Chalcogen Atoms Regulate the Organic Solar Cell Performance of B-N-Based Polymer Donors.

Donor polymers play a key role in the development of organic solar cells (OSCs). B-N-based polymer donors, as new types of materials, have attracted a lot of attention due to their special characteristics, such as high E(T1), small ΔEST, and easy synthesis, and they can be processed with real green solvents. However, the relationship between the chemical structure and device performance has not been systematically studied. Herein, chalcogen atoms that regulate the OSCs performance of B-N-based polymer donors were systematically studied. Fortunately, the substitution of a halogen atom did not affect the high E(T1) and small ΔEST character of the B-N-based polymer. The absorption and energy levels of the polymer were systematically regulated by O, S, and Se atom substitution. The PBNT-TAZ:Y6-BO-based OSCs device demonstrated a high power conversion efficiency of 15.36%. Moreover, the layer-by-layer method was applied to further optimize the device performance, and the PBNT-TAZ/Y6-BO-based OSCs device yielded a PCE of 16.34%. Consequently, we have systematically demonstrated how chalcogen atoms modulated the electronic properties of B-N-based polymers. Detailed and systematic structure-performance relationships are important for the development of next-generation B-N-based materials.

Self-Powering Gas Sensing System Enabled by Double-Layer Triboelectric Nanogenerators Based on Poly(2-vinylpyridine)@BaTiO3 Core-Shell Hybrids with Superior Dispersibility and Uniformity.

Current core-shell hybrids used in diverse energy-related applications possess limited dispersibility and film uniformity that govern their overall performances. Herein, we showcase superdispersible core-shell hybrids (P2VP@BaTiO3) composed of a poly(2-vinylpyridine) (P2VP) (5-20 wt %) and a barium titanate oxide (BaTiO3), maximizing dielectric constants by forming the high-quality uniform films. The P2VP@BaTiO3-based triboelectric nanogenerators (TENGs), especially the 10 wt % P2VP (P2VP10@BaTiO3)-based one, deliver significantly enhanced output performances compared to physically mixed P2VP/BaTiO3 counterparts. The P2VP10@BaTiO3-based double-layer TENG exhibits not only an excellent transferred charge density of 281.7 µC m-2 with a power density of 27.2 W m-2 but also extraordinary device stability (∼100% sustainability of the maximum output voltage for 54,000 cycles and ∼68.7% voltage retention even at 99% humidity). Notably, introducing the MoS2/SiO2/Ni-mesh layer into this double-layer TENG enables ultrahigh charge density of up to 1228 µC m-2, which is the top value reported for the TENGs so far. Furthermore, we also demonstrate a near-field communication-based sensing system for monitoring CO2 gas using our developed self-powered generator with enhanced output performance and robustness.

High-Precision Tailored Polymer Molecular Weights for Specific Photovoltaic Applications through Ultrasound-Induced Simultaneous Physical and Chemical Events.

It is highly challenging to reproducibly prepare semiconducting polymers with targeted molecular weight tailored for next-generation photovoltaic applications. Once such an easily accessible methodology is established, which can not only contribute to overcome the current limitation of the statistically determined nature of semiconducting polymers, but also facilitate rapid incorporation into the broad synthetic chemists' toolbox. Here, we describe a simple yet robust ultrasonication-assisted Stille polymerization for accessing semiconducting polymers with high-precision tailored molecular weights (from low to ultrahigh molecular weight ranges) while mitigating their interbatch variations. We propose that ultrasound-induced simultaneous physical and chemical events enable precise control of the semiconducting polymers' molecular weights with high reproducibility to satisfy all the optical/electrical and morphological demands of diverse types of high-performance semiconducting polymer-based devices; as demonstrated in in-depth experimental screenings in applications of both organic and perovskite photovoltaics. We believe that this methodology provides a fast development of new and existing semiconducting polymers with the highest-level performances possible on various photovoltaic devices.

Tethered Trimeric Small-molecular Acceptors through Aromatic-core Engineering for Highly Efficient and Thermally Stable Polymer Solar Cells.

Polymer solar cells (PSCs) rely on a blend of small molecular acceptors (SMAs) with polymer donors, where thermodynamic relaxation of SMAs poses critical concerns on operational stability. To tackle this issue, tethered SMAs, wherein multiple SMA-subunits are connected to the aromatic-core via flexible chains, are proposed. This design aims to an elevated glass transition temperature (Tg) for a dynamical control. However, attaining an elevated Tg value with additional SMA subunits introduces complexity to the molecular packing, posing a significant challenge in realizing both high stability and power conversion efficiency (PCE). In this study, we initiate isomer engineering on the benzene-carboxylate core and find that meta-positioned dimeric BDY-ß exhibits more favorable molecular packing compared to its para-positioned counterpart, BDY-α. With this encouraging result, we expand our approach by introducing an additional SMA unit onto the aromatic core of BDY-ß, maintaining a meta-position relative to each SMA unit location in the tethered acceptor. This systematic aromatic-core engineering results in a star-shaped C3h-positioned molecular geometry. The supramolecular interactions of SMA units in the trimer contribute to enhancements in Tg value, crystallinity, and a red-shifted absorption compared to dimers. These characteristics result in a noteworthy increase in PCE to 18.24 %, coupled with a remarkable short-circuit current density of 27.06 mA cm-2. More significantly, the trimer-based devices delivered an excellent thermal stability with over 95 % of their initial efficiency after 1200 h thermal degradation. Our findings underscore the promise and feasibility of tethered trimeric structures in achieving highly ordered aggregation behavior and increased Tg value in PSCs, simultaneously improving in device efficiency and thermal stability.

Three-in-One Strategy Enables Single-Component Organic Solar Cells with Record Efficiency and High Stability.

Single-component organic solar cells (SCOSCs) with covalently bonding donor and acceptor are becoming increasingly attractive because of their superior stability over traditional multicomponent blend organic solar cells (OSCs). Nevertheless, the efficiency of SCOSCs is far behind the state-of-the-art multicomponent OSCs. Herein, by combination of the advantages of three-component and single-component devices, this work reports an innovative three-in-one strategy to boost the performance of SCOSCs. In this three-in-one strategy, three independent components (PM6, D18, and PYIT) are covalently linked together to create a new single-component active layer based on ternary conjugated block copolymer (TCBC) PM6-D18-b-PYIT by a facile polymerization. Precisely manipulating the component ratios in the polymer chains of PM6-D18-b-PYIT is able to broaden light utilization, promote charge dynamics, optimize, and stabilize film morphology, contributing to the simultaneously enhanced efficiency and stability of the SCOSCs. Ultimately, the PM6-D18-b-PYIT-based device exhibits a power conversion efficiency (PCE) of 14.89%, which is the highest efficiency of the reported SCOSCs. Thanks to the aggregation restriction of each component and chain entanglement in the three-in-one system, the PM6-D18-b-PYIT-based SCOSC displays significantly higher stability than the corresponding two-component (PM6-D18:PYIT) and three-component (PM6:D18:PYIT). These results demonstrate that the three-in-one strategy is facile and promising for developing SCOSCs with superior efficiency and stability.

Sensitive Organic Photodetectors With Spectral Response up to 1.3 µm Using a Quinoidal Molecular Semiconductor.

Detecting short-wavelength infrared (SWIR) light has underpinned several emerging technologies. However, the development of highly sensitive organic photodetectors (OPDs) operating in the SWIR region is hindered by their poor external quantum efficiencies (EQEs) and high dark currents. Herein, the development of high-sensitivity SWIR-OPDs with an efficient photoelectric response extending up to 1.3 µm is reported. These OPDs utilize a new ultralow-bandgap molecular semiconductor featuring a quinoidal tricyclic electron-deficient central unit and multiple non-covalent conformation locks. The SWIR-OPD achieves an unprecedented EQE of 26% under zero bias and an even more impressive EQE of up to 41% under a -4 V bias at 1.10 µm, effectively pushing the detection limit of silicon photodetectors. Additionally, the low energetic disorder and trap density in the active layer lead to significant suppression of thermal-generation carriers and dark current, resulting in excellent detectivity (Dsh *) exceeding 1013 Jones from 0.50 to 1.21 µm and surpassing 1012 Jones even at 1.30 µm under zero bias, marking the highest achievements for OPDs beyond the silicon limit to date. Validation with photoplethysmography measurements, a spectrometer prototype in the 0.35-1.25 µm range, and image capture under 1.20 µm irradiation demonstrate the extensive applications of this SWIR-OPD.

Acceptor-only oligomers with high coplanarity enable efficient and stable organic solar cells.

Acceptor-only oligomers are developed as guest components to construct oligomer-assisted active layers for high performance organic solar cells. Due to the high planarity and structural similarity with the host polymer donor, BDD-based acceptor-only oligomers formed an alloy phase with PM6 and optimized the phase morphology effectively, achieving a stable device displaying 18% efficiency.

An A-D-A'-D-A-Type Narrow Bandgap Electron Acceptor Based on Selenophene-Flanked Diketopyrrolopyrrole for Sensitive Near-Infrared Photodetection.

Near-infrared organic photodetectors possess great application potential in night vision, optical communication, and image sensing, but their development is limited by the lack of narrow bandgap organic semiconductors. A-D-A'-D-A-type molecules, featuring multiple intramolecular charge transfer effects, offer a robust framework for achieving near-infrared light absorption. Herein, we report a novel A-D-A'-D-A-type narrow bandgap electron acceptor named DPPSe-4Cl, which incorporates a selenophene-flanked diketopyrrolopyrrole (Se-DPP) unit as its central A' component. This molecule demonstrates exceptional near-infrared absorption properties with an absorption onset reaching 1120 nm and a low optical bandgap of 1.11 eV, owing to the strong electron-withdrawing ability and quinoidal resonance effect induced by the Se-DPP unit. By implementing a doping compensation strategy assisted by Y6 to reduce the trap density in the photoactive layer, the optimized organic photodetector based on DPPSe-4Cl exhibited efficient spectral response and remarkable sensitivity in the range of 300-1100 nm. Particularly, a specific detectivity surpassing 1012 Jones in the wavelength range of 410-1030 nm is achieved. This work offers a promising approach for developing highly sensitive visible to near-infrared broadband photodetection technology using organic semiconductors.

Multifunctional Acrylic Polymers with Enhanced Adhesive Property Serving as Excellent Edge Encapsulant for Stable Optoelectronic Devices.

Pendant groups in acrylic adhesive polymers (Ads) have a profound influence on adhesive and cohesive properties and additionally on encapsulant application. However, a systematic investigation to assess the impact of the pendant groups' length and bulkiness is rare, and there is not even a single report on applying Ads as interfacial adhesion promotors and encapsulation materials simultaneously. Herein, we have developed a series of multifunctional methacrylic polymers, namely, R-co-Ads, with varying pendant length and bulkiness (R = methyl (C1), ethyl (C2), propyl (C3), butyl (C4), pentyl (C5), hexyl (C6), isobutyl (iC4), and 2-ethylhexyl (2EH)). The adhesion-related experimental results reveal that R-co-Ads have high transparency, strong adhesion strength to the various contact surfaces, and a fast cure speed. In particular, C1-co-Ad shows a superior adhesion performance with an improved cross-cut index of 4B and a shear bonding strength of 1.56 MPa. We also have adopted C1-co-Ad for encapsulation of various emerging optoelectronic applications (e.g., perovskite solar cell-, charge transport-, and conductivity-related characteristics), demonstrating its excellent edge encapsulant served to improve the device stability against ambient air conditions. Our study establishes the structure-adhesion-surface relationships, advancing the better design of adhesives and encapsulants for various research fields.

Thickness Tolerance in Large-Area Organic Photovoltaics with Fluorine-Substituted Regioregular Conjugated Polymer.

Large areas and simple processing methods are necessary for the commercialization of organic photovoltaics (OPVs). However, the efficiency drop due to the variation in thickness of OPVs limits their large-scale applications. Regioregular polymers with good crystallinity and packing properties that exhibit high charge mobility and extraction ability can help overcome these limitations. In this study, a regioregular polymer named PDBD-2FBT was synthesized. The crystallinity and packing properties of PDBD-2FBT were enhanced by a simple thermal treatment. Using PDBD-2FBT material as a donor and Y6-HU as an acceptor, we fabricated binary blend OPV devices. The devices with optimized active layer thickness achieved a power conversion efficiency (PCE) of 14.14%. A PCE of 13.18% was maintained even in thick-film conditions (400 nm), and thickness tolerance was observed. Based on the thickness tolerance, a 5-line module measuring 36 cm2 was fabricated via the bar-coating method, and a PCE of approximately 10% was achieved.

Octafluoronaphthalene as a thermal-annealing-free volatile solid additive enables high-performance organic solar cells.

A thermal annealing-free solid additive octafluoronaphthalene was developed for high-performance organic solar cells. In an additive-modified device, an impressive power conversion efficiency of 18.59% from 17.27% was achieved with simultaneously enhanced current density from 26.86 to 27.53 mA cm-2 and fill factor from 74.34% to 78.85%.

Electronic Configuration Tuning of Centrally Extended Non-Fullerene Acceptors Enabling Organic Solar Cells with Efficiency Approaching 19 .

In the molecular optimizations of non-fullerene acceptors (NFAs), extending the central core can tune the energy levels, reduce nonradiative energy loss, enhance the intramolecular (donor-acceptor and acceptor-acceptor) packing, facilitate the charge transport, and improve device performance. In this study, a new strategy was employed to synthesize acceptors featuring conjugation-extended electron-deficient cores. Among these, the acceptor CH-BBQ, embedded with benzobisthiadiazole, exhibited an optimal fibrillar network morphology, enhanced crystallinity, and improved charge generation/transport in blend films, leading to a power conversion efficiency of 18.94 % for CH-BBQ-based ternary organic solar cells (OSCs; 18.19 % for binary OSCs) owing to its delicate structure design and electronic configuration tuning. Both experimental and theoretical approaches were used to systematically investigate the influence of the central electron-deficient core on the properties of the acceptor and device performance. The electron-deficient core modulation paves a new pathway in the molecular engineering of NFAs, propelling relevant research forward.

Regulating the Sequence Structure of Conjugated Block Copolymers Enables Large-Area Single-Component Organic Solar Cells with High Efficiency and Stability.

Single-component organic solar cells (SCOSCs) based on conjugated block copolymers (CBCs) by covalently bonding a polymer donor and polymer acceptor become more and more appealing due to the formation of a favorable and stable morphology. Unfortunately, a deep understanding of the effect of the assembly behavior caused by the sequence structure of CBCs on the device performance is still missing. Herein, from the aspect of manipulating the sequence length and distribution regularity of CBCs, we synthesized a series of new CBCs, namely D18(20)-b-PYIT, D18(40)-b-PYIT and D18(60)-b-PYIT by two-pot polymerization, and D18(40)-b-PYIT(r) by traditional one-pot method. It is observed that precise manipulation of sequence length and distribution regularity of the polymer blocks fine-tunes the self-assembly of the CBCs, optimizes film morphology, improves optoelectronic properties, and reduces energy loss, leading to simultaneously improved efficiency and stability. Among these CBCs, the D18(40)-b-PYIT-based device achieves a high efficiency of 13.4 % with enhanced stability, which is an outstanding performance among SCOSCs. Importantly, the regular sequence distribution and suitable sequence length of the CBCs enable a facile film-forming process of the printed device. For the first time, the blade-coated large-area rigid/flexible SCOSCs are fabricated, delivering an impressive efficiency of 11.62 %/10.73 %, much higher than their corresponding binary devices.

Conformational Locking Control of 2D Outer Side Chains via Fluorine Atom Positioning for Improving the Thermal Stability of Organic Solar Cells.

Alongside high power conversion efficiencies (PCEs), device stability, especially thermal issues, is another key factor for the successful commercialization of nonfullerene acceptor (NFA)-based organic solar cells (OSCs). Considering the significant effects of the side-chain engineering of NFAs on molecular packing and/or locking strongly associated with the thermal stability of OSCs, herein, we present two new isomeric NFAs with 4-fluoro- and 2-fluoro-substituted hexylphenyl two-dimensional (2D) outer side chains (4FY and 2FY, respectively). In contrast with the 2FY having a horizontal stretching conformation, 4FY exhibits a diagonal stretching conformation of the 2D outer side chains and a higher dipole moment, resulting in a huge difference in their crystalline/aggregation characteristics, i.e., 4FY possesses a higher crystallinity with a denser molecular packing than the 2FY neat film, as evidenced by thermal and morphological characterizations. Encouragingly, relative to the one based on 2FY, the OSC based on 4FY delivers a PCE as high as 16.4%, together with excellent thermal stability (88.4% PCE retention under 85 °C for 360 h), which is attributed to a more optimal and robust blend morphology induced by its better compatibility into the used donor component and stronger crystallinity. This work demonstrates that in addition to the improved photovoltaic property, the appropriate F-positioning on the 2D outer side chains can play a key role in controlling their conformations, which can promote the increase of the thermal stability of OSCs.

Constructing High-Performance Ternary Device Using Analogous Polymer Donors.

Both ternary copolymerization and ternary blending are effective methods to fine-tune polymer structure and manipulate thin-film morphology to improve device performance. In this work, three D-A-A-A (D: donor, A: acceptor) terpolymer donors (FY1, FY2, and FY3) are synthesized by introducing BDD (1,3-bis(2-ethylhexyl)-5,7-di(thiophen-2-yl)benzo[1,2-c:4,5-c']dithiophene-4,8-dione) units into the D-A alternating copolymer PM6 backbone. Owing to the promoted conjugated planarity and excellent absorption of BDD, the obtained terpolymers display an extended absorption range and enhanced π-π stacking orientation, which is a promising third component in ternary device. As a result, the optimal FY1:PM6:BTP-eC9-based ternary device afforded an impressive power conversion efficiency (PCE) as high as 18.52%, owing to the efficient charge transport, negligible energy loss, and suitable domain size. The result provides an efficient method to obtain high-performance polymer solar cells by using analogous polymer donors in ternary device.

An electron acceptor with an intrinsic quinoidal core for bulk-heterojunction organic solar cells and photodetectors.

An electron acceptor based on a quinoidal dipyrrolopyrazinedione core was synthesized for organic solar cells and photodetectors. A power conversion efficiency of 6.7% and a specific detectivity of 4.1 × 1013 Jones at 800 nm have been obtained, suggesting the promising prospects of quinoidal molecules for optoelectronic devices.

Revealing the Molecular Weight Effect on Highly Efficient Polythiophene Solar Cells.

Polythiophenes (PTs) are promising electron donors in organic solar cells (OSCs) due to their simple structures and excellent synthetic scalability. Benefiting from the rational molecular design, the power conversion efficiency (PCE) of PT solar cells has been greatly improved. Herein, five batches of the champion PT (P5TCN-F25) with molecular weights ranging from 30 to 87 kg mol-1 were prepared, and the effect of the molecular weight on the blend film morphology and photovoltaic performance of PT solar cells was systematically investigated. The results showed that the PCEs of the devices improved first and then maintained a high value with the increase of molecular weight, and the highest PCE of 16.7% in binary PT solar cells was obtained. Further characterizations revealed that the promotion in photovoltaic performance mainly comes from finer phase separation structures and more compact molecular packing in the blend film. The best device stabilities were also achieved by polymers with high molecular weights. Overall, this study highlights the importance of optimizing the molecular weight for PTs and offers directions to further improve the PCE of PT solar cells.

Naphthalene diimide-based random terpolymers with axisymmetric and asymmetric electron acceptors for controllable morphology and enhanced fill factors in all-polymer solar cells.

All-polymer solar cells (all-PSCs), based on p-type polymer donors and n-type acceptors as the active layer, offer exceptional promise because of excellent thermal stability, superior film formation, and good mechanical stress as a unique bulk heterojunction (BHJ) solar cell combination. Therefore, tuning the molecular composition between polymers is crucial for optimizing power conversion efficiency (PCE) in these all-PSC systems. In this study, we synthesized a series of naphthalene diimide (NDI)-based random terpolymers P(NDI-BDD10), P(NDI-TPD10), P(NDI-TT10), and P(NDI-2FQ10) with axisymmetric (BDD, TPD) and asymmetric (TT, 2FQ) electron acceptors. Compared with the blend morphology of PBDB-T:N2200, their diverse effects due to the addition of trace amounts of axisymmetric and asymmetric components were comprehensively investigated using physical and surface analyses and structural simulations. Consequently, most of our polymer acceptors demonstrated improved fill factors (FFs) in the optimal morphology. P(NDI-BDD10)-based devices achieved the highest PCE of 6.80% and FF of 69.1%, while the architecturally most asymmetric P(NDI-TT10)-based devices reached the lowest PCE of 4.52% despite an enhanced FF of 65.4%. As a result, the appropriate molecular arrangement is crucial for obtaining the desired morphology and improved PCE. Our findings give novel molecular design insight into the distinctions between axisymmetric and asymmetric electron acceptors and seem significant for achieving improved morphological features and efficiency.

Anthradithiophene (ADT)-Based Polymerized Non-Fullerene Acceptors for All-Polymer Solar Cells.

Realizing efficient all-polymer solar cell (APSC) acceptors typically involves increased building block synthetic complexity, hence potentially unscalable syntheses and/or prohibitive costs. Here we report the synthesis, characterization, and implementation in APSCs of three new polymer acceptors P1-P3 using a scalable donor fragment, bis(2-octyldodecyl)anthra[1,2-b : 5,6-b']dithiophene-4,10-dicarboxylate (ADT) co-polymerized with the high-efficiency acceptor units, NDI, Y6, and IDIC. All three copolymers have comparable photophysics to known polymers; however, APSCs fabricated by blending P1, P2 and P3 with donor polymers PM5 and PM6 exhibit modest power conversion efficiencies (PCEs), with the champion P2-based APSC achieving PCE=5.64 %. Detailed morphological and microstructural analysis by AFM and GIWAXS reveal a non-optimal APSC active layer morphology, which suppresses charge transport. Despite the modest efficiencies, these APSCs demonstrate the feasibility of using ADT as a scalable and inexpensive electron rich/donor building block for APSCs.

High-Performance Electrochemical and Photoelectrochemical Water Splitting at Neutral pH by Ir Nanocluster-Anchored CoFe-Layered Double Hydroxide Nanosheets.

Highly efficient electrocatalysts for the oxygen evolution reaction (OER) in neutral electrolytes are indispensable for practical electrochemical and photoelectrochemical water splitting technologies. However, there is a lack of good, neutral OER electrocatalysts because of the poor stability when H+ accumulates during the OER and slow OER kinetics at neutral pH. Herein, we report Ir species nanocluster-anchored, Co/Fe-layered double hydroxide (LDH) nanostructures in which the crystalline nature of LDH-restrained corrosion associated with H+ and the Ir species dramatically enhanced the OEC kinetics at neutral pH. The optimized OER electrocatalyst demonstrated a low overpotential of 323 mV (at 10 mA cm-2) and a record low Tafel slope of 42.8 mV dec-1. When it was integrated with an organic semiconductor-based photoanode, we obtained a photocurrent density of 15.2 mA cm-2 at 1.23 V versus reversible hydrogen in neutral electrolyte, which is the highest among all reported photoanodes to our knowledge.