Stereoisomeric Non-Fullerene Acceptors-Based Organic Solar Cells.

Chiral alkyl chains are ubiquitously observed in organic semiconductor materials and can regulate solution processability and active layer morphology, but the effect of stereoisomers on photovoltaic performance has rarely been investigated. For the racemic Y-type acceptors widely used in organic solar cells, it remains unknown if the individual chiral molecules separate into the conglomerate phase or if racemic phase prevails. Here, the photovoltaic performance of enantiomerically pure Y6 derivatives, (S,S)/(R,R)-BTP-4F, and their chiral mixtures are compared. It is found that (S,S) and (R,R)-BTP-4F molecule in the racemic mixtures tends to interact with its enantiomer. The racemic mixtures enable efficient light harvesting, fast hole transfer, and long polaron lifetime, which is conducive to charge generation and suppresses the recombination losses. Moreover, abundant charge diffusion pathways provided by the racemate contribute to efficient charge transport. As a result, the racemate system maximizes the power output and minimizes losses, leading to a higher efficiency of 18.16% and a reduced energy loss of 0.549 eV, as compared to the enantiomerically pure molecules. This study demonstrates that the chirality of non-fullerene acceptors should receive more attention and be designed rationally to enhance the efficiency of organic solar cells.

Effect of Embedded g-C3N4 Nanosheets on the Hydration and Thermal Response Behavior of Cross-Linked Thermoresponsive Copolymer Films.

The effect of embedded graphitic carbon nitride (g-C3N4) nanosheets on hydration and thermal response behavior of cross-linked thermoresponsive poly(di(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate), abbreviated as P(MA-co-MA300), thin films is probed by white light interferometry. Compared with that of the cross-linked pure P(MA-co-MA300) films, the surface roughness of the cross-linked hybrid films is slightly increased, which is caused by the minor aggregation of g-C3N4 nanosheets during the spin-coating process. After exposure to a water vapor atmosphere, both cross-linked pure and hybrid films can absorb water and swell. However, the introduction of g-C3N4 not only induces a larger hydration extent but also triggers a nonlinear transition behavior upon heating. This prominent difference might be related to the residual hydrophilic groups (-NH2 and N-H) on the surface of g-C3N4 nanosheets, which enhance the interaction and absorption capability for water molecules in the hybrid films. Upon further increasing the amount of embedded g-C3N4 nanosheets in films, more hydrogen bonds are formed and a larger hydration extent of films is observed. To break all of the hydrogen bonds in films, a higher transition temperature (TT) is required. The observed hydration and transition behaviors of hybrid films can be used to design hydrogel-based films for hydrogen evolution or wastewater treatment.

A bromide substituted 2D additive for stable and efficient perovskite photovoltaics.

In this article, a bromide substituted 2D layered perovskite having a repeated vertical orientation and coexisting with the bulk of a 3D perovskite is reported for the first time. This novel structure is obtained through controlled compositional engineering of the perovskite precursor solution. The photovoltaic performance of this novel 2D/3D perovskite was higher than that of 3D MAPbI3 and a maximum photoconversion efficiency (PCE) of 17.4% was achieved. The devices fabricated using this perovskite heterostructure were stable and retained their initial PCE up to 20 days when kept open in a laboratory environment with 40% relative humidity.

Bis(benzoselenadiazol)ethane: A π-Extended Acceptor-Dimeric Unit for Ambipolar Polymer Transistors with Hole and Electron Mobilities Exceeding 10†cm2 V-1 s-1.

The lack of ambipolar polymers with balanced hole (µh) and electron mobilities (µe) >10 cm2 V-1 s-1 is the main bottleneck for developing organic integrated circuits. Herein, we show the design and synthesis of a π-extended selenium-containing acceptor-dimeric unit, namely benzo[c][1,2,5]selenadiazol-4-yl)ethane (BBSeE), to address this dilemma. In comparison to its sulfur-counterpart, BBSeE demonstrates enlarged co-planarity, selective noncovalent interactions, polarized Se-N bond, and higher electron affinity. The successful stannylation of BBSeE offers a great opportunity to access acceptor-acceptor copolymer pN-BBSeE, which shows a narrower band gap, lower-lying lowest unoccupied molecular orbital level (-4.05 eV), and a higher degree of backbone planarity. Consequently, the pN-BBSeE-based organic transistors display an ideally balanced ambipolar transporting property with µh and µe of 10.65 and 10.72 cm2 V-1 s-1, respectively. To the best of our knowledge, the simultaneous µh/µe values >10.0 cm2 V-1 s-1 are the best performances ever reported for ambipolar polymers. In addition, pN-BBSeE shows an excellent shelf-storage stability, retaining over 85 % of the initial mobility values after two months storage. Our study demonstrates the π-extended acceptor-dimeric BBSeE is a promising acceptor building block for constructing high-performance ambipolar polymers applied in next-generation organic integrated circuit.

A High-Mobility n-Type Noncovalently-Fused-Ring Polymer for High-Performance Organic Thermoelectrics.

Conjugated polymers are emerging as competitive candidates for organic thermoelectrics (OTEs). However, to make the device truly pervasive, both p- and n-type conjugated polymers are essential. Despite great efforts, no n-type equivalents to the p-type benchmark PEDOT:PSS exist to date mainly due to the low electrical conductivity (σ). Herein, a near-amorphous n-type conjugated polymer, namely pDFSe, is reported with high σ by achieving the synergy between charge transport and doping efficiency. The polymer pDFSe is synthesized based on an acceptor-triad moiety of diketopyrrolopyrrole-difluorobenzoselenadiazole-diketopyrrolopyrrole (DFSe), which has the noncovalently-fused-ring structure to reinforce the backbone rigidity. Furthermore, an axisymmetric thiophene-selenophene-thiophene donor is introduced, which enables the formation of near-amorphous microstructures. The above merits ensure good doping efficiency without scarifying efficient intrachain charge-carrier transport. Thus, pDFSe-based n-type transistors exhibit high electron mobility up to 6.15 cm2 V-1 s-1, much higher than its reference polymer pDSe without the noncovalently-fused-ring structure (0.77 cm2 V-1 s-1). Further upon n-doping, pDFSe demonstrates excellent σ of 62.6 S cm-1 and maximum power factor of 133.1 µW m-1 K-2, which are among the highest values reported for solution-processed n-type polymers. The results demonstrate the great potential of near-amorphous n-type conjugated polymers with noncovalently-fused-ring structure for the next-generation OTEs.

Regulating the Layered Stacking of a Covalent Triazine Framework Membrane for Aromatic/Aliphatic Separation.

Membrane separation of aromatics and aliphatics is a crucial requirement in chemical and petroleum industries. However, this task presents a significant challenge due to the lack of membrane materials that can endure harsh solvents, exhibit molecular specificity, and facilitate easy processing. Herein, we present a novel approach to fabricate a covalent triazine framework (CTF) membrane by employing a mix-monomer strategy. By incorporating a spatial monomer alongside a planar monomer, we were able to subtly modulate both the pore aperture and membrane affinity, enabling preferential permeation of aromatics over aliphatics with molecular weight below 200 Dalton (Da). Consequently, we achieved successful all-liquid phase separation of aromatic/aliphatic mixtures. Our investigation revealed that the synergistic effects of size sieving and the affinity between the permeating molecules and the membrane played a pivotal role in separating these closely resembling species. Furthermore, the membrane exhibited remarkable robustness under practical operating conditions, including prolonged operation time, various feed compositions, different applied pressure, and multiple feed components. This versatile strategy offers a feasible approach to fabricate membranes with molecule selectivity toward aromatic/aliphatic mixtures, taking a significant step forward in addressing the grand challenge of separating small organic molecules through membrane technology.

Tailoring the Position of Ester Group on N-Alkyl Chains of Benzotriazole-based Small Molecule Acceptors for High-Performance Organic Solar Cells.

Side chain engineering plays a vital role in exploring high-performance small molecule acceptors (SMAs) for organic solar cells (OSCs). In this work, we designed and synthesized a series of A-DA'D-A type SMAs by introducing different N-substituted alkyl and ester alkyl side chains on benzotriazole (BZ) central unit and aimed to investigate the effect of different ester substitution positions on photovoltaic performances. All the new SMAs with ester groups exhibit lower the lowest unoccupied molecular orbital (LUMO) energy levels and more blue-shifted absorption, but relatively higher absorption coefficients than alkyl chain counterpart. After blending with the donor PM6, the ester side chain-based devices demonstrate enhanced charge mobility, reduced amorphous intermixing domain size and long-lived charge transfer state compared to the alkyl chain counterpart, which are beneficial to achieve higher short-circuit current density (Jsc ) and fill factor (FF), simultaneously. Thereinto, the PM6 : BZ-E31 based device achieves a higher power conversion efficiency (PCE) of 18.33 %, which is the highest PCE among the OSCs based on the SMAs with BZ-core. Our work demonstrated the strategy of ester substituted side chain is a feasible and effective approach to develop more efficient SMAs for OSCs.

Suppressing Exciton-Vibration Coupling to Prolong Exciton Lifetime of Nonfullerene Acceptors Enables High-Efficiency Organic Solar Cells.

The limited exciton lifetime (τ, generally <1 ns) leads to short exciton diffusion length (LD ) of organic semiconductors, which is the bottleneck issue impeding the further improvement of power conversion efficiencies (PCEs) for organic solar cells (OSCs). However, efficient strategies to prolong intrinsic τ are rare and vague. Herein, we propose a facile method to efficiently reduce vibrational frequency of molecular skeleton and suppress exciton-vibration coupling to decrease non-radiative decay rate and thus prolong τ via deuterating nonfullerene acceptors. The τ remarkably increases from 0.90 ns (non-deuterated L8-BO) to 1.35 ns (deuterated L8-BO-D), which is the record for organic photovoltaic materials. Besides, the inhibited molecular vibration improves molecular planarity of L8-BO-D for enhanced exciton diffusion coefficient. Consequently, the LD increases from 7.9 nm (L8-BO) to 10.7 nm (L8-BO-D). The prolonged LD of L8-BO-D enables PM6 : L8-BO-D-based bulk heterojunction OSCs to acquire higher PCEs of 18.5 % with more efficient exciton dissociation and weaker charge carrier recombination than PM6 : L8-BO-based counterparts. Moreover, benefiting from the prolonged LD , D18/L8-BO-D-based pseudo-planar heterojunction OSCs achieve an impressive PCE of 19.3 %, which is among the highest values. This work provides an efficient strategy to increase the τ and thus LD of organic semiconductors, boosting PCEs of OSCs.

Precisely Manipulating Molecular Packing via Tuning Alkyl Side-Chain Topology Enabling High-Performance Nonfused-Ring Electron Acceptors.

In the development of high-performance organic solar cells (OSCs), the self-organization of organic semiconductors plays a crucial role. This study focuses on the precisely manipulation of molecular assemble via tuning alkyl side-chain topology in a series of low-cost nonfused-ring electron acceptors (NFREAs). Among the three NFREAs investigated, DPA-4, which possesses an asymmetric alkyl side-chain length, exhibits a tight packing in the crystal and high crystallinity in the film, contributing to improved electron mobility and favorable film morphology for DPA-4. As a result, the OSC device based on DPA-4 achieves an excellent power conversion efficiency of 16.67 %, ranking among the highest efficiencies for NFREA-based OSCs.

A Wide Bandgap Acceptor with Large Dielectric Constant and High Electrostatic Potential Values for Efficient Organic Photovoltaic Cells.

Low-bandgap materials have achieved rapid development and promoted the enhancement of power conversion efficiencies (PCEs) of organic photovoltaic (OPV) cells. However, the design of wide-bandgap non-fullerene acceptors (WBG-NFAs), required by indoor applications and tandem cells, has been lagging far behind the development of OPV technologies. Here, we designed and synthesized two NFAs named ITCC-Cl and TIDC-Cl by finely optimizing ITCC. In contrast with ITCC and ITCC-Cl, TIDC-Cl can maintain a wider bandgap and a higher electrostatic potential simultaneously. When blending with the donor PB2, the highest dielectric constant is also obtained in TIDC-Cl-based films, enabling efficient charge generation. Therefore, the PB2:TIDC-Cl-based cell possessed a high PCE of 13.8% with an excellent fill factor (FF) of 78.2% under the air mass 1.5G (AM 1.5G) condition. Furthermore, an exciting PCE of 27.1% can be accomplished in the PB2:TIDC-Cl system under the illumination of 500 lux (2700 K light-emitting diode). Combined with the theoretical simulation, the tandem OPV cell based on TIDC-Cl was fabricated and exhibited an excellent PCE of 20.0%.

Small Molecule Donors Design Rules for Non-Halogen Solvent Fabricated Organic Solar Cells.

Compared with all-small-molecule (ASM) and other types of organic solar cells (OSCs), the small molecule donor:polymer acceptor (SMD:PA) OSCs develop much slower due to the lack of material matching rules. Herein, by changing the end-cap substituent of the small molecule donor from ethyl (MPhS-C2) to benzyl (MPhS-Ph), the different selection rules of donor properties and thermal annealing (TA) treatment between the ASM and the SMD:PA system under tetrahydrofuran processing are thoroughly investigated. Therefore, MPhS-Ph exhibits more ordered molecular packing, leading to better adaptability in the SMD:PA system without TA; while the inferior molecular packing of MPhS-C2 after spin-coating performs better in the ASM system with TA. Whether spin-coating or TA process dominates morphological optimization also dominates their energy loss. Therefore, the MPhS-Ph:PYF-T-o and MPhS-C2:BTP-eC9 based devices achieve the highest power conversion efficiency (PCE) of 12.1% and 15.7%, respectively, both of which are cutting-edge PCEs in their own type of OSCs fabricated by non-halogen solvent. This result suggests that intrinsic strong crystallization independent of the thermal drive is hoped in SMD:PA-OSCs, while high miscibility after spin-coating and proper assembly under thermal drive is expected in ASM-OSCs, providing deep understanding and guidance in highly efficient materials design rules in both ASM-OSCs and SMD:PA-OSCs.

Sideband cooling of a trapped ion in strong sideband coupling regime.

Conventional theoretical studies on the ground-state laser cooling of a trapped ion have mostly focused on the weak sideband coupling (WSC) regime, where the cooling rate is inverse proportional to the linewidth of the excited state. In a recent work [New J. Phys.23, 023018 (2021)10.1088/1367-2630/abe273], we proposed a theoretical framework to study the ground state cooling of a trapped ion in the strong sideband coupling (SSC) regime, under the assumption of a vanishing carrier transition. Here we extend this analysis to more general situations with nonvanishing carrier transitions, where we show that by properly tuning the coupling lasers a cooling rate proportional to the linewidth can be achieved. Our theoretical predictions closely agree with the corresponding exact solutions in the SSC regime, which provide an important theoretical guidance for sideband cooling experiments.

Ultratough graphene-black phosphorus films.

Graphene-based films with high toughness have many promising applications, especially for flexible energy storage and portable electrical devices. Achieving such high-toughness films, however, remains a challenge. The conventional mechanisms for improving toughness are crack arrest or plastic deformation. Herein we demonstrate black phosphorus (BP) functionalized graphene films with record toughness by combining crack arrest and plastic deformation. The formation of covalent bonding P-O-C between BP and graphene oxide (GO) nanosheets not only reduces the voids of GO film but also improves the alignment degree of GO nanosheets, resulting in high compactness of the GO film. After further chemical reduction and π-π stacking interactions by conjugated molecules, the alignment degree of rGO nanosheets was further improved, and the voids in lamellar graphene film were also further reduced. Then, the compactness of the resultant graphene films and the alignment degree of reduced graphene oxide nanosheets are further improved. The toughness of the graphene film reaches as high as ∼51.8 MJ m-3, the highest recorded to date. In situ Raman spectra and molecular dynamics simulations reveal that the record toughness is due to synergistic interactions of lubrication of BP nanosheets, P-O-C covalent bonding, and π-π stacking interactions in the resultant graphene films. Our tough black phosphorus functionalized graphene films with high tensile strength and excellent conductivity also exhibit high ambient stability and electromagnetic shielding performance. Furthermore, a supercapacitor based on the tough films demonstrated high performance and remarkable flexibility.

PubPredict: Prediction of progression and survival in oncology leveraging publications and early efficacy data.

In oncology/hematology early phase clinical trials, efficacies were often observed in terms of response rate, depth, timing, and duration. However, the true clinical benefits that eventually support registrational purpose are progression-free survival (PFS) and/or overall survival (OS), the follow-up of which are typically not long enough in early phase trials. This gap imposes challenges in strategies for late phase drug development. In this article, we tackle the question by leveraging published study to establish a quantitative link between early efficacy outcomes and late phase efficacy endpoints. We used solid tumor cancer as disease model. We modeled the disease course of a RECISTv1.1 assessed solid tumor with a continuous Markov chain (CMC) model. We parameterize the transition intensity matrix of a CMC model based on published aggregate-level summary statistics, and then simulate subject-level time-to-event data. The simulated data is shown to have good approximation to published studies. PFS and/or OS could be predicted with the transition intensity matrix modified given clinical knowledge to reflect various assumptions on response rate, depth, timing, and duration. The authors have built a R shiny application named PubPredict, the tool implements the algorithm described above and allows customized features including multiple response levels, treatment crossover and varying follow-up duration. This toolset has been applied to advise phase 3 trial design when only early efficacy data are available from phase 1 or 2 studies.

Macrocyclic Encapsulation in a Non-fused Tetrathiophene Acceptor for Efficient Organic Solar Cells with High Short-Circuit Current Density.

Non-fullerene acceptors have shown great promise for organic solar cells (OSCs). However, challenges in achieving high efficiency molecular system with conformational unicity and effective molecular stacking remain. In this study, we present a new design of non-fused tetrathiophene acceptor R4T-1 via employing the encapsulation of tetrathiophene with macrocyclic ring. The single crystal structure analysis reveals that cyclic alkyl side chains can perfectly encapsulate the central part of molecule and generate a conformational stable and planar molecular backbone. Whereas, the control 4T-5 without the encapsulation restriction displays cis- and twisted conformation. As a result, R4T-1 based OSCs achieved an outstanding power conversion efficiency (PCE) exceeding 15.10 % with a high short-circuit current density (Jsc ) of 25.48 mA/cm2 , which is significantly improved by ≈30 % in relative to that of the control. Our findings demonstrate that the macrocyclic encapsulation strategy could assist fully non-fused electron acceptors (FNEAs) to achieve a high photovoltaic performance and pave a new way for FNEAs design.

An Efficient Direct Arylation Polycondensation via C-S Bond Cleavage.

The direct arylation polycondensation (DArP) has become one of the most important methods to construct conjugated polymers (CPs). However, the homocoupling side-reactions of aryl halides and the low regioseletive reactivities of unfunctionalized aryls hinder the development of DArP. Here, an efficient Pd and Cu co-catalyzed DArP was developed via inert C-S bond cleavage of aryl thioethers, of which robustness was exemplified by over twenty conjugated polymers (CPs), including copolymers, homopolymers, and random polymers. The capture of oxidative addition intermediate together with experimental and theoretic results suggested the important role of palladium (Pd) and copper (Cu) co-catalysis with a bicyclic mechanism. The studies of NMR, molecular weights, trap densities, two-dimensional grazing-incidence wide-angle X-ray scattering (2D-GIWAXS), and the charge transport mobilities revealed that the homocoupling reactions were significantly suppressed with high regioselectivity of unfunctionalized aryls, suggesting this method is an excellent choice for synthesizing high performance CPs.

Achieving Record-Efficiency Organic Solar Cells upon Tuning the Conformation of Solid Additives.

Volatile solid additives (SADs) are considered as a simple yet effective approach to tune the film morphology for high-performance organic solar cells (OSCs). However, the structural effects of the SADs on the photovoltaic performance are still elusive. Herein, two volatilizable SADs were designed and synthesized. One is SAD1 with twisted conformation, while the other one is planar SAD2 with the S···O noncovalent intramolecular interactions (NIIs). The theoretical and experimental results revealed that the planar SAD2 with smaller space occupation can more easily insert between the Y6 molecules, which is beneficial to form a tighter intermolecular packing mode of Y6 after thermal treatment. As a result, the SAD2-treated OSCs exhibited less recombination loss, more balanced charge mobility, higher hole transfer rate, and more favorable morphology, resulting in a record power conversion efficiency (PCE) of 18.85% (certified PCE: 18.7%) for single-junction binary OSCs. The universality of this study shed light on understanding the conformation effects of SADs on photovoltaic performances of OSCs.

Chiral Non-Fullerene Acceptor Enriched Bulk Heterojunctions Enable High-Performance Near-Infrared Circularly Polarized Light Detection.

Organic photodetectors that can sensitively convert near-infrared (NIR) circularly polarized light (CPL) into modulable electrical signals have promising applications in spectroscopy, imaging, and communications. However, the preparation of chiral NIR organic photodetectors with simultaneously high dissymmetry factor, responsivity, detectivity, and response speed is challenging. Here, direct CPL detectors based on the bulk heterojunctions (BHJs) of chiral BTP-4Cl non-fullerene acceptor with dilute achiral PM6 donor are constructed, which successfully address these issues. The chiral acceptor-enriched BHJs with a donor/acceptor ratio of 1/10 achieve an optimal trade-off between chiroptical properties and optoelectronic performance. The supramolecular chirality from the acceptor aggregates provides the BHJs with a true absorption dissymmetry factor (gabs ) of ±0.02 at 830 nm, the highest value among NIR-sensitive detectors, which endows the photodetector with a photocurrent dissymmetry factor (gsc ) of ±0.03. Impressively, the photodetector demonstrates an external quantum efficiency as high as 60%, a responsivity of 0.4 A W-1 , a detectivity of 3 × 1011 Jones (based on noise current), and a fast response speed on the microsecond scale with the -3 dB bandwidth over 7000 Hz in the NIR region. This study exhibits a promising strategy for building high-performing direct NIR CPL detectors by introducing supramolecular chirality into BHJs.

Hydrophilicity gradient in covalent organic frameworks for membrane distillation.

Desalination can help to alleviate the fresh-water crisis facing the world. Thermally driven membrane distillation is a promising way to purify water from a variety of saline and polluted sources by utilizing low-grade heat. However, membrane distillation membranes suffer from limited permeance and wetting owing to the lack of precise structural control. Here, we report a strategy to fabricate membrane distillation membranes composed of vertically aligned channels with a hydrophilicity gradient by engineering defects in covalent organic framework films by the removal of imine bonds. Such functional variation in individual channels enables a selective water transport pathway and a precise liquid-vapour phase change interface. In addition to having anti-fouling and anti-wetting capability, the covalent organic framework membrane on a supporting layer shows a flux of 600 l m-2 h-1 with 85 °C feed at 16 kPa absolute pressure, which is nearly triple that of the state-of-the-art membrane distillation membrane for desalination. Our results may promote the development of gradient membranes for molecular sieving.

Broadband polarization-insensitive metalens integrated with a charge-coupled device in the short-wave near-infrared range.

The performance of a charge-coupled device is important in detection accuracy for terminal sensitivity of a short-wave near-infrared spectrometer. The sizes of pixel pitch and pixel itself are reducing with the development of CCD technologies. However, the fill factor of CCD pixels has not been significantly improved due to the limits of the shift registers, which makes a lower utilization rate of incident light of CCD. In recent years, the advance of metasurface optics provides a new solution for solving this problem. In this paper, a polarization-insensitive metalens is experimentally demonstrated to increase the fill factor of short-wave near-infrared CCD pixels by 4 times, and the simulated results show that the designed metalens has an excellent optical crosstalk (≤0.8%). It proves that the fill factor of CCD pixels can be further improved by the proposed approach which would pave the way for the overall integration of metalens array and photodetectors, as well as the development of CCD miniaturization and lightweight.