Conspectus In the last three decades, p-type (hole-transporting) organic and polymeric semiconductors have achieved great success in terms of materials diversity and device performance, while the ...development of n-type (electron-transporting) analogues greatly lags behind, which is limited by the scarcity of highly electron-deficient building blocks with compact geometry and good solubility. However, such n-type semiconductors are essential due to the existence of the p–n junction and a complementary metal oxide semiconductor (CMOS)-like circuit in organic electronic devices. Among various electron-deficient building blocks, imide-functionalized arenes, such as naphthalene diimide (NDI) and perylene diimide (PDI), have been proven to be the most promising ones for developing n-type organic and polymeric semiconductors. Nevertheless, phenyl-based NDI and PDI lead to sizable steric hindrance with neighboring (hetero)arenes and a high degree of backbone distortion in the resultant semiconductors, which greatly limits their microstructural ordering and charge transport. To attenuate the steric hindrance associated with NDI and PDI, a novel imide-functionalized heteroarene, bithiophene imide (BTI), was designed; however, the BTI-based semiconductors suffer from high-lying frontier molecular orbital (FMO) energy levels as a result of their electron-rich thiophene framework and monoimide group, which is detrimental to n-type performance. In this Account, we review a series of BTI derivatives developed via various strategies, including ring fusion, thiazole substitution, fluorination, cyanation, and chalcogen substitution, and elaborate the synthesis routes designed to overcome the synthesis challenges due to their high electron deficiency. After structural optimization, these BTI derivatives can not only retain the advantages of good solubility, a planar backbone, and small steric hindrance inherited from BTI but also have greatly suppressed FMO levels. These novel building blocks enable the construction of a great number of n-type organic and polymeric semiconductors, particularly acceptor–acceptor (or all-acceptor)-type polymers, with remarkable performance in various devices, including electron mobility (μe) of 3.71 cm2 V–1 s–1 in organic thin-film transistors (OTFTs), a power conversion efficiency (PCE) of 15.2% in all-polymer solar cells (all-PSCs), a PCE of 20.8% in inverted perovskite solar cells (PVSCs), electrical conductivity (σ) of 0.34 S cm–1 and a power factor (PF) of 1.52 μW m–1 K–2 in self-doped diradicals, and σ of 23.3 S cm–1 and a PF of ∼10 μW m–1 K–2 in molecularly n-doped polymers, all of which are among the best values in each type of device. The structure–property–device performance correlations of these n-type semiconductors are elucidated. The design strategy and synthesis of these novel BTI derivatives provide important information for developing highly electron-deficient building blocks with optimized physicochemical properties. Finally, we offer our insights into the further development of BTI derivatives and semiconductors built from them.
High-performance n-type (electron-transporting or n-channel) polymer semiconductors are critical components for the realization of various organic optoelectronic devices and complementary circuits, ...and recent progress has greatly advanced the performance of organic thin-film transistors, all-polymer solar cells, and organic thermoelectrics, to cite just a few. This Perspective focuses on the recent development of high-performance n-type polymer structures, particularly those based on the most investigated and novel electron-deficient building blocks, as well as summarizes the performance achieved in the above devices. In addition, this Perspective offers our insights into developing new electron-accepting building blocks and polymer design strategies, as well as discusses the challenges and opportunities in advancing n-type device performance.
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Challenges and opportunities:•Designing and synthesizing novel highly electron-deficient building blocks with very low-lying and delocalized lowest unoccupied molecular orbitals (LUMOs), reduced steric hindrance, and excellent solubilizing capability.•Developing facile polymerization methods that can effectively incorporate various electron-deficient building blocks into polymers. The n-type polymers have good solubility, a high content of acceptor units in polymeric backbones, optimized optoelectronic properties, high molecular weight, and minimal structural defects.•Achieving excellent n-type performance with robust stability in material processing and under device operation conditions.
n-Type (electron-transporting or n-channel) polymer semiconductors have been widely investigated for application in various organic optoelectronic devices. In this Perspective, we summarize the recent progress in electron-accepting building-block design and synthetic strategies for n-type polymers for realizing high-performance organic thin-film transistors, all-polymer solar cells, and organic thermoelectrics.
Imide‐Functionalized Polymer Semiconductors Sun, Huiliang; Wang, Lei; Wang, Yingfeng ...
Chemistry : a European journal,
January 2, 2019, Letnik:
25, Številka:
1
Journal Article
Recenzirano
Imide‐functionalized π‐conjugated polymer semiconductors have received a great deal of interest owing to their unique physicochemical properties and optoelectronic characteristics, including ...excellent solubility, highly planar backbones, widely tunable band gaps and energy levels of frontier molecular orbitals, and good film morphology. The organic electronics community has witnessed rapid expansion of the materials library and remarkable improvement in device performance recently. This review summarizes the development of imide‐functionalized polymer semiconductors as well as their device performance in organic thin‐film transistors and polymer solar cells, mainly achieved in the past three years. The materials mainly cover naphthalene diimide, perylene diimide, and bithiophene imide, and other imide‐based polymer semiconductors are also discussed. The perspective offers our insights for developing new imide‐functionalized building blocks and polymer semiconductors with optimized optoelectronic properties. We hope that this review will generate more research interest in the community to realize further improved device performance by developing new imide‐functionalized polymer semiconductors.
An engineering drive: Imide‐functionalized arenes are of particularly importance for constructing high‐performance semiconducting polymers owing to their unique combination of various device performance improving characteristics. The recent development of imide‐functionalized arenes and their polymer semiconductors has resulted in greatly improved device performance in both organic thin‐film transistors and polymer solar cells.
Development of high-performance unipolar n-type organic semiconductors still remains as a great challenge. In this work, all-acceptor bithiophene imide-based ladder-type small molecules BTIn and ...semiladder-type homopolymers PBTIn (n = 1–5) were synthesized, and their structure–property correlations were studied in depth. It was found that Pd-catalyzed Stille coupling is superior to Ni-mediated Yamamoto coupling to produce polymers with higher molecular weight and improved polymer quality, thus leading to greatly increased electron mobility (μe). Due to their all-acceptor backbone, these polymers all exhibit unipolar n-type transport in organic thin-film transistors, accompanied by low off-currents (10–10–10–9 A), large on/off current ratios (106), and small threshold voltages (∼15–25 V). The highest μe, up to 3.71 cm2 V–1 s–1, is attained from PBTI1 with the shortest monomer unit. As the monomer size is extended, the μe drops by 2 orders to 0.014 cm2 V–1 s–1 for PBTI5. This monotonic decrease of μe was also observed in their homologous BTIn small molecules. This trend of mobility decrease is in good agreement with the evolvement of disordered phases within the film, as revealed by Raman spectroscopy and X-ray diffraction measurements. The extension of the ladder-type building blocks appears to have a large impact on the motion freedom of the building blocks and the polymer chains during film formation, thus negatively affecting film morphology and charge carrier mobility. The result indicates that synthesizing building blocks with more extended ladder-type backbone does not necessarily lead to improved mobilities. This study marks a significant advance in the performance of all-acceptor-type polymers as unipolar electron transporting materials and provides useful guidelines for further development of (semi)ladder-type molecular and polymeric semiconductors for applications in organic electronics.
The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have improved considerably in recent years with the development of fused‐ring electron acceptors (FREAs). Currently, FREAs‐based ...OSCs have achieved high PCEs of over 19% in single‐junction OSCs. Whereas the relatively high synthetic complexity and the low yield of FREAs typically result in high production costs, hindering the commercial application of OSCs. In contrast, noncovalently fused‐ring electron acceptors (NFREAs) can compensate for the shortcomings of FREAs and facilitate large‐scale industrial production by virtue of the simple structure, facile synthesis, high yield, low cost, and reasonable efficiency. At present, OSCs based on NFREAs have exceeded the PCEs of 15% and are expected to reach comparable efficiency as FREAs‐based OSCs. Here, recent advances in NFREAs in this review provide insight into improving the performance of OSCs. In particular, this paper focuses on the effect of the chemical structures of NFREAs on the molecule conformation, aggregation, and packing mode. Various molecular design strategies, such as core, side‐chain, and terminal group engineering, are presented. In addition, some novel polymer acceptors based on NFREAs for all‐polymer OSCs are also introduced. In the end, the paper provides an outlook on developing efficient, stable, and low‐cost NFREAs for achieving commercial applications.
Noncovalently fused‐ring electron acceptors (NFREAs) have attracted much attention because of the advantage of simple structure, facile synthesis, and low cost, which have great potential for commercial applications in organic solar cells. This review presents the recent development of NFREAs for organic solar cells and focuses on the effect of their chemical structure on the molecule conformation, aggregation, and packing structure.
It is widely recognized that subtle changes in the chemical structure of organic semiconductors can induce dramatic variations in their optoelectronic properties and device performance, especially ...for the nonfullerene small‐molecule acceptors (SMAs). For instance, halogenation of the end groups in the acceptor–donor–acceptor‐type SMAs is an effective strategy to modulate the properties of the end group and thus the entire SMA. While previous position modulations have focused on only one substituent, this study shows the development of three isomeric SMAs (BTP‐ClBr, BTP‐ClBr1, and BTP‐ClBr2) via manipulating the position of two halogen substituents (chlorine and bromine) on the terminal unit. BTP‐ClBr exhibits a blueshifted absorption, a shallower lowest unoccupied molecular orbital energy level, and a weaker crystallization tendency relative to BTP‐ClBr1 and BTP‐ClBr2. A power conversion efficiency (16.82%) and an excellent fill factor (FF) (0.79) are realized in the optimal PM6:BTP‐ClBr organic solar cell device. The higher FF is consistent with the results of the characterization including a longer charge recombination lifetime, a faster photocurrent decay, a weaker bimolecular recombination, and a more favorable domain size for PM6:BTP‐ClBr, which all originate from a subtle change in the substitution sites that strongly influences the physicochemical properties of the SMA.
Three isomeric small‐molecule acceptors (SMAs) are developed by altering the substitution site of Cl and Br on the benzene‐fused end group, namely, BTP‐ClBr, BTP‐ClBr1, and BTP‐ClBr2, and the effects of substitution position in the SMAs on the photoelectric properties and photovoltaic performance are systematically investigated.
Degradation of the kinetically trapped bulk heterojunction film morphology in organic solar cells (OSCs) remains a grand challenge for their practical application. Herein, we demonstrate highly ...thermally stable OSCs using multicomponent photoactive layer synthesized via a facile one-pot polymerization, which show the advantages of low synthetic cost and simplified device fabrication. The OSCs based on multicomponent photoactive layer deliver a high power conversion efficiency of 11.8% and exhibit excellent device stability for over 1000 h (>80% of their initial efficiency retention), realizing a balance between device efficiency and operational lifetime for OSCs. In-depth opto-electrical and morphological properties characterizations revealed that the dominant PM6-b-L15 block polymers with backbone entanglement and the small fraction of PM6 and L15 polymers synergistically contribute to the frozen fine-tuned film morphology and maintain well-balanced charge transport under long-time operation. These findings pave the way towards the development of low-cost and long-term stable OSCs.
Imide-functionalized arenes, exemplified by naphthalene diimides (NDIs), perylene diimides (PDIs), and bithiophene imides (BTIs), are the most promising building blocks for constructing ...high-performance n-type polymers. In order to reduce the steric hindrance associated with NDI- and PDI-based polymers and to address the high-lying LUMO issue of BTI-based polymers, herein a highly electron-deficient imide-functionalized bithiazole, N-alkyl-5,5′-bithiazole-4,4′-dicarboximide (BTzI), was successfully synthesized via an efficient C–H activation. Single crystal of BTzI model compound showed a planar backbone with close π-stacking distances (3.2–3.3 Å). The N,N′-bis(2-alkyl)-2,2′-bithiazolethienyl-4,4′,10,10′-tetracarboxdiimide (DTzTI) was also used for constructing polymer semiconductors. Compared to DTzTI, BTzI is more electron-deficient, rendering it highly appealing for enabling n-type polymers. On the basis of BTzI and DTzTI, a series of polymers, including acceptor–acceptor homopolymers, and donor–acceptor and donor–acceptor–acceptor copolymers, were synthesized, which feature different contents of acceptor units in polymeric backbones. As imide content increases, the polymer FMO levels were gradually lowered, yielding a transition of charge carrier from ambipolarity to unipolar n-type in organic thin-film transistors (OTFTs). The acceptor–acceptor homopolymer PBTzI possesses the deepest LUMO/HOMO level of −3.94/-6.17 eV, enabling minimal off-current (I off) of 10–10–10–11 A in OTFTs. The highest electron mobility of 1.61 cm2 V–1 s–1 accompanied by small I off of 10–10–10–11 A and high on-current/off-current ratio (I on/I off) of 107–108 was achieved from OTFTs using PDTzTI homopolymer, showing the pronounced advantages of acceptor-acceptor homopolymer approach for developing unipolar n-type polymer semiconductors. The correlations between the FMO levels and the transistor performances underscore the significance of FMO tuning for enabling unipolar electron transport. The results demonstrate that imide-functionalized thiazoles are excellent units for constructing high-performance n-type polymers. Moreover, the synthetic routes to these highly electron-deficient imide-functionalized thiazoles and the polymer structure–property correlations developed here are informative for materials invention in organic electronics.
The aggregation/crystallinity of classic n‐type terpolymers based on naphthalene diimide and perylene diimide is challenging to tune due to their rigid and extended cores, leading to suboptimal film ...morphology. A new strategy for developing high‐performance n‐type terpolymers by incorporating imide‐functionalized heteroarenes is reported here to balance crystallinity and miscibility without sacrificing charge carrier mobilities. The introduction of thienopyrroledione (TPD) into the copolymer f‐BTI2‐FT results in a series of terpolymers BTI2‐xTPD having distinct TPD content. The irregular backbone reduces crystallinity, yielding improved miscibility with the polymer donor. More importantly, TPD triggers noncovalent S⋯O interactions, increasing backbone planarity and in‐chain charge transport. Such interactions also promote face‐on polymer packing. As a result, all‐polymer solar cells (all‐PSCs) based on BTI2‐30TPD achieve an optimal power conversion efficiency (PCE) of 8.28% with a small energy loss (0.53 eV). This efficiency is substantially higher than that of TPD (4.4%) or a BTI2‐based copolymer (6.8%) and is also the highest for additive‐free all‐PSCs based on a terpolymer acceptor. Moreover, the BTI2‐30TPD cell exhibits excellent stability with the PCE retaining 90% of its initial value after 400 h of aging. The results demonstrate that random polymerization using imide‐functionalized heteroarenes is a powerful approach to develop terpolymer acceptors toward efficient and stable all‐polymer solar cell PSCs.
A facile and highly effective approach to balance the crystallinity and miscibility of terpolymer acceptors is reported. Random incorporation of thienopyrroledione triggers noncovalent sulfur∙∙∙oxygen interactions, enabling optimized blend morphology and polymer orientation without sacrificing charge carrier mobility; hence, an excellent efficiency of 8.28% is obtained from additive‐free all‐polymer solar cell devices.
Drug resistance is a major challenge in the treatment of epilepsy. Drug-resistant epilepsy (DRE) accounts for 30% of all cases of epilepsy and is a matter of great concern because of its ...uncontrollability and the high burden, mortality rate, and degree of damage. At present, considerable research has focused on the development of predictors to aid in the early identification of DRE in an effort to promote prompt initiation of individualized treatment. While multiple predictors and risk factors have been identified, there are currently no standard predictors that can be used to guide the clinical management of DRE. In this review, we discuss several potential predictors of DRE and related factors that may become predictors in the future and perform evidence rating analysis to identify reliable potential predictors.
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•Overcoming drug resistance is a key challenge in epilepsy treatment.•Clinical and biochemical predictors can identify drug-resistant epilepsy (DRE).•Reliable predictors of DRE were obtained by evidence rating analysis.
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