2023-11-03, Gogesch, Franciska S., Laininger, Lukas, Sokov, Nick, Schupp, Stefan, Senft, Laura, Linseis, Michael, Schmidt-Mende, Lukas, Unterlass, Miriam M., Winter, Rainer F.

We report on the synthesis of the new bis(alkenylruthenium) complex DBTTF-(ViRu)₂ with a longitudinally extended, π-conjugated dibenzotetrathiafulvalene (DBTTF) bridge, characterized by multinuclear NMR, IR, and UV/vis spectroscopy, mass spectrometry, and single-crystal X-ray diffraction. Cyclic and square-wave voltammetry revealed that DBTTF-(ViRu)₂ undergoes four consecutive oxidations. IR, UV/vis/near-IR, and electron paramagnetic resonance spectroscopy indicate that the first oxidation involves the redox-noninnocent DBTTF bridge, while the second oxidation is biased toward one of the peripheral styrylruthenium entities, thereby generating an electronically coupled mixed-valent state ({Ru}-CH═CH)^•+-DBTTF^•+-(CH═CH-{Ru}) [{Ru} = Ru(CO)Cl(PiPr₃)₂]. The latter is apparently in resonance with the ({Ru}-CH═CH)•+-DBTTF-(CH═CH-{Ru})^•+ and ({Ru}-CH═CH)-DBTTF²⁺-(CH═CH-{Ru}) forms, which are calculated to lie within 19 kJ/mol. Higher oxidized forms proved too unstable for further characterization. The reaction of DBTTF-(ViRu)₂ with the strong organic acceptors 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, tetracyano-p-benzoquinodimethane (TCNQ), and F₄TCNQ resulted in formation of the DBTTF-(ViRu)₂^•+ radical cation, as shown by various spectroscopic techniques. Solid samples of these compounds were found to be highly amorphous and electrically insulating.

2023, Mohanty, Ankita, Noby, Sohaila Z., Schmidt-Mende, Lukas, Ramadoss, Ananthakumar

Designing of 3D heterostructured hybrid materials are effective step, in the pursuit of attaining higher electrochemical performance compared to their pristine metal/metal oxide counterparts, owing to the enlarged active area of electrode-electrolyte interaction, and fast ion transportation path. In this regard, binder-free heterostructured electrodes, 3D-Co-MOF@CoO/Ni (positive) and 3D-C-Fe₄N@NiCu/SS (negative) are fabricated to construct a hybrid supercapacitor (HSC). This core-shell structured positive electrode revealed better electrochemical performance (592.8mC/cm² at 2mA/cm²) than bare CoO/Ni, which is nearly twice as good. Meanwhile, the hierarchical microporous 3D-C-Fe₄N@NiCu/SS electrode achieved a broad potential of 0 to − 1 V with a maximum areal capacity of 852 mC/cm² at 2mA/cm² and 72 % stability over 10000 GCD cycles. The 3D heterostructured morphologies of the electrodes endowed the 3D-Co-MOF@CoO/Ni‖3D-C-Fe₄N@NiCu/SS HSC with a high volumetric energy value of 2.305mWh/cm³ with a volumetric power of 325mW/cm³. The unique architecture and engineering strategies adopted in this research work can pave the way to attain desired electrochemical output in the future.

2023, Ali, Nazakat, Hussain, Sajad, Waqas, Muhammad, Faheem, M., Ahmad, Naveed, Ali, Adnan, Ali, Muhammad Yasir, Mahmood, Khalid, Schmidt-Mende, Lukas

The deposition potential affects the structural, morphological, optical, and electrochemical impedance spectroscopy properties of cuprous oxide (Cu₂O) thin films formed on copper (Cu) substrates adopting a three-electrode electrochemical deposition procedure. XRD data revealed that the deposited films have a cubic structure established with desired (111) growth orientation. Scanning electron microscopy (SEM) images reveal that Cu₂O film has very well three-sided pyramid-shaped grains which are equally spread over the surface of the Cu substrates and change substantially when the plating potential is changed. The photo-current density of prepared Cu₂O thin films was increased from −1.41 × 10⁻⁴ to −3.01 × 10⁻⁴ A/cm² with increasing the deposition potential of −0.3 to −0.6 V, respectively. Further, Cu₂O thin films obtained at −0.6 V have the minimum charge transfer resistance (R_ct) than Cu₂O thin films synthesized at −0.3 to −0.5 V, suggesting that Cu₂O thin films produced at −0.6 V have the highest electron transfer efficiency.

2022, Ramadoss, Ananthakumar, Wong, Ka Kan, Swain, Nilimapriyadarsini, Mohanty, Ankita, Kirubavathi, K., Selvaraju, K., Schmidt-Mende, Lukas

In the present work, we have introduced lightweight, ultrabendable, rough graphite sheets on a polyimide tape substrate as a current collector. The flexible current collector was fabricated by the peel-off method. The as-prepared graphite-sheet-coated polyimide substrate is ultraflexible (bendable, rollable, and twistable), thin, and lightweight, has better conductivity, high mechanical durability, and ease of fabrication, and is cost-effective, rough, and environment friendly. The fabricated flexible current collector could be directly used as the substrate for constructing RuO₂–MnO₂/graphite flexible supercapacitors. The as-prepared electrode delivered a maximum gravimetric capacitance of 183 F g^–1 (73.5 mF cm^–2) at a current density of 1 A g^–1 with better rate capability and 96% capacitance retention (after 5000 cycles). The better electrochemical performance of the electrode is due to the rough surface and good electrical conductivity of the current collector leads to the better attachment of active material and rapid ions/electron transfer.

2023-10-18, Yalcinkaya, Yenal, Rohrbeck, Pascal N., Schütz, Emilia R., Fakharuddin, Azhar, Schmidt-Mende, Lukas, Weber, Stefan A.L.

Abstract Understanding electron and ion dynamics is an important task for improving modern energy materials, such as photovoltaic perovskites. These materials usually have delicate nano‐ and microstructures that influence the device parameters. To resolve detailed structure–function relationships on the relevant micro‐ and nanometer length scales, the current macroscopic and microscopic measurement techniques are often not sufficient. Here, nanoscale surface photovoltage spectroscopy (nano‐SPV) and nanoscale ideality factor mapping (nano‐IFM) via time‐resolved Kelvin probe force microscopy are introduced. These methods can map nanoscale variations in charge carrier recombination, ion migration, and defects. To show the potential of nano‐SPV and nano‐IFM, these methods are applied to perovskite samples with different morphologies. The results clearly show an improved uniformity of the SPV and SPV decay distribution within the perovskite films upon passivation and increasing the grain size. Nevertheless, nano‐SPV and nano‐IFM can still detect local variations in the defect density on these optimized samples, guiding the way for further optimization.

2023, Qureshi, Akbar Ali, Javed, Sofia, Fakharuddin, Azhar, Akram, Muhammad Aftab, Schmidt-Mende, Lukas

The mixed halide perovskite solar cells (PSC) have manifested as a contender to market-dominating silicon counterparts owing to their low-temperature solution processing and high efficiency. In PSCs, the electron extraction layer (EEL) plays a vital role as it controls charge transport/extraction from the perovskite absorber layer to the EEL and also determines interfacial recombination and charge accumulation at the EEL/perovskite interface. In this work, high-purity natural hematite (α-Fe₂O₃) is reported for the first time as the EEL in triple-cation perovskite (CsFAMA) solar cells. To show the cost-effectiveness of this novel EEL, the entire device fabrication process was carried out at a temperature below 150 °C. The optimal α-Fe₂O₃ EEL shows a mobility value of 9.5 × 10⁻⁴ cm⁻² V⁻¹ s⁻¹ and trap densities of around 2.40 × 10¹⁶ cm⁻³; the latter is close to state-of-the-art SnO2 EEL (1.26 × 10¹⁶ cm⁻³). The PSCs employing optimal EEL concentration of 10 mg/mL demonstrated a power conversion efficiency (PCE) of 13.3 %, fill factor of 68 %, and V_OC of 1.03 V. X-ray diffraction studies show a high crystallinity of natural hematite whereas the photoluminescence studies show a fast carrier extraction from the perovskite to the EEL. The natural α-Fe₂O₃-based PSCs exhibited superior shelf-life stability of over 30 days due to less charge recombination and smoother CsFAMA thin film deposited over α-Fe₂O₃ EEL. The low-temperature processed natural α-Fe₂O₃ EEL can therefore be a promising EEL material for low-cost efficient PSCs.

2023, Thirumurugan, Arun, Dhanabalan, Shanmuga Sundar, Shanavas, Shajahan, Udayabhaskar, R., Morel, Mauricio J., Dineshbabu, N., Ravichandran, K., Schmidt-Mende, Lukas, Ramadoss, Ananthakumar

Hybrid supercapacitors (HSCs) are made by the combination of electric double-layer capacitor (EDLC) materials, various types of pseudocapacitive, and battery-type materials. The progress made on the improvement of energy density without sacrificing the power density attracted the researchers to move toward HSC. The specific capacitance of the HSC showed a superior value than the EDLC or pseudocapacitance-based supercapacitors. Numerous advancements have been made on the HSCs with the development in preparation of electrode materials, electrolyte, formation of component, device structure, and the new mechanisms for the improvement of electrochemical characteristics. This chapter specifically emphasis the new development made on the HSCs based on the layered double hydroxides, metal–organic frameworks (MOFs), MOF-derived materials and their composites. The specific characteristics requirement of the electrode material, electrolyte, the substrate in support of electrode materials, and the progress made on them for smart supercapacitors are discussed.

2023, Cuzzupe, Daniele T., Öz, Seren Dilara, Ling, JinKiong, Illing, Elias, Seewald, Tobias, Jose, Rajan, Olthof, Selina, Fakharuddin, Azhar, Schmidt-Mende, Lukas

In the quest for perovskite materials with reduced toxicity, Sn perovskites are emerging. However, they suffer from material instability and rapid crystallization, leading to high defect densities in the films. In this work, the methylammonium chloride (MACl)-assisted crystallization as a route to improve stability and optoelectronic quality of quasi 2D/3D PEA_0.08FA_0.92SnI₃ perovskite is demonstrated. For an optimal additive amount (10 mol%), a 37% increase in power conversion efficiency is found. Notably, MACl enhances the films' stability, evidenced by temporal PL tracking. Understanding the effect of MACl addition in this system is interesting for the pursuit of efficient and stable tin-based devices. The investigations show that MACl addition causes a shift in the optical bandgap and improves morphology, indicating effects in the bulk crystal structure. X-ray photoelectron spectroscopy confirms the presence of Cl on the surface, but no indication of MA⁺ is found. Intriguingly, UV photoelectron spectroscopy shows pronounced changes in the density of states. For the first time, it is shown that MACl promotes the formation of a two-dimensional layer via the surface accumulation of PEA⁺. The MACl additive lowers the absorber's ionization energy, possibly facilitating hole extraction. Overall, this work highlights a facile route to control the crystallization of Sn perovskites.

2023, Ganesh, Gayathry, Yasin, Amina, Misnon, Izan Izwan, Fakharuddin, Azhar, Schmidt-Mende, Lukas, Ab Rahim, Mohd Hasbi, Thomas, Sabu, Jose, Rajan

Perovskite solar cells (PSCs) are intensively studied over the past decade to enhance the renewable contribution to the total energy mix; however, their market potential is hampered mostly by their poor operational stability. Polymers as encapsulants, UV-filters, charge transport layers, and interfacial layers are shown to be a potential remedy not only to improve stability but also to positively contribute to other figures of merits of solar cells. Highly efficient PSCs (>15 %) with prolonged operational stability (>3000 h) in various device architectures including fibres, yarns, and woven and knitted cloths are reported using perovskite embedded polymers. This article critically and comprehensively reviews the synergistic interactions between various polymers and the organic–inorganic lead halide perovskite material to establish a structure–property correlation and to examine the viability of the PSCs technology for practical deployment. Mechanistic details of polymers in the photoactive, charge transport and interfacial layers on the morphology, optical and photovoltaic properties, and stability are analysed and discussed. Particularly on stability, the role of polymers on defect tolerance, phase and structure evolution, and external stimuli (heat, moisture, light, electric field, and oxygen) are elaborated. The dielectric properties of polymers enable them to be superior encapsulants over their corresponding monomers or other organic molecules. Based on these broad considerations, adopting the polymeric approach is shown to be a more efficient and greener leap towards the sustainable commercialization of perovskites.

2022, Ramadoss, Ananthakumar, Mohanty, Ankita, Saravanan, K. Gobi, Kundu, Manab, Noby, Sohaila Z., Kirubavathi, K., Selvaraju, K., Schmidt-Mende, Lukas

The energy storage devices for flexible/wearable and portable electronics are on immediate requirement demanding for high-performance flexible supercapacitors. Nevertheless, the real-time application of advanced electronics necessitates supercapacitors to own admirable mechanical properties to endure rigorous straining environments. Also, it is necessary to reduce the mass and volume of the whole device. Therefore, constructing a high-performance flexible supercapacitor based on better electrochemical and significant mechanical properties is still a formidable task. Herein, we have successfully fabricated a vanadium nitride thin film electrode onto the flexible, thin, and light-weight graphite paper substrate via reactive direct current (DC) magnetron sputtering method. The as-fabricated graphite sheets current collector is flexible, thin, light-weight, electrically conductiviting, cost-effective, and easy to fabricate. Furthermore, the as-prepared binder-free flexible negative electrode displayed better supercapacitor performance in terms of specific capacitance and cycle stability. The negative electrode exhibited an areal capacitance of 91 mF cm⁻² and better cycling stability with > 64% capacitance retention after 2000 cycles. Moreover, the flexible hybrid supercapacitor is fabricated with NiCo hydroxide and VN films and showed a maximum energy density of 1.80 μWh cm⁻² and power density of 387.5 μW cm⁻² and good stability. These results propose that the fabricated electrode has great prospective as a power source for flexible, wearable, and portable electronic devices.