以昇陳

The spirobifluorene is one of the most important scaffold used in organic electronics. Attaching two spirobifluorenes generates 10 dimers, each possessing its own structural specificity. Herein, the importance of the two main parameters involved in the electronic properties of spirobifluorene dimers, namely the nature of the phenyl linkages and the steric congestion between the two spirobifluorene units, is discussed.

Abstract

Spirobifluorene (SBF) is one of the most important scaffolds used in the design of organic semi-conductors (OSCs) for electronics. In recent years, among all the structures developed for these applications, SBF dimers have been highlighted due to their great potential in thermally activated delayed fluorescence and in phosphorescent organic light-emitting diodes. Attaching two SBF units generate 10 dimers, each possessing its own structural specificity, which in turn drives its electronic properties. These ten SBF dimers are gathered herein. Understanding how the molecular assembly determines the electronic properties has been one of the pillars of organic electronics. This is the goal of this article. As positional isomerism is a key tool to design OSCs, defining the design guidelines for the SBF scaffold appears of interest for the future of this building block. Herein, the importance of the two main parameters involved in the electrochemical and photophysical properties, namely the nature of the phenyl linkages and the steric congestion between the two SBF units is discussed. The combination of these two parameters drives the electronic properties but their respective weight is different as a function of the regioisomer involved or of the property considered (frontier orbitals energy level, absorption, fluorescence, phosphorescence).

A novel low-molecular-weight supramolecular-polymer double-network (SP-DN) strategy is developed to fabricate conductive SP-DN eutectogels with high stretchability and excellent toughness, as well as self-healing, self-adhesive, and anti-freezing/anti-drying characteristics. These unique features allow for the successful application of SP-DN eutectogels for self-adhesive and bidirectional sensors with high sensitivity and long-term stability over a wide temperature range (−40 to 60 °C).

Abstract

Ionic conducting eutectogels have attracted enormous attention as an alternative to the conventional temperature-intolerant hydrogels and costly ionic liquid gels in constructing flexible electronic devices. However, current eutectogels prepared via cross-linked polymer or low-molecular-weight gelators suffer from limited stretchability and insufficient surface-adaptive adhesion. Herein, a low-molecular-weight supramolecular network is introduced into a covalent polymer network in a eutectogel architecture, and a novel supramolecular-polymer double-network (SP-DN) strategy is demonstrated to fabricate conductive SP-DN eutectogels with high stretchability (>4000% elongation) and toughness (≈800 J m⁻²), as well as self-healing, self-adhesive and anti-freezing/anti-drying characteristics. These unique features lead to the successful realization of SP-DN eutectogels in wearable self-adhesive strain sensors, which can conformally deform with the skin and dynamically monitor body movements with high sensitivity and long-term stability over a wide temperature range (−40 to 60 °C). Furthermore, the strain sensors can accurately detect body movements along two opposite directions (bend up or bend down), which are rarely reported in the literature. Distinct from the widely explored polymer double-network (P-DN) hydrogels, the developed SP-DN eutectogel platform is capable of well-regulating molecular-scale noncovalent and covalent interactions, providing a paradigm for the creation of smart soft materials with versatile performance and high environmental adaptability.

Hot-casting is demonstrated to boost the performance of halogen-free solvents processed organic solar cells (OSCs), achieving power conversion efficiency higher than that of the halogen solvents processed counterparts, and is effective in both binary and ternary OSCs.

Abstract

Despite the substantial climb of the power conversion efficiency (PCE) of organic solar cells (OSCs), the majority of processing solvent remains halogenated and stand as a critical issue for commercialization. Herein, a halogen-free solvent system consisting of toluene (Tol) and 1-phenylnaphthalene (PN) is used to replace the traditional halogenated chloroform (CF) and1-chloronaphthalene (CN) for the processing of the PM6:M36 OSC, reducing the maximum PCE from 15.0% to 13.3%. Hot-casting is demonstrated to boost the maximum PCE of halogen-free solvents processed OSCs back to 15.2%. The preheated substrate fastens the evaporation of Tol and enables similar film-forming kinetics to CF, resulting in the inhibition of immoderate molecular aggregation and excessive phase separation. Ternary OSCs, with either another donor or acceptor as the third component, can further improve device PCE to 15.8%, confirming the versatile photovoltaic systems that this hot-casting method can be applied to. Encouragingly, the hot-casting processed binary and ternary OSCs also exhibit retained storage stability. Therefore, hot-casting is demonstrated as a superior strategy to fabricate OSCs without efficiency and stability loss using halogen-free solvents.

A dihydrophenazine-based conjugated porous polymer cathode with donor–acceptor molecular structure shows a high reversible capacity of 192 mAh g⁻¹ at 0.2 A g⁻¹ with excellent rate performance and ultra-stable cyclability more than 10 000 cycles.

Abstract

Recent studies have demonstrated that dihydrophenazine (Pz) with high redox-reversibility and high theoretical capacity is an attractive building block to construct p-type polymer cathodes for dual-ion batteries. However, most reported Pz-based polymer cathodes to date still suffer from low redox activity, slow kinetics, and short cycling life. Herein, a donor–acceptor (D–A) Pz-based conjugated microporous polymer (TzPz) cathode is constructed by integrating the electron-donating Pz unit and the electron-withdrawing 2,4,6-triphenyl-1,3,5-triazine (Tz) unit into a polymer chain. The D–A type structure enhances the polymer conjugation degree and decreases the band gap of TzPz, facilitating electron transportation along the polymer skeletons. Therefore the TzPz cathode for dual-ion battery shows a high reversible capacity of 192 mAh g⁻¹ at 0.2 A g⁻¹ with excellent rate performance (108 mAh g⁻¹ at 30 A g⁻¹), which is much higher than that of its counterpart polymer BzPz produced from 1,3,5-triphenylbenzene (Bz) and Pz (148 and 44 mAh g⁻¹ at 0.2 and 10 A g⁻¹, respectively). More importantly, the TzPz cathode also shows a long and stable cyclability of more than 10 000 cycles. These results demonstrate that the D–A structural design is an efficient strategy for developing high-performance polymer cathodes for dual-ion batteries.

Efficient large-area flexible solar cells and modules are demonstrated based on a printable, transparent, low-surface-roughness, flexible electrode (silver nanowires:zinc-chelated polyethylenimine). A power conversion efficiency of 13.2% is obtained for a 54 cm² solar module. The flexible electrode is also demonstrated in high-performance flexible quantum-dot light-emitting diodes.

Abstract

Development of large-area flexible organic solar cells (OSCs) is highly desirable for their practical applications. However, the efficiency of the large-area flexible OSCs severely lags behind small-area devices. Here, efficient large-area flexible single cells with power conversion efficiency (PCE) of 13.1% and 12.6% for areas of 6 and 10 cm², and flexible modules with a PCE of 13.2% (54 cm²) based on poly(ethylene terephthalate)/Ag grid/silver nanowires (AgNWs):zinc-chelated polyethylenimine (PEI-Zn) composite electrodes are reported. The solution-processed flexible transparent electrode of AgNWs:PEI-Zn shows low surface roughness and good optoelectronic and mechanical properties. PEI-Zn is conductive and optically transparent. It can adhere to and wrap the AgNWs under electrostatic interaction between the negatively charged surface (AgNWs) and positively charged protonated amine groups (in PEI-Zn). It wraps the AgNWs networks and fills the void space to achieve a smooth surface. The flexible electrode is validated in both flexible OSCs and flexible quantum-dots light-emitting diodes (QLEDs). Small-area flexible OSCs show a PCE of 16.1%, and flexible QLEDs show an external quantum efficiency of 13.3%. In the end, a flexible module is demonstrated to charge a mobile phone as a flexible power source (shown in Video S1, Supporting Information).

A synaptic indium-gallium-zinc-oxide (IGZO) layer is integrated into a novel organic light-emitting transistor (OLET) device. The UV-light-driven photoinduced synaptic effect is used to power a persistent bright afterglow emission in an organic light-emitting material. The unique OLETs are integrated in active-matrix light-emitting arrays operating as visual UV sensors capable of long-lifetime green-light emission in the irradiated regions.

Abstract

Long-lasting luminescence in optoelectronic devices is highly sought after for applications in optical data storage and display technology. While in light-emitting diodes this is achieved by exploiting long-afterglow organic materials as active components, such a strategy has never been pursued in light-emitting transistors, which are still rather unexplored and whose technological potential is yet to be demonstrated. Herein, the fabrication of long-afterglow organic light-emitting transistors (LAOLETs) is reported whose operation relies on an unprecedented strategy based on a photoinduced synaptic effect in an inorganic indium-gallium-zinc-oxide (IGZO) semiconducting channel layer, to power a persistent electroluminescence in organic light-emitting materials. Oxygen vacancies in the IGZO layer, produced by irradiation at λ = 312 nm, free electrons in excess yielding to a channel conductance increase. Due to the slow recombination kinetics of photogenerated electrons to oxygen vacancies in the channel layer, the organic material can be fueled by postsynaptic current and displays a long-lived light-emission (hundreds of seconds) after ceasing UV irradiation. As a proof-of-concept, the LAOLETs are integrated in active-matrix light-emitting arrays operating as visual UV sensors capable of long-lifetime green-light emission in the irradiated regions.

Nature Energy, Published online: 29 July 2021; doi:10.1038/s41560-021-00880-z

Nature Communications, Published online: 11 August 2021; doi:10.1038/s41467-021-25135-z

By fine-tuning the optical field distribution and employing photovoltaic materials with low energy losses in tandem photovoltaic cell, a power conversion efficiency of 19.64% is achieved.

Abstract

Despite more potential in realizing higher photovoltaic performance, the highest power conversion efficiency (PCE) of tandem organic photovoltaic (OPV) cells still lags behind that of state-of-the-art single-junction cells. In this work, highly efficient double-junction tandem OPV cells are fabricated by optimizing the photoactive layers with low voltage losses and developing an effective method to tune optical field distribution. The tandem OPV cells studied are structured as indium tin oxide (ITO)/ZnO/bottom photoactive layer/interconnecting layer (ICL)/top photoactive layer/MoO _x /Ag, where the bottom and top photoactive layers are based on blends of PBDB-TF:ITCC and PBDB-TF:BTP-eC11, respectively, and ICL refers to interconnecting layer structured as MoO _x /Ag/ZnO:PFN-Br. As these results indicate that there is not much room for optimizing the bottom photoactive layer, more effort is put into fine-tuning the top photoactive layer. By rationally modulating the composition and thickness of PBDB-TF:BTP-eC11 blend films, the 300 nm-thick PBDB-TF:BTP-eC11 film with 1:2 D/A ratio is found to be an ideal photoactive layer for the top sub-cell in terms of photovoltaic characteristics and light distribution control. For the optimized tandem cell, a PCE of 19.64% is realized, which is the highest result in the OPV field and certified as 19.50% by the National Institute of Metrology.

Highly efficient organic solar cells are fabricated using a ternary approach, wherein a novel non-fullerene acceptor L8-BO-F is designed and incorporated into the PM6:BTP-eC9 blend. L8-BO-F and BTP-eC9 are found to form a homogeneous mixed phase, which improves the molecular packing of both donor and acceptor materials, and optimizes the ternary blend morphology. A record-high efficiency of 18.66% is consequently achieved.

Abstract

The ternary strategy, introducing a third component into a binary blend, opens a simple and promising avenue to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). The judicious selection of an appropriate third component, without sacrificing the photocurrent and voltage output of the OSC, is of significant importance in ternary devices. Herein, highly efficient OSCs fabricated using a ternary approach are demonstrated, wherein a novel non-fullerene acceptor L8-BO-F is designed and incorporated into the PM6:BTP-eC9 blend. The three components show complementary absorption spectra and cascade energy alignment. L8-BO-F and BTP-eC9 are found to form a homogeneous mixed phase, which improves the molecular packing of both the donor and acceptor materials, and optimizes the ternary blend morphology. Moreover, the addition of L8-BO-F into the binary blend suppresses the non-radiative recombination, thus leading to a reduced voltage loss. Consequently, concurrent increases in open-circuit voltage, short-circuit current, and fill factor are realized, resulting in an unprecedented PCE of 18.66% (certified value of 18.2%), which represents the highest efficiency values reported for both single-junction and tandem OSCs so far.

A new polymer, PDTDT, is developed as hole-transporting material for CsPbI₂Br solar cells. Using PDTDT, an ultra-high efficiency of 17.36% with V _OC of 1.42 V under one sun and 34.20% with V _OC of 1.14 V under 200 lux indoor light are achieved. The PDTDT-based cells also show superior/comparable stability to dopant-free P3HT reference.

Abstract

To abate the issue of moisture-assisted phase transition of CsPbI₂Br, caused by hygroscopic dopants used in the hole-transporting material (HTM), developing dopant-free HTMs is necessary. In this work, a new polymer, PDTDT, is developed as a dopant-free HTM for CsPbI₂Br solar cells, and the device performance and stability are systematically compared with cells employing dopant-free P3HT. CsPbI₂Br solar cells using PDTDT show an efficiency of 17.36% with V _OC of 1.42 V and FF of 81.29%, which is one of the highest values for CsPbI₂Br cells. Moreover, a record-high efficiency of 34.20% with V _OC of 1.14 V under 200 lux indoor light illumination and efficiency of 14.54% (certified efficiency of 13.86%) for a 1 cm² device under one sun are accomplished. Importantly, PDTDT shows superior/comparable device stability to P3HT, promising its potential to be an alternative to popular doped Spiro-OMeTAD and P3HT HTM.

Narrowband photomultiplication-type organic photodetectors (PMOPDs) are prepared by employing one optical field adjusting (OFA) layer to adjust the optical filed distribution of the device and one photomultiplication layer for achieving photocurrent multiplication. The spectral response of narrowband PMOPDs can be tuned by different OFA layers, which is promising in achieving narrowband PMOPDs with a tunable spectral response.

Abstract

Narrowband photomultiplication-type organic photodetectors (PMOPDs) are realized with poly(3-hexylthiophene-2,5-diyl) (P3HT) as the optical field adjusting (OFA) layer and transfer-printed P3HT: [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) (50:1, w/w) as the photomultiplication (PM) layer. The thickness of the OFA layers is adjusted to optimize interfacial trapped electron distribution and density, which determines the external quantum efficiency (EQE) and spectral response range of PMOPDs. Narrowband PMOPDs with 2.5 µm thick P3HT as the OFA layer exhibit two narrow response peaks at 350 and 660 nm, and the corresponding EQE values at 350 and 660 nm are 180% and 760% under an applied bias of −20 V. A wide bandgap polymer poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (P-TPD) is deliberately incorporated into OFA layer for adjusting interfacial trapped electron distribution near Al electrode. Narrowband PMOPDs exhibit only one response peak at 660 nm with the enhanced EQE value of 1120% under the same bias. The enhanced EQE of PMOPDs with P-TPD is primarily attributed to the increased hole tunneling injection and transport, which can be ascribed to the enhanced trapped electron density near the Al electrode and the improved hole mobility, respectively. Clearly resolved images can be obtained from the imaging system with the narrowband PMOPDs as sensing pixel without any current preamplifier, indicating the promising potential of PMOPDs in imaging sense.

This study explores how incorporating the internal heavy atom (IHA) effect can impact the reverse intersystem crossing (RISC) and device performance. The spectroscopic and theoretical results indicate that a fast RISC may not be the sole factor important for reducing efficiency roll-off and that the spin-flip cycles should be carefully considered to derive a complete picture of the IHA effect.

Abstract

Thermally activated delayed fluorescence (TADF) is beneficial for improving the efficiency of organic light-emitting diodes (OLEDs) by providing pathways to convert non-emissive triplet excitons into singlet excitons. To ensure TADF is efficient, it is critical to enhance the reverse intersystem crossing (RISC) rate. To this end, most approaches propose thus far have focused on reducing the energy difference between S₁ and T₁ states. The present study explores how incorporating the internal heavy atom (IHA) effect can impact the RISC and device performance. By introducing a series of halogen atoms to charge-transfer molecules, TADF molecules exhibiting RISC over 7 × 10⁷ s⁻¹ are realized. These molecules are then applied to OLEDs, and the effect of incorporating these moieties is investigated. The results show that efficiency roll-off is still significant even with RISC-enhanced TADF emitters. Spectroscopic and theoretical results indicate that a fast RISC may not be the sole factor important for reducing efficiency roll-off and that the spin-flip cycles considering both T₁→S₁ and S₁→T₁ should be carefully taken into account to derive a complete picture of the IHA effect on efficiency roll-off behavior.

Three 2,6-diphenylpyridine-3,5-dicarbonitrile-based compounds with excellent photoluminescent quantum yields (79–100%) and high horizontal dipole ratios (86−88%) in the thin films are demonstrated. With two methyl groups on the triarylamines, the spin−orbit coupling is enhanced due to the elevated locally excited triplet states (³LE), leading to a fast reverse intersystem crossing. Green thermally activated delayed fluorescence (TADF) organic light-emitting diodes based on them exhibit a record-high external quantum efficiency of 39.8% without any optical extraction technique.

Abstract

Highly efficient thermally activated delayed fluorescence (TADF) molecules are in urgent demand for solid-state lighting and full-color displays. Here, the design and synthesis of three triarylamine-pyridine-carbonitrile-based TADF compounds, TPAPPC, TPAmPPC, and tTPAmPPC, are shown. They exhibit excellent photoluminescence quantum yields of 79−100% with small ΔE _ST values, fast reverse intersystem crossing (RISC), and high horizontal dipole ratios (Θ_// = 86−88%) in the thin films leading to the enhancement of device light outcoupling. Consequently, a green organic light-emitting diode (OLED) based on TPAmPPC shows a high average external quantum efficiency of 38.8 ± 0.6%, a current efficiency of 130.1 ± 2.1 cd A^–1, and a power efficiency of 136.3 ± 2.2 lm W^–1. The highest device efficiency of 39.8% appears to be record-breaking among TADF-based OLEDs to date. In addition, the TPAmPPC-based device shows superior operation lifetime and high-temperature resistance. It is worth noting that the TPA-PPC-based materials have excellent optical properties and the potential for making them strong candidates for TADF practical application.

A regioregular narrow-bandgap n-type polymer, L15, is synthesized, showing higher electron mobility and larger absorption coefficient compared to its random analog. When applied as an electron acceptor in all-polymer solar cells (all-PSCs), L15 yields outstanding efficiencies of 15.2% and 16.2% in binary and ternary all-PSCs, respectively.

Abstract

Narrow-bandgap n-type polymers with high electron mobility are urgently demanded for the development of all-polymer solar cells (all-PSCs). Here, two regioregular narrow-bandgap polymer acceptors, L15 and MBTI, with two electron-deficient segments are synthesized by copolymerizing two dibrominated fused-ring electron acceptors (FREA) with distannylated aromatic imide, respectively. Taking full advantage of the FREA and the imide, both polymer acceptors show narrow bandgap and high electron mobility. Benefiting from the more extended absorption, better backbone ordering, and higher electron mobility than those of its regiorandom analog, the L15-based all-PSC yields a high power conversion efficiency (PCE) of 15.2% when blended with the polymer donor PM6. More importantly, MBTI incorporating a benzothiophene-core FREA segment shows relatively higher frontier molecular orbital levels than L15, forming a cascade-like energy level alignment with L15 and PM6. Based on this, ternary all-PSCs are designed where MBTI is introduced as a guest into the PM6:L15 host system. Thanks to further optimal blend morphology and more balanced charge transport, the PCE is improved up to 16.2%, which is among the highest values for all-PSCs. The results demonstrate that combining an FREA and an aromatic imide to construct regioregular narrow-bandgap polymer acceptors provides an effective approach to fabricate highly efficient all-PSCs.

Horizontal emitter orientation can significantly increase the efficiency of organic light-emitting diodes. Intense research over the past decade has provided a large amount of data on the factors that may drive horizontal orientation of organic emitters. This research is reviewed, and a meta-analysis of the data is combined with quantum-chemical calculations to identify key parameters that influence this orientation.

Abstract

In organic light-emitting diodes (OLEDs), horizontal orientation of the emissive transition dipole moment (TDM) can improve light outcoupling efficiency by up to 50% relative to random orientation. Therefore, there have been extensive efforts to identify drivers of horizontal orientation. The aspect ratio of the emitter molecule and the glass-transition temperature (T _g) of the films are currently regarded as particularly important. However, there remains a paucity of systematic studies that establish the extent to which these and other parameters control orientation in the wide range of emitter systems relevant for state-of-the-art OLEDs. Here, recent work on molecular orientation of fluorescent and thermally activated delayed fluorescent emitters in vacuum-processed OLEDs is reviewed. Additionally, to identify parameters linked to TDM orientation, a meta-analysis of 203 published emitter systems is conducted and combined with density-functional theory calculations. Molecular weight (MW) and linearity are identified as key parameters in neat systems. In host–guest systems with low-MW emitters, orientation is mostly influenced by the host T _g, whereas the length and MW of the emitter become more relevant for systems involving higher-MW emitters. To close, a perspective of where the field must advance to establish a comprehensive model of molecular orientation is given.

Dielectric polymer nanocomposites with ultralow filler loadings exhibit considerably improved dielectric constant and breakdown strength, giving rise to remarkable discharged energy densities. A mathematical model is established to predict the dielectric constant of composites with low filler contents, revealing the significant contribution of the interphase to the polarization.

Abstract

Polymer dielectrics with excellent processability and high breakdown strength (E _b) enable the development of high-energy-density capacitors. Although the improvement of dielectric constant (K) of polymer dielectric has been realized by adding high-K inorganic fillers with high contents (>10 vol%), this approach faces significant challenges in scalable film processing. Here, the incorporation of ultralow ratios (<1 vol%) of low-K Cd_{1− x} Zn _x Se_{1− y} S _y nanodots into a ferroelectric polymer is reported. The polymer composites exhibit substantial and concurrent increase in both K and E _b, yielding a discharged energy density of 26.0 J cm⁻³, outperforming the current dielectric polymers and nanocomposites measured at ≤600 MV m⁻¹. The observed unconventional dielectric enhancement is attributed to the structural changes induced by the nanodot fillers, including transformation of polymer chain conformation and induced interfacial dipoles, which have been confirmed by density function theory calculations. The dielectric model established in this work addresses the limitations of the current volume-average models on the polymer composites with low filler contents and gives excellent agreement to the experimental results. This work provides a new experimental route to scalable high-energy-density polymer dielectrics and also advances the fundamental understanding of the dielectric behavior of polymer nanocomposites at atomistic scales.