以昇陳

A fused‐ring electron acceptor, FINIC, with fluorination of both end groups and side chains is designed and synthesized, and compared with its nonfluorinated analogue, INIC. FINIC exhibits 3D molecular stacking, exciton transport and charge transport. FINIC‐based organic solar cells yield an efficiency of 14.0%, far exceeding that of the INIC‐based devices (5.1%).

Abstract

A new fluorinated electron acceptor (FINIC) based on 6,6,12,12‐tetrakis(3‐fluoro‐4‐hexylphenyl)‐indacenobis(dithieno[3,2‐b ;2′ ,3′ ‐d ]thiophene) as the electron‐donating central core and 5,6‐difluoro‐3‐(1,1‐dicyanomethylene)‐1‐indanone as the electron‐deficient end groups is rationally designed and synthesized. FINIC shows similar absorption profile in dilute solution to the nonfluorinated analogue INIC. However, compared with INIC, FINIC film shows red‐shifted absorption, down‐shifted frontier molecular orbital energy levels, enhanced crystallinity, and more ordered molecular packing. Single‐crystal structure data show that FINIC molecules pack into closer 3D “network” motif through H‐bonding and π–π interaction, while INIC molecules pack into incompact “honeycomb” motif through only π–π stacking. Theoretical calculations reveal that FINIC has stronger electronic coupling and more molecular interactions than INIC. FINIC has higher electron mobilities in both horizontal and vertical directions than INIC. Moreover, FINIC and INIC support efficient 3D exciton transport. PBD‐SF/FINIC blend has a larger driving force for exciton splitting, more efficient charge transfer and photoinduced charge generation. Finally, the organic solar cells based on PBD‐SF/FINIC blend yield power conversion efficiency of 14.0%, far exceeding that of the PBD‐SF/INIC‐based devices (5.1%).

Nature Energy, Published online: 13 April 2020; doi:10.1038/s41560-020-0598-5

Adding an extension: A novel aza‐annulative π‐extension reaction of unfunctionalized aromatics is demonstrated, providing facile and rapid access to nitrogen‐containing polycyclic aromatic compounds and nitrogen‐doped nanographenes. Imidoyl chlorides serve as nitrogen‐containing π‐extending agents, affording the polyaromatics with excellent regioselectivities in up to 84 % yield. The reaction proceeds through a formal [4+2] cycloaddition between an unfunctionalized arene and a nitrilium intermediate.

Abstract

Nitrogen‐containing polycyclic aromatic compounds (N‐PACs) are an important class of compounds in materials science. Reported here is a new aza‐annulative π‐extension (aza‐APEX) reaction that allows rapid access to a range of N‐PACs in 11–84 % yields from readily available unfunctionalized aromatics and imidoyl chlorides. In the presence of silver hexafluorophosphate, arenes and imidoyl chlorides couple in a regioselective fashion. The follow‐up oxidative treatment with p‐chloranil affords structurally diverse N‐PACs, which are very difficult to synthesize. DFT calculations reveal that the aza‐APEX reaction proceeds through the formal [4+2] cycloaddition of an arene and an in situ generated diarylnitrilium salt, with sequential aromatizations having relatively low activation energies. Transformation of N‐PACs into nitrogen‐doped nanographenes and their photophysical properties are also described.

A rigid, simple, spiro compact electron donor/acceptor (D/A) dyad shows a long‐lived triplet charge transfer (³CT) state (0.94 μs) with a high energy level (ca. 2.12 eV), based on a new electron spin‐control method using spin‐orbit charge transfer intersystem crossing (SOCT‐ISC) (¹NI*→¹CT→³NI*→³CT; NI=naphthalimide), without heavy atoms or chromophores with intrinsic intersystem crossing (ISC) ability.

Abstract

We prepared conceptually novel, fully rigid, spiro compact electron donor (Rhodamine B, lactam form, RB)/acceptor (naphthalimide; NI) orthogonal dyad to attain the long‐lived triplet charge‐transfer (³CT) state, based on the electron spin control using spin‐orbit charge transfer intersystem crossing (SOCT‐ISC). Transient absorption (TA) spectra indicate the first charge separation (CS) takes place within 2.5 ps, subsequent SOCT‐ISC takes 8 ns to produce the ³NI* state. Then the slow secondary CS (125 ns) gives the long‐lived ³CT state (0.94 μs in deaerated n‐hexane) with high energy level (ca. 2.12 eV). The cascade photophysical processes of the dyad upon photoexcitation are summarized as ¹NI*→¹CT→³NI*→³CT. With time‐resolved electron paramagnetic resonance (TREPR) spectra, an EEEAAA electron‐spin polarization pattern was observed for the naphthalimide‐localized triplet state. Our spiro compact dyad structure and the electron spin‐control approach is different to previous methods for which invoking transition‐metal coordination or chromophores with intrinsic ISC ability is mandatory.

The active layer morphology of all‐small‐molecule organic solar cells (SM‐OSCs) is tuned by side chain engineering of the donor molecules and thermal annealing (TA) of the devices. An SM‐OSC based on A–D–A‐structured SM1‐F with fluorine and alkyl substituents as the donor and Y6 as the acceptor, and with TA, demonstrates a high power conversion efficiency of 14.07%.

Abstract

It is very important to fine‐tune the nanoscale morphology of donor:acceptor blend active layers for improving the photovoltaic performance of all‐small‐molecule organic solar cells (SM‐OSCs). In this work, two new small molecule donor materials are synthesized with different substituents on their thiophene conjugated side chains, including SM1‐S with alkylthio and SM1‐F with fluorine and alkyl substituents, and the previously reported donor molecule SM1 with an alkyl substituent, for investigating the effect of different conjugated side chains on the molecular aggregation and the photophysical, and photovoltaic properties of the donor molecules. As a result, an SM1‐F‐based SM‐OSC with Y6 as the acceptor, and with thermal annealing (TA) at 120 °C for 10 min, demonstrates the highest power conversion efficiency value of 14.07%, which is one of the best values for SM‐OSCs reported so far. Besides, these results also reveal that different side chains of the small molecules can distinctly influence the crystallinity characteristics and aggregation features, and TA treatment can effectively fine‐tune the phase separation to form suitable donor–acceptor interpenetrating networks, which is beneficial for exciton dissociation and charge transportation, leading to highly efficient photovoltaic performance.

A fullerene derivative (indene‐C₆₀ bisadduct) is introduced into organic solar cells via blade coating, which can eliminate the efficiency loss caused by different printing methods. This ternary strategy overcomes the morphology issues, and based on this strategy, the blade‐coating device (1.05 cm²) achieves an efficiency of 13.70%.

Abstract

Regarded as a critical step in commercial applications, scalable printing technology has become a research frontier in the field of organic solar cells. However, inevitable efficiency loss always occurs in the lab‐to‐manufacturing translation due to the different fabrication processes. In fact, the decline of photovoltaic performance is mainly related to voltage loss, which is mainly affected by the diversity of phase separation morphology and the chemical structures of photoactive materials. Fullerene derivative indene‐C₆₀ bisadduct (ICBA) is introduced into a PBDB‐T‐2F:IT‐4F system to control the active layer morphology during blade‐coating process. Accordingly, as a symmetrical fullerene derivative, ICBA can regulate the crystallization tendency and molecular packing orientation and suppress charge carrier recombination. This ternary strategy overcomes the morphology issues caused by weaker shear impulse in blade‐coating process. Benefiting from the reduced nonradiative recombination loss, 1.05 cm² devices are fabricated by blade coating with a power conversion efficiency of 13.70%. This approach provides an effective support for recovering the voltage loss during scalable printing approaches.

Two novel n‐type semiconducting FBDOPV‐based polymers are reported and studied in their neutral state and after doping with N‐DMBI. The relationships between morphology, charge carrier transport, and thermoelectric properties are unravelled and discussed. The best polymer shows a thermoelectric power factor of up to 0.72 µW m⁻¹ K⁻² and a figure of merit of 5.0 × 10⁻⁴ at 388 K.

Abstract

The impact of the chemical structure and molecular order on the charge transport properties of two donor–acceptor copolymers in their neutral and doped states is investigated. Both polymers comprise 3,7‐bis((E)‐7‐fluoro‐1‐(2‐octyl‐dodecyl)‐2‐oxoindolin‐3‐ylidene)‐3,7‐dihydrobenzo[1,2‐b :4,5‐b ′]difuran‐2,6‐dione (FBDOPV) as electron‐accepting unit, copolymerized with 9,9‐dioctyl‐fluorene (P(FBDOPV‐F)) or with 3‐dodecyl‐2,2′‐bithiophene (P(FBDOPV‐2T‐C₁₂)). These copolymers possess an amorphous and semi‐crystalline nature, respectively, and exhibit remarkable electron mobilities of 0.065 and 0.25 cm² V^–1 s^–1 in field effect transistors. However, after chemical n‐doping with 4‐(1,3‐dimethyl‐2,3‐dihydro‐1H ‐benzoimidazol‐2‐yl)phenyl)dimethylamine (N‐DMBI), electrical conductivities four orders of magnitude higher can be achieved for P(FBDOPV‐2T‐C₁₂) (σ = 0.042 S cm⁻¹). More charge‐transfer complexes are formed between P(FBDOPV‐F) and N‐DMBI, but the highly localized polaronic states poorly contribute to the charge transport. Doped P(FBDOPV‐2T‐C₁₂) exhibits a negative Seebeck coefficient of –265 µV K⁻¹ and a thermoelectric power factor (PF) of 0.30 µW m⁻¹ K⁻² at 303 K which increases to 0.72 µW m⁻¹ K⁻² at 388 K. The in‐plane thermal conductivity (κ_|| = 0.53 W m⁻¹ K⁻¹) on the same micrometer‐thick solution‐processed film is measured, resulting in a figure of merit (ZT) of 5.0 × 10⁻⁴ at 388 K. The results provide important design guidelines to improve the doping efficiency and thermoelectric properties of n‐type organic semiconductors.

A novel half‐fused diketopyrrolopyrrole‐based conjugated donor–acceptor polymer is identified for use as high‐performance, ambipolar field‐effect transistors and high‐gain inverters.

Abstract

A novel building block, denoted as half‐fused diketopyrrolopyrrole (DPP) (9‐(3‐octadecylhenicosyl)‐8‐(thiophen‐2‐yl)‐7H ‐pyrrolo[3,4‐a ]thieno[3,2‐g ]indolizine‐7,10(9H )‐dione), in which one of the flanking thiophene units is fused to one of the DPP rings via a carbon‐carbon double bond at the N‐position is reported. The half‐fused DPP is successfully utilized as an electron acceptor to prepare the conjugated donor–acceptor polymer PTFDFT , which exhibits ambipolar semiconducting behavior in ambient air. Theoretical calculations and absorption spectral studies show that the backbone of PTFDFT is more planar compared to the reference polymer with conventional DPP units. As a result, PTFDFT shows a narrow bandgap and low lowest unoccupied molecular orbital level. The more planar backbone with fewer side chains favors the dense packing of the polymer chains of PTFDFT with a short π–π stacking distance (3.49 Å). Grazing‐incidence wide‐angle X‐ray scattering data further confirm the predominant edge‐on packing mode of the PTFDFT polymer chains on the substrate. As expected, the PTFDFT thin film shows excellent ambipolar semiconducting properties under ambient conditions, reaching 2.23 and 1.08 cm² V⁻¹ s⁻¹ for the n‐ and p‐channels, respectively. In addition, complementary‐like inverter with gain value as high as 141 is successfully constructed using the PTFDFT thin film.

Multiple donor–acceptor‐type carbazole–benzonitrile derivatives with both linear donor–π–donor and acceptor–π–acceptor structures to promote triplet upconversion are utilized as a sensitizer, realizing organic light‐emitting diodes with deep‐blue narrow‐band emission, maximum external quantum efficiency of 32.5%, and a T80 (time to 80% of the initial luminance) of >3000 h at an initial luminance of 100 cd m⁻² simultaneously.

Abstract

Multiple donor–acceptor‐type carbazole–benzonitrile derivatives that exhibit thermally activated delayed fluorescence (TADF) are the state of the art in efficiency and stability in sky‐blue organic light‐emitting diodes. However, such a motif still suffers from low reverse intersystem crossing rates (k _RISC) with emission peaks <470 nm. Here, a weak acceptor of cyanophenyl is adopted to replace the stronger cyano one to construct blue emitters with multiple donors and acceptors. Both linear donor–π–donor and acceptor–π–acceptor structures are observed to facilitate delocalized excited states for enhanced mixing between charge‐transfer and locally excited states. Consequently, a high k _RISC of 2.36 × 10⁶ s⁻¹ with an emission peak of 456 nm and a maximum external quantum efficiency of 22.8% is achieved. When utilizing this material to sensitize a blue multiple‐resonance TADF emitter, the corresponding device simultaneously realizes a maximum external quantum efficiency of 32.5%, CIE _y ≈ 0.12, a full width at half maximum of 29 nm, and a T80 (time to 80% of the initial luminance) of > 60 h at an initial luminance of 1000 cd m⁻².

An all‐organic dielectric polymer with repeat units of a fairly rigid fused bicyclic structure and alkenes separated by freely rotating single bonds is proposed for energy storage at elevated temperatures. The piston‐like crankshaft structure endows it with a large bandgap of ≈5 eV and flexibility, while being temperature‐invariantly stable over −160 to 160 °C.

Abstract

Flexible dielectrics operable under simultaneous electric and thermal extremes are critical to advanced electronics for ultrahigh densities and/or harsh conditions. However, conventional high‐performance polymer dielectrics generally have conjugated aromatic backbones, leading to limited bandgaps and hence high conduction loss and poor energy densities, especially at elevated temperatures. A polyoxafluoronorbornene is reported, which has a key design feature in that it is a polyolefin consisting of repeating units of fairly rigid fused bicyclic structures and alkenes separated by freely rotating single bonds, endowing it with a large bandgap of ≈5 eV and flexibility, while being temperature‐invariantly stable over −160 to 160 °C. At 150 °C, the polyoxafluoronorbornene exhibits an electrical conductivity two orders of magnitude lower than the best commercial high‐temperature polymers, and features an unprecedented discharged energy density of 5.7 J cm⁻³ far outperforming the best reported flexible dielectrics. The design strategy uncovered in this work reveals a hitherto unexplored space for the design of scalable and efficient polymer dielectrics for electrical power and electronic systems under concurrent harsh electrical and thermal conditions.

A fullerene derivative (indene‐C₆₀ bisadduct) is introduced into organic solar cells via blade coating, which can eliminate the efficiency loss caused by different printing methods. This ternary strategy overcomes the morphology issues, and based on this strategy, the blade‐coating device (1.05 cm²) achieves an efficiency of 13.70%.

Abstract

Regarded as a critical step in commercial applications, scalable printing technology has become a research frontier in the field of organic solar cells. However, inevitable efficiency loss always occurs in the lab‐to‐manufacturing translation due to the different fabrication processes. In fact, the decline of photovoltaic performance is mainly related to voltage loss, which is mainly affected by the diversity of phase separation morphology and the chemical structures of photoactive materials. Fullerene derivative indene‐C₆₀ bisadduct (ICBA) is introduced into a PBDB‐T‐2F:IT‐4F system to control the active layer morphology during blade‐coating process. Accordingly, as a symmetrical fullerene derivative, ICBA can regulate the crystallization tendency and molecular packing orientation and suppress charge carrier recombination. This ternary strategy overcomes the morphology issues caused by weaker shear impulse in blade‐coating process. Benefiting from the reduced nonradiative recombination loss, 1.05 cm² devices are fabricated by blade coating with a power conversion efficiency of 13.70%. This approach provides an effective support for recovering the voltage loss during scalable printing approaches.

Publication date: June 2020

Source: Nano Energy, Volume 72

Author(s): Tao Jia, Jiabin Zhang, Wenkai Zhong, Yuanying Liang, Kai Zhang, Sheng Dong, Lei Ying, Feng Liu, Xiaohui Wang, Fei Huang, Yong Cao

By finely optimizing the alkyl chains, the nonfullerene acceptor named BTP‐eC9 is synthesized and a maximum power conversion efficiency of 17.8% in organic photovoltaic cells is recorded. This work demonstrates that the optimization of alkyl chains to get suitable solubility and enhanced intermolecular packing has a great potential in further improving its photovoltaic performance.

Abstract

Optimizing the molecular structures of organic photovoltaic (OPV) materials is one of the most effective methods to boost power conversion efficiencies (PCEs). For an excellent molecular system with a certain conjugated skeleton, fine tuning the alky chains is of considerable significance to fully explore its photovoltaic potential. In this work, the optimization of alkyl chains is performed on a chlorinated nonfullerene acceptor (NFA) named BTP‐4Cl‐BO (a Y6 derivative) and very impressive photovoltaic parameters in OPV cells are obtained. To get more ordered intermolecular packing, the n‐undecyl is shortened at the edge of BTP‐eC11 to n‐nonyl and n‐heptyl. As a result, the NFAs of BTP‐eC9 and BTP‐eC7 are synthesized. The BTP‐eC7 shows relatively poor solubility and thus limits its application in device fabrication. Fortunately, the BTP‐eC9 possesses good solubility and, at the same time, enhanced electron transport property than BTP‐eC11. Significantly, due to the simultaneously enhanced short‐circuit current density and fill factor, the BTP‐eC9‐based single‐junction OPV cells record a maximum PCE of 17.8% and get a certified value of 17.3%. These results demonstrate that minimizing the alkyl chains to get suitable solubility and enhanced intermolecular packing has a great potential in further improving its photovoltaic performance.