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Solvation engineering plays a critical role in tailoring the performance of batteries, particularly through the use of highly concentrated electrolytes, which offer heterogeneous solvation structures of mobile ions with distinct electrochemical properties. In this study, we employed spectroscopic techniques and molecular dynamics simulations to investigate mixed-cation (Li+/K+) acetate aqueous electrolytes. Our research unravels the pivotal role of water in facilitating ion transport within a highly viscous medium. Notably, Li+cations primarily form ion aggregates, predominantly interacting with acetate anions, while K+cations emerge as the principal charge carriers, which is attributed to their strong interaction with water molecules. Intriguingly, even at a concentration as high as 40 m, a substantial amount of water molecules persistently engages in hydrogen bonding with one another, creating mobile regions rich in K+ions. Our observations of a redshift of the OH stretching band of water suggest that the strength of the hydrogen bond alone cannot account for the expansion of the electrochemical stability window. These findings offer valuable insights into the cation transfer mechanism, shedding light on the contribution of water-bound cations to both the ion conductivity and the electrochemical stability window of aqueous electrolytes for rechargeable batteries. Our comprehensive molecular-level understanding of the interplay between cations and water provides a foundation for future advances in solvation engineering, leading to the development of high-performance batteries with improved energy storage and safety profiles.

Understanding chemical exchange in carbonate-based electrolytes employed in Li-ion batteries (LIBs) is crucial for elucidating ion transport mechanisms. Ultrafast two-dimensional (2D) IR spectroscopy has been widely used to investigate the solvation structure and dynamics of Li-ions in organic carbonate-based electrolytes. However, the interpretation of cross-peaks observed in picosecond carbonyl stretch 2D-IR spectra has remained contentious. These cross-peaks could arise from various phenomena, including vibrational couplings between neighboring carbonyl groups in the first solvation shell around Li-ions, vibrational excitation transfers between carbonyl groups in distinct solvation environments, and local heating effects. Therefore, it is imperative to resolve the interpretation of 2D-IR cross-peaks to avoid misinterpretations regarding ultrafast dynamics found in LIB carbonate-based electrolytes. In this study, we have taken a comprehensive investigation of carbonate-based electrolytes utilizing 2D-IR spectroscopy and molecular dynamics (MD) simulations. Through meticulous analyses and interpretations, we have identified that the cross-peaks observed in the picosecond 2D-IR spectra of LIB electrolytes predominantly arise from intermolecular vibrational excitation transfer processes between the carbonyl groups of Li-bound and free carbonate molecules. We further discuss the limitations of employing a picosecond 2D-IR spectroscopic technique to study chemical exchange and intermolecular vibrational excitation transfer processes, particularly when the effects of the molecular photothermal process cannot be ignored. Our findings shed light on the dynamics of LIB electrolytes and resolve the controversy related to 2D-IR cross-peaks. By discerning the origin of these features, we could provide valuable insights for the design and optimization of next-generation Li-ion batteries.

Water-in-salt electrolytes (WiSEs) are promising electrolytes for next-generation lithium-ion batteries (LIBs), offering critical advantages like nonflammability and improved safety. These electrolytes have extremely high salt concentrations and exhibit unique solvation structures and transport mechanisms dominated by the formation of ion networks and aggregates. These ion networks are central to the performance of WiSEs, govern the transport properties and stability of the electrolyte, deviating from conventional dilute aqueous or organic electrolytes.

Organic thin-film transistors (OTFTs) are essential components for future flexible/wearable electronics. To fabricate OTFTs in an industrial level, following requirements should be met: high carrier mobility, low-voltage operation, compatibility with a reliable high-resolution patterning process, and high mechanical and electrical stability. Here, we report the synthesis of six-branched cross-linkers (6Bx) having an ultrahigh photo-cross-linking efficiency and its application to photo-patterning gate dielectric (GD) polymers and channel semiconducting (CS) polymers in polymer-based OTFTs. The use of 6Bx permits the generation of a high-resolution-patterned ultra-thin polymer gate dielectric with a low leakage current (7 × 10–9A cm–2at 1 MV cm–1). Moreover, cross-linking the GD polymer interfaced with p- or n-type CS polymer induces alignment of CS polymer chains at the interface. This yields excellent hole and electron mobilities of 12.42 and 10.11 cm2V–1s–1, respectively, from p- and n-type OTFTs operated at <3 V, which are remarkably improved carrier mobilities at substantially low operation voltages compared to those by conventional test beds. Further, the fabrication of logic gates and ring oscillators demonstrates the reliability of polymer OTFTs cross-linked with 6Bx. This work presents a universal strategy for high mobility, reliable, and low-voltage operating OTFTs.

Density functional theory (DFT), time‐dependent DFT, and Marcus theory were used to probe the optoelectronic and charge‐transport properties of compounds obtained by inserting long‐chain aliphatic alkenes or condensed aromatic rings between the planar quinacridone core and the terminal donor diphenylamine moiety of a reference hole‐transporting material (HTM). Compared to the reference HTM, its newly designed derivatives showed lower‐lying highest occupied molecular orbitals that were well matched in energy with the valence band maximum of a representative perovskite absorber. HTMs obtained via the insertion of condensed aromatic rings showed higher hole mobilities than those obtained via the insertion of aliphatic alkenes. Overall, hole mobility was mainly influenced by the charge‐transfer integral, while other factors, such as the hole reorganization energy, hole hopping rate, and centroid distance, had only minor effects. Hole mobility of hole‐transporting materials (HTMs) is mainly influenced by charge‐transfer integral. In the HTMs featuring diphenylamine‐π‐quinacridone, condensed aromatic rings are more efficient in increasing hole mobility than aliphatic long‐chain double bonds.

Lithium‐ion battery (LIB) electrolytes based on room‐temperature ionic liquids (RTIL) are promising as safe and sustainable LIB electrolytes. However, there are no reports on the solvation structure and dynamics of RTIL due to the existence of various solvation species in RTIL. Here, we investigated the solvation structure and dynamics of binary mixtures of the phosphonium ionic liquid, tributyl(2‐methoxyethyl)phosphonium bis(trifluoromethanesulfonyl)imide (P444102TFSI), and methylthiocyanate (CH3SCN), with ultrafast mid‐IR Spectroscopy. The changes of vibrational and rotational dynamics of CH3SCN∙∙∙Li+complex and free CH3SCN with an increase in CH3SCN concentration suggest the presence of at least four solvation species, providing superior resolving power for various solvation species existing in complex LIB electrolytes. Our experimental results show that the environment of free CH3SCN and CH3SCN∙∙∙Li+complex changes drastically with change in CH3SCN mole fraction and Li salt concentration in the mixture. We expect that this can affect the Li‐ion transport mechanism in the IL‐based electrolytes. The figure depicts different types of molecular species in free and complex forms in 1 M and 2 M LiTFSI solutions of IL‐CH3SCN binary mixtures along with the corresponding steady state absorption spectra. Time‐resolved vibrational dynamics and rotational dynamics studies revealed the nature of different species present in the binary mixtures.

The effect of heat treatment and vacuum conditions on the textural properties and electrochemical performance of commercially available activated carbons (ACs) was investigated. The AC after post-heat treatment was characterized by nitrogen adsorption–desorption, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy measurements. The ACs treated under vacuum conditions exhibit a higher specific surface area and micropore surface area than those treated under nitrogen atmospheric pressure without significantly affecting the graphite structure of the AC. Under 800 °C temperature and vacuum conditions (AC-V800), the AC with the highest Brunauer–Emmett–Teller surface area of 1951.9 m2g−1(16.4% improvement relative to that of the original AC (1677.2 m2g−1)) was obtained. This is attributed to the removal of oxygen-containing functional groups and volatile matters in the carbon by thermal treatment under vacuum conditions. Consequently, the electric double-layer capacitor using ACs treated under vacuum conditions (1 kPa) at 800 °C (AC-V800) shows considerably improved electrochemical performance in terms of higher specific capacitance and better cycling stability at a high working voltage (3.1 V), compared to the nitrogen-treated and commercial ACs.

Organic carbonate electrolytes are widely used materials for lithium-ion batteries. However, detailed solvation structures and solvent coordination numbers (CNs) of lithium cations in such solutions have not been accurately described nor determined yet. Because transmission-type IR spectroscopy is not of use for measuring the carbonyl stretch modes of electrolytes due to their absorption saturation problem, we here show that simple spacer-free thin cell IR spectroscopy can provide quantitative information on the number of solvating carbonate molecules around each lithium ion. We could estimate the solvent (carbonate) CNs of lithium ions in dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, and butylene carbonate over a wide range of lithium salt concentrations accurately, and they are compared with the previous results obtained with attenuated total reflection IR spectroscopy technique. We anticipate that our spacer-free thin cell approach will potentially be used to investigate the solvation dynamics, chemical exchange process, and vibrational energy transfers between solvating carbonate molecules in lithium salt electrolytes when combined with time-resolved IR spectroscopy.

Investigating the separate dynamics of electrons and holes has been challenging, although it is critical for the fundamental understanding of semiconducting nanomaterials. n-Type self-doped colloidal quantum dots (CQDs) with excess electrons occupying the low-lying state in the conduction band (CB) have attracted a great deal of attention because of not only their potential applications to infrared optoelectronics but also their intrinsic system that offers a platform for investigating electron dynamics without elusive contributions from holes in the valence band. Here, we show an unprecedented ultrafast intraband Auger process, electron relaxation between spin-orbit coupling states, and exciton-to-ligand vibrational energy transfer process that all occur exclusively in the CB of the self-doped β-HgS CQDs. The electron dynamics obtained by femtosecond mid-infrared spectroscopy will pave the way for further understanding of the blinking phenomenon, disproportionate charging in light-emitting diodes, and hot electron dynamics in higher quantum states coupled to surface states of CQDs.

In operando observation of reaction intermediates is crucial for unraveling reaction mechanisms. To address the sensitivity limitations of commercial ReactIR, a flow cell was integrated with a Fourier transform infrared (FTIR) spectrometer yielding a “flow FTIR” device coupled with an NMR spectrometer for the elucidation of reaction mechanisms. The former device detects the low-intensity IR peaks of reaction intermediates by adjusting the path length of the FTIR sample cell, whereas the flow NMR allows the quantitative analysis of reaction species, thus offsetting the limitations of IR spectroscopy resulting from different absorption coefficients of the normal modes. Using the flow NMR and FTIR device, the controversial mechanism of benzoxazole synthesis was conclusively determined by spectroscopic evaluation of the reaction intermediates. This system enabled the accurate acquisition of previously elusive kinetic data, such as the reaction time and rate-determining step. The implementation of reaction flow cells into NMR and FTIR systems could be widely applied to study various reaction mechanisms, including dangerous and harsh reactions, thus avoiding contact with potentially harmful reaction intermediates.

The thermodynamics of Am(III) complex formation in natural groundwater systems is one of the major topics of research in the field of high-level radioactive waste management. In this study, we investigate the absorption and luminescence properties of aqueous Am(III) complexes with a series of aliphatic dicarboxylates in order to learn the thermodynamic complexation behaviors in relation to binding geometries. The formation of Am(III) complexes with these carboxylate ligands induced distinct red shifts in the absorption spectra, which enabled chemical speciation. The formation constants determined by deconvolution of the absorption spectra showed a linear decrease for the three ligands (oxalate (Ox), malonate (Mal), and succinate (Suc)) and a mild decrease for the remaining ligands (glutarate (Glu) and adipate (Adi)). Time-resolved laser fluorescence spectroscopy (TRLFS) was used to obtain information about the aqua ligand, which indirectly indicated the bidentate bindings of these dicarboxylate ligands. A complementary attenuated total reflectance Fourier transform infrared (ATR-FTIR) study on Eu(III), which is a nonradioactive analogue of Am(III) ion, showed that the coordination modes differ depending on the alkyl chain length. Ox and Mal bind to Am(III) via side-on bidentate bindings with two carboxylate groups, resulting in the formation of stable 5- and 6-membered ring structures, respectively. On the other hand, Suc, Glu, and Adi form end-on bidentate bindings with a single carboxylate group, resulting in a 4-membered ring structure. Density functional theory calculations provided details about the bonding properties and supported the experimentally proposed coordination geometries. This study demonstrates that coordination mode-dependent changes in optical properties occur along with thermodynamic stability changes in Am(III)-dicarboxylate complexes.

Understanding the photodegradation mechanism of photoactive materials is critical for enhancing the long-term stability of organic photovoltaic cells (OPVs). However, definitive photodegradation mechanisms have not been reported yet. Here we report the comprehensive understanding of the photodegradation mechanism of the PTB7-Th polymer film. UV/vis absorption and photoluminescence spectra show that the π-conjugated backbone and the intermolecular π–π interactions are simultaneously broken under sunlight in air. Raman spectra reveal that the initial photooxidation begins at the thiophene ring in the benzo[1,2-b;3,3-b]dithiophene (BDT) unit, followed by the ring-opening of the thiophene and the break of the π-conjugated system. Infrared spectra indicate that −S–C═O and −COOH groups are formed as a result of the photooxidation. On the basis of these observations, we propose that the thiophene ring in the BDT unit reacts with oxygen to generate the BDT–O2adduct, which then produces thioester and carboxylic acid. The reaction sites in the BDT unit are consistent with the electrophilic attack positions of oxygen predicted by condensed Fukui functions. Furthermore, the DFT calculated spectrum of the proposed oxidation product agrees well with all the spectroscopic observations. Conclusively, the present work provides an important clue for understanding photodegradation of OPV materials.

Lithium ion battery (LIB) technology is undoubtedly indispensable to modern life. However, despite enormous and extended effort to improve LIB performance, our understanding of the underlying principles and mechanisms of lithium ion transport in nonaqueous LIB electrolytes remained limited until recently. There is a particular lack of knowledge of the microscopic solvation structures and fluctuation dynamics around charge carriers in real electrolytes. Typical electrolytes found in commercially available LIBs consist of lithium salts and mixed carbonate solvents, with the latter playing an essential role in promoting lithium ion transport and forming an electrically stable solid electrolyte interphase. Although a number of linear spectroscopic studies of LIB electrolytes aiming at understanding the complex nature of lithium ion solvation processes have been reported, the notion that each lithium ion is strongly solvated by carbonate molecules to form a long-lasting solvation sheath structure has remained the subject of intense debate. Here, we present the results of FTIR, fs IR pump–probe, two-dimensional IR spectroscopy, and molecular dynamics simulations reported by us and others and discuss the possible interplay of picosecond solvation dynamics and macroscopic ion transport processes within the framework of the fluctuation–dissipation relationship. Further, by measuring the time-dependent fluctuations and spectral diffusions of carbonate carbonyl stretch modes that act as excellent infrared probes for the local electrostatic environment, we show that lithium cations are not only solvated by carbonate molecules but also interact with counteranions at equilibrium depending on solvent composition. Molecular dynamics simulations support the notion that rapid chemical exchanges between carbonate solvent molecules in the first and outer solvation shells are critical for describing mobile lithium ion transport phenomena. We thus anticipate that time-resolved coherent multidimensional vibrational spectroscopy is capable of providing decisive evidence on the ultrafast solvent dynamics of various electrolytes, which is potentially helpful for designing improved and more efficient LIB electrolytes in the future.

Developing infrared (IR) probes is of great interest in biomolecular imaging and spectroscopy. We report our attempt to improve the IR properties of alkyne-derivatized compounds. The vibrational properties of the alkyne (C≡C) stretch mode of aromatic silylacetylene 1and aliphatic silylacetylene 2were studied using Fourier transform infrared and femtosecond IR pump–probe spectroscopies. We find that the insertion of silicon at the position adjacent to the alkyne group, separating it from the compound’s main body, causes an approximately 10-fold increase in the dipole strength of the C≡C stretch mode and a lengthening of its vibrational lifetime from 5.6 ps for the acetylenic compound without a silicon atom acting like a thermal insulator to 50.6 and 50.4 ps for 1and 2, respectively. The enhanced dipole strength and the increased lifetime of 1allowed us to measure the 2D IR spectra for long waiting times up to 450 ps, which suggests that the dynamic observation range of 2D IR spectroscopy with these IR probes can be extended into the subnanosecond range where protein skeletal movements occur.

Attenuated total reflection–Fourier transform infrared (ATR-FTIR) spectroscopy is widely used to study condensed materials due to its convenient sample preparation and ability to avoid absorption saturation. Recently, it has been applied to in situand in operandoobservations of chemical reactions within electrochemical devices, such as lithium-ion batteries. However, because ATR-FTIR spectroscopy relies on frequency-dependent attenuated reflectance, quantitative concentration measurements of chemical species using the Beer–Lambert law are challenging. Despite the availability of several correction methods, discrepancies remain in the solvation structures around Li+ions when comparing transmission-type FTIR and ATR-FTIR spectroscopy results, which complicate the determination of solvation and desolvation energies. In this study, we investigate ATR-FTIR correction algorithms, elucidate the reasons for the discrepancies between ATR-FTIR and transmission FTIR spectroscopy results, and develop a method to correct the ATR-FTIR spectrum to accurately determine the solvation structures around Li+ions.

Previous studies along the banks of the tidal Meghna River of the Ganges-Brahmaputra-Meghna Delta demonstrated the active sequestration of dissolved arsenic (As) on newly formed iron oxide minerals (Fe(III)-oxides) within riverbank sands. The sand with high solid-phase As (>500 mg/kg) was located within the intertidal zone where robust mixing occurs with oxygen-rich river water. Here we present new evidence that upwelling groundwater through a buried silt layer generates the dissolved products of reductive dissolution of Fe(III)-oxides, including As, while mobilization of DOC by upwelling groundwater prevents their reconstitution in the intertidal zone by lowering the redox state. A three end-member conservative mixing model demonstrated mixing between riverbank groundwater above the silt layer, upwelling groundwater through the silt layer, and river water. An electrochemical mass balance model confirmed that Fe(III)-oxides were the primary electron acceptor driving the oxidation of DOC sourced from sediment organic carbon in the silt. Thus, the presence of an intercalating silt layer in the riverbanks of tidal rivers can represent a biogeochemical hotspot of As release while preventing its retention in the hyporheic zone.

Lithium-ion batteries (LIBs) have been deployed in a wide range of energy-storage applications and helped to revolutionize technological development. Recently, a lithium ion battery that uses superconcentrated salt water as its electrolyte has been developed. However, the role of water in facilitating fast ion transport in such highly concentrated electrolyte solutions is not fully understood yet. Here, femtosecond IR spectroscopy and molecular dynamics simulations are used to show that bulk-like water coexists with interfacial water on ion aggregates. We found that dissolved ions form intricate three-dimensional ion–ion networks that are spontaneously intertwined with nanometric water hydrogen-bonding networks. Then, hydrated lithium ions move through bulk-like water channels acting like conducting wires for lithium ion transport. Our experimental and simulation results indicate that water structure-breaking chaotropic anion salts with a high propensity to form ion networks in aqueous solutions would be excellent candidates for water-based LIB electrolytes. We anticipate that the present work will provide guiding principles for developing aqueous LIB electrolytes.

Total synthesis of anguibactin was accomplished for the first time, and the following biochemical characterizations allowed for the determination of its Fe(III) binding mode as well as the demonstration of its iron delivery capability for Acinetobacter baumannii. These properties, in addition to the thermal stability over acinetobactin, render anguibactin as a competent surrogate siderophore that can be useful for the future development of a siderophore-based antibiotic delivery system against A. baumannii.

The electrochemical reduction of trivalent samarium in a LiCl–KCl eutectic melt produced highly stable divalent samarium, whose electrochemical properties and electronic structure in the molten salt were investigated using cyclic voltammetry, UV–vis absorption spectroscopy, laser-induced emission spectroscopy, and density functional theory (DFT) calculations. Diffusion coefficients of Sm2+and Sm3+were electrochemically measured to be 0.92 × 10–5and 1.10 × 10–5cm2/s, respectively, and the standard apparent potential of the Sm2+/3+couple was estimated to be −0.82 V vs Ag|Ag+at 450 °C. The spectroelectrochemical study demonstrated that the redox behavior of the samarium cations obeys the Nernst equation (E°′ = −0.83 V, n= 1) and the trivalent samarium cation was successfully converted to the divalent cation having characteristic absorption bands at 380 and 530 nm with molar absorptivity values of 1470 and 810 M–1cm–1, respectively. Density function theory calculations for the divalent samarium complex revealed that the absorption signals originated from the 4f6to 4f55d1transitions. Additionally, laser-induced emission measurements for the Sm cations in the LiCl–KCl matrix showed that the Sm3+ion in the LiCl–KCl melt at 450 °C emitted an orange color of fluorescence, whereas a red colored emission was observed from the Sm2+ion in the solidified LCl-KCl salt at room temperature.

Area-selective atomic layer deposition (AS-ALD) of insulating metallic oxide layers could be a useful nanopatterning technique for making increasingly complex semiconductor circuits. Although the alkanethiol self-assembled monolayer (SAM) has been considered promising as an ALD inhibitor, the low inhibition efficiency of the SAM during ALD processes makes its wide application difficult. We investigated the deposition mechanism of Al2O3on alkanethiol-SAMs using temperature-dependent vibrational sum-frequency-generation spectroscopy. We found that the thermally induced formation of gauche defects in the SAMs is the main causative factor deteriorating the inhibition efficiency. Here, we demonstrate that a discontinuously temperature-controlled ALD technique involving self-healing and dissipation of thermally induced stress on the structure of SAM substantially enhances the SAM’s inhibition efficiency and enables us to achieve 60 ALD cycles (6.6 nm). We anticipate that the present experimental results on the ALD mechanism on the SAM surface and the proposed ALD method will provide clues to improve the efficiency of AS-ALD, a promising nanoscale patterning and manufacturing technique.

We have demonstrated that amine and alkyl groups, applied by a simple spin-coating method, can provide an n-type doping effect on graphene sheets. The organic compounds used in this work are based on amine, phenyl amine, butylphenyl amine, benzoylphenyl amine, and tolylvinylphenyl amine groups. The increases in sheet resistance, decreases in transmittance and work function, and shifts of the G peak to higher wavenumbers and the 2D peak to lower wavenumbers in the Raman spectra indicate that graphene was doped to n-type after the graphene sheets were spin-coated by the amine-based compounds. In particular, graphene doped with butylphenyl amine showed the strongest n-type effect among all of the samples because butylphenyl amine has the strongest binding energy with graphene sheets and disperses in nonpolar solvents, suggesting that the binding energy with graphene sheets and the degree of dispersion in solvents are important factors in the doping process. Molecular calculations based on density functional theory confirmed the n-type properties of graphene doped with amine-based compounds. These results suggest that amine and alkyl groups play a crucial role in the n-type doping of graphene.

We synthesized a series of acceptor–donor–acceptor-type small molecules (SIDPP-EE, SIDPP-EO, SIDPP-OE, and SIDPP-OO) consisting of a dithienosilole (SI) electron-donating moiety and two diketopyrrolopyrrole (DPP) electron-withdrawing moieties each bearing linear n-octyl (O) and/or branched 2-ethylhexyl (E) alkyl side chains. X-ray diffraction patterns revealed that SIDPP-EE and SIDPP-EO films were highly crystalline with pronounced edge-on orientation, whereas SIDPP-OE and SIDPP-OO films were less crystalline with a radial distribution of molecular orientations. Near-edge X-ray absorption fine structure spectroscopy disclosed an edge-on orientation with a molecular backbone tilt angle of ∼22° for both SIDPP-EE and SIDPP-EO. Our analysis of the molecular packing and orientation indicated that the shorter 2-ethylhexyl groups on the SI core promote tight π–π stacking of the molecular backbone, whereas n-octyl groups on the SI core hinder close π–π stacking to some degree. Conversely, the longer linear n-octyl groups on the DPP arms facilitate close intermolecular packing viaoctyl–octyl interdigitation. Quantum mechanics/molecular mechanics molecular dynamics simulations determined the optimal three-dimensional positions of the flexible alkyl side chains of the SI and DPP units, which elucidates the structural cause of the molecular packing and orientation explicitly. The alkyl-chain-dependent molecular stacking significantly affected the electrical properties of the molecular films. The edge-on oriented molecules showed high hole mobilities in organic field-effect transistors, while the radially oriented molecules exhibited high photovoltaic properties in organic photovoltaic cells. These results demonstrate that appropriate positioning of alkyl side chains can modulate crystallinity and molecular orientation in SIDPP films, which ultimately have a profound impact on carrier transport and photovoltaic performance.

We developed high performance PM6:N3 bulk-heterojunctions by synthesizing polymers as the second acceptor. The acceptor PY-P2 where a biphenyl linker makes the polymer chain to have high dihedral angles forms intricate alloy-like composites in N3 domains whereas stiff polymer chain of PY-T2 exists separated from the acceptor domain. Introduction of PY-P2 results in much longer lifetimes and diffusion lengths of excitons generated in N3 domain of the PM6:N3:PY-P2 blend compared to those of the excitons in PM6:N3 as well as PM6:N3:PY-T2. Consequently, the PM6:N3:PY-P2 based OPV devices show improved exciton dissociation and change transport with reduced charge recombination. The PM6:N3:PY-P2 organic photovoltaic (OPV) devices prepared with blade-coating at 1 cm2active area achieved efficiency of 15.2% compared with 12.9% of the PM6:N3 control device; whereas, the corresponding OPV device using PY-T2 shows decreased efficiency of 11.7%. OPV mini-module (active area 5.4 cm2) with PY-P2 achieves high efficiency of 14.7% compared with 11.9% of the PM6:N3 devices. Furthermore, the alloyed PY-P2 acceptor effectively improves OPV thermal stability under 85 °C heating for 1000 h, compared with PY-T2 and control devices. We demonstrated importance of the second polymer acceptor for achieving high-performance large-area OPV, which is significantly affected by its chemical structure.

Automatically controlling the optical transmittance of solar light provides an energy-saving strategy for designing energy-efficient buildings. Ideally, the smart windows should be able to show homogeneous and large-scale color-switching performance while modulating the intensity of daylight. Among the suitable candidates for smart windows, the photochromic device has a great potential for homogenous and large-scale color-switching material. In a photochromic device, the intercalation/deintercalation of Li-ions is a key step determining the kinetics and efficiencies of the coloring/bleaching process. Herein, we exploit operando Raman spectroscopy to investigate the photochromic mechanism, which reveals the movement of Li ions into specific sites within the tunnels that exist in hexagonal tungsten oxide (WO3). These spectroscopic results demonstrate that the intercalation/deintercalation of the Li ions is related to specific sites in the WO3lattice which stabilizes the energy of the intermediate state during the coloring/self-bleaching process. Additionally, theoretical simulation supports that electrons, as well as Li ions, participate in the color-switching performance. This study improves our understanding of the photochromic performance of this special device and opens up a research field toward the development of smart windows applications.

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