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.

Prioritizing prognostic-associated subpopulations and individualized recurrence risk signatures from single-cell transcriptomes of colorectal cancer.

Colorectal cancer (CRC) is one of the most common gastrointestinal malignancies. There are few recurrence risk signatures for CRC patients. Single-cell RNA-sequencing (scRNA-seq) provides a high-resolution platform for prognostic signature detection. However, scRNA-seq is not practical in large cohorts due to its high cost and most single-cell experiments lack clinical phenotype information. Few studies have been reported to use external bulk transcriptome with survival time to guide the detection of key cell subtypes in scRNA-seq data. We proposed scRankXMBD, a computational framework to prioritize prognostic-associated cell subpopulations based on within-cell relative expression orderings of gene pairs from single-cell transcriptomes. scRankXMBD achieves higher precision and concordance compared with five existing methods. Moreover, we developed single-cell gene pair signatures to predict recurrence risk for patients individually. Our work facilitates the application of the rank-based method in scRNA-seq data for prognostic biomarker discovery and precision oncology. scRankXMBD is available at https://github.com/xmuyulab/scRank-XMBD. (XMBD:Xiamen Big Data, a biomedical open software initiative in the National Institute for Data Science in Health and Medicine, Xiamen University, China.).

Unraveling the Photovoltaic, Mechanical, and Microstructural Properties and Their Correlations in Simple Poly(3-pentylthiophene) Solar Cells.

The power conversion efficiency of polythiophene organic solar cells is constantly refreshed. Despite the renewed device efficiency, very few efforts have been devoted to understanding how the type of electron acceptor alters the photovoltaic and mechanical properties of these low-cost solar cells. Herein, the authors conduct a thorough investigation of photovoltaic and mechanical characteristics of a simple yet less-explored polythiophene, namely poly(3-pentylthiophene) (P3PT), in three different types of organic solar cells, where ZY-4Cl, PC71 BM, and N2200 are employed as three representative acceptors, respectively. Compared with the reference poly(3-hexylthiophene) (P3HT)-based solar cells, P3PT-based devices, all perform more efficiently. Particularly, the P3PT:ZY-4Cl blend exhibits the highest efficiency (ca. 10%) among the six combinations and outperforms the prior top-performance system P3HT:ZY-4Cl. Furthermore, the blend films based on N2200 exhibit a high crack-onset strain of ∼38% on average, which is approximately 15- and 17-times higher than those of ZY-4Cl and PC71 BM, respectively. The microstructural origins for the above difference are well elucidated by detailed grazing incidence X-ray scattering and microscopy analysis. This work not only underlines the potential of P3PT in prolific solar cell research but also demonstrates the superior tensile properties of polythiophene-based all-polymer blends for the preparation of stretchable solar cells.

Simple Tricyclic-Based A-π-D-π-A-Type Nonfullerene Acceptors for High-Efficiency Organic Solar Cells.

Nonfused-ring electron acceptors have attracted much attention in recent years due to their advantages of simple synthetic routes, high yields, low costs, reasonable power conversion efficiencies (PCEs), and so on. Herein, three simple A-π-D-π-A-type acceptors (DTC-BO-4F, DTS-BO-4F, and DTP-BO-4F) comprising a tricyclic fused-ring core, two 2,5-bis(alkyloxy)phenylene spacers, and two difluorinated terminal groups (DF-IC) were developed. Compared with DTS-BO-4F, DTC-BO-4F and DTP-BO-4F exhibit higher molar extinction coefficients, stronger crystallinity, and more orderly stacking. The PBDB-T:DTC-BO-4F-based blend film shows suitable phase separation and higher and more balanced charge mobilities. Finally, the photovoltaic devices based on DTC-BO-4F give an outstanding PCE of 13.26% with a small nonradiative voltage loss of 0.23 eV.

High-Performance Simple Nonfused Ring Electron Acceptors with Diphenylamino Flanking Groups.

Four simple nonfused ring electron acceptors (H-2F, CH3-2F, OCH3-2F, and SCH3-2F) were designed and synthesized. The use of diphenylamine derivatives as the flanking group for the construction of nonfused ring electron acceptors can improve solubility, avoid the formation of oversized aggregates, and enhance the intramolecular charge-transfer effect to extend absorption spectra. The substituent group at the diphenylamine unit has a great impact on the absorption and energy level of acceptors, electron mobility and morphology of blend films. Unlike the other three acceptors, CH3-2F can form ordered molecular stacking and a face-on orientation in the donor/acceptor blend film. A single-crystal analysis demonstrates that CH3-2F can form a two-dimensional electron transport network. Among these four acceptors, CH3-2F-based organic solar cells provide the highest PCE of 12.28%. Our work has demonstrated that triarylamine is a helpful construction unit for low-cost and high efficiency nonfused ring electron acceptors.

Designing high performance conjugated materials for photovoltaic cells with the aid of intramolecular noncovalent interactions.

Organic semiconductors including conjugated polymers and small molecules can be applied in many fields due to their unique advantages, such as light weight, solution processability, easy functionalization etc. During the past ten years, we mainly focused on the design and synthesis of conjugated polymer donor materials and small molecular acceptor materials for organic solar cells and hole transport materials for perovskite solar cells. To obtain planar conjugated polymers, low cost small molecular acceptors, and dopant-free hole transport polymers, we adopted intramolecular noncovalent interactions (INCIs) as the design strategy. In this brief review, we will demonstrate that the INCI strategy is very efficient in the design of high performance photovoltaic materials.

Hybrid Nonfused-Ring Electron Acceptors with Fullerene Pendant for High-Efficiency Organic Solar Cells.

The rapid advance of fused-ring electron acceptors (FREAs) has made them a potential substitute to fullerene-based acceptors and offered new avenues for the construction of organic solar cells (OSCs). Nonfused-ring acceptors (NFRAs) could significantly reduce the synthetic cost while achieving reasonable power conversion efficiencies (PCEs). Widely used fullerene acceptors have been applied as a second acceptor to regulate the morphology, absorption, and electron transport. To take full advantage of both nonfullerene and fullerene acceptors at the same time, we rationally designed and synthesized two novel NFRAs with phenyl-C61-butyric acid methyl ester (PCBM) as the lateral pendent. With the incorporation of fullerene pendent in PCBM-C6 and PCBM-C10, varied UV-vis absorption and photoluminescence (PL) quenching behaviors were observed, and isotropic diffraction patterns were obtained via grazing incidence wide-angle X-ray scattering (GIWAXS) measurements. The bulky, spherical, and electronic isotropic fullerene pendent could effectively suppress severe molecular aggregation and form the preferred blend morphology. This strategy significantly improved the efficiencies for exciton separation and charge collection relative to the control acceptor CH3COO-C6. Finally, the Voc, Jsc, and fill factor (FF) of PCBM-C10-based devices were simultaneously improved and an enhanced PCE of 13.55% was accomplished.

Realizing Efficient Single Organic Molecular White Light-Emitting Diodes from Conformational Isomerization of Quinazoline-Based Emitters.

Single pure organic molecular white light emitters (SPOMWLEs) are of significance as a new class of material for white lighting applications; however, few of them are able to emit white electroluminescence from organic light-emitting diodes. Herein, donor-π-acceptor conjugated emitters, 2PQ-PTZ and 4PQ-PTZ, were designed and synthesized as SPOMWLEs for white light emission considering the distinct advantages of their conformation isomers. The coexistence of conformational isomers in 2PQ-PTZ, which is the first experimental evidence of the coexisting quasi-axial and quasi-equatorial conformers, provides ideal flexibility to obtain white light emission from their simultaneous and well-separated fluorescence and thermally activated delayed fluorescence. With these remarkable properties, a 2PQ-PTZ-based white light-emitting diode (LED) with a CIE of (0.32, 0.34) and color rendering index (CRI) of 89 is demonstrated. Further, the white organic light-emitting diode (OLED) of 2PQ-PTZ exhibits a high external quantum efficiency (EQE) of 10.1%, which is the reported highest performance among SPOMWLE-based OLEDs.

Photovoltaic Performances of Fused Ring Acceptors with Isomerized Ladder-Type Dipyran Cores.

We precisely design and synthesize two A-π-D-π-A type dipyran-cored nonfullerene acceptors (NFAs) Ph-DTDPo-OT and Ph-DTDPi-OT with oxygen atoms at the outer and inner positions, respectively. 3-Hexyloxythiophene is used as the π-spacer to expand the effective conjugation length of the acceptors. These two NFAs possess similar optical band gaps and energy levels. However, the position of the oxygen atom at the dipyran core can markedly influence the molecular packing and aggregation behavior of the resulted acceptors. Ph-DTDPo-OT with a strong intermolecular affinity tends to form larger aggregates blending with PBDB-T, leading to a lower photovoltaic performance; Ph-DTDPi-OT presents good miscibility with PBDB-T and the blend films preferentially adopt a face-on orientation. Ph-DTDPi-OT-based devices display high and balanced hole and electron mobilities, leading to an optimal power conversion efficiency of 11.38%, which is much higher than those of Ph-DTDPo-OT-based ones (7.60%). Moreover, Ph-DTDPi-OT-based devices also exhibit a lower nonradiative recombination voltage loss of 0.268 eV. Our work demonstrates that the π-spacer and chemical structure of the core unit can greatly influence the molecular packing and the morphology of blend films, which are critical to the photovoltaic performance of devices.

Noncovalently fused-ring electron acceptors with near-infrared absorption for high-performance organic solar cells.

Non-fullerene fused-ring electron acceptors boost the power conversion efficiency of organic solar cells, but they suffer from high synthetic cost and low yield. Here, we show a series of low-cost noncovalently fused-ring electron acceptors, which consist of a ladder-like core locked by noncovalent sulfur-oxygen interactions and flanked by two dicyanoindanone electron-withdrawing groups. Compared with that of similar but unfused acceptor, the presence of ladder-like structure markedly broadens the absorption to the near-infrared region. In addition, the use of intramolecular noncovalent interactions avoids the tedious synthesis of covalently fused-ring structures and markedly lowers the synthetic cost. The optimized solar cells displayed an outstanding efficiency of 13.24%. More importantly, solar cells based on these acceptors demonstrate very low non-radiative energy losses. This research demonstrates that low-cost noncovalently fused-ring electron acceptors are promising to achieve high-efficiency organic solar cells.

Impact of the Bonding Sites at the Inner or Outer π-Bridged Positions for Non-Fullerene Acceptors.

Two A-π-D-π-A-type non-fullerene acceptors (IDT-ToFIC and IDT-TiFIC) with 5-hexylthienyl chains substituted at the inner and outer ß-positions of the thiophene π-bridge have been designed, respectively. Impacts of varied positional modifications are systematically studied. By utilizing PBDB-T as the donor, polymer solar cells are constructed with these two molecules as acceptors. Power conversion efficiencies of 11.09 and 9.46% are acquired for IDT-ToFIC- and IDT-TiFIC-based devices, respectively. Our studies have demonstrated that the use of thiophene spacers carrying one conjugated side chain at different positions can markedly enhance the photovoltaic properties relative to the corresponding control molecule IDTT2F.

Facile Synthesis of the O-Functionalized Ladder-Type Dipyran Building Block and Its Application in Polymer Solar Cells.

A new centrosymmetrical dipyran unit (DTDP) is successfully prepared by means of an efficient and universal way, and a series of PDTDP polymers have been prepared so as to assess their potential application in organic photovoltaic. The function of pyran moiety is not merely limited to tune the electron-donating roles and energy levels but it also contributes to solubility improvement. Interestingly, all pyran-based polymers displayed wide absorption ranging from 350 to 780 nm, but varied aggregation phenomena are observed. Furthermore, the quantum chemistry calculations for dimers, morphology study and grazing-incidence wide-angle X-ray scattering analysis for blend films have been utilized to understand the variations at photovoltaic performances. Finally, PDTDP-4 achieved the highest power conversion efficiency of 7.26% ( Voc = 0.72 V, FF = 0.66, and Jsc = 15.30 mA/cm2), demonstrating promising usage for high-efficiency polymer donors in polymer solar cells. In all, not only a promising dipyran building block is provided by this study, more dipyran derivatives and polymers could be prepared via this facile synthetic route.

Dibenzopyran-Based Wide Band Gap Conjugated Copolymers: Structural Design and Application for Polymer Solar Cells.

With the efficient synthesis of the crucial dibenzopyran building block, a series of PDBPTBT polymers containing different alkyl side chains and/or fluorine substitution were designed and synthesized via the microwave-assisted Suzuki polycondensation. Quantum chemistry calculations based on density functional theory indicated that different substitutions have significant impacts on the planarity and rigidity of the polymer backbones. Interestingly, the alkyloxy chains of PDBPTBT-4 tend to stay in the same plane with the benzothiadiazole unit, but the others appear to be out of plane. With the S···O and F···H/F···S supramolecular interactions, the conformations of the four polymers will be locked in different ways as predicted by the quantum chemistry calculation. Such structural variation resulted in varied solid stacking and photophysical properties as well as the final photovoltaic performances. Conventional devices based on these four polymers were fabricated, and PDBPTBT-5 displayed the best PCE of 5.32%. After optimization of the additive types, ratios, and the interlayers at the cathode, a high PCE of 7.06% (Voc = 0.96 V, Jsc = 11.09 mA/cm2, and FF = 0.67) is obtained for PDBPTBT-5 with 2.0% DIO as the additive and PFN-OX as the electron-transporting layer. These results indicated DBP-based conjugated polymers are promising wide band gap polymer donors for high-efficiency polymer solar cells.

Planar Heptathienoacenes Based on Unsymmetric Dithieno[3,2-b:3',4'-d]thiophene: Synthesis and Photophysical Properties.

The unsymmetric dithieno[3,2-b:3',4'-d]thiophene (ts-DTT) was efficiently synthesized, and two novel heptathienoacenes with linear and bull's horn shapes were designed and prepared via different ring cyclization connection manners. All intermediates and aimed heptathienoacenes were fully characterized by (1)H NMR, (13)C NMR, and HRMS. Their UV-vis absorption behavior, fluorescence, and electrochemical properties are characterized. In addition, DFT quantum calculation was employed to further understand the electron distribution and the origin of the absorption bands.

Thiophene-Based Double Helices: Syntheses, X-ray Structures, and Chiroptical Properties.

We demonstrate facile and efficient construction of conjugated double helical ladder oligomers from the saddle-shaped cyclooctatetrathiophene (COTh) building blocks. The key step involves deprotonation of tetra[3,4]thienylene (ß,ß-COTh) with n-BuLi which displays remarkably high ipsilateral selectivity. Three racemic double helical ladder oligomers, rac-DH-1, rac-DH-2, and rac-DH-3, containing two, three, and five COTh annelated moieties are efficiently synthesized by diastereoselective coupling of the racemic precursors. The X-ray crystallographic studies of rac-DH-1, rac-DH-2 and rac-DH-3 unambiguously revealed that each double helical scaffold has two single helices intertwined with each other via the C-C single bonds. Following removal of TMS groups, double helical ladder oligomer rac-DH-1-D had sufficient solubility to be resolved via chiral HPLC, thus enabling determination of its chirooptical properties such as CD spectra and optical rotation. (+)-DH-1-D has a large barrier for racemization, with lower limit of ΔG(‡) > 48 kcal mol(-1), which may be compared to DFT-computed barrier of 51 kcal mol(-1). The enantiomers of DH-1-D show 1 order of magnitude stronger chirooptical properties than the carbon-sulfur [7]helicene, as determined by the anisotropy factor g = Δε/ε = -0.039, based on Δεmax = -11 and ε = 2.8 × 10(2) L mol(-1) cm(-1) in cyclohexane at 327 nm.

Naphthotetrathiophene-Based Helicene-Like Molecules: Synthesis and Photophysical Properties.

Two novel helicene-like molecules based on naphthotetrathiophene are successfully synthesized. All target molecules and intermediates are characterized by (1)H NMR, (13)C NMR, IR, and HRMS. Their electrochemical and photophysical properties are studied. The configurations of the molecules are optimized by DFT quantum calculations and UV-vis behaviors are also predicted to further understand the origin of different absorption bands. We believe the current work illustrated an efficient way for the design and synthesis of sophisticated structures with naphthotetrathiophene as building blocks.

Silicon Spiro Double Helicene-like Compounds Based on Dithieno[2,3-b:3',2'-d]thiophene: Syntheses and Crystal Structures.

Silicon spiro carbon-sulfur double helicene-like compounds 1 and rac-2 were synthesized from 2,5-bis-trimethylsilanyldithieno[2,3-b:3',2'-d]thiophene, with total yields of 17% and 7%, respectively. (1)H and (13)C NMR spectra and X-ray crystallographic analysis showed the predicted 4-fold symmetry for 1 and rac-2 and confirmed their spiro double helicene-like spatial configurations. The absorption behavior of compounds 1 and rac-2 was also investigated.

Small Molecules of Cyclopentadithiophene Derivatives: Effect of Sulfur Atoms Position and Substituted Groups on Their UV-abs Properties.

Thiophene-based organic semiconductors used as the active components have received much attention. Their photoelectric properties can be easily tuned with various substitutions at different positions on molecular structures. Here, we synthesized series cyclopentadithiophene (CDT) derivatives with sulfur atoms at ortho- (o-CDT), meta- (m-CDT) and para-position (p-CDT) of the bridge carbon. These CDT derivatives were substituted by carbonyl/dicyanomethylene at the bridge position and/or by phenyl groups at α position, respectively. Due to the different conjugation extent and the variation of donor-acceptor (D-A) interaction originating from the change of sulfur atom position, diverse absorption spectra were observed. Especially for dicyanomethylene substituted o-CDT with phenyl as substitution group (DPCN-o-CDT), its absorption spectrum covers the whole region of visible light. Combining with the electrochemical behaviors and theoretical calculations, it was found that the sulfur atoms mainly contribute to the molecular conjugation in these CDT derivatives, especially for o-CDT derivatives. For phenyl groups, they primarily act as electron donor in m-CDT derivatives, and chiefly contribute to molecular conjugation in p-CDT derivatives, and simultaneously work as electron donor and conjugation component in o-CDT derivatives, respectively.

Synthesis and characterization of cyclooctatetrathiophenes with different connection sequences.

Based on the selectivity of deprotonation of 5,5'-bistrimethylsilyl-2,3'-bithiophene (4) in the presence of n-BuLi, three new cyclooctatetrathiophenes (COThs), COTh-1, COTh-2, and COTh-3 have been efficiently developed via intermolecular or intramolecular cyclizations. Their crystal structures clearly show that the different connectivity sequence of the thiophene rings in the molecules. The CV data and UV-vis absorbance spectra of COThs are also described. In addition, the time-dependent density functional theory (TDDFT) calculations accurately reproduce experimental observations and afford band assignment.

Selectivity of Br/Li exchange and deprotonation of 4,4'-dibromo-3,3'-bithiophene for synthesis of symmetrical and unsymmetrical dithienoheteroaromatic rings.

The novel selective synthesis of symmetrical and unsymmetrical dithienoheteroaromatic rings (DTHAs) has been developed via intramolecular cyclization of 4,4'-dibromo-3,3'-bithiophene (3). Four reaction conditions including n-BuLi/Et2O, n-BuLi/THF, s-BuLi/Et2O, and t-BuLi/Et2O were employed to react with 3 for selective formation of two types of dicarbanions, which generate the symmetrical and unsymmetrical DTHAs after quenching with three electrophilic reagents (4a-c). The possible mechanism of formation of DTHAs was proposed. In addition, two unsymmetrical DTHAs were confirmed by X-ray single-crystal analyses.