Almantas Pivrikas

Knowledge of charge transport and exciton behavior in organic semiconductor materials is essential to develop high-performance devices. Experimental methods based on the photogeneration of charges offer the opportunity to probe both exciton dissociation and the subsequent charge transport in the same device under the same conditions. In this work, we study the common organic light-emitting diode material tris(2-phenylpyridine)iridium(III), Ir(ppy)3, and show that the yield of free charge carriers from photogenerated excitons is strongly dependent on the electric field in the semiconductor. We simultaneously measure the hole mobility in this material. Our experiments are based on the accumulation of charge carriers at a semiconductor–insulator interface, and we find that the dynamics of this charging process provide information about exciton dissociation and charge carrier mobility. This work illustrates the importance of considering the electric field dependence of exciton dissociation when interpreting charge transport experiments.

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Biomass-derived porous carbon electrodes have attracted significant attention for high-performance supercapacitor applications due to their sustainability, cost-effectiveness, and tunable porosity. To accelerate the design and evaluation of these materials, it is essential to develop accurate and efficient strategies for optimizing their physicochemical and electrochemical properties. Herein, a machine learning (ML) approach is employed to analyze experimental data from previously reported sources, enabling the prediction of specific capacitance (F g−1) based on various material characteristics and processing conditions. The trained ML model evaluates the influence of factors such as biomass type, electrolyte, activating agent, and key synthesis parameters, including activation and carbonization temperatures and durations, on supercapacitor performance. Despite growing interest, comprehensive studies that correlate these variables with performance metrics remain limited. This work addresses this gap by using ML algorithms to uncover the interrelationships between biomass-derived carbon properties, synthesis conditions, and specific capacitance. Herein, it is demonstrated that an optimal combination of a carbonized honeydew peel to H3PO4 ratio of 1:4 and an activation temperature of 500 °C yields a highly porous carbon material. When used in a symmetric device with 1 M H2SO4 electrolyte, this material, rich in oxygen and phosphorus species, achieves a high specific capacitance of 611 F g−1 at a current density of 1.3 A g−1. Correlation analysis reveals a strong synergy between surface area and pore volume (correlation coefficient = 0.8473), and the ML-predicted capacitance closely aligns with experimental results. This ML-assisted framework offers valuable insights into the critical physicochemical and electrochemical parameters that govern supercapacitor performance, providing a powerful tool for the rational design of next-generation energy storage materials.

Biogas, consisting mainly of CO2 and CH4, offers a sustainable source of energy. However, this gaseous stream has been undervalued in wastewater treatment plants owing to its high CO2 content. Biogas upgrading by capturing CO2 broadens its utilisation as a substitute for natural gas. Although biogas upgrading is a widely studied topic, only up to 35% of produced raw biogas is upgraded in the world. To open avenues for development research on biogas upgrading, this paper reviews biogas as a component in global renewable energy production and upgrading technologies focusing on electrochemically driven CO2 capture systems. Recent progress in electrochemical CO2 separation including its energy requirement, CO2 recovery rate, and challenges for upscaling are critically explored. Electrochemical CO2 separation systems stand out for achieving the most affordable technology among the upgrading systems with a low net energy requirement of 0.25 kWh/kg CO2. However, its lower CO2 recovery rate compared to conventional technologies, which leads to high capital expenditure limits the commercialisation of this technology. In the last part of this review, the future perspectives to overcome the challenges associated with electrochemical CO2 capture are discussed.

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.
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Numerical computations through the finite element method (FEM) are used to determine the impact of doping on carrier concentration and recombination between charges in time for organic semiconductor diodes having low mobility. The Hall effect is used to determine the effects of doping on the performance and reliability of organic semiconductor devices by accurately modeling these processes. In this work, the number density of charge carriers and Hall voltages are computed for n-type doped semiconductors with two different recombination processes, such as non-Langevin and Langevin-type. The findings reveal that in the Langevin system with 𝛽′=1, the number density of charge carriers is almost five and four times lower compared with the non-Langevin system with 𝛽′=0.01 for increasing dopant concentrations of 𝑁𝑝𝑑 = 1 and 3, respectively. The Langevin system also had lower Hall voltages than the steady-state and non-Langevin systems for different magnetic fields with dopants, and the non-Langevin system had nearly identical Hall voltages as the steady-state case. The outcome of the current work provides insights into charge transportation mechanisms in low-mobility doped organic semiconductors with Hall effect measurements to improve device efficiency.

The traditional electrochemical caustic soda recovery system uses the generated pH gradient across the ion exchange membrane for the regeneration of spent alkaline absorbent from CO 2 capture. This electrochemical CO 2 capture system releases the by-products H 2 and O 2 at the cathode and anode, respectively. Although effective for capturing CO 2 , the slow kinetics of the oxygen evolution reaction (OER) limit the energy efficiency of this technique. Hence, this study proposed and validated a hybrid electrochemical cell based on the H 2-cycling from the cathode to the anode to eliminate the reliance on anodic oxygen generation. The results show that our lab-scale prototype enabled effective spent caustic soda recovery with an electron utilisation efficiency of 90%, and a relative carbonate/bicarbonate diffusional flux of approximately 40%. The system also enabled the regeneration of spent alkaline absorbent with a minimum electrochemical energy input of 0.19 kWh/kg CO 2 at a CO 2 recovery rate of 0.7 mol/m 2 /h, accounting for 30% lower energy demand than a control system without H 2-recycling, making this technique a promising alternative to the conventional thermal regeneration technology.

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. TiO 2 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/TiO 2 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.

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.

Inorganic semiconductors like silicon and germanium are the foundation of modern electronic devices. However, they have certain limitations, such as high production costs, limited flexibility, and heavy weight. Additionally, the depletion of natural resources required for inorganic semiconductor production raises concerns about sustainability. Therefore, the exploration and development of organic semiconductors offer a promising solution to overcome these challenges and pave the way for a new era of electronics. New applications for electronic and optoelectronic devices have been made possible by the recent emergence of organic semiconductors. Numerous innovative results on the performance of charge transport have been discovered with the growth of organic electronics. These discoveries have opened up new possibilities for the development of organic electronic devices, such as organic solar cells, organic light-emitting diodes, and organic field-effect transistors. The use of organic materials in these devices has the potential to revolutionise the electronics industry by providing low-cost, flexible, and lightweight alternatives to traditional inorganic materials. The understanding of charge carrier transport in organic semiconductors is crucial for the development of efficient organic electronic devices. This review offers a thorough overview of the charge carrier transport phenomenon in semiconductors with a focus on the underlying physical mechanisms and how it affects device performance. Additionally, the processes of carrier generation and recombination are given special attention. Furthermore, this review provides valuable insights into the fundamental principles that govern the behaviour of charge carriers in these materials, which can inform the design and optimisation of future devices.

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.