to make the short-free patterns. Additionally, a laser beam is also capable of isolating the burnt/dead pixels in a display, which otherwise lead to dark or bright lines during operation. Thus, our findings are very important for the display industry to develop defect-free panels and for the repair of certain operational defects to increase the production yield and lifetime.

Green electromagnetic interference (EMI) shielding materials are the most promising among EM wave attenuating solutions because of their less environmental hazard resulting from efficiently attenuating spurious waves with minimal secondary reflection. Against this background, the present paper reports a facile strategy for developing green and ultra-lightweight aerogels-based EM wave absorbers with low carbon content. Herein, we realized a peculiar 3D nanoarchitectured aerogel using nanowires of a layered oxide V2O5, which was further reinforced by a conducting polymer, polyaniline (PANI). The structure, morphology, formation of gel, and the EMI shielding properties of V2O5- PANI composite aerogel were investigated in detail. The mesoporous aerogel has a very low density of ~0.02 g/cc with maximum EMI shielding efficiency (EMI SE) of 34 dB in the X band, with an impressive specific shielding efficiency of 1662.2 dB cm3 g−1. Green index (gs) is found to be one of the highest so far (~2.91). The excellent show of EMI SE is ascribed to the multiple internal reflections inside the layered structure of V2O5 and intrinsic conducting properties of the polyaniline. Ours is the first-ever report of an eco-friendly, lightweight EMI shielding solution employing inorganic V2O5 nanowires forming robust EMI attenuating aerogel, which are free of carbonaceous fillers like carbon nanotube, graphene or even MXene.

In this work MoS2 nanostructures with near commercial mass loading (30 mg cm−2) are grown over Ni foam substrates by a simple hydrothermal process conducted at different growth times. MoS2 nanorods in a brush-like arrangement grown over Ni foam obtained after 36 h exhibit excellent electrochemical performance in three electrode measurements with a maximum specific capacitance (Csp) of 766 F g-1 at 1 mVs−1. A symmetric supercapacitor based on the sample exhibits relatively high Csp (244 F g-1), a good energy density (12.2 wh kg−1) at 1 A g-1, and a competent cycling stability (92% after 9000 charge-discharge cycles at 5 A g-1).

Ultraviolet (UV) photodetectors have drawn extensive attention due to their numerous applications in both civilian and military areas including flame detection, UV sterilization, aerospace UV monitoring, missile early warning, and ultraviolet imaging. Zinc oxide (ZnO)-based UV detectors exhibit remarkable performance; however, many of them are not visible-blind, and the fabrication techniques involve a high-temperature annealing step. Here, we fabricated a p–n junction photodiode based on annealing-free ZnO thin films prepared from ZnO nanoparticles and N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB). NPB was chosen due to its transparent nature in the visible region and high hole mobility. The ZnO nanoparticles and thin films were characterized by UV-visible absorption spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), dynamic light scattering (DLS) particle size analysis, Fourier-transform infrared (FTIR) spectroscopy, photoluminescence spectroscopy, XRD and profilometry. The device exhibited responsivity of 0.037 A/W and an external quantum efficiency (EQE) of 12.86% at 5 V bias under 360 nm illumination. In addition, with no biasing, the device exhibited an on–off ratio of more than 103 and a linear dynamic range (LDR) of 63 dB. A high built-in potential at the ZnO/NPB interface could be the reason for this performance at zero bias. The rise and fall times were 156 ms and 319 ms, respectively. The results suggest that a visible-blind UV photodetector with acceptable performance can be fabricated using annealing-free ZnO films, which may lead to the realization of flexible detectors due to the low-temperature processes involved.

A study of transient and steady state electrical currents in the solution-processed thin films of thieno[3,2-b]thiophene oligomers has demonstrated charge carrier mobility of about 10−2 cm2 V−1 s−1. Thieno[3,2-b]thiophene moieties serve as reasonable charge transport sites providing the high mobility. Varying end alkyl chains in such oligomers is suggested as a viable tool to tune the mobility.

Novel heteroleptic cyclometalated platinum(II) complexes consisting of 5′-benzoylated 2-phenylpyridinate (ppy) cyclometalated and acetylacetonate ancillary ligands were synthesized, and their photoluminescence (PL) properties were investigated. The 5′-benzoylated complex without any other substituents exhibited phosphorescence-based monomer emission at 479 nm in dichloromethane (10 μM, rt) with a PL quantum yield of 0.28. On the other hand, in poly(methyl methacrylate) (PMMA) film, remarkable excimer emission additionally emerged at ca. 600 nm with a relatively high PL quantum yield of 0.47 as the doping level increased to 0.20 mmmol g−1, which was comparably intense in comparison with the monomer emission. In the case of the complexes with unsubstituted, 4′-benzoylated, and 5′-fluorinated ppy cyclometalated ligands, excimer emission was modestly generated at the same doping level, and thus the introduction of a benzoyl group to the 5′-position is effective to obtain remarkable excimer emission. The combination of benzoyl and fluoro groups was more effective at inducing excimer emission, and the intensity of excimer emission of the 2-(5-benzoyl-4,6-difluorophenyl)pyridinate-based complex was 3.5 times larger than that of monomer emission at a doping level of 0.20 mmmol g−1 in PMMA. From the analysis of PL lifetimes at varying concentrations, photokinetic profiles were fully analyzed according to the model system for the irreversible excimer formation, and the excimer formation rate constant of the 5′-benzoylated complex was determined in dichloromethane as 2.2 × 109 M−1 s−1, which is 4.4 times larger than that of the unsubstituted complex. We also fabricated an organic light-emitting diode using the 2-(5-benzoyl-4,6-difluorophenyl)pyridinate-based complex as a single emitter. The device exhibited pseudo-white EL with the Commission internationale de l’eclairage chromaticity coordinates of (0.42, 0.42).

Doped transport layers are essential for achieving high efficiency in organic light emitting diodes (OLEDs). We have studied the effect of doping the electron transport layer (ETL), tris-(8-hydroxyquinoline) aluminum (Alq3) with different percentages of lithium fluoride (LiF). We have also studied the effect of different electron blocking layers (EBLs) such as Tris (4-carbazoyl-9-ylphenyl)amine (TCTA), N,N'-Bis (naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine(NPB), and Di-[4-(N,N-di-p-tolyl-amino)-phenyl]cyclohexane (TAPC) in an Alq3:2,3,6,7-Tetrahydro-1,1,7,7,-tetramethyl-1H, 5H, 11H −10-(2-benzothiazolyl)quinolizino[9,9a, 1gh] coumarin (C545T) based organic light emitting diode (OLED) with optimized ETL doping. TCTA was found to effectively block the electrons and influence the recombination region in the process. At a brightness of 1000 cd/m2, an improvement of 27.8% was observed in external quantum efficiency (EQE) for the device with TCTA as the EBL and doped Alq3 as the ETL, compared to the one with just NPB as both EBL and HTL.

If an organic light emitting diode is to be used as part of a matrix addressed array, it should exhibit low reverse leakage current. In this paper we present a method to improve the on/off ratio of such a diode by simultaneous application of heat and electric field post device fabrication. A green OLED with excellent current efficiency was seen to be suffering from a poor on/off ratio of 10(2). After examining several combinations of annealing along with the application of a reverse bias voltage, the on/off ratio of the same device could be increased by three orders of magnitude, specifically when the device was annealed at 80 °C under reverse bias (-15 V) followed by slow cooling also under the same bias. Simultaneously, the forward characteristics of the device were relatively unaffected. The reverse leakage in the OLED is mainly due to the injection of minority carriers in the hole transport layer (HTL) and the electron transport layer (ETL), in this case, of holes in tris-(8-hydroxyquinoline)aluminum(Alq3) and electrons in 4,4',4''-tris(N-3-methylphenyl-N-phenylamino)triphenylamine (m-MTDATA). Hence, to investigate these layers adjacent to the electrodes, we fabricated their single layer devices. The possibility of bulk traps present adjacent to electrodes providing states for injection was ruled out after estimating the trap density both before and after the reverse biased annealing. The temperature independent current in reverse bias ruled out the possibility of thermionic injection. The origin of the reverse bias current is attributed to the availability of interfacial hole levels in Alq3 at the cathode work function level in the as-fabricated device; the suppression of the same being attributed to the fact that these levels in Alq3 are partly removed after annealing under an electric field.

Organic light emitting diode (OLED) based displays have matured into commercial products. However, while we consider OLED for a low-cost high-resolution and high-contrast displays with a long life span, still there are performance gaps. This review addresses various techniques used for increasing the ambient contrast ratio of OLED displays. There are techniques which are integral to the OLED device, such as black cathodes and absorbing transport layers. In contrast, anti-reflection (AR) coatings and circular polarizer are applied externally to the device. This review provides a brief overview of each technique along with a discussion on its merits and demerits. The choice of a particular contrast enhancement technique for a display depends on the ambient where the same is intended to be used. Accordingly, for indoor and outdoor applications, the best possible methods are suggested.

A blue organic light emitting device (OLED) with improved efficiency and good color purity is reported. The highest occupied molecular orbital (HOMO) level of the hole transport layer (HTL) and that of the emissive layer (EML) differs by 0.3 eV. This energy level mismatch confines the carriers at the HTL/EML interface. Conventional devices have only one HTL/EML interface, with a current efficiency of 2.9 cd/A. Without adding a separate hole blocking layer, incorporating multi-layers of the same HTL and EML increases this efficiency to 5.8 cd/A, with only a small increase in operating voltage yielding increased power efficiency also. But, there are an optimum number of layers, beyond which efficiency loss results. Also, including the multilayer structure simultaneously improves the blue color co-ordinates. To gain insight into the role of multilayer structures in modifying charge transport and recombination zone a simulator was developed. The simulated results could qualitatively explain the experimental observations.

Organic field-effect transistors were fabricated where the active semiconductor layer consisted of a co-evaporated film of pentacene and a perylene derivative, N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide. The device characteristics were evaluated in an oxygen-free environment. The field-effect transistor showed excellent ambipolar operation with field-effect hole mobility of 0.09 cm2 V−1 s−1 and field-effect electron mobility of 9.3 × 10−3 cm2 V−1 s−1. The threshold voltage for p-channel operation was −18 V and the same for n-channel operation was 15 V. This ambipolar device could be a building block to form flexible integrated circuits with low-power consumption and ease of design.

Single crystal diamond films of varying quality are deposited using microwave plasma chemical vapor deposition (MPCVD) apparatus. Unpolished natural diamond seeds are used as substrates in the temperature (Ts) range 850–1200 °C. The gas mixture of methane (CH4), hydrogen (H2) and oxygen (O2) is used for the deposition of diamond. The deposition pressure is varied in the range 90 to 150 Torr. The films are characterized using scanning electron microscopy (SEM), Atomic force microscopy (AFM) and Raman spectroscopy techniques. The growth morphology of the films is found to be a sensitive function of the deposition parameters. The crystalline nature of the films change from polycrystalline to single crystal as we increase Ts and for a certain set of parameters the filamentary growth of the diamond crystals can be seen. The films are polycrystalline in the range of substrate temperatures 850–900 °C and oriented grains of diamond crystals are evident as the Ts increases. The single crystal diamond growth is observed to proceed via the step growth mechanism with the evidence of bunching of the steps. Our study explores evolution of the growth of single crystal diamond in a wide range of parameters.

Organic field-effect transistors were fabricated with quaterthiophene as the active material and various polymeric dielectrics as the gate insulator. The conduction parameters such as mobility, threshold voltage, subthreshold swing, the maximum density of surface states etc. were found out. The performances of the devices were compared with respect to the dielectric constant, thickness and surface morphology of the gate insulator and the leakage current through the gate. Out of the three dielectrics investigated viz. parylene-C, cyanoethylpullulan and poly(methylmethacrylate); parylene-C was found to be best suited for applications in organic FETs.

Organic field-effect transistors were fabricated using N,N′-ditridecylperylene-3, 4, 9, 10-tetracarboxylic diimide (PTCDI-C13H27) as the active material and a polymeric insulator polymethylmethacrylate (PMMA) as the gate dielectric. A mobility value of 1.7 × 10−2 cm2 V−1 s−1 was estimated from the transistor characteristics. The threshold voltage was 0.2 V and the inverse subthreshold slope was 7.6 V/decade. At low gate and high drain voltages, the device exhibits injection of holes from the Al drain electrode. This was rectified by using LiF as a buffer layer between Al and (PTCDI-C13H27). Such modified devices exhibited mobility 1.2 × 10−2 cm2 V−1 s−1, threshold voltage −0.3 V, and inverse subthreshold swing of 5 V/decade.

Organic field-effect transistors using pentacene have been fabricated employing polyimide gate dielectric layers. The root-mean square surface roughness of polyimide films is 9 A. Devices with thin polyimide films as gate achieved a mobility of 0.16 cm2 V−1 s−1, threshold voltage −6.4 V, on–off ratio ~ 104 and subthreshold slope 7.5 dec−1 with the gate voltage span between 0 and −30 V. The upper limit of interface trap density has been estimated to be 3.9 × 1012 cm−2 eV−1. The mobility is found to be gate bias dependent.

Organic field-effect transistors were fabricated with Quaterthiophene (4T) as the active material and a ferroelectric copolymer poly(vinylidene fluoride-trifluoroethylene) as the gate insulator. As-prepared devices showed normal p-type transistor operation. The ON and OFF-states could be written to the device by applying appropriate voltages to the gate with respect to short-circuited source and drain electrodes. The devices exhibited promising memory retention properties.

Thin films of europium diphthalocyanine were prepared on glass substrates by vacuum sublimation. The absorption and reflection spectra were recorded in the UV-Visible range. The B band absorption occurs at 360 nm and the Q band shows a doublet at 632 and 680 nm. From the absorption and reflectivity data, various optical parameters such as absorption coefficient (alpha), refractive index (n), extinction coefficient (k) and real and imaginary parts of the optical dielectric constant (epsilon.) were determined. (C) 2002 .

Vacuum-sublimed thin films of nickel phthalocyanine were prepared. Post-evaporation annealing was done at temperatures of 323, 373, 423 and 473 K. The electrical conductivity and optical absorption spectra of these films were studied. Their structure and grain size have been determined.

Organic field-effect transistors were fabricated with pentacene as the active material and different polymeric dielectrics such as cyanoethylpullulan, poly(4-vinyl phenol), polymethylmethacrylate, parylene-C and polyimide as the gate material. The performance of the devices is compared with respect to the parameters, field-effect mobility, threshold voltage, subthreshold swing, and the maximum possible value of interface traps.

Organic field-effect transistors were fabricated with pentacene as the active material and a ferroelectric copolymer poly(vinylidene fluoride–trifluoroethylene) as the gate insulator. As-prepared devices showed normal p-type transistor operation. The ON- and OFF-states could be written to the device by applying appropriate voltages to the gate with respect to short-circuited source and drain electrodes. The devices exhibited excellent memory retention properties.

Static and dynamic characteristics of an organic static induction transistor (SIT) fabricated using copper phthalocyanine (CuPc) thin films are reported. Layered structure using CuPc as active layer consists of Au(drain)/CuPc/Al (gate)/Al(discontinuous)/CuPc/Au(source)/glass. Excellent electrical characteristics are obtained at low negative gate voltages.