以昇陳

New n‐dopable copolymers consisting of naphthodithiophenediimide and bithiopheneimide units are synthesized by direct arylation polymerization. The backbone orientation is found to significantly impact the electrical conductivity and the power factor (PF). Thus, a polymer characterized by the bimodal orientation with both face‐on and edge‐on fractions shows PF of up to 53.4 µW m⁻¹ K⁻² at room temperature, which is among the highest for n‐doped conjugated polymers.

Abstract

The development of n‐type conjugated polymers with high electrical conductivity (σ) has continued to pose a massive challenge in organic thermoelectrics (OTEs). New structural insights into the charge‐carrier transport are necessitated for the realization of high‐performance OTEs. In this study, three new n‐type copolymers, named pNB, pNB‐Tz, and pNB‐TzDP, consisting of naphthodithiophenediimide (NDTI) and bithiopheneimide (BTI) units, are synthesized by direct arylation polymerization. The backbone orientation is altered by incorporating thiazole units into the backbone and tuning the branching point of the side chain. The alteration of the backbone orientation from face‐on to bimodal orientation with both face‐on and edge‐on fractions significantly impacts the σ and the power factors (PFs) of the polymers. As a result, pNB‐TzDP, with the bimodal orientation, demonstrates a high σ of up to 11.6 S cm⁻¹ and PF of up to 53.4 µW m⁻¹ K⁻², which are among the highest in solution‐processed n‐doped conjugated polymers reported so far. Further studies reveal that the bimodal orientation of pNB‐TzDP introduces 3D conduction channels and leads to better accommodation of dopants, which should be the key factors for the excellent thermoelectric performance.

An electric field is demonstrated to enhance the photo‐thermoelectric effect by promoting the exciton separation efficiency with a coupled modulation process. The increased photoinduced carrier concentration and abnormal trade‐off relationship of the thermoelectric parameters together lead to an enhancement in the power factor of more than 500% to 11.2 μW m⁻¹ K⁻².

Abstract

Modulating photophysical processes is a fundamental way for tuning performance of many organic devices. However, it has not been explored as an effective strategy to manipulate the thermoelectric (TE) conversion of organic semiconductors (OSCs) owing to their critical requirement to carrier concentration (>10¹⁸ cm⁻³) and the fact of low exciton separation efficiency in single element OSCs. Here, an electric field modulated photo‐thermoelectric (P‐TE) effect in an n‐type OSC is demonstrated to realize a significant improvement of TE performance. The electrical and spectroscopy characterizations reveal that the electric field gating generates combined modulation of exciton separation, charge screening, and carrier recombination, which produces a more than ten times improvement of photoinduced carrier concentration. These coupled processes contribute to the unconventional Seebeck coefficient (S)‐electrical conductivity (σ) trade‐off relationship of the photoexcited films, therefore leading to a more than 500% enhancement in the power factor for n‐type OTE semiconductors. This work opens a unique way toward state‐of‐the‐art organic P‐TE materials for energy harvesting applications.

The nematic liquid‐crystalline small‐molecule donor benzodithiophene terthiophene rhodamine (BTR) works as a successful third component in PM6:Y6‐based organic solar cells. The doping of BTR significantly enhances the crystallinity with slightly reducing donor/acceptor phase separation of the photoactive layer. This uncommon morphology evolution facilitates charge separation, transport, and collection and ultimately boosts the efficiency from 15.7% to 16.6%.

Abstract

Achieving an ideal morphology is an imperative avenue for enhancing key parameters toward high‐performing organic solar cells (OSCs). Among a myriad of morphological‐control methods, the strategy of incorporating a third component with structural similarity and crystallinity difference to construct ternary OSCs has emerged as an effective approach to regulate morphology. A nematic liquid‐crystalline benzodithiophene terthiophene rhodamine (BTR) molecule, which possesses the same alkylthio‐thienyl‐substituted benzo moiety but obviously stronger crystallinity compared to classical medium‐bandgap polymeric donor PM6, is employed as a third component to construct ternary OSCs based on a PM6:BTR:Y6 system. The doping of BTR (5 wt%) is found to be enough to improve the OSC morphology—significantly enhancing the crystallinity of the photoactive layer while slightly reducing the donor/acceptor phase separation scale simultaneously. Rarely is such a morphology evolution reported. It positively affects the electronic properties of the device—prolongs the carrier lifetime, shortens the photocurrent decay time, facilitates exciton dissociation, charge transport, and collection, and ultimately boosts the power conversion efficiency from 15.7% to 16.6%. This result demonstrates that the successful synergy of liquid‐crystalline small‐molecule and polymeric donors delicately adjusts the active‐layer morphology and refines device performance, which brings vibrancy to the OSC research field.

A simple, generic, and effective concentration‐induced morphology manipulation approach is demonstrated to prompt the state‐of‐the‐art all‐small‐molecule (ASM) BTR‐Cl:Y6 and BTR:PC₇₁BM organic solar cells (OSCs) to a record level. This approach provides a promising way to delicately control the morphology toward high‐performance ASM OSCs.

Abstract

Morphology is a critical factor to determine the photovoltaic performance of organic solar cells (OSCs). However, delicately fine‐tuning the morphology involving only small molecules is an extremely challenging task. Herein, a simple, generic, and effective concentration‐induced morphology manipulation approach is demonstrated to prompt both the state‐of‐the‐art thin‐film BTR‐Cl:Y6 and thick‐film BTR:PC₇₁BM all‐small‐molecule (ASM) OSCs to a record level. The morphology is delicately controlled by subtly altering the prepared solution concentration but maintaining the identical active layer thickness. The remarkable performance enhancement achieved by this approach mainly results from the enhanced absorption, reduced trap‐assistant recombination, increased crystallinity, and optimized phase‐separated network. These findings demonstrate that a concentration‐induced morphology manipulation strategy can further propel the reported best‐performing ASM OSCs to a brand‐new level, and provide a promising way to delicately control the morphology towards high‐performance ASM OSCs.

Photoprogrammable mesogenic helical soft materials with both photosensitive and mesogenic moieties in molecules possess typical chiro‐optical properties, showing handedness dependency on the transmission, reflection, and absorption of an incident circularly polarized light (photonic bandgap and circular dichroism). This can be modulated readily by light irradiation, thus paving the way toward future chiro‐optical devices and systems.

Abstract

Mesogenic soft materials, having single or multiple mesogen moieties per molecule, commonly exhibit typical self‐organization characteristics, which promotes the formation of elegant helical superstructures or supramolecular assemblies in chiral environments. Such helical superstructures play key roles in the propagation of circularly polarized light and display optical properties with prominent handedness, that is, chiro‐optical properties. The leveraging of light to program the chiro‐optical properties of such mesogenic helical soft materials by homogeneously dispersing photosensitive chiral material into an achiral soft system or covalently connecting photochromic moieties to the molecules has attracted considerable attention in terms of materials, properties, and potential applications and has been a thriving topic in both fundamental science and application engineering. State‐of‐the‐art technologies are described in terms of the material design, synthesis, properties, and modulation of photoprogrammable chiro‐optical mesogenic soft helical architectures. Additionally, the scientific issues and technical problems that hinder further development of these materials for use in various fields are outlined and discussed. Such photoprogrammable mesogenic soft helical materials are competitive candidates for use in stimulus‐controllable chiro‐optical devices with high optical efficiency, stable optical properties, and easy miniaturization, facilitating the future integration and systemization of chiro‐optical chips in photonics, photochemistry, biomedical engineering, chemical engineering, and beyond.

n‐Type polymer semiconductors with a broad absorption and ultranarrow bandgap down to 1.28 eV are synthesized. When applied as electron acceptor materials, a power conversion efficiency of over 10% with a photoresponse reaching 950 nm is realized for all‐polymer solar cells.

Abstract

Compared to organic solar cells based on narrow‐bandgap nonfullerene small‐molecule acceptors, the performance of all‐polymer solar cells (all‐PSCs) lags much behind due to the lack of high‐performance n‐type polymers, which should have low‐aligned frontier molecular orbital levels and narrow bandgap with broad and intense absorption extended to the near‐infrared region. Herein, two novel polymer acceptors, DCNBT‐TPC and DCNBT‐TPIC, are synthesized with ultranarrow bandgaps (ultra‐NBG) of 1.38 and 1.28 eV, respectively. When applied in transistors, both polymers show efficient charge transport with a highest electron mobility of 1.72 cm² V⁻¹ s⁻¹ obtained for DCNBT‐TPC. Blended with a polymer donor, PBDTTT‐E‐T, the resultant all‐PSCs based on DCNBT‐TPC and DCNBT‐TPIC achieve remarkable power conversion efficiencies (PCEs) of 9.26% and 10.22% with short‐circuit currents up to 19.44 and 22.52 mA cm⁻², respectively. This is the first example that a PCE of over 10% can be achieved using ultra‐NBG polymer acceptors with a photoresponse reaching 950 nm in all‐PSCs. These results demonstrate that ultra‐NBG polymer acceptors, in line with nonfullerene small‐molecule acceptors, are also available as a highly promising class of electron acceptors for maximizing device performance in all‐PSCs.

Nature Energy, Published online: 08 June 2020; doi:10.1038/s41560-020-0624-7

An improved understanding of charge transport physics has enabled high‐performance organic field‐effect transistors through microstructure and electronic structure control by altering various donor and acceptor units. This report discusses in detail the relationship between donor–acceptor‐conjugated polymer structure and charge transport and summarizes the key features of the molecular design strategies.

Abstract

Polymeric semiconductors have demonstrated great potential in the mass production of low‐cost, lightweight, flexible, and stretchable electronic devices, making them very attractive for commercial applications. Over the past three decades, remarkable progress has been made in donor–acceptor (D–A) polymer‐based field‐effect transistors, with their charge‐carrier mobility exceeding 10 cm² V⁻¹ s⁻¹. Numerous molecular designs of D–A polymers have emerged and evolved along with progress in understanding the charge transport physics behind their high mobility. In this review, the current understanding of charge transport in polymeric semiconductors is covered along with significant features observed in high‐mobility D–A polymers, with a particular focus on polymeric microstructures. Subsequently, emerging molecular designs with further prospective improvements in charge‐carrier mobility are described. Moreover, the current issues and outlook for future generations of polymeric semiconductors are discussed.

Incorporation of a small portion of a novel polymer donor named PBT(E)BTz with a deeper highest occupied molecular orbital level than that of the host materials is proven promising to construct highly efficient ternary polymer solar cells (PSCs). In addition to the role of a “solid additive” for ternary PSCs, PBT(E)BTz shows great potential to be a thermal and light stabilizer in ternary PSCs.

Abstract

Ternary strategies have attracted extensive attention due to their potential in improving power conversion efficiencies (PCEs) of single‐junction polymer solar cells (PSCs). In this work, a novel wide bandgap polymer donor (E _g ^opt ≈ 2.0 eV) named PBT(E)BTz with a deep highest occupied molecular orbital (HOMO) level (≈−5.73 eV) is designed and synthesized. PBT(E)BTz is first incorporated as the third component into the classic PBDB‐T‐SF:IT‐4F binary PSC system to fabricate efficient ternary PSCs. A higher PCE of 13.19% is achieved in the ternary PSCs with a 5% addition of PBT(E)BTz over binary PSCs (12.14%). Similarly, addition of PBT(E)BTz improves the PCE for PBDB‐T:IT‐M binary PSCs from 10.50% to 11.06%. The study shows that the improved PCE in ternary PSCs is mainly attributed to the suppressed charge carrier recombination and more balanced charge transport. The generality of PBT(E)BTz as a third component is further evidenced in another efficient binary PSC system—PBDB‐TF:BTP‐4Cl: an optimized PCE of 16.26% is realized in the ternary devices. This work shows that PBT(E)BTz possessing a deep HOMO level as an additional component is an effective ternary PSC construction strategy toward enhancing device performance. Furthermore, the ternary device with 5% PBT(E)BTz displays better thermal and light stability over binary devices.

The aza[5]helicene‐based hole‐transporter is superior to its congener with the planar N‐annulated perylene π‐linker. This study has highlighted that the use of a helical π‐linker for donor−π linker−donor typed organic semiconductors can retain stronger intermolecular π⋅⋅⋅π interactions and attenuated interface charge recombination, leading to better power conversion efficiency of perovskite solar cells.

Abstract

The superior role of helical π‐linkers is demonstrated for the design of donor−π linker−donor typed molecular semiconductors in perovskite solar cells (PSCs). Flat N‐annulated perylene (NP) and contorted aza[5]helicene (A5H) are side‐functionalized with methoxyphenyl and end‐capped with dimethoxydiphenylamine electron‐donor to afford two small‐molecule hole‐transporters J3 and J4. For methoxyphenyl functionalized π‐linkers, intermolecular π⋅⋅⋅π interactions in planar NP exist more extensively than those in helical A5H. However, for the dimethoxydiphenylamine derived hole‐transporters with high highest occupied molecular orbital energy levels, a part of the π⋅⋅⋅π interaction remains for J4 with A5H, while this desirable effect for charge transport is completely deprived for J3 with NP. Thus, the theoretically predicted hole mobility of J4 single‐crystal is even over two times higher than that of J3 one. Because of the larger size of the molecular aggregate, the hole mobility of the spin‐coated J4 thin film is also over three times as high as that of the J3 analog. Due to the reduced transport resistance and enhanced recombination resistance, PSCs with J4 exhibit a power conversion efficiency of 21.0% at standard air mass 1.5 global conditions, which is higher than that of 19.4% with J3 and that of 20.3% with spiro‐OMeTAD control.

The origins and critical factors, which lead to organic field‐effect transistors (OFETs) with deviations from the ideal device models, are comprehensively uncovered from the view point of device physics. Also, the recent progress in optimizing strategies and new perspectives on nonideal OFETs are presented.

Abstract

Many advanced materials have been developed for organic field‐effect transistors (OFETs) or thin‐film transistors (TFTs) based on organic and organic hybrid materials. However, although many new OFETs exhibit superior characteristic parameters (such as high mobility), most of them show nonideal performances that have strongly limited progress in the design of molecules, the understanding of transport mechanisms, and the circuit applications of OFETs. In this review, the device physics of ideal and nonideal OFETs is discussed first to understand the factors that limit effective mobility in semiconducting channels, distort the potential distribution, or reduce the drift electric field. Then, recent advances in optimizing the material combinations, device structures, and fabrications of OFETs toward ideal transistors are discussed. Based on the good control of materials and interfaces, some new and novel concepts to utilize the nonideal properties of OFETs to build low‐power circuits and integrated sensors are also discussed.

Incorporation of a small portion of a novel polymer donor named PBT(E)BTz with a deeper highest occupied molecular orbital level than that of the host materials is proven promising to construct highly efficient ternary polymer solar cells (PSCs). In addition to the role of a “solid additive” for ternary PSCs, PBT(E)BTz shows great potential to be a thermal and light stabilizer in ternary PSCs.

Abstract

Ternary strategies have attracted extensive attention due to their potential in improving power conversion efficiencies (PCEs) of single‐junction polymer solar cells (PSCs). In this work, a novel wide bandgap polymer donor (E _g ^opt ≈ 2.0 eV) named PBT(E)BTz with a deep highest occupied molecular orbital (HOMO) level (≈−5.73 eV) is designed and synthesized. PBT(E)BTz is first incorporated as the third component into the classic PBDB‐T‐SF:IT‐4F binary PSC system to fabricate efficient ternary PSCs. A higher PCE of 13.19% is achieved in the ternary PSCs with a 5% addition of PBT(E)BTz over binary PSCs (12.14%). Similarly, addition of PBT(E)BTz improves the PCE for PBDB‐T:IT‐M binary PSCs from 10.50% to 11.06%. The study shows that the improved PCE in ternary PSCs is mainly attributed to the suppressed charge carrier recombination and more balanced charge transport. The generality of PBT(E)BTz as a third component is further evidenced in another efficient binary PSC system—PBDB‐TF:BTP‐4Cl: an optimized PCE of 16.26% is realized in the ternary devices. This work shows that PBT(E)BTz possessing a deep HOMO level as an additional component is an effective ternary PSC construction strategy toward enhancing device performance. Furthermore, the ternary device with 5% PBT(E)BTz displays better thermal and light stability over binary devices.

In article number https://doi.org/10.1002/aenm.2019042341904234, Feng Liu and co‐workers report a detailed structure‐performance relationship to help understand the success of Y6 non‐fullerene acceptors. Through the analysis of the single crystal structure of Y6, it is found that Y6 forms a polymer‐like conjugated backbone through its banana‐shaped structure and π‐π interactions between molecules, and forms a 2D electron transport network under the ordered arrangement of the lattice.

A simple yet highly compatible interconnecting layer for organic tandem solar cell is presented. All double‐junction tandem devices with different active layers show high reproducibility and efficiencies in several laboratories. Among these tandem devices, an excellent PCE of 16.1% is achieved. In addition, most of the tandem devices achieve more than 40% enhancement from the single‐junction organic photovoltaic device.

Abstract

Tandem structure provides a practical way to realize high efficiency organic photovoltaic cells, it can be used to extend the wavelength coverage for light harvesting. The interconnecting layer (ICL) between subcells plays a critical role in the reproducibility and performance of tandem solar cells, yet the processability of the ICL has been a challenge. In this work the fabrication of highly reproducible and efficient tandem solar cells by employing a commercially available material, PEDOT:PSS HTL Solar (HSolar), as the hole transporting material used for the ICL is reported. Comparing with the conventional PEDOT:PSS Al 4083 (c‐PEDOT), HSolar offers a better wettability on the underlying nonfullerene photoactive layers, resulting in better charge extraction properties of the ICL. When FTAZ:IT‐M and PTB7‐Th:IEICO‐4F are used as the subcells, a power conversion efficiency (PCE) of 14.7% is achieved in the tandem solar cell. To validate the processability of these tandem solar cells, three other research groups have successfully fabricated tandem devices using the same recipe and the highest PCE obtained is 16.1%. With further development of donor polymers and device optimization, the device simulation results show that a PCE > 22% can be realized in tandem cells in the near future.