Ethylenedioxythiophene-Based Small Molecular Donor with Multiple Conformation Locks for Organic Solar Cells with Efficiency of 19.3 .

Ternary organic solar cells (T-OSCs) represent an efficient strategy for enhancing the performance of OSCs. Presently, the majority of high-performance T-OSCs incorporates well-established Y-acceptors or donor polymers as the third component. In this study, a novel class of conjugated small molecules has been introduced as the third component, demonstrating exceptional photovoltaic performance in T-OSCs. This innovative molecule comprises ethylenedioxythiophene (EDOT) bridge and 3-ethylrhodanine as the end group, with the EDOT unit facilitating the creation of multiple conformation locks. Consequently, the EDOT-based molecule exhibits two-dimensional charge transport, distinguishing it from the thiophene-bridged small molecule, which displays fewer conformation locks and provides one-dimensional charge transport. Furthermore, the robust electron-donating nature of EDOT imparts the small molecule with cascade energy levels relative to the electron donor and acceptor. As a result, OSCs incorporating the EDOT-based small molecule as the third component demonstrate enhanced mobilities, yielding a remarkable efficiency of 19.3 %, surpassing the efficiency of 18.7 % observed for OSCs incorporating thiophene-based small molecule as the third component. The investigations in this study underscore the excellence of EDOT as a building block for constructing conjugated materials with multiple conformation locks and high charge carrier mobilities, thereby contributing to elevated photovoltaic performance in OSCs.

Dual-Strategy Tailoring Molecular Structures of Dopant-Free Hole Transport Materials for Efficient and Stable Perovskite Solar Cells.

Dopant-free hole transport materials (HTMs) are ideal materials for highly efficient and stable n-i-p perovskite solar cells (PSCs), but most current design strategies for tailoring the molecular structures of HTMs are limited to single strategy. Herein, four HTMs based on dithienothiophenepyrrole (DTTP) core are devised through dual-strategy methods combining conjugate engineering and side chain engineering. DTTP-ThSO with ester alkyl chain that can form six-membered ring by the S⋅⋅⋅O noncovalent conformation lock with thiophene in the backbone shows good planarity, high-quality film, matching energy level and high hole mobility, as well as strong defect passivation ability. Consequently, a remarkable power conversion efficiency (PCE) of 23.3 % with a nice long-term stability is achieved by dopant-free DTTP-ThSO-based PSCs, representing one of the highest values for un-doped organic HTMs based PSCs. Especially, the fill factor (FF) of 82.3 % is the highest value for dopant-free small molecular HTMs-based n-i-p PSCs to date. Moreover, DTTP-ThSO-based devices have achieved an excellent PCE of 20.9 % in large-area (1.01 cm2) devices. This work clearly elucidates the structure-performance relationships of HTMs and offers a practical dual-strategy approach to designing dopant-free HTMs for high-performance PSCs.

Electrocatalytic conversion of biomass-derived furan compounds: mechanisms, catalysts and perspectives.

Renewable biomass, with its abundant resources, provides a viable solution to address the energy crisis and mitigate environmental pollution. Furan compounds, including 5-hydroxymethylfurfural (HMF) and furfural (FF), serve as versatile platform molecules derived from the degradation of lignocellulosic cellulose, offering a crucial pathway for the conversion of renewable biomass. The electrocatalytic conversion of furan compounds using renewable electricity represents an enticing approach for transforming them into value-added chemicals. However, the complex chemistry of furan compounds leads to low selectivity of the target product, and the lower current density and Faraday efficiency make it difficult to achieve molded applications. Therefore, it is crucial to gain a better understanding of the mechanism and conditions of the reaction, enhance reaction activity and selectivity, and indicate the direction for industrial applications. Herein, we provide a comprehensive review of the recent advancements in the electrocatalytic of HMF and FF, focusing on mechanisms and pathways, catalysts, and factors affecting like electrolyte pH, potential, and substrate concentration. Furthermore, challenges and future application prospects are discussed. This review aims to equip researchers with a fundamental understanding of the electrochemical dehydrogenation, hydrogenation, and hydrolysis reactions involving furan compounds. Such insights are expected to accelerate the development of cost-effective electrochemical conversion processes for biomass derivatives and their scalability in large-scale applications.

Regulating Crystallinity Mismatch Between Donor and Acceptor to Improve Exciton/Charge Transport in Efficient Organic Solar Cells.

Achieving a more balanced charge transport by morphological control is crucial in reducing bimolecular and trap-assisted recombination and enhancing the critical parameters for efficient organic solar cells (OSCs). Hence, a facile strategy is proposed to reduce the crystallinity difference between donor and acceptor by incorporating a novel multifunctional liquid crystal small molecule (LCSM) BDTPF4-C6 into the binary blend. BDTPF4-C6 is the first LCSM based on a tetrafluorobenzene unit and features a low liquid crystal phase transition temperature and strong self-assembly ability, conducive to regulating the active layer morphology. When BDTPF4-C6 is introduced as a guest molecule into the PM6 : Y6 binary, it exhibits better compatibility with the donor PM6 and primarily resides within the PM6 phase because of the similarity-intermiscibility principle. Moreover, systematic studies revealed that BDTPF4-C6 could be used as a seeding agent for PM6 to enhance its crystallinity, thereby forming a more balanced and favourable charge transport with suppressed charge recombination. Intriguingly, dual Förster resonance energy transfer was observed between the guest molecule and the host donor and acceptor, resulting in an improved current density. This study demonstrates a facile approach to balance the charge mobilities and offers new insights into boosting the efficiency of single-junction OSCs beyond 20 %.

Impact of Electrostatic Interaction on Vertical Morphology and Energy Loss in Efficient Pseudo-Planar Heterojunction Organic Solar Cells.

Although a suitable vertical phase separation (VPS) morphology is essential for improving charge transport efficiency, reducing charge recombination, and ultimately boosting the efficiency of organic solar cells (OSCs), there is a lack of theoretical guidance on how to achieve the ideal morphology. Herein, a relationship between the molecular structure and the VPS morphology of pseudo-planar heterojunction (PPHJ) OSCs is established by using molecular surface electrostatic potential (ESP) as a bridge. The morphological evolution mechanism is revealed by studying four binary systems with vary electrostatic potential difference (∆ESP) between donors (Ds) and acceptors (As). The findings manifest that as ∆ESP increases, the active layer is more likely to form a well-mixed phase, while a smaller ∆ESP favors VPS morphology. Interestingly, it is also observed that a larger ∆ESP leads to enhanced miscibility between Ds and As, resulting in higher non-radiative energy losses (ΔE3). Based on these discoveries, a ternary PPHJ device is meticulously designed with an appropriate ∆ESP to obtain better VPS morphology and lower ΔE3, and an impressive efficiency of 19.09% is achieved. This work demonstrates that by optimizing the ΔESP, not only the formation of VPS morphology can be controlled, but also energy losses can be reduced, paving the way to further boost OSC performance.

Green-Solvent Processed Blade-Coating Organic Solar Cells with an Efficiency Approaching 19% Enabled by Alkyl-Tailored Acceptors.

Power-conversion-efficiencies (PCEs) of organic solar cells (OSCs) in laboratory, normally processed by spin-coating technology with toxic halogenated solvents, have reached over 19%. However, there is usually a marked PCE drop when the blade-coating and/or green-solvents toward large-scale printing are used instead, which hampers the practical development of OSCs. Here, a new series of N-alkyl-tailored small molecule acceptors named YR-SeNF with a same molecular main backbone are developed by combining selenium-fused central-core and naphthalene-fused end-group. Thanks to the N-alkyl engineering, NIR-absorbing YR-SeNF series show different crystallinity, packing patterns, and miscibility with polymeric donor. The studies exhibit that the molecular packing, crystallinity, and vertical distribution of active layer morphologies are well optimized by introducing newly designed guest acceptor associated with tailored N-alkyl chains, providing the improved charge transfer dynamics and stability for the PM6:L8-BO:YR-SeNF-based OSCs. As a result, a record-high PCE approaching 19% is achieved in the blade-coating OSCs fabricated from a green-solvent o-xylene with high-boiling point. Notably, ternary OSCs offer robust operating stability under maximum-power-point tracking and well-keep > 80% of the initial PCEs for even over 400 h. Our alkyl-tailored guest acceptor strategy provides a unique approach to develop green-solvent and blade-coating processed high-efficiency and operating stable OSCs, which paves a way for industrial development.

Impact of Electrostatic Interaction on Non-radiative Recombination Energy Losses in Organic Solar Cells Based on Asymmetric Acceptors.

Reducing non-radiative recombination energy loss (ΔE3 ) is one key to boosting the efficiency of organic solar cells. Although the recent studies have indicated that the Y-series asymmetric acceptors-based devices featured relatively low ΔE3 , the understanding of the energy loss mechanism derived from molecular structure change is still lagging behind. Herein, two asymmetric acceptors named BTP-Cl and BTP-2Cl with different terminals were synthesized to make a clear comparative study with the symmetric acceptor BTP-0Cl. Our results suggest that asymmetric acceptors exhibit a larger difference of electrostatic potential (ESP) in terminals and semi-molecular dipole moment, which contributes to form a stronger π-π interaction. Besides, the experimental and theoretical studies reveal that a lower ESP-induced intermolecular interaction can reduce the distribution of PM6 near the interface to enhance the built-in potential and decrease the charge transfer state ratio for asymmetric acceptors. Therefore, the devices achieve a higher exciton dissociation efficiency and lower ΔE3 . This work establishes a structure-performance relationship and provides a new perspective to understand the state-of-the-art asymmetric acceptors.

Li-Ion Conductivity of Single-Step Synthesized Glassy-Ceramic Li10GeP2S12 and Post-heated Highly Crystalline Li10GeP2S12.

Li10GeP2S12 is a phosphosulfide solid electrolyte that exhibits exceptionally high Li-ion conductivity, reaching a conductivity above 10-3 S cm-1 at room temperature, rivaling that of liquid electrolytes. Herein, a method to produce glassy-ceramic Li10GeP2S12 via a single-step utilizing high-energy ball milling was developed and systematically studied. During the high energy milling process, the precursors experience three different stages, namely, the 'Vitrification zone' where the precursors undergo homogenization and amorphization, 'Intermediary zone' where Li3PS4 and Li4GeS4 are formed, and the 'Product stage' where the desired glassy-ceramic Li10GeP2S12 is formed after 520 min of milling. At room temperature, the as-milled sample achieved a high ionic conductivity of 1.07 × 10-3 S cm-1. It was determined via quantitative phase analyses (QPA) of transmission X-ray diffraction results that the as-milled Li10GeP2S12 possessed a high degree of amorphization (44.4 wt %). To further improve the crystallinity and ionic conductivity of the Li10GeP2S12, heat treatment of the as-milled sample was carried out. The optimal heat-treated Li10GeP2S12 is almost fully crystalline and possesses a room temperature ionic conductivity of 3.27 × 10-3 S cm-1, an over 200% increase compared to the glassy-ceramic Li10GeP2S12. These findings help provide previously lacking insights into the controllable preparation of Li10GeP2S12 material.

Disentangling the Li-Ion transport and Boundary Phase Transition Processes in Li10 GeP2 S12 Electrolyte by In-Operando High-Pressure and High-Resolution NMR Spectroscopy.

Li-ion transport and phase transition of solid electrolytes are critical and fundamental issues governing the rate and cycling performances of solid-state batteries. In this work, in-operando high-pressure nuclear magnetic resonance (NMR) spectroscopy for the solid-state battery is developed and applied, in combination with 6 Li-tracer NMR and high-resolution NMR spectroscopy, to investigate the Li10 GeP2 S12 electrolyte under true-to-life operation conditions. The results reveal that the Li10 GeP2 S12 phase may become more disordered and a large amount of conductive metastable ß-Li3 PS4 as the glassy matrix in the electrolyte transforms into less conductive phases, mainly γ-Li3 PS4 , when high current densities (e.g., ≥0.5 mA cm-2 ) are applied to the electrolyte. The overall Li-transport also varies and shows a tendency of boundary phases and Li10 GeP2 S12 synergistic dominant conduction at high currents. Accordingly, a mechanism of structural change induced by stress variation due to the drastic morphological change during Li-In alloying at high currents, and the local Li+ diffusion coefficient discrepancy is proposed. These new findings of Li-ion transport and boundary phase transition in Li10 GeP2 S12 solid electrolyte under high-pressure and high current density are first reported and will help provide previously lacking insights into the relationship of structure and performance of Li10 GeP2 S12 .

Terpolymerization and Regioisomerization Strategy to Construct Efficient Terpolymer Donors Enabling High-Performance Organic Solar Cells.

Terpolymerization and regioisomerization strategies are combined to develop novel polymer donors to overcome the difficulty of improving organic solar cells (OSCs) performance. Two novel isomeric units, bis(2-hexyldecyl)-2,5-bis(4-chlorothiophen-2-yl)thieno[3,2-b]thiophene-3,6-dicarboxylate (TTO) and bis(2-hexyldecyl) 2,5-bis(3-chlorothiophen-2-yl)thieno[3,2-b]thiophene-3,6-dicarboxylate (TTI), are obtained and incorporated into the PM6 backbone via random copolymerization to form a series of terpolymers. Interestingly, it is found that different chlorine (Cl) substituent positions can significantly change the molecular planarity and electrostatic potential (ESP) owing to the steric hindrance effect of the heavy Cl atom, which leads to different molecular aggregation behaviors and miscibility between the donor and acceptor. The TTO unit features a higher number of multiple S···O non-covalent interactions, more positive ESP, and fewer isomer structures than TTI. As a result, the terpolymer PM6-TTO-10 exhibits a much better molecular coplanarity, stronger crystallinity, more obvious aggregation behavior, and proper phase separation in the blend film, which are conducive to more efficient exciton dissociation and charge transfer. Consequently, the PM6-TTO-10:BTP-eC9-based OSCs achieve a champion power conversion efficiency of 18.37% with an outstanding fill factor of 79.97%, which are among the highest values reported for terpolymer-based OSCs. This work demonstrates that terpolymerization combined with Cl regioisomerization is an efficient approach for achieving high-performance polymer donors.

Disentangling Phase and Morphological Evolution During the Formation of the Lithium Superionic Conductor Li10 GeP2 S12.

The structural and morphological changes of the Lithium superionic conductor Li10 GeP2 S12 , prepared via a widely used ball milling-heating method over a comprehensive heat treatment range (50 - 700 °C), are investigated. Based on the phase composition, the formation process can be distinctly separated into four zones: Educt, Intermediary, Formation, and Decomposition zone. It is found that instead of Li4 GeS4 -Li3 PS4 binary crystallization process, diversified intermediate phases, including GeS2 in different space groups, multiphasic lithium phosphosulfides (Lix Py Sz ), and cubic Li7 Ge3 PS12 phase, are involved additionally during the formation and decomposition of Li10 GeP2 S12 . Furthermore, the phase composition at temperatures around the transition temperatures of different formation zones shows a significant deviation. At 600 °C, Li10 GeP2 S12 is fully crystalline, while the sample decomposed to complex phases at 650 °C with 30 wt.% impurities, including 20 wt.% amorphous phases. These findings over such a wide temperature range are first reported and may help provide previously lacking insights into the formation and crystallinity control of Li10 GeP2 S12 .

Flexible Miniaturized Multispectral Detector Derived from Blade-Coated Organic Narrowband Response Unit Array.

Multispectral sensing is extremely desired in intelligent systems, e.g., autonomous vehicles, encrypted information communication, and health biometric monitoring, due to its highly sensitive spectral discrimination ability. Nevertheless, rigid bulky optics and delicate optical paths in devices significantly increase their complexity and size, which subsequently impede their integration in smart optoelectronic chips for universal applications. In this work, a filterless miniaturized multispectral photodetector is realized with an organic narrowband response unit array. With the manipulation of Frenkel exciton dissociation in active layers, a series of narrowband organic sensing units with full-width-at-half-maximum (fwhm) narrowing to ∼50 nm are achieved from 700 to 1050 nm with a laudable performance of responsivity of over 60 mA/W, -3 dB bandwidth over 10 kHz, linear dynamic range (LDR) reaching ∼120 dB, and a low noise current of less than 4 × 10-14 A·Hz-0.5. Furthermore, a 6 × 8 multispectral sensing array on a flexible substrate was fabricated with blade-coating. Assisted by a computational process, we successfully demonstrate the spectral recognition with a resolution of ∼50 nm and a mismatch of ∼10 nm. Finally, the function of matter identification is successfully achieved with our multispectral detector array.

Achieving efficient and stabilized organic solar cells by precisely controlling the proportion of copolymerized units in electron-rich polymers.

A series of random polymers based on the donor polymer PM6 were designed from the perspective of regulating the surface electrostatic potential (ESP) distribution of the polymers and applied in organic solar cells (OSCs). Random polymers with different ESPs were obtained by introducing structural units of polymer PM6 into the polymer structure as the third unit. The simulation results showed that the random polymers feature a wider electron-donating region after the introduction of BDT units, indicating a more efficient charge generation probability. Benefiting from the optimized morphology of the active layer and the stronger interaction between the donor and the acceptor in the active layer, the device exhibited the best charge transport efficiency and lower charge recombination after the introduction of 5% BDT units, and a high power conversion efficiency (PCE) of 16.76% was achieved. In addition, OSC devices based on random polymers incorporating 5% BDT units exhibit excellent device stability. In contrast, the devices based on random polymers after the introduction of BDD units showed a much lower PCE of around 13% due to the inferior charge generation and charge transport. This work not only provides a new perspective for the molecular design of efficient random polymers, but also demonstrates that the OSC devices based on random polymers can still achieve better stability.

Semicrystalline Conjugated Polymers with Well-Defined Active Sites for Nitrogen Fixation in a Seawater Electrolyte.

Faradaic efficiency for the nitrogen reduction reaction (NRR) is often limited by low N2 solubility in the electrolyte, while a large number of intimate contacts between the electrolyte and solid catalyst can also inevitably sacrifice many active sites for the NRR. Here, it is reported that a "quasi-gas-solid" interface formed in donor-acceptor-based conjugated polymers (CPs) is beneficial to boosting the NRR process and at the same time suppressing the competing hydrogen evolution reaction. Of particular interest, it is found that a semicrystalline CP catalyst, SC-PBDT-TT, exhibits a high Faradaic efficiency of up to 60.5% with a maximum NH3 production rate of 16.8 µg h-1 mg-1 in a neutral-buffered seawater electrolyte. Molecular dynamics and COMSOL Multiphysics simulations reveal the origin of the observed high NRR performance arising from the presence of desirable crystal regions to resist the penetration of H2 O molecules, leading to the formation of a "quasi-gas-solid" interface inside the catalyst for a favorable direct-contact between the catalyst and N2 molecules. Furthermore, high-throughput computations, based on density functional theory, reveal the actual real active site for N2 adsorption and reduction in SC-PBDT-TT. This work provides a new framework for optimizing NRR performance of metal-free catalysts by controlling their crystallinities.

Alkylsilyl Fused Ring-Based Polymer Donor for Non-Fullerene Solar Cells with Record Open Circuit Voltage and Energy Loss.

The energy loss (Eloss ), especially the nonradiative recombination loss and energetic disorder, needs to be minimized to improve the device performance with a small voltage (VOC ) loss. Urbach energy (EU ) of organic photovoltaic materials is related to energetic disorder, which can predict the Eloss of the corresponding device. Herein, a polymer donor (PBDS-TCl) with Si and Cl functional atoms for organic solar cells (OSCs) is synthesized. It can be found that the VOC and Eloss can be well manipulated by regulation of the energy level of the polymer donor and EU , which is dominated by the morphology. A low energetic disorder with an EU of 23.7 meV, a low driving force of 0.08 eV, and a low Eloss of 0.41 eV are achieved for the PBDS-TCl:Y6-based OSCs. Consequently, an impressive open circuit voltage (VOC ) of 0.92 V is obtained. To the best of knowledge, the VOC value and Eloss are both the record values for the Y6-based device. These results demonstrate that fine-tuning the polymer donor by functional atom modification on the side chain is a promising way to reduce EU and energy loss, as well as obtain small driving force and high VOC for highly efficient OSCs.

Thickness-Insensitive Anode Interface Layer for High-Efficiency Organic Solar Cells.

Thickness-insensitive anode interface layer materials are extremely crucial for commercial applications of organic solar cells (OSCs). Here, we have demonstrated a solution-processed and thickness-insensitive anode interfacial layer PCPDT-2Ph-H and employed it in large-area OSCs. The power conversion efficiency (PCE) of a PM6:Y6 device with a 0.04 cm2 area using PCPDT-2Ph-H as the anode interface layer can reach 16.5%. More importantly, when the thickness of PCPDT-2Ph-H reaches 100 nm, a device with a 1.0 cm2 effective area can still achieve a high efficiency of 10.3%, which is highly favorable to large-area printing of OSCs. Due to its advantages of thickness insensitivity and solution processing, PCPDT-2Ph-H would be a promising anode interface layer for large-area OSCs.

Printable Hole Transport Layer for 1.0 cm2 Organic Solar Cells.

Currently, most of the hole transport layers (HTLs) of organic solar cells (OSCs) are unable to meet the requirements of printing preparation, which imposes restrictions on the commercial process of the OSCs severely. Here, we report a printable HTL, PCPDTK0.50H0.50-TT. The PM6:Y6:PC71BM device with PCPDTK0.50H0.50-TT as an HTL exhibits a power conversion efficiency (PCE) of 16.3% (with an area of 0.04 cm2). More importantly, the PCE of the device is up to 10.2%, with an area of 1.0 cm2 prepared by the wire-bar coating PCPDTK0.50H0.50-TT HTL, which is in favor of the printing fabrication of the OSCs. In view of the superiorities of the large-area printing and the impressive PCE, we believe that PCPDTK0.50H0.50-TT should be a potential HTL for industrial production of OSCs.

Isomeric Effect of Wide Bandgap Polymer Donors with High Crystallinity to Achieve Efficient Polymer Solar Cells.

Two highly crystalline polymer donors (PBTz4T2C-a, PBTz4T2C-b) with isomers (4T2C-a, 4T2C-b) are synthesized and applied in polymer solar cells. The developed polymers possess proper energy levels and complementary absorption with an efficient electron acceptor IT2F. It is interesting that the photophysical properties, crystallinity, and active layer morphology characteristic can be significantly changed by just slightly regulating the substitution position of the carboxylate groups. A series of simulation calculations of the two isomers are conducted in the geometry and electronic properties to explore the difference induced by the position adjustment of carboxylate groups. The results decipher that 4T2C-b moiety features much stronger intramolecular noncovalent S⋯O interactions compared to that of 4T2C-a, implying a higher coplanarity and much stronger crystallinity, and leading to excessive phase separation in PBTz4T2C-b:IT2F blend film. In contrast, PBTz4T2C-a with 4T2C-a moiety exhibits suitable crystallinity with a lower the highest occupied molecular orbital level, higher film absorption coefficient, and charge mobilities, resulting in a much higher power conversion efficiency of 11.02%. This research demonstrates that the molecular conformation is of great importance to be considered for developing high-performance polymer donors.

Bio-inspired vertebral design for scalable and flexible perovskite solar cells.

The translation of unparalleled efficiency from the lab-scale devices to practical-scale flexible modules affords a huge performance loss for flexible perovskite solar cells (PSCs). The degradation is attributed to the brittleness and discrepancy of perovskite crystal growth upon different substrates. Inspired by robust crystallization and flexible structure of vertebrae, herein, we employ a conductive and glued polymer between indium tin oxide and perovskite layers, which simultaneously facilitates oriented crystallization of perovskite and sticks the devices. With the results of experimental characterizations and theoretical simulations, this bionic interface layer accurately controls the crystallization and acts as an adhesive. The flexible PSCs achieve the power conversion efficiencies of 19.87% and 17.55% at effective areas of 1.01 cm2 and 31.20 cm2 respectively, retaining over 85% of original efficiency after 7000 narrow bending cycles with negligible angular dependence. Finally, the modules are assembled into a wearable solar-power source, enabling the upscaling of flexible electronics.

Fused selenophene-thieno[3,2-b]thiophene-selenophene (ST)-based narrow-bandgap electron acceptor for efficient organic solar cells with small voltage loss.

A novel near-infrared-light-absorbing fused-ring electron acceptor, STIC, was developed for organic solar cells. STIC exhibited a narrow bandgap with an absorption edge reaching 940 nm, which was ascribed to the strong electron-rich selenophene-thieno[3,2-b]thiophene-selenophene (ST) unit and strong intramolecular charge transfer of STIC. Also, STIC-based devices showed low open-circuit voltage (Voc) loss values, attributed to the rigid ST core providing low reorganization energy. The device based on the PBDB-T:STIC blend exhibited a power conversion efficiency (PCE) of 9.68% with a high short-circuit current density (Jsc) of 19.96 mA cm-2 and a low Voc loss of 0.55 eV.