The third component in a ternary organic solar cell (OSC) is generally selected to maximize absorption of the solar spectrum. The fused ring non-fullerene acceptor 2,2 '-[({4,4,9,9-tetra-n-octyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-2,7-diyl}bis{benzo[c][1,2,5]thiadiazole-7,4-diyl})bis(methaneylylidene)]dimalononitrile (o-IDT-BT-DCV) was investigated for use in binary and ternary OSCs. The optimized binary device with o-IDT-BT-DCV as the acceptor and PM6 as the donor had a maximum power conversion efficiency (PCE) of 10.8%. Incorporation of o-IDT-BT-DCV into a donor:acceptor PM6:Y6 blend delivered a ternary OSC with a maximum PCE of 16.2%. Femtosecond transient absorption spectroscopy (fs-TAS), transient photovoltage (TPV), and transient photocurrent (TPC) measurements in combination showed that o-IDT-BT-DCV in the ternary blend did not behave as an acceptor. Instead, it contributed to charge carrier generation through a sub-picosecond energy transfer process to Y6, followed by a photoinduced hole transfer mechanism with PM6 and/or spontaneous exciton dissociation within the Y6 phase. Encapsulated ternary blend devices were found to be more stable than the binary blend solar cells. Under 1-sun illumination and maximum power point (MPP) tracking, excluding the initial burn-in loss, the ternary device retained approximate to 80% of its MPP over 1200 h compared to the 40% retained by the PM6:Y6 devices.

The use of G-series nerve agents represents a significant threat and there is a need for rapid and selective in-field identification. We report that sensing materials composed of ESIPT-based silyl ethers can be used to detect the hydrogen fluoride that is present in phosphonofluoridate agents such as sarin and its simulant di-iso-propyl iso-propyl fluorophosphate (DFP). We find that the ability of the sensing material to detect the hydrogen fluoride in DFP is dependent on the basicity of the nitrogen atom that forms part of the ESIPT moiety upon deprotection. When the pKa of the conjugate acid of the nitrogen atom was lower than that of hydrogen fluoride the ability of the sensing material to detect the acid and hence simulant was curtailed. However, when the pKa of the conjugate acid was 3 or higher, then hydrogen fluoride could be rapidly detected. The best performing sensing material could detect hydrogen fluoride concentrations as low as 3 ppb in DFP of 99 % purity in one minute. Based on sarin having the same purity level, we estimate that it would be detectable at a concentration of approximate to 40 ppb in one minute, which is lower than the Acute Exposure Guideline 3 (life-threatening effects) of 64 ppb for a 10-min exposure.

This study reports the optoelectronic and device properties of solution-processable green emissive phosphorescent iridium(iii) complex-cored light-emitting dendrimers composed of different generations and/or number of emissive dendronised ligands.

Film‐based fluorescence sensors are attractive for illicit drugs detection due to their potential for rapid response, low limits of detection, and portability. However, it is still a significant challenge to achieve real‐time identification of suspected illicit drugs using fluorescence detection. Herein, four novel 1,8‐naphthalimide (NI) derivatives with different substituents at the 4‐position, namely NI‐1 [phenyl], NI‐2 [4‐({2‐ethylhexyl}oxy)phenyl], NI‐3 [4,4''‐bis({2‐ethylhexyl}oxy)‐(1,1':3',1''‐terphenyl)‐5'‐yl] and NI‐4 [4‐(dimesitylboraneyl)phenyl] are reported. The four NI derivatives had different thin film optoelectronic properties and mass densities, and showed distinct fluorescence responses to methamphetamine hydrochloride, 3,4‐methylenedioxyamphetamine hydrochloride, cocaine hydrochloride, fentanyl hydrochloride, and tetrahydrocannabinol. The contrasting fluorescence responses of NI‐1 , NI‐2 , NI‐3 and NI‐4 were utilized as the basis for a constructed sensor array, which can distinguish between five drugs, three compounds commonly found around the home (paracetamol, aspirin and caffeine) and a null class (a blank swab) in 18 s with a mean classification accuracy of 81%. By grouping analyte predictions into binary “drug” and “other” categories, a 94% mean classification accuracy is achieved. This highlights the potential for thin film fluorescent NI derivatives to be used for rapid on‐site drug screening.

The power conversion efficiency (PCE) of perovskite solar cells is sensitive to their method of fabrication as well as the combination of materials in the perovskite layer. Air knife-assisted blade coating enables good quality perovskite films to be formed but the device efficiencies still tend to lag behind those fabricated using spin-coated perovskite layers. Herein we report the use of three 2,3,4,5,6-pentafluorophenylethylammonium halides (FEAX, where X = I-, Br- or Cl-) as additives in nitrogen knife-assisted blade-coated methylammonium lead iodide (MAPbI3) perovskite solar cells. The additives were all found to passivate defects in the MAPbI3 films. The use of chloride as the counteranion led to additive containing films with the largest crystal size and fewest defects and consequently the FEACl film was found to have the highest photoluminescence (PL) intensity, longest average PL lifetime and lowest trap density. These features led to the devices having a high open-circuit voltage (V oc) of 1.17 V and a PCE of 21.4%. In addition, the hydrophobic fluorinated cations led to the additive containing devices being more stable, with those containing FEACl having the best thermal stability and performance under maximum-power-point (MPP) tracking in a humid (approximate to 65%) environment at 50 +/- 1 degrees C.

Y6 homojunction solar cells are prepared using the exciton/electron-blocking material poly[9,9-di-n-octylfluorene-alt-N-(4-sec-butylphenyl)diphenylamine] (TFB) as a secondary hole transport layer material in conjunction with PEDOT:PSS. Using this device architecture, a maximum power conversion efficiency (PCE) of 2.57% is achieved, which is the highest reported thus far for a solution-processed small molecule homojunction organic photovoltaic (OPV) device. The devices display an unexpectedly low thickness dependence, with the average PCE only decreasing by approximate to 17% when the Y6 active layer thickness is increased from 80 to 300 nm. Time-resolved photoluminescence measurements show that the TFB does not contribute to charge generation through photoinduced hole or electron transfer. However, transient absorption spectroscopy on thin films of neat Y6 and a 1:1 blend of Y6:TFB shows that the TFB enhances the formation of the long-lived Y6 intermolecular charge-transfer state in the blend film. It is found that careful selection of the electron transport layer (ETL) is required to avoid unintended charge generation at the interface with Y6 so as to ensure that the device is a true homojunction. The improved efficiency of this architecture is attributed to the electron-blocking and hole-extraction effects of the TFB layer.

Vanadium pentoxide (V2O5) and molybdenum oxide (MoOx) interlayers were used with graphene-coated poly(ethylene terephthalate) (PET) as the transparent conductive anode for organic solar cells (OSCs). The transmittances of the two transparent conductive anodes were found to be similar but the anode composed of the V2O5 was found to have a smaller sheet resistance, smoother surface topology, and larger work function. Small area OSCs (0.2 cm(2)) with V2O5 or MoOx interlayers and a thick photoactive layer (similar to 300 nm) to ameliorate any residual roughness of the graphene anode had power conversion efficiencies (PCEs) of 5.6 % and 5.5 %, respectively. The PCEs of the medium area cells (1.35 cm(2)) were lower (best = 2.9 %), with the devices containing the V2O5 outperforming those using the MoOx interlayer. Furthermore, the V2O5 interlayer containing device was more stable, with the small area devices retaining around 60 % of their PCE over a 24-h period at the maximum powerpoint and simulated 1 sun illumination. Ultraviolet photoelectron spectroscopy measurements showed that upon photoexcitation the oxidation state of the molybdenum of the MoOx modified graphene anode was reduced, which explains the faster degradation of the OSCs containing that anode. In contrast, V2O5 maintained its oxidation state upon illumination.

Film-based fluorescence sensors are attractive for rapid and on-site detection of illicit drugs, due to their potential for portability, high sensitivity and reusability. Three new bay-substituted perylene diimide derivatives are synthesized , P1-CH3 (1-methyl), P1-CF3 (1-trifluoromethyl), and P1-(CF3)2 (1,7-di-trifluoromethyl) that can be solution processed into thin films capable of detecting methamphetamine hydrochloride (MA center dot HCl) and cocaine center dot HCl via a luminescence quenching mechanism. The ionization potentials of the materials are sufficiently high to enable photoinduced hole transfer to occur, which led to the luminescence quenching. The trifluoromethyl-substituted PDIs exhibit superior sensitivity and reversibility of the luminescence quenching process. In particular, P1-(CF3)2 shows a limit of detection to MA center dot HCl of approximate to 100 ng after a 15-second exposure, and its luminescence can be fully recovered either through mild heating or being placed in an air flow. Furthermore, by using the luminescence quenching and recovery responses of four PDI sensing materials it is possible to differentiate MA center dot HCl, cocaine center dot HCl, from aspirin, caffeine, sugar, and (sebum) skin oil in around a minute. Films of perylene diimide (PDI) derivatives can detect methamphetamine hydrochloride (MA.HCl) via a luminescence quenching mechanism - photoinduced hole transfer. A di-trifluoromethyl-substituted PDI shows a limit of detection to MA center dot HCl of approximate to 100 ng after a 15-second exposure. Using four PDI derivatives enabled differentiation of MA center dot HCl from cocaine.HCl, aspirin, caffeine and sugar within 60 seconds.image

Excited-state intramolecular proton transfer emitters have emission that is significantly red shifted relative to the absorption spectra, which enables the sensitive detection of extant hydrogen fluoride found in G-series nerve agents.

Solution processed organic photovoltaic (OPV) devices are promising for low-embedded energy and large-scale renewable energy production. The efficiency of charge carrier generation is a critical factor influencing the performance of photovoltaic devices. However, quantifying charge carrier generation can be challenging, with the results from experimental methods not always being easily correlated with solar cell performance. In this paper, we describe how photoinduced metal-insulating-semiconductor charge-extraction-by-linearly-increasing-voltage (photo-MIS-CELIV) can be used to determine the free charge carrier generation efficiency (FCGE) in OPV films. One of the benefits of this approach is that the FCGE can be measured alongside the charge mobility to provide a holistic picture of the fate of charges, from generation to extraction. We demonstrate this method through quantifying the FCGE of bulk heterojunctions of PCE10:ITIC-4F, D18:Y6 and PPDT2FBT:PC71BM, obtaining values of 47.4 +/- 1.6 %, 75.0 +/- 2.5 % and 70.6 +/- 4.6 %, respectively. The measured FCGEs for these blends were consistent with the device-based external quantum efficiencies (EQEs) at the excitation wavelength used. The use of photo-MIS-CELIV for quantifying the FCGE increases its utility beyond simple charge mobility measurements and provides an extra method to enable optimisation of OPV device performance.

Luminescence-based sensing provides a method for the rapid detection of nerve agents. Previous approaches have generally focused on sensing materials containing a nucleophilic group that can react with the electrophilic phosphorus atom found in nerve agents. Herein we report an alternative approach for the detection of phosphonofluoridate-based G-series nerve agents that utilizes the fact they contain hydrogen fluoride. We have developed silylated sensing materials based on an excited-state intramolecular proton transfer (ESIPT) reporter compound, 2-[benzo[d]thiazol-2-yl]phenol. Thin films of differently silylated 2-[benzo[d]thiazol-2-yl]phenol were found to react with the hydrogen fluoride found in di-iso-propyl fluorophosphate (DFP), a simulant of sarin (G-series nerve agent), and turn on the ESIPT emission of the reporter compound. The use of the ESIPT emission reduced the impact of background fluorescence and improved the sensitivity of the detection. The effectiveness of the approach was dependent on the stability of the silyl protecting group used, with the least sterically hindered (trimethylsilyl) found to be too unstable to the ambient environment while the most sterically hindered, e.g., tri-iso-propylsilyl and tert-butyldiphenylsilyl were found to be insufficiently reactive to be useful in a real detection scenario. The sensing material composed of the tert-butyl dimethylsilyl protected 2-[benzo[d]thiazol-2-yl]phenol was found to have the best balance between stability under ambient conditions, and reactivity and selectivity to hydrogen fluoride. In a 3 s exposure, it could detect hydrogen fluoride down to a concentration of around 23 ppm in DFP with 99% purity.

AbstractFluorescence‐based sensing is a promising method for detecting trace quantities (vapors) of chemical threats. However, direct detection at standard temperature and pressure of chemicals with low volatilities, such as the salts of illegal drugs, is difficult to achieve. Herein, the development of a testing platform designed to maximize the response from fluorescent material detection of low volatility analytes, using the salts of illicit drugs as exemplars, is described. The challenges encountered in detecting low‐volatility analytes are highlighted, and the hardware solutions employed to overcome them are detailed. The testing platform is composed of a swab heating unit, a sensing chamber, and optical components that enable detection of illicit drugs via a fluorescence quenching mechanism. The swab heating unit facilitates volatilization of the analytes, with the shape of the sensing chamber and its fabrication material optimized to maximize the interaction of the analyte with the sensing element, increasing sensitivity. The detection platform is able to detect trace amounts (down to 30 ng) of (±)‐3,4‐methylenedioxyamphetamine hydrochloride (MDA•HCl), along with other common illicit drug salts such as cocaine hydrochloride (cocaine•HCl), fentanyl•HCl, and methamphetamine•HCl (MA•HCl).

It has been proposed that organic semiconductors with a dielectric constant of over 10 could undergo spontaneous free charge carrier generation upon photoexcitation. To explore the effect of variations in the low and high (optical) frequency dielectric constants on free charge generation in homojunction devices, we have prepared a series of monomeric donor-acceptor (D-A) and dimeric acceptor-donor-donor-acceptor (A-D-D-A) compounds, with cyclopentadithiophene donors and benzothiadiazole-dicyanovinyl acceptors, where the benzothiadiazole units are either fluorinated or protonated. Fluorination had a major effect on the low and high frequency dielectric constants. The as-cast fluorinated dimer film was found to have a low frequency dielectric constant of over 10 at 0.1 MHz (the regime where charge recombination could occur), but an optical frequency dielectric constant of only 4.0 at 10(14) Hz (the regime where exciton dissociation occurs). In contrast, the protonated version had a low frequency dielectric constant of only around 6 but an optical frequency dielectric constant of 4.6. Thermal annealing of the film led to an increase in the optical frequency dielectric constant of the fluorinated dimer to 4.7 but a decrease for the protonated material to 3.9. Homojunction devices composed of the as-cast fluorinated dimer had low maximum photoconversion efficiencies (less than 1%) despite a low frequency dielectric constant of 10 and relatively balanced hole and electron mobilities of order 10(-5) cm(2) V-1 s(-1). The results provide further evidence that the optical frequency dielectric constant is a critical parameter for designing materials for efficient single chromophore homojunction devices.

Tris-bidentate iridium(III) complexes used in organic light-emitting diodes (OLEDs) are typically homoleptic or heteroleptic with three or two identical emissive ligands, respectively. Herein red phosphorescence emitting dendrimers composed of first generation biphenyl dendrons, 2-ethylhexyloxy surface groups and an iridium(III) complex core with three, two or one emissive [4-phenyl]-2-[thiophen-2-yl]quinoline ligands are reported. The dendrimers have similar photoluminescence quantum yields (PLQYs) in solution (84-88%), neat film (23-25%) and when blended with tris(4-carbazoyl-9-ylphenyl)amine (72-73%), enabling the effect of the number of emissive ligands on OLED performance to be determined. The external quantum efficiency (EQE) of OLEDs composed of neat dendrimer films increased with decreasing number of emissive ligands, with the device composed of the dendrimer having a single emissive ligand having an EQE of 9.2%, which is almost double that expected from a bottom emitting device and a film PLQY of 25 +/- 3.6%. The emission is Lambertian and the higher-than-expected EQE is ascribed to alignment of the single emissive ligand being optimal for light-outcoupling. The EQE of OLEDs containing the blend film also increased with decreasing emissive number of ligands (maximum EQE = 15.4%). Red phosphorescent dendrimers composed of first generation biphenyl dendrons, 2-ethylhexyloxy surface groups and an iridium(III) complex core with three, two or one emissive [4-phenyl]-2-[thiophen-2-yl]quinoline ligands provide organic light-emitting diodes with external quantum efficiencies up to double that expected from a bottom emitting device based on the photoluminescence quantum yield and standard outcoupling efficiency. image

Engineering the dielectric constant (epsilon) to lower the exciton binding energy of the light-absorbing semiconductor can improve organic photovoltaic (OPV) device performance. Here, a series of materials are reported with 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (INCN) acceptor end groups and a central glycolated bis(4H-cyclopenta[2,1-b:3,4-b ']dithiophene) unit with large low-frequency (epsilon lf = 7.4-7.9 at 0.1-0.2 MHz) and optical-frequency (epsilon opt up to 6.6 at 2 x 1014 Hz) dielectric constants. The INCN end groups differed in whether they were protonated, chlorinated, or fluorinated, with the latter having the highest epsilon opt. An epsilon opt of 6.6 is predicted to lead to a low exciton binding energy of approximate to 0.04 eV. Time-resolved microwave conductivity measurements showed a temperature-dependent yield-mobility product, with it increasing linearly from 340 K. The onset temperature was near that required to overcome the calculated exciton binding energy and indicates increased free charge generation in a homojunction film. Room temperature transient absorption spectroscopy revealed that photoexcitation rapidly converted to a lower energy state that was consistent with the formation of polarons or a charge transfer state. This work provides experimental evidence of the importance of epsilon opt for the generation of free charges, and a strategy for development of efficient single chromophore homojunction OPV devices.

Controlled functionalization of 2D black phosphorus (BP) nanosheets provides unique opportunities to tune their chemical, physical, and electronic properties. Herein, the preparation of single‐atom nickel‐doped BP (Ni–BP) sheets using a simple solution‐based strategy is reported. Using the Ni–BP sheets as a passivation layer on top of a perovskite film leads to standard perovskite solar cells (PSCs) with improved performance. The standard n –i– p PSCs with the Ni–BP interlayer achieve maximum power conversion efficiencies of over 22%, with negligible hysteresis and a modest improvement in stability when subjected to different testing conditions. The perovskite films prepared with Ni–BP sheets‐based passivation are found to have reduced defect densities as well as improved charge‐transfer properties and carrier lifetimes. Density‐functional theory calculations support the experimental results through showing that the atomic Ni‐doping increases the work function of the BP interlayer, enabling better hole extraction, as well as increasing the surface hydrophobicity of the BP layer, hence reducing water sorption into the perovskite film.

Efficient detection of chemical analytes using fluorescence-based sensors necessitates an in-depth understanding of the physical interaction between the analyte molecules and the sensor films. This study explores the interplay between the thermal properties of a series of triphenylamine-centered fluorescent dendrimers with different glass transition temperatures (T-g) for detecting nitroaromatic explosives. When exposed to 4-nitrotoluene (pNT) vapors, biphasic diffusion kinetics were observed for all the dendrimers, corresponding to Super Case II kinetics, suggesting rapid film swelling during initial analyte uptake. The diffusion kinetics were further analyzed using a diffusion-relaxation model, where a strong T-g dependence was observed for both the initial concentration-driven diffusion phase and the slower film relaxation phase. Additionally, a difference in kinetics between analyte uptake and release was observed. The photoluminescence (PL) kinetics also showed a T-g dependence, with more efficient PL recovery observed for films composed of dendrimers that had a lower T-g. Rapid quenching of over 40% with little PL recovery was seen in the dendrimer with the highest T-g (107 degrees C), while a smaller quench with efficient PL recovery was observed in the dendrimer that had a T-g close to room temperature. The results highlight the critical role of the thermal properties of sensor films in achieving rapid and sensitive detection.

The advent of small molecule non-fullerene acceptor (NFA) materials for organic photovoltaic (OPV) devices has led to a series of breakthroughs in performance and device lifetime. The most efficient OPV devices have a combination of electron donor and acceptor materials that constitute the light absorbing layer in a bulk heterojunction (BHJ) structure. For many BHJ-based devices reported to date, the weight ratio of donor to acceptor is near equal. However, the morphology of such films can be difficult to reproduce and manufacture at scale. There would be an advantage in developing a light harvesting layer for efficient OPV devices that contains only a small amount of either the donor or acceptor. In this work we explore low donor content OPV devices composed of the polymeric donor PM6 blended with high performance NFA materials, Y6 or ITIC-4F. We found that even when the donor:acceptor weight ratio was only 1:10, the OPV devices still have good photoconversion efficiencies of around 6% and 5% for Y6 and ITIC-4F, respectively. It was found that neither charge mobility nor recombination rates had a strong effect on the efficiency of the devices. Rather, the overall efficiency was strongly related to the film absorption coefficient and maintaining adequate interfacial surface area between donor and acceptor molecules/phases for efficient exciton dissociation.

In‐field rapid and reliable identification of nerve agents is critical for the protection of Defence and National Security personnel as well as communities. Fluorescence‐based detectors can be portable and provide rapid detection of chemical threats. However, most current approaches cannot differentiate between dilute vapors of nerve agent classes and are susceptible to false positives due to the presence of common acids. Here a fluorescence‐based method is shown for rapid differentiation between the V‐series and phosphonofluoridate G‐series nerve agents and avoids false positives due to common acids. Differentiation is achieved through harnessing two different mechanisms. Detection of the V‐series is achieved using photoinduced hole transfer whereby the fluorescence of the sensing material is quenched in the presence of the V‐series agent. The G‐series is detected using a turn‐on mechanism in which a silylated excited state intramolecular proton transfer sensing molecule is selectively deprotected by hydrogen fluoride, which is typically found as a contaminant and/or breakdown product in G‐series agents such as sarin. The strategy provided discrimination between classes, as the sensor for the G‐series agent class is insensitive to the V‐series agent, and vice versa, and neither responded to common acids.