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Anion exchange membrane (AEM)-equipped electrochemical cells can be used for removing the carbon dioxide (CO2) from biogas, thereby upgrading its energy content. The CO2 absorbed in the catholyte can be transported across the AEM as (bi)carbonate and then recovered in the anodic chamber of the electrochemical cell. However, CO2 regeneration in the anode chamber diminishes the oxygen (O2) content in the anodic gas stream. Given this electrochemically produced oxygen can have a high-industrial application value, such as for promoting more efficient biological wastewater treatment processes, we hereby proposed and validated a three-chamber electrochemical cell configuration capable of removing CO2 and recovering it in an intermediate chamber, with a concomitant anodic generation of high-purity O2 gas. Our prototype successfully facilitated CO2 recovery in a separate chamber preventing CO2 contamination of the anodic O2 gas stream. Results also suggested that an approximately tenfold increase in CO2 loading rate enhanced the relative CO2 diffusion flux from 5 to 43% through the AEM, by lowering the catholyte pH as well as improving gas–liquid CO2 transfer. A mathematical model was also developed to accurately predict the polarization performance of the electrochemical cell. [ABSTRACT FROM AUTHOR]

The performance of electronic and semiconductor devices is critically dependent on the distribution of guest molecules or atoms in a host matrix. One prominent example is that of organic light‐emitting diode (OLED) displays containing phosphorescent emitters, now ubiquitous in handheld devices and high‐end televisions. In such OLEDs the phosphorescent guest [normally an iridium(III)‐based complex] is typically blended into a host matrix, and charge injection and transport, exciton formation and decay, and hence overall device performance are governed by the distribution of the emissive guest in the host. Here high‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) is used with depth sectioning to reconstruct the 3D distribution of emissive iridium(III) complexes, fac‐tris(2‐phenylpyridine)iridium(III) [Ir(ppy)3], blended into the amorphous host material, tris(4‐carbazoyl‐9‐ylphenyl)amine (TCTA), by resolving the position of each single iridium(III) ion. It is found that most Ir(ppy)3 complexes are clustered with at least one other, even at low concentrations, and that for films of 20 wt.% Ir(ppy)3 essentially all the complexes are interconnected. The results validate the morphology of blend films created using molecular dynamics simulations which mimic the evaporation film‐forming process and are also consistent with the experimentally measured charge transport and photophysical properties. [ABSTRACT FROM AUTHOR]

Charge transport characteristics in organic semiconductor devices become altered in the presence of traps due to defects or impurities in the semiconductors. These traps can lead to a decrease in charge carrier mobility and an increase in recombination rates, thereby ultimately affecting the overall performance of the device. It is therefore important to understand and mitigate the impact of traps on organic semiconductor devices. In this contribution, the influence of the capture and release times of trap states, recombination rates, and the Lorentz force on the net charge of a low-mobility organic semiconductor was determined using the finite element method (FEM) and Hall effect method through numerical simulations. The findings suggest that increasing magnetic fields had a lesser impact on net charge at constant capture and release times of trap states. On the other hand, by increasing the capture time of trap states at a constant magnetic field and fixed release time, the net charge extracted from the semiconductor device increased with increasing capture time. Moreover, the net charge extracted from the semiconductor device was nearly four and eight times greater in the case of the non-Langevin recombination rates of 0.01 and 0.001, respectively, when compared to the Langevin rate. These results imply that the non-Langevin recombination rate can significantly enhance the performance of semiconductor devices, particularly in applications that require efficient charge extraction. These findings pave the way for the development of more efficient and cost-effective electronic devices with improved charge transport properties and higher power conversion efficiencies, thus further opening up new avenues for research and innovation in this area of modern semiconductor technology. [ABSTRACT FROM AUTHOR]

We report on the realization of charge selective CELIV (charge extraction by linearly increasing voltage) via the selective extraction of each charge carrier species in a SiO 2 inserted MIS (metal-insulator-semiconductor) structure. The experiments are performed in a typical active layer of P3HT (poly (3-hexylthiophene)):PCBM (phenyl C 61 -butyric acid methyl ester) with a composition ratio of 1:1. The presence of double CELIV peaks indicates the involvement of deep trap states in the charge transport process. Furthermore the difference in excitation intensity dependence between photo-excited holes and electrons suggests a difference in population probabilities of electrons and holes for shallow and deep trap states. Charge selective CELIV experiments also show that the simultaneous extraction of holes and electrons is not a simple linear superposition of the cases where they are extracted separately, indicating that a fraction of photo-excited charges populating shallow trap states can escape from the device. [ABSTRACT FROM AUTHOR]

We present experimental evidence of combined effects of temperature, carrier concentration, electric field as well as disorder on charge transport in an organic field-effect transistor (OFET). Transfer characteristics of an OFET based on sexithiophene active layer were measured from 80 to 300 K. Thermally activated carrier mobility followed Arrhenius law with two activation energies. Carrier density variation led to finite extrapolated Meyer–Neldel (MN) temperature (780 K) at low fields. Negative electric field-dependent mobility was observed in available field range. MN temperature shifted towards higher temperature when the electric field increased, and did not retain its finite character above the field of 4 × 103 V cm−1. [ABSTRACT FROM AUTHOR]

Abstract: The solid-state photophysical and charge transport properties of two first-generation dendrimers are presented. The dendrimers are comprised of a triphenylamine core, dendrons containing a phenyl branching unit with thiophene (Dendrimer 1) or bithiophene (Dendrimer 2) moieties, and dodecyl surface groups. For Dendrimer 1, the excited state is located within the center of the dendrimer giving rise to a moderate solid-state photoluminescence quantum yield (Φpl) (0.13) and significant charge trapping, with both observations due to the degree of overlap of the main electroactive chromophores on adjacent dendrimers. For Dendrimer 2, the excited state is located within the dendron and in the solid-state this leads to a strongly red-shifted and weakened emission (Φpl ~0.02) due to strong intermolecular chromophore interactions. For films of Dendrimer 2 the charge mobility was higher than Dendrimer 1 but was still limited by a low density of strongly interacting electroactive chromophores. The pronounced difference between the solid-state properties of the two dendrimers is simply engineered by the addition of an extra thiophene in each of the dendrons. [Copyright &y& Elsevier]

The time-dependent charge carrier transport and recombination processes in low-mobility organic semiconductor diodes are obtained through numerical simulations using the finite element method (FEM). The application of a Lorentz force across the diode alters the charge transport process leading to the Hall effect. In this contribution, the Hall effect parameters, such as the Hall voltage and charge carrier concentration with varying magnetic fields, are computed for both Langevin and non-Langevin type recombination processes. The results indicate the charge carrier concentration within the diode for the Langevin system is about seven and fourteen times less while the maximum amount of extracted charge is nearly five and ten times less than that in the non-Langevin system of 0.01 and 0.001, respectively. The Hall voltage values obtained for the steady-state case are similar to the non-Langevin system of β β L = 0.01 . However, the values obtained for the Langevin and non-Langevin systems of β β L = 1 and 0.001 exhibit anomalies. The implications of these findings advance the understanding of the charge transport and Hall effect measurements in organic semiconductors that underpins the device's performance. [ABSTRACT FROM AUTHOR]

Abstract: Research and development towards high efficiency plastic solar cells have been accelerating in recent years. Polymer-based bulk heterojunction solar cells are offering an attractive and inexpensive concept for large scale production by solution processing as well as advantageous flexible and aesthetic form factors. The thin film nano-morphology of bulk-heterojunction solar cells has been shown to dramatically influence the photovoltaic performance of the devices. This article reviews the different methods used to control the film nano-morphology of bulk-heterojunction solar cells focussing on the chemical additives during solution processing. All power conversion efficiency limiting mechanisms of bulk-heterojunction solar cells are discussed in detail. It is shown, how the formation of optimal percolation pathways between donor and acceptor influences the photovoltaic device performance. It is explained how the film nano-morphology relates to light absorption, free charge carrier generation as well as charge transport to the electrodes. [Copyright &y& Elsevier]

Abstract: New poly(p-phenylenevinylene) (PPV)-type conducting polymers containing different concentrations of thiophene and fluorene functional units were investigated in this work and the photophysical and electrochemical properties were evaluated. We observed a dependence of these properties on the concentration of thiophene units in the polymer backbone. The hole mobilities were estimated to be on the order of 10−6 cm2 V−1 s−1. The polymers were combined with different concentrations of a soluble fullerene derivative (PCBM) and applied in bulk-heterojunction photovoltaic cells. The effects of PCBM concentration and of annealing (post-production treatment) on these devices were investigated. The best results were obtained for the materials containing higher concentrations of thiophene units. [ABSTRACT FROM AUTHOR]

Abstract: Postproduction treatment of poly (3-alkylthiophene) based bulk-heterojunction solar cells is an important and required procedure in order to fabricate organic solar cells with highest power conversion efficiencies. Postproduction treatment, by means of annealing solar cells at elevated temperatures during which an external voltage is simultaneously applied, is not very suitable for large scale production schemes due to the need for well controlled environment and involvement of flexible substrates. A faster and easier method for improving the efficiency, like a simple addition of chemicals, would be highly desirable. We have studied the effect of alkyl thiol addition into bulk-heterojunction solar cells, based on poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) mixtures as reported first by Santa Barbara group [J. Peet, C. Soci, R.C. Coffin, T.Q. Nguyen, A. Mikhailovsky, D. Moses, G. C. Bazan, Appl. Phys. Lett. 89 (2006) 252105, J. Peet, J.Y. Kim, N.E. Coates, W.L. Ma, D. Moses, A.J. Heeger, G.C. Bazan, Nat. Mater. 6 (2007) 497], which gives the same final results in even higher performance of organic solar cells through increased power conversion efficiency and thus substitutes the postproduction treatment. Red-shift in optical absorption is seen in the films with alkyl thiol, resembling the absorption of thermally annealed films. Based on steady-state current–voltage characteristics and transient charge carrier extraction by linearly increasing voltage (CELIV) measurements, the conductivity of thermally annealed and films with alkyl thiol is found to be an order of magnitude higher than in films spun from pristine blends of P3HT and PCBM. Charge carrier mobility measurements indicate significant increase in carrier mobility, consistent with the improved structural order and formation of interpenetrating network between the donor and acceptor in the bulk-heterojunction solar cells. [Copyright &y& Elsevier]

Abstract: The charge transport properties in a novel electroluminescent poly{[2-(4′,5′-bis(3″-methylbutoxy)-2′-p-methoxy-phenyl)phenyl-1,4-phenylene vinylene]-co-(9,9-dioctyl-2,7-fluorenylene vinylene)} (BPPPV-PF) have been studied using a time-of-flight (TOF) photoconductivity technique. The TOF transients for holes were recorded over a range of temperatures (207–300K) and electric fields (1.5×105–6.1×105 V/cm). The hole transport in this polymer was weakly dispersive in nature with a mobility at 300K of 5×10−5 cm2/Vs at 2.5×105 V/cm. This increased to 8.4×10−5 cm2/Vs at 6.1×105 V/cm. The temperature and field dependence of charge mobility has been analyzed using the disorder formalisms (Bässler’s Gaussian disorder model (GDM) and correlated disorder model (CDM)). The fit with Gaussian disorder (GDM) model yielded the mobility pre-factor μ ∞ =1.2×10−3 cm2/Vs, energetic disorder parameter σ =82meV and positional disorder parameter Σ =1.73. The average inter-site separation (a =7Å) and the charge localization length (L =3.6Å) was estimated by assuming the CDM type charge transport. The microscopic charge transport parameters derived for this polymer are almost identical to the reported values for fully conjugated polymers with high chemical purity. The results presented indicate that the charge transport parameters can be controlled and optimized for organic optoelectronic applications. [Copyright &y& Elsevier]

Charge transport measurement using the Metal-Insulator-Semiconductor Charge Extraction by Linearly Increasing Voltage (MIS-CELIV) technique is a promising method for determining charge mobility in organic semiconductors because of its ability to study electron and hole mobilities independently. However, MIS-CELIV measurements have a number of parameters that can potentially affect the calculated mobility. There are only a few reports on MIS-CELIV being used to determine the charge mobility for materials typically used in organic light-emitting diodes (OLEDs), and the impact of each of the MIS-CELIV experimental parameters on the mobility is presently unknown. We find that the pulse duration, injection time, maximum voltage, offset voltage, and external load resistance have different levels of influence on the calculated mobility. Using the hole transporting OLED host material, tris(4-carbazoyl-9-ylphenyl)amine (TCTA), we show that having an injection time sufficient to fully charge the insulator layer, a pulse duration comparable to the transit time, and an external circuit time constant much smaller than the transit time is required to give a mobility relevant to an OLED. The optimized MIS-CELIV parameters led to the measurement having a similar current density and electric field to that of an operational OLED. Under these conditions, the hole mobility of TCTA was determined to be 2.90 ± 0.07 × 10−4 cm2 V−1 s−1, which is similar to that measured using time-of-flight techniques. Using inappropriate experimental parameters could lead to an underestimation of the mobility by an order of magnitude. Simulations of the MIS-CELIV measurements verified the effect the different parameters played in determining the charge mobility. [ABSTRACT FROM AUTHOR]

The conversion of biogas to biomethane represents an attractive solution to replace fossil gas with a renewable gas. However, removal of such a large percentage of CO 2 from a fuel gas comes at a significant energy cost using the conventional CO 2 capture technologies and hence has led to an opportunity to develop an alternative technique for large-scale carbon capture. Results of the current study suggest that employing an anion exchange membrane (AEM)-based alkaline water electrolyser for CO 2 removal from gas mixtures offers an energy-efficient strategy for the capture and removal of CO 2 from biogas. After capturing CO 2 in an aqueous absorption column, the resulting bicarbonate solution was fed through the cathode of an AEM-based electrolyser. Although the CO 2 absorption rate increased from about 300 to 900 mol m−3 h−1 when the pH was elevated from 9 to 13, the system's energy requirement was lowest at pH = 9. The economic assessment shows that the electrochemical work requirement for CO 2 removal from biogas using the AEM-based alkaline electrolyser ranges between 0.25 and 0.92 kWh/kg CO 2 at optimum conditions (pH = 9). This could potentially reduce the energy input for CO 2 removal by about 50% compared to commercially available biogas upgrading technologies. [ABSTRACT FROM AUTHOR]

A commercial pure titanium (cp‐Ti) powder was used to produce a photoelectrode substrate via 3D‐printing and a commercial titanium foil (Ti‐foil) was used as substrate for direct comparison. TiO2 nanotubes were prepared on both Ti substrates via electrochemical anodization. Characterisation of electrodes showed similar results in all aspects analysed: morphology, absorbance, crystallinity, and photo‐current response. The efficiency of photoelectrocatlytic treatment of methylene blue dye (MB) in water with a single‐chip UVA‐LED was identical. The cp‐Ti/TiO2 electrode achieved 93±4 % removal of MB after 210 min, when combined with a four‐chip UVA‐LED. The cp‐Ti photoelectrode was also tested for the first time for photoelectrocatalytic treatment of benzothiazole (BTH). The highest degradation of BTH (98±2 %, 120 min) was also achieved using the four‐chip UVA‐LED. This study supports further development of 3D‐printed electrodes, maximizing the potential for the creation of novel electrodes for use in PEC technologies for abatement of organic pollutants. [ABSTRACT FROM AUTHOR]

Virtual power plants (VPPs) are an effective platform for attracting private investment and customer engagement to speed up the integration of green renewable resources. In this paper, a robust bidding strategy to participate in both energy and ancillary service markets in the wholesale electricity market is proposed for a realistic VPP in Western Australia. The strategy is accurate and fast, so the VPP can bid in a very short time period. To engage customers in the demand management schemes of the VPP, the gamified approach is utilized to make the exercise enjoyable while not compromising their comfort levels. The modelling of revenue, expenses, and profit for the load-following ancillary service (LFAS) is provided, and the effective bidding strategy is developed. The simulation results show a significant improvement in the financial indicators of the VPP when participating in both the LFAS and energy markets. The payback period can be improved by 3 years to the payback period of 6 years and the internal rate of return (IRR) by 7.5% to the IRR of 18% by participating in both markets. The accuracy and speed of the proposed bidding strategy method is evident when compared with a mathematical method. [ABSTRACT FROM AUTHOR]

Secondary photocurrents offer an alternative mechanism to photomultiplier tubes and avalanche diodes for making high gain photodetectors that are able to operate even at extremely low light conditions. While in the past secondary currents were studied mainly in ordered crystalline semiconductors, disordered systems offer some key advantages such as a potentially lower leakage current and typically longer photocarrier lifetimes due to trapping. In this work, we use numerical simulations to identify the critical device and material parameters required to achieve high photocurrent and gain in steady state. We find that imbalanced mobilities and suppressed, non-Langevin-type charge carrier recombination will produce the highest gain. A low light intensity, strong electric field, and a large single carrier space charge limited current are also beneficial for reaching high gains. These results would be useful for practical photodetector fabrication when aiming to maximize the gain. [ABSTRACT FROM AUTHOR]

Red‐emitting organic light‐emitting diodes (OLEDs) are important for displays and lighting, with the latter benefiting from solution processable materials, which would enable low embedded energy, scalable fabrication. Herein, the effect of annealing and phase separation on the performance of solution‐processed OLEDs incorporating a light‐emitting layer composed of the exciplex host, m‐MTDATA:OXD‐7, and a red phosphorescent light‐emitting dendrimer, Ir(tDCpq)3, is described. Solution‐processed OLEDs containing an annealed emissive layer with a low dendrimer concentration (2 wt%) are found to have the best performance, which is higher than the device in which the light‐emitting layer is not annealed. The improvement in the performance of the annealed device is ascribed to improved charge mobility within the emissive layer caused by phase separation of the OXD‐7. The OLEDs containing annealed m‐MTDATA:OXD‐7:(2 wt%) Ir(tDCpq)3 have maximum current, power, and external quantum efficiencies of 17.9 cd A−1, 19.4 lm W−1, and 14.8 ± 0.6%, respectively. The fact that the maximum external quantum efficiency (EQE) of 14.8% is larger than that expected based on the photoluminescence quantum yield (PLQY) and the normal out‐coupling efficiency of 20% from a bottom‐emitting device is determined to arise from the different pathways of exciton formation under photoexcitation and charge injection. [ABSTRACT FROM AUTHOR]

Red‐emitting organic light‐emitting diodes (OLEDs) are important for displays and lighting, with the latter benefiting from solution processable materials, which would enable low embedded energy, scalable fabrication. Herein, the effect of annealing and phase separation on the performance of solution‐processed OLEDs incorporating a light‐emitting layer composed of the exciplex host, m‐MTDATA:OXD‐7, and a red phosphorescent light‐emitting dendrimer, Ir(tDCpq)3, is described. Solution‐processed OLEDs containing an annealed emissive layer with a low dendrimer concentration (2 wt%) are found to have the best performance, which is higher than the device in which the light‐emitting layer is not annealed. The improvement in the performance of the annealed device is ascribed to improved charge mobility within the emissive layer caused by phase separation of the OXD‐7. The OLEDs containing annealed m‐MTDATA:OXD‐7:(2 wt%) Ir(tDCpq)3 have maximum current, power, and external quantum efficiencies of 17.9 cd A−1, 19.4 lm W−1, and 14.8 ± 0.6%, respectively. The fact that the maximum external quantum efficiency (EQE) of 14.8% is larger than that expected based on the photoluminescence quantum yield (PLQY) and the normal out‐coupling efficiency of 20% from a bottom‐emitting device is determined to arise from the different pathways of exciton formation under photoexcitation and charge injection. [ABSTRACT FROM AUTHOR]

• Modelling of oxygen mass transfer from single bubbles to the water. • By 20% increase in mass transfer coefficient by replacing air bubbles with oxygen. • Using oxygen in activated sludge offsets energy usage of water electrolysis by 30% • Replacing air with oxygen in aquaculture provides 14 times higher energy efficiency. One strategy to cut down the cost of hydrogen production by electrolysis is effective utilization of the byproduct oxygen. The oxygen can be used to replace the air in the aeration of wastewater in the activated sludge process, or in the aquaculture industry. To determine the benefit of replacing air with oxygen in the aeration process, an analytical simulation of a single bubble rising in stagnant water and a comparison with literature is established. Our results show up to 30 % energy return can be obtained by using oxygen in wastewater treatment by the activated process. The greater benefit of replacing air with pure oxygen in industries requiring higher dissolved oxygen such as the aquaculture industry is also presented. [ABSTRACT FROM AUTHOR]

Charge carrier recombination is studied in operational organic solar cells made from the polymer: fullerene system PCDTBT:PC71BM (poly[N-9"-heptadecanyl-2,7-carbazole-ali-5,5-(4',7'-di-2- thienyl-2',1',3/-benzothiadiazole)]: [6,6]-phenyl-C70-butyric acid methyl ester). A newly developed technique High Intensity Resistance dependent PhotoVoltage is presented for reliably quantifying the bimolecular recombination coefficient independently of variations in experimental conditions, thereby resolving key limitations of previous experimental approaches. Experiments are performed on solar cells of varying thicknesses and varying polymeric molecular weights. It is shown that solar cells made from low molecular weight PCDTBT exhibit Langevin recombination, whereas suppressed (non-Langevin) recombination is found in solar cells made with high molecular weight PCDTBT. [ABSTRACT FROM AUTHOR]

The relationship between charge carrier lifetime and mobility in a bulk heterojunction based organic solar cell, utilizing diketopyrrolopyrole-naphthalene co-polymer and PC71BM in the photoactive blend layer, is investigated using the photoinduced charge extraction by linearly increasing voltage technique. Light intensity, delay time, and temperature dependent experiments are used to quantify the charge carrier mobility and density as well as the temperature dependence of both. From the saturation of photoinduced current at high laser intensities, it is shown that Langevin-type bimolecular recombination is present in the studied system. The charge carrier lifetime, especially in Langevin systems, is discussed to be an ambiguous and unreliable parameter to determine the performance of organic solar cells, because of the dependence of charge carrier lifetime on charge carrier density, mobility, and type of recombination. It is revealed that the relation between charge mobility (μ) and lifetime (τ) is inversely proportional, where the μτ product is independent of temperature. The results indicate that in photovoltaic systems with Langevin type bimolecular recombination, the strategies to increase the charge lifetime might not be beneficial because of an accompanying reduction in charge carrier mobility. Instead, the focus on non-Langevin mechanisms of recombination is crucial, because this allows an increase in the charge extraction rate by improving the carrier lifetime, density, and mobility simultaneously. [ABSTRACT FROM AUTHOR]

Phosphorescent emissive materials in organic light‐emitting diodes (OLEDs) manufactured using evaporation are usually blended with host materials at a concentration of 3–15 wt% to avoid concentration quenching of the luminescence. Here, experimental measurements of hole mobility and photoluminescence are related to the atomic level morphology of films created using atomistic nonequilibrium molecular dynamics simulations mimicking the evaporation process with similar guest concentrations as those used in operational test devices. For blends of fac‐tris[2‐phenylpyridinato‐C2,N]iridium(III) [Ir(ppy)3] in tris(4‐carbazoyl‐9‐ylphenyl)amine (TCTA), it is found that clustering of the Ir(ppy)3 (surface of the molecules within ≈0.4 nm) in the simulated films is directly relatable to the experimentally‐measured hole mobility. Films containing 1–10 wt% of Ir(ppy)3 in TCTA have a mobility of up to two orders of magnitude lower (≈10−6 cm2 V−1 s−1) than the neat TCTA film, which is consistent with the Ir(ppy)3 molecules acting as hole traps due to their smaller ionization potential. Comparison of the simulated film morphologies with the measured photoluminescence properties shows that for luminescence quenching to occur, the Ir(ppy)3 molecules have to have their ligands partially overlapping. Thus, the results show that the effect of guest interactions on charge transport and luminescence are markedly different for OLED light‐emitting layers. [ABSTRACT FROM AUTHOR]

Here we report, a novel two-step dipping technique via post-immersion polar solvent engineering for controlled secondary grain growth (Ostwald Ripening) to fabricate efficient mixed organic cation based MA 0.6 FA 0.4 PbI 3 perovskite solar cell (PSC) in conjunction with low temperature (140 °C) processed sol-gel ZnO ETL for full process compatibility with flexible substrates. The reported MTD-SE method (stands for Modified Two Step Dipping - Solvent Engineering) limits the grain coarsening effect during post-immersion stage of two-step dipping method and provides substantially smooth perovskite surface morphology for enhanced charge transport properties compared to conventional two-step techniques by means of controlled Ostwald Ripening process. The grain coarsening process and concomitant irregular grain size distribution are judiciously controlled by increasing the chemical potential or free energy change (ΔG) of the system at the post-immersion. The photovoltaic performance and photo-current hysteresis phenomena of the reported MTD-SE PSC have been compared with PSCs fabricated with conventional two-step techniques, incorporating 2-Propanol or ethyl alcohol as dipping solvents. The enhanced device performance of MTD-SE PSCs is correlated with the conducive role of the evenly distributed grain boundaries in them, which act as carrier dissociation interfaces and carrier transport pathways to charge selective contacts for superior charge separation and extraction properties. Adding to the merits, MTD-SE PSCs also demonstrate significantly suppressed photo-current hysteretic behaviour which has been elucidated in the context of faster ion migration kinetics with the increased grain boundaries, which exhibit higher ionic diffusivity. The favourable ion migration kinetics with MTD-SE PSC have also been comprehensively analysed from the frequency-dependent capacitive spectra. [ABSTRACT FROM AUTHOR]

A typical signature of charge extraction in disordered organic systems is dispersive transport, which implies a distribution of charge carrier mobilities that negatively impact on device performance. Dispersive transport has been commonly understood to originate from a time-dependent mobility of hot charge carriers that reduces as excess energy is lost during relaxation in the density of states. In contrast, we show via photon energy, electric field and film thickness independence of carrier mobilities that the dispersive photocurrent in organic solar cells originates not from the loss of excess energy during hot carrier thermalization, but rather from the loss of carrier density to trap states during transport. Our results emphasize that further efforts should be directed to minimizing the density of trap states, rather than controlling energetic relaxation of hot carriers within the density of states. [ABSTRACT FROM AUTHOR]

Photovoltaic performance in relation to charge transport is studied in efficient (7.6%) organic solar cells (PTB7:PC71BM). Both electron and hole mobilities are experimentally measured in efficient solar cells using the resistance dependent photovoltage technique, while the inapplicability of classical techniques, such as space charge limited current and photogenerated charge extraction by linearly increasing voltage is discussed. Limits in the short-circuit current originate from optical losses, while charge transport is shown not to be a limiting process. Efficient charge extraction without recombination can be achieved with a mobility of charge carriers much lower than previously expected. The presence of dispersive transport with strongly distributed mobilities in high efficiency solar cells is demonstrated. Reduced non-Langevin recombination is shown to be beneficial for solar cells with imbalanced, low, and dispersive electron and hole mobilities. [ABSTRACT FROM AUTHOR]

A novel technique based upon injection-charge extraction by linearly increasing voltage (i-CELIV) in a metal-insulator-semiconductor (MIS) diode structure is described for studying charge transport in organic semiconductors. The technique (MIS-CELIV) allows selective measurement of both electron and hole mobilities of organic solar cells with active layers thicknesses representative of operational devices. The method is used to study the model high efficiency bulk heterojunction combination poly[ N-9′′-heptadecanyl-2,7-carbazole- alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C70-butyric acid methyl ester (PC70BM) at various blend ratios. The absence of bipolar transport in PCDTBT-and-PC70BM-only diodes is shown and strongly imbalanced carrier mobility is found in the most efficient 'optimized' blend ratios. The mobility measurements are correlated with overall device performance and it is found that balanced and high charge carrier mobility are not necessarily required for high efficiencies in thin film organic solar cells. [ABSTRACT FROM AUTHOR]

Solution-processed monochrome and white organic light-emitting diodes (OLEDs) that have a light-emitting layer composed of a 4,4′,4″-tris(carbazol-9-yl)triphenylamine (TCTA) and (5-terphenyl-1,3-phenylene)bis(diphenylphosphine oxide) (POPH) exciplex host and soluble blue, green and/or red phosphorescent dendrimers have been fabricated and characterised. The OLED performance characteristics were found to be scan dependent, with the first scans having large external quantum efficiencies (EQEs) at low luminance, with subsequent scans showing stable performance. The monochrome (blue, green and red) films were found to have high photoluminescence quantum yields, relatively balanced hole and electron mobilities, and the OLEDs had stable EQEs of between 9 and 12% at 100 cd m−2 over multiple scans. The blue, green and red emissive materials were blended with the exciplex host, with their ratio tuned to achieve white emission. The optimal blend ratio provided white OLEDs that had EQEs of 11.7% and 10.6% at 100 cd m−2 and 1000 cd m−2, respectively. The best balance of 1931 Commission Internationale d'Eclairage (CIE) coordinates (0.40,0.40), Colour Rendering Index (70), and Delta uv (0.003) was achieved for an OLED with the light-emitting layer containing the blue, green and red dendrimers in a ratio of 20.0:0.4:0.8 wt%. A feature of the white OLEDs was the stability of the CIE coordinates, with a change of only (0.013,0.005) between a luminance of 100 cd m−2 and 4000 cd m−2. [Display omitted] • A common exciplex host composed for solution processed blue, green, red and white emissive OLEDs. • Monochrome light-emitting dendrimer:exciplex host blend films have relatively balanced hole and electron mobilities. • Monochrome OLEDs with external quantum efficiencies of up to 22.5%. • White emitting OLEDs external quantum efficiencies of 10.6% at 1000 cd m−2 • White OLEDs with stable CIE coordinates across a broad range of luminance. [ABSTRACT FROM AUTHOR]

Fac -tris[2-phenylpyridinato- C 2 , N ]iridium(III) [Ir(ppy) 3 ] is a well-known phosphorescent material for organic light-emitting diodes (OLEDs) and while uniform thin films can be formed using evaporation under high vacuum, it is not sufficiently soluble to enable it to be processed from solution. Ir(ppy) 3 -cored dendrimers with solubilizing surface groups can be processed from solution to form good quality neat or guest:host blends, even when the host has relatively poor solubility. In this manuscript, we report the effect of adding different solubilizing surface groups, namely 2-ethylhexyloxy, n -propyl or t -butyl to first generation dendrons attached to the Ir(ppy) 3 core on the optoelectronic properties of neat and blend films with tris(4-carbazoyl-9-ylphenyl)amine (TCTA). The different dendrons were found to have minimal effect on the photoluminescence spectra and efficiency of energy transfer from the host to the guest in the blend films. The hole mobility of neat films of the solution-processed Ir(ppy) 3 -cored dendrimer films was around 10−6 cm2 V−1 s−1, which was an order of magnitude less than Ir(ppy) 3 films formed by evaporation. Blending the dendrimers with TCTA at a concentration of 11 mol% (the concentration of the highest film photoluminescence quantum yield) led to an order of magnitude decrease in the hole mobility compared to the neat films. However, despite the relatively low mobilities, simple two-layer OLEDs composed of a blend light-emitting layer and an electron transporting layer were found to reach a maximum EQE of 11.1% at a luminance of 1000 cd m−2 for a film with a PLQY of 60%. [Display omitted] • Ir(ppy)3-cored dendrimers with solubilising surface groups are solution processed. • Good quality guest:host blend films formed with poorly soluble TCTA host. • Dendron type was found to have minimal effect on the host to guest energy transfer. • Charge mobility in dendrimer:TCTA blends less than in neat film. • Simple two-layer OLEDs had maximum EQEs of 11.1% at a luminance of 1000 cd m-2. [ABSTRACT FROM AUTHOR]

We report the fabrication and charge transport characterization of carbazole dendrimer-based organic field-effect transistors (OFETs) for the sensing of explosive vapors. After exposure to para-nitrotoluene (pNT) vapor, the OFET channel carrier mobility decreases due to trapping induced by the absorbed pNT. The influence of trap states on transport in devices before and after exposure to pNT vapor has been determined using temperature-dependent measurements of the field-effect mobility. These data clearly show that the absorption of pNT vapor into the dendrimer active layer results in the formation of additional trap states. Such states inhibit charge transport by decreasing the density of conducting states. [ABSTRACT FROM AUTHOR]

We report on the effects of screening of the electric field by doping-induced mobile charges on photocurrent collection in operational organic solar cells. Charge transport and recombination were studied using double injection (DI) and charge extraction by linearly increasing voltage (CELIV) transient techniques in bulk-heterojunction solar cells made from acceptor-donor blends of poly(3- n-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PC60BM). It is shown that the screening of the built-in field in operational solar cells can be controlled by an external voltage while the influence on charge transport and recombination is measured. An analytical theory to extract the bimolecular recombination coefficient as a function of electric field from the injection current is also reported. The results demonstrate that the suppressed (non-Langevin) bimolecular recombination rate and charge collection are not strongly affected by native doping levels in this materials combination. Hence, it is not necessary to reduce the level of doping further to improve the device performance of P3HT-based solar cells. [ABSTRACT FROM AUTHOR]

We present a technique called 'injected charge extraction by linearly increasing voltage' (i-CELIV) and apply it to evaluate bimolecular recombination in organic solar cells. The experimental setup is straightforward requiring no laser or optical-electrical pulse synchronization. The applicability of the method is discussed and non-Langevin recombination in a model poly(3-n-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PC60BM) solar cell is quantified and confirmed. Further, Langevin recombination in the low optical gap high efficiency blend, poly[2,6-(4,4-bis-{2-ethylhexyl}-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)]:phenyl-C71-butyric acid methyl ester is reported using i-CELIV. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated the charge carrier mobility and photovoltaic response of two thiophene-[P1 (MEH-PPE1-PThV2) and P2 (MEH-PThE1-PPV2)] as well as two anthracene-containing poly (phenylene-ethynylene) family of polymers [P3 (MEH-PPE1-PAnV2) and P4 (MEH-PAnE1-PPV2)], whereby the position of thiophene or anthracene has been shifted from between two double bonds (P1 and P3) to the bridge between triple bond and double bond (P2 and P4). P2 shows better photovoltaic performance than P1, whereas similar photovoltaic characteristics were found for P3 and P4. The devices using the blends of P2 as donor and PCBM as acceptor (1:3 weight ratio) exhibited a short-circuit current density of J SC=5.2mA/cm2, an open-circuit voltage of V OC=800mV, fill factor FF=0.44 and resulting power conversion efficiency η AM1.5=1.8%. [Copyright &y& Elsevier]

Abstract: Considerable interest exists in the development of novel n-type conjugated polymers, since many currently available polymer systems have insufficient electron mobility and/or electron affinity. In this work, a universal synthesis route is presented towards a new class of n-type conjugated polymers, i.e. poly(p-fluoranthene vinylene) (PFV) and its derivatives. This route is illustrated with three examples, i.e. unsubstituted PFV and functionalized hexyl-PFV and dodecyl-PFV. All polymers have been synthesized via the dithiocarbamate precursor route. Solubility was introduced by incorporation of alkyl side chains, which leads to a significantly enhanced purity and processability as compared to unsubstituted PFV. Under the applied electrochemical conditions PFV-type polymers demonstrate typical n-type behavior. Additional CELIV mobility measurements on dodecyl-PFV reveal an excellent electron mobility, μe =1.4×10−4 cm2/Vs. Hence, poly(p-fluoranthene vinylene) and its derivatives are promising n-type materials for organic optoelectronic applications. [Copyright &y& Elsevier]

Abstract: Electropolymerization of N-methylaniline (NMA) and N-butylaniline (NBA) was studied on glassy carbon and optically transparent tin oxide electrodes in mixtures of aqueous and organic solvents. Five different organic solvents, dimethyl formamide, dimethyl sulfoxide, tetrahydrofuran (THF), propylene carbonate (PC) and acetonitrile (ACN) were mixed with aqueous 1.0M HClO4 solutions. Our results show that NMA and NBA can be electropolymerized in aqueous–organic solvent mixtures with maximum 30 and 50% (v/v) organic solvents, respectively. The choice of organic solvent strongly influences the film formation. With addition of 10–20% THF, ACN and PC to the aqueous polymerization solution, the film formation was highly improved. The poly(N-methylaniline) and poly(N-butylaniline) films were characterized with cyclic voltammetry, in situ UV–vis spectroscopy, size exclusion chromatography and with electrical conductivity measurements. [Copyright &y& Elsevier]

To integrate large-scale renewable energy into energy systems, an effective participation from private investors and active customer engagement are essential. Virtual power plants (VPPs) are a very promising approach. To realize this engagement, an efficient monitoring and control system needs to be implemented for the VPP to be flexible, scalable, secure, and cost-effective. In this paper, a realistic VPP in Western Australia is studied, comprising 67 dwellings, including a 810 kW rooftop solar photovoltaic (PV) system, a 700 kWh vanadium redox flow battery (VRFB), a heat pump hot water system (HWS), an electric vehicle (EV) charging station, and demand management mechanisms. The practical and detailed concept design of the monitoring and control system for EEBUS-enabled appliances, and also for the PV and VRFB system, with smart inverters, is proposed. In addition, a practical fog-based storage and computing system is developed to enable the VPP owner to manage the PV, VRFB, and EV charging station for maximizing the benefit to the customers and the VPP owner. Further, the proposed cloud-based applications enable customers to participate in gamified demand response programs for increasing the level of their engagement while satisfying their comfort level. All proposed systems and architecture in this paper have the capability of being implemented fully and relevant references for practical devices are given where necessary. [ABSTRACT FROM AUTHOR]

• Ultra-Violet-ozone treatment increases the work function of indium tin oxide (ITO). • The Ultra-Violet-ozone treated ITO work function is time sensitive in air. • A triarylamine-based small molecule can stabilise the work function of ITO. • Organic light-emitting diodes have an ≈20% up-lift in external quantum efficiency. UV-ozone treatment is one of the most common ways to increase the work function of indium tin oxide (ITO), which is used as the transparent conducting anode in organic light-emitting diodes (OLEDs). However, the work function increase is time sensitive when the samples are left or processed in air, often returning to a similar value to that measured before UV-ozone treatment. We found that for OLEDs formed by solution processing and containing a poly(ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole injection layer that there was no advantage in terms of device efficiency of using UV-ozone treated ITO. However, if a triarylamine-based small molecule [ N 1, N 3, N 5-tris(4- n -butylphenyl)- N 1, N 3, N 5-triphenylbenzene-1,3,5-triamine, 4- n -BTDAB] was introduced onto the UV-ozone treated ITO then the work function was stabilised. When 4- n -BTDAB was introduced between UV-ozone treated ITO and PEDOT:PSS, the resultant solution processed OLEDs were found to have a maximum external quantum efficiency ≈20% higher (corresponding to an absolute increase of ≈2% to around 12%) compared to devices with the same structure but without the triarylamine layer. [ABSTRACT FROM AUTHOR]

We report on the charge transport properties of a simple solution processable small-molecule electron acceptor, 2-[{7-(9,9-di-n-propyl-9H-fluoren-2-yl)benzo[c][1,2,5]thiadiazol-4-yl}methylene]malononitrile (K12), designed for use in bulk-heterojunction organic photovoltaic cells. It was found that the molecular order in as-cast films can be dramatically improved by annealing at moderate temperatures (60 °C), which leads to a greatly enhanced electron mobility. Using the photoinduced charge extraction in linearly increasing voltage technique we measured bulk electron mobilities to be as high as 10-4 cm2 V-1 s-1, comparable with some of the best nonfullerene acceptor materials reported to date. [ABSTRACT FROM AUTHOR]

Achieving the renewable energy integration target will require the extensive engagement of consumers and the private sector in investment and operation of renewable-based energy systems. Virtual power plants are an efficient way to implement this engagement. In this paper, the detailed costs and benefits of implementing a realistic virtual power plant (VPP) in Western Australia, comprising 67 dwellings, are calculated. The VPP is designed to integrate and coordinate rooftop solar photovoltaic panels (PV), vanadium redox flow batteries (VRFB), heat pump hot water systems (HWSs), and demand management mechanisms. An 810-kW rooftop solar PV system is designed and located using the HelioScope software. The charging and the discharging of a 700-kWh VRFB are scheduled for everyday use over a year using an optimization algorithm, to maximize the benefit of it for the VPP owners and for the residents. The use of heat pump HWSs provides a unique opportunity for the residents to save energy and reduce the total cost of electricity along with demand management on some appliances. The cost-and-benefit analysis shows that the cost of energy will be reduced by 24% per dwelling in the context of the VPP. Moreover, the internal rate of return for the VPP owner is at least 11% with a payback period of about 8.5 years, which is a promising financial outcome. [ABSTRACT FROM AUTHOR]

Light harvesting systems based upon disordered materials are not only widespread in nature, but are also increasingly prevalent in solar cells and photodetectors. Examples include organic semiconductors, which typically possess low charge carrier mobilities and Langevin-type recombination dynamics - both of which negatively impact the device performance. It is accepted wisdom that the 'drift distance' (i.e., the distance a photocarrier drifts before recombination) is defined by the mobility-lifetime product in solar cells. We demonstrate that this traditional figure of merit is inadequate for describing the charge transport physics of organic light harvesting systems. It is experimentally shown that the onset of the photocarrier recombination is determined by the electrode charge and we propose the mobility-recombination coefficient product as an alternative figure of merit. The implications of these findings are relevant to a wide range of light harvesting systems and will necessitate a rethink of the critical parameters of charge transport. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to an article related to hot exciton dissociation in organic solar cells, published in previous issue.

In this work the detailed charging and extraction current transients in the channel of organic field effect transistors are presented. This allows for precise estimation of the charge carrier mobility along the channel and in the direction perpendicular to the layer. The charge carrier mobility is experimentally obtained by various methods: from the extraction transients (in small charge and space charge limited current modes) as well as from the duration of the gate charging. The results are in good agreement with the results obtained by steady state current, photogenerated carrier extraction by linearly increasing voltage, and time-of-flight. [ABSTRACT FROM AUTHOR]