Designed Polar Cosolvent-Prepared Zinc Oxide Film for Efficient and Stable Inverted Organic Solar Cells.

Here, a simple method of applying dimethylformamide (DMF) as cosolvent in the sol-gel technology is used to improve the quality of ZnO bulk films. First-principles calculations show that with the addition of polar solvent DMF, the adsorption energy (Eads) between the solvent and Zn(OH)2 increases from -1.42 to -1.74 eV, which can stabilize the existence of Zn(OH)2, thereby promoting the ZnO synthesis. Besides, the elimination of amine residues in the DMF-ZnO film significantly suppress the photocatalytic activity induced by amine-induced coordination or redox reactions. Inverted organic solar cells (OSCs) based on PM6:Y6 and PM6:BTP-eC9 achieves impressive power conversion efficiencies (PCE) of 17.58 and 18.14%, respectively. Furthermore, benefiting from the reduced defects of bulk ZnO, pseudo-bilayer bulk heterojunction (PBHJ) devices based on the optimized ZnO film exhibited superior stability, the PM6:Y6 devices based on DMF-ZnO ETLs can maintain 90.28% of their initial PCE after 1000 h of thermal aging at 85 °C, and 80.98% of their initial PCE after 168 h of UV aging. This simple solvent optimization strategy can significantly improve the charge transport of ZnO bulk films, making it a reliable strategy for the preparation of electron transport layers in OSCs.

Strategies and Applications for Supramolecular Protein Self-Assembly.

Supramolecular chemistry achieves higher-order molecular self-assembly through non-covalent interactions. Utilizing supramolecular methods to explore the polymorphism of proteins, the building blocks of life, from a "bottom-up" perspective is essential for constructing diverse and functional biomaterials. In recent years, significant progress has been achieved in the design strategies and functional applications of supramolecular protein self-assembly, becoming a focal point for researchers. This paper reviews classical supramolecular strategies driving protein self-assembly, including electrostatic interactions, metal coordination, hydrogen bonding, hydrophobic interactions, host-guest interactions, and other mechanisms. We discuss how these supramolecular interactions regulate protein assembly processes and highlight protein supramolecular assemblies' unique structural and functional advantages in constructing artificial photosynthetic systems, protein hydrogels, bio-delivery systems, and other functional materials. The enormous potential and significance of supramolecular protein materials are elucidated. Finally, the challenges in preparing and applying protein supramolecular assemblies are summarized, and future development directions are projected.

Negatively Curved Octagon-Incorporated Aza-nanographene and its Assembly with Fullerenes.

A negatively curved aza-nanographene (NG) containing two octagons was synthesized by a regioselective and stepwise cyclodehydrogenation procedure, in which a double aza[7]helicene was simultaneously formed as an intermediate. Their saddle-shaped structures with negative curvature were unambiguously confirmed by X-ray crystallography, thereby enabling the exploration of the structure-property relationship by photophysical, electrochemical and conformational studies. Moreover, the assembly of the octagon-embedded aza-NG with fullerenes was probed by fluorescence spectral titration, with record-high binding constants (Ka=9.5×103 M-1 with C60, Ka=3.7×104 M-1 with C70) found among reported negatively curved polycyclic aromatic compounds. The tight association of aza-NG with C60 was further elucidated by X-ray diffraction analysis of their co-crystal, which showed the formation of a 1 : 1 complex with substantial concave-convex interactions.

Synthesis of a π-Extended Double [9]Helicene.

Double helicenes are appealing chiral frameworks. Their π-extension is desirable to achieve (chir)optical response in the visible and near-infrared (NIR) region, but access to higher double [n]helicenes (n≥8) has remained challenging. Herein, we report an unprecedented π-extended double [9]helicene (D9H), unambiguously revealing its structure by single-crystal X-ray diffraction. D9H shows remarkable NIR emission from 750 to 1100 nm with a high photoluminescence quantum yield of 18 %. In addition, optically pure D9H exhibits panchromatic circular dichroism with a notable dissymmetry factor (gCD ) of 0.019 at 590 nm, which is among the highest in the visible region for reported helicenes.

The Synthesis of a Multiple D-A Conjugated Macrocycle and Its Application in Organic Photovoltaic.

As a novel class of materials, D-A conjugated macrocycles hold significant promise for chemical science. However, their potential in photovoltaic remains largely untapped due to the complexity of introducing multiple donor and acceptor moieties into the design and synthesis of cyclic π-conjugated molecules. Here, we report a multiple D-A ring-like conjugated molecule (RCM) via the coupling of dimer molecule DBTP-C3 as a template and thiophenes in high yields. RCM exhibits a narrow optical gap (1.33 eV) and excellent thermal stability, and shows a remarkable photoluminescence yield (ΦPL ) of 11.1 % in solution, much higher than non-cyclic analogues. Organic solar cell (OSC) constructed with RCM as electron acceptor shows efficient charge separation at donor-acceptor band offsets and achieves a power conversion efficiency (PCE) of 14.2 %-approximately fourfold higher than macrocycle-based OSCs reported so far. This is partly due to low non-radiative voltage loss down to 0.20 eV and a high electroluminescence yield (ΦEL ) of 4×10-4 . Our findings emphasize the potential of D-A cyclic conjugated molecules in advancing organic photovoltaic technology.

Controlling the Emissive, Chiroptical, and Electrochemical Properties of Double [7] Helicenes through Embedded Aromatic Rings.

We present here the synthesis and in-depth physicochemical characterization of a double hetero[7]helicene fused with four triazole rings at both helical ends. The comparison of this triazole-fused double helicene with the previously reported all-carbon and thiadiazole-fused analogs revealed the huge impact of the embedded aromatic rings on the photophysical features. The small structural variation of the terminal rings from thiadiazole to triazole caused a dramatic change of the photoluminescence quantum yields (PLQYs) from <1 % to 96 %, while the replacement of the terminal benzene rings with triazole rings induced a tenfold enhancement of the circularly polarized luminescence dissymmetry factor. These observations were well corroborated with transient absorption analysis and/or theoretic calculations. In addition, the triazole-fused double helicene exhibited ambipolar redox behavior, enabling the generation of radical cation and anion species by electrochemical and chemical methods and showing its potential for spin-related applications.

Monolayer Nanosheets Exfoliated from Cage-Based Cationic Metal-Organic Frameworks.

The rational design and preparation of monolayer metal-organic framework (MOF) nanosheets remain great challenges. Recently, we found that monolayer MOF nanosheets can be facially exfoliated on a large scale from pristine two-dimensional (2D) MOFs with substantially reduced interlaminar interaction. By employing cage-like bicyclocalix[2]arene[2]triazine tri-imidazole as the building block, a family of cationic two-dimensional metal-organic frameworks (2D MOFs) with steric layer were designed and prepared. The single crystal structures have clearly identified that only very weak and sparse distributed C-H···π interaction exists between adjacent layers.On the basis of density functional theory calculation, the interlayer interaction of these cage-based cationic 2D MOFs was estimated to be 1/46th of that of graphite. Due to the extremely weak interaction, these cationic 2D MOFs tend to degenerate into an "amorphous" state after being soaked in other solvents; they can be readily exfoliated into 1.1 nm thick monolayer nanosheets with a high degree of thickness homogeneity, large lateral size, and significantly enlarged surface area. This work has identified that a cage-like molecule is the ideal building block for 2D cationic MOFs and ultrathin nanosheets; It was futher confirmed that weakening the interlaminar interaction is an effective strategy for facilely producing monolayer nanosheets.

Potassium-Presenting Zinc Oxide Surfaces Induce Vertical Phase Separation in Fullerene-Free Organic Photovoltaics.

Bulk heterojunction (BHJ) structure based organic photovoltaics (OPVs) have recently showed great potential for achieving high power conversion efficiencies (PCEs). An ideal BHJ structure would feature large donor/acceptor interfacial areas for efficient exciton dissociation and gradient distributions with high donor and acceptor concentrations near the anode and cathode, respectively, for efficient charge extraction. However, the random mixing of donors and acceptors in the BHJ often suffers the severe charge recombination in the interface, resulting in poor charge extraction. Herein, we propose a new approach-treating the surface of the zinc oxide (ZnO) as an electron transport layer with potassium hydroxide-to induce vertical phase separation of an active layer incorporating the nonfullerene acceptor IT-4F. Density functional theory calculations suggested that the binding energy difference between IT-4F and the PBDB-T-2Cl, to the potassium (K)-presenting ZnO interface, is twice as strong as that for IT-4F and PBDB-T-2Cl to the untreated ZnO surface, such that it would induce more IT-4F moving toward the K-presenting ZnO interface than the untreated ZnO interface thermodynamically. Benefiting from efficient charge extraction, the best PCEs increased to 12.8% from 11.8% for PBDB-T-2Cl:IT-4F-based devices, to 12.6% from 11.6% for PBDB-T-2Cl:Y1-4F-based devices, to 13.5% from 12.2% for PBDB-T-2Cl:Y6-based devices, and to 15.7% from 15.1% for PM6:Y6-based devices.

Correction: A new non-fullerene acceptor based on the combination of a heptacyclic benzothiadiazole unit and a thiophene-fused end group achieving over 13% efficiency.

Correction for 'A new non-fullerene acceptor based on the combination of a heptacyclic benzothiadiazole unit and a thiophene-fused end group achieving over 13% efficiency' by Yunqiang Zhang et al., Phys. Chem. Chem. Phys., 2019, DOI: .

Realizing Efficient Charge/Energy Transfer and Charge Extraction in Fullerene-Free Organic Photovoltaics via a Versatile Third Component.

Solution-processed organic photovoltaics (OPVs) based on bulk-heterojunctions have gained significant attention to alleviate the increasing demend of fossil fuel in the past two decades. OPVs combined of a wide bandgap polymer donor and a narrow bandgap nonfullerene acceptor show potential to achieve high performance. However, there are still two reasons to limit the OPVs performance. One, although this combination can expand from the ultraviolet to the near-infrared region, the overall external quantum efficiency of the device suffers low values. The other one is the low open-circuit voltage (VOC) of devices resulting from the relatively downshifted lowest unoccupied molecular orbital (LUMO) of the narrow bandgap. Herein, the approach to select and incorporate a versatile third component into the active layer is reported. A third component with a bandgap larger than that of the acceptor, and absorption spectra and LUMO levels lying within that of the donor and acceptor, is demonstrated to be effective to conquer these issues. As a result, the power conversion efficiencies (PCEs) are enhanced by the elevated short-circuit current and VOC; the champion PCEs are 11.1% and 13.1% for PTB7-Th:IEICO-4F based and PBDB-T:Y1 based solar cells, respectively.

Fluorination Enhances NIR-II Fluorescence of Polymer Dots for Quantitative Brain Tumor Imaging.

Here, we describe a fluorination strategy for semiconducting polymers for the development of highly bright second near-infrared region (NIR-II) probes. Tetrafluorination yielded a fluorescence QY of 3.2 % for the polymer dots (Pdots), over a 3-fold enhancement compared to non-fluorinated counterparts. The fluorescence enhancement was attributable to a nanoscale fluorous effect in the Pdots that maintained the molecular planarity and minimized the structure distortion between the excited state and ground state, thus reducing the nonradiative relaxations. By performing through-skull and through-scalp imaging of the brain vasculature of live mice, we quantitatively analyzed the vascular morphology of transgenic brain tumors in terms of the vessel lengths, vessel branches, and vessel symmetry, which showed statistically significant differences from the wild type animals. The bright NIR-II Pdots obtained through fluorination chemistry provide insightful information for precise diagnosis of the malignancy of the brain tumor.

A new non-fullerene acceptor based on the combination of a heptacyclic benzothiadiazole unit and a thiophene-fused end group achieving over 13% efficiency.

A new non-fullerene acceptor, namely Y10, based on dithienothiophen[3,2-b]-pyrrolobenzothiadiazole (TPBT) as the central core and 2-(6-oxo-5,6-dihydro-4H-cyclopenta[c]thiophen-4-ylidene)malononitrile (TC) as the electron-deficient end group, has been designed and synthesized. Y10 reveals a narrow optical energy gap (Eoptg) of 1.35 eV with a broad absorption band from 600 to 900 nm. A wide bandgap polymer, J11, as the donor material (Eoptg = 1.96 eV) is used to blend with Y10 for the construction of organic solar cell devices, which achieve an impressive power conversion efficiency (PCE) of 13.46% with an open circuit voltage (Voc) of 0.89 V, a short circuit current (Jsc) of 21.21 mA cm-2, and a fill factor (FF) of 71.55%, with thermal annealing treatment at 100 °C for 5 min and 0.8 wt% 1-chloronaphthalene (CN) as an additive. These results indicate that the incorporation of the TPBT unit as the central core and the TC unit as the electron-deficient end group provides an efficient strategy for the construction of high performance solar cells.

Naphthodifuran-based zigzag-type polycyclic arene with conjugated side chains for efficient photovoltaics.

Ladder-type conjugated structures with rigid and coplanar molecular frameworks feature longer effective conjugation, affirmative optoelectronic properties and strong intermolecular π-π interactions, which are ideal characteristics for organic photovoltaics. Here, a new "zigzag" angular-fused naphthodifuran (zNDF) based on alkoxyphenyl side chains was designed and synthesized. The distannylated zNDF building block was copolymerized with 4,7-di(5-bromothiophen-2-yl)-5,6-dioctyloxybenzo[c][1,2,5]thiadiazole and 5,8-bis(5-bromothiophen-2-yl)-2,3-bis(4-(2-ethylhexyloxy)-3-fluorophenyl)-6,7-difloroquinoxaline (Br-BT and Br-ffQx) acceptor units by Stille cross coupling reaction to form two new medium bandgap donor-acceptor polymers PzNDFP-BT and PzNDFP-ffQx, respectively. The photovoltaic properties of the copolymers blended with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an electron acceptor were investigated. A 6.9% efficiency was achieved from the single device based on the PzNDFP-BT : PC71BM (1 : 1.5, w/w) blend film with a 0.25% 1,8-diiodooctane (DIO) additive, which is among the highest efficiency for zNDF-based polymer solar cells.

Synthesis and photovoltaic properties of two new alkoxylphenyl substituted thieno[2,3-f]benzofuran based polymers.

Two new alkoxylphenyl substituted thieno[2,3-f]benzofuran (TBFP)-based polymers (PTBFP-BT and PTBFP-BO) were designed and synthesized. Their structures were verified by nuclear magnetic resonance (NMR) spectroscopy, the molecular weights were determined by gel permeation chromatography (GPC) and the thermal properties were investigated by thermogravimetric analysis (TGA). The two polymers showed similar UV-Vis absorption spectra with a broad and strong absorption band from 300-750 nm in solid state. The resulting copolymers exhibited relatively deep highest occupied molecular orbital (HOMO) energy levels (-5.47 and -5.61 eV) for PTBFP-BT and PTBFP-BO, respectively. The device fabricated with PTBFP-BT : PC71BM (1 : 2) showed better balanced hole and electron mobility of 2.49 × 10(-4) cm(2) V(-1) s(-1) and 9.12 × 10(-4) cm(2) V(-1) s(-1), respectively, than those of PTBFP-BO based devices. The polymer solar cells (PSCs), based on the single layer device structure of ITO/PEDOT:PSS/PTBFP-BT : PC71BM (1 : 2, w/w)/ZrAcac/Al with 3 vol% 1,8-diiodooctane (DIO) as additive, showed a relatively high power conversion efficiency (PCE) of 6% under the illumination of AM 1.5G, 100 mW cm(-2), with a high fill factor (FF) of 0.69.

Biological imaging using nanoparticles of small organic molecules with fluorescence emission at wavelengths longer than 1000 nm.

Embedded in a polymer: A hydrophobic organic molecule that fluoresces in the near-infrared II (NIR-II) region was made water-soluble and biocompatible by its embedment in a polymer nanoparticle, which was then coated with hydrophilic poly(ethylene glycol) chains. The resulting nanoparticles exhibit bright fluorescence in the NIR-II window and high photostability in aqueous media and were used for in vivo imaging in mice.

Observation of an Exciton-Plasma Transition in a Molecular Semiconductor.

The nonfullerene electron acceptors (NFAs) for organic solar cells are attracting intense research efforts due to their impressive performance. Understanding the temporal evolution of the excited states in NFAs is essential to gain insights into the working mechanism of these state-of-the-art devices. Here we characterized the photoconductivities of a neat Y6 film and a Y6:PM6 blend film using time-resolved terahertz spectroscopy. Three different types of excited states were identified based on their distinct terahertz responses, i.e., plasma-like carriers, weakly bound excitons, and spatially separated carriers. Under high-intensity excitation, the many-body interaction of excitons in the Y6 film leads to the plasma-like state, giving rise to a terahertz response characteristic for a dispersive charge transport. This transient state decays quickly into exciton gas due to fast Auger annihilation. Under low-intensity excitation, only isolated excitons are created and the plasma state is absent.

What We have Learnt from PM6:Y6.

Over the past three years, remarkable advancements in organic solar cells (OSCs) have emerged, propelled by the introduction of Y6-an innovative A-DA'D-A type small molecule non-fullerene acceptor (NFA). This review provides a critical discussion of the current knowledge about the structural and physical properties of the PM6:Y6 material combination in relation to its photovoltaic performance. The design principles of PM6 and Y6 are discussed, covering charge transfer, transport, and recombination mechanisms. Then, the authors delve into blend morphology and degradation mechanisms before considering commercialization. The current state of the art is presented, while also discussing unresolved contentious issues, such as the blend energetics, the pathways of free charge generation, and the role of triplet states in recombination. As such, this review aims to provide a comprehensive understanding of the PM6:Y6 material combination and its potential for further development in the field of organic solar cells. By addressing both the successes and challenges associated with this system, this review contributes to the ongoing research efforts toward achieving more efficient and stable organic solar cells.

Alkyl side chain engineering enables high performance as-cast organic solar cells of over 17% efficiency.

Achieving high-performance as-cast OSCs is crucial for industrialization in the future, owing to the advantages of better stability, environmental-friendly, and decreasing production cost. In this regard, we synthesized an A-DA'D-A type acceptor, Y6-eC6-BO, by shortening the straight alkyl side-chains on the thiophene position from C11 to C6 as well as lengthening the branched alkyl side-chains on the pyrrole position of Y6 to achieve a stronger crystallization and better miscibility than Y6. As a result, the corresponding chloroform-processed as-cast PM6: Y6-eC6-BO OSC showed a high PCE of 17.33%, which was one of the highest efficiencies of as-cast OSCs. And the as-cast PM6:Y6-eC6-BO OSCs processed from o-xylene displayed a PCE of 16.38%, as far as we know, this is among the highest efficiencies of non-halogenated-solvent processed as-cast OSCs. These results demonstrated tailoring the alkyl side-chain of NFAs is a feasible and simple approach to achieve high performance as-cast OSCs and provides guideline in molecular design in the future.

Atomic-level chemical reaction promoting external quantum efficiency of organic photomultiplication photodetector exceeding 108% for weak-light detection.

Low-cost, solution-processed photomultiplication organic photodetectors (PM-OPDs) with external quantum efficiency (EQE) above unity have attracted enormous attention. However, their weak-light detection is unpleasant because the anode Ohmic contact causes exacerbation in dark current. Here, we introduce atomic-level chemical reaction in PM-OPDs which can simultaneously suppress dark current and increase EQE via depositing a 0.8 nm thick Al2O3 by the atomic layer deposition. Suppression in dark current mainly originates from the built-in anode Schottky junction as a result of work function decrease of hole-transporting layer of which the chemical groups can react chemically with the bottom surface of Al2O3 layer at the atomic-level. Such strategy of suppressing dark current is not adverse to charge injection under illumination; instead, responsivity enhancement is realized because charge injection can shift from cathode to anode, of which the neighborhood possesses increased photogenerated carriers. Consequently, weak-light detection limit of the forwardly-biased PM-OPD with Al2O3 treatment reaches a remarkable level of 2.5 nW cm-2, while that of the reversely-biased control is 25 times inferior. Meanwhile, the PM-OPD yields a record high EQE and responsivity of 4.31 × 108% and 1.85 × 106 A W-1, respectively, outperforming all other polymer-based PM-OPDs.

A C3-symmetric triple oxa[6]helicene with circularly polarized luminescence featuring parallel transition dipole moments.

We present the synthesis and characterization of the first triple oxa[6]helicene with C3 symmetry. In contrast to the reported D3-symmetric triple oxa[7]helicene, the C3-symmetric analogue holds parallel electric and magnetic transition dipole moments and thus enhanced luminescence dissymmetry, shedding light on the critical role of molecular symmetry on chiroptical response.