以昇陳

To address the conflict between long afterglow lifetimes (τ_AG) and high afterglow quantum yields (Φ_AG) in room-temperature organic afterglow systems, spiroBF₂-MeOBP dopant–matrix systems which feature small phosphorescence decay, modest reverse intersystem crossing, and very small nonradiative decay and quenching, are conceived and reported to simultaneously achieve Φ_AG > 60% and τ_AG > 1.0 s.

Abstract

In organic systems, it is very challenging to simultaneously achieve long afterglow lifetimes (τ_AG) and high afterglow efficiency (Φ_AG). Here, luminescent dopants which feature a small rate of phosphorescence decay (k _P) and modest rate of reverse intersystem crossing (k _RISC) are designed and k _nr + k _q values (nonradiative decay and quenching) of triplet excited states are suppressed by all means that include increasing molecular rigidity of luminescent dopants, screening organic matrices to strongly inhibit intramolecular motions of luminescent dopants, and deuteration of the luminescent dopants. Organic matrices are selected with large dipole moments to stabilize the singlet excited states of luminescent dopants via dipole–dipole interactions, reduce singlet–triplet splitting energy, and thus enhance Φ_ISC, leading to significant population of triplet excited states. Thermally activated delayed fluorescence mechanism is also used with modest k _RISC to harvest triplet energies, significantly improve Φ_AG to 64%, and maintain long τ_AG > 1.0 s. The obtained materials display intense afterglow brightness, excellent processability, and temperature-sensing function.

A fused boron/nitrogen/oxygen multiresonance skeleton is demonstrated as a simple design strategy for narrowband emissive deep blue to blue thermally activated delayed fluorescence (TADF) emitters. The resulting blue narrowband organic light-emitting diodes (OLEDs) achieve the maximum external quantum efficiencies (EQEs) up to nearly 30%.

Abstract

Thermally activated delayed fluorescence (TADF) materials based on multiple resonance (MR) effect exhibit enormous potentials in organic light-emitting diodes (OLEDs) with high color purity due to their intrinsically narrow emission. However, most of MR-TADF emitters are limited to the boron-nitrogen-based rigid skeleton. In this work, three novel MR-TADF emitters, namely CzBNO, DMAcBNO and DPAcBNO, are elaborately constructed, the TADF properties of which are realized by virtue of opposite MR effect of boron and nitrogen/oxygen atom. CzBNO-based deep blue-emitting OLEDs achieve a maximum external quantum efficiency (EQE) of 13.6% with a small FWHM of 36 nm, as well as a Commission Internationale de l'Eclairage (CIE) coordinate of (0.14,0.08). While the other two emitter-based devices exhibit blue emission with a maximum EQE of up to 23.0%. To further improve the OLEDs performances, DMAcBNO and DPAcBNO-based devices assisted by a sensitizer exhibit an excellent EQE of up to 29.6% with a relatively small efficiency roll-off.

By using organo-boron based emitters, an excellent hyperfluorescence (HF) OLED system is designed. As a result, a high external quantum efficiency (EQE) of over 40% and pure blue color with a CIE y coordinate of 0.15 are achieved. Further, a long lifetime (LT₅₀) of 440 h with the designed HF systems is reached. Additionally, the detailed parameters for such high EQE values are analyzed.

Abstract

In the field of organic light-emitting diodes, organo-boron based thermally activated delayed fluorescence (TADF) emitters have witnessed outstanding achievements. However, it is still challenging to achieve pure blue color (CIE y < 0.20) along with high efficiencies. To overcome these hurdles, the hyperfluorescence (HF) system suggests a key strategy for future display applications. Here, two TADF host materials, pMDBA-DI and mMDBA-DI, and a pure blue multi-resonance type tert-butyl substituted TADF fluorescence emitter t-Bu-ν-DABNA are reported, for efficient HF devices. Among the synthesized TADF sensitized host materials, the mMDBA-DI HF device exhibits a high external quantum efficiency of 39.1% along with narrow emission with full width at half maximum of 19 nm (CIE y = 0.15). The high device efficiency is mainly attributed to the high molecular orientation factor, enhanced photoluminescence quantum yield, and a good TADF characteristic of t-Bu-ν-DABNA with efficient Förster energy transfer.

The authors demonstrate that designing functional fullerenes with roles beyond defect passivation is essential for perovskite solar cells (PSCs). By taking the advantages of fullerene, porphyrin, and pentafluorophenyl, a novel fullerene-porphyrin dyad is intentionally synthesized to stitch grain boundaries and trap lead ions in the perovskite film by forming chemical interactions in-situ. This robust strategy yields high-performance and eco-friendly PSCs.

Abstract

Designing functional fullerenes with roles beyond defect passivation and electron-transporting for perovskite solar cells (PSCs) is essential to the development of fullerenes and PSCs. Here, the authors design and synthesize a functional fullerene, FPD, composed of a C₆₀ cage, a porphyrin ring, and three pentafluorophenyl groups. The structure features of FPD enable it can form chemical interactions with the perovskite lattices. These interactions enhance the defect passivation effect and prevent the decomposition of perovskite under irradiation. As a result, the FPD-based device yields an improved power conversion efficiency of 23% with substantially enhanced operational stability (T ₈₀ > 1500 h). Furthermore, once got damaged, the FPD can prevent lead leakage by forming a stable and water-insoluble complex (FPD-Pb). Their findings provide a novel strategy to achieve high-performance and eco-friendly PSCs with functional fullerene materials.

A symmetric all-organic proton battery is developed in mild ZnSO₄ electrolyte, which exhibits enhanced electrochemical performance and broadens proton-based battery chemistry.

Abstract

All-organic proton batteries are attracting extensive attention due to their sustainability merits and excellent rate capability. Generally, strong acids (e.g. H₂SO₄) have to be employed as the electrolytes to provide H⁺ for all-organic proton batteries due to the high H⁺ intercalation energy barrier. Until now, the design of all-organic proton batteries in mild electrolytes is still a challenge. Herein, a poly(2,9-dihydroquinoxalino[2,3-b]phenazine) (PO) molecule was designed and synthesized, where the adjacent C=N groups show two different chemical environments, resulting in two-step redox reactions. Moreover, the two reactions possess considerable voltage difference because of the large LUMO energy gap between PO and its reduction product. More impressively, the C=N groups endow the π-conjugated PO molecule with H⁺ uptake/removal in the ZnSO₄ electrolyte. As a result, a symmetric all-organic proton battery is achieved in a mild electrolyte for the first time, which exhibits enhanced electrochemical performance and also broadens the chemistry of proton-based batteries.

Cyanine-based SH1 is reported as a structure-inherent tumor-targeting (SITT) fluorophore without targeting-ligands. A tumor-associated immune-cell-mediated targeting mechanism for SITT strategy is suggested, which is confirmed via in vitro flow cytometry and in vivo second near-infrared spectral window imaging. SH1 provides ubiquitous tumor targetability in pancreatic, breast, and lung cancer models with a high tumor-to-background ratio.

Abstract

The strategy of structure-inherent tumor targeting (SITT) with cyanine-based fluorophores is receiving more attention because no chemical conjugation of targeting moieties is required. However, the targeting mechanism behind SITT has not yet been well explained. Here, it is demonstrated that heptamethine-cyanine-based fluorophores possess not only targetability of tumor microenvironments without the need for additional targeting ligands but also second near-infrared spectral window (NIR-II) imaging capabilities, i.e., minimum scattering and ultralow autofluorescence. The new SITT mechanism suggests that bone-marrow-derived and/or tissue-resident/tumor-associated immune cells can be a principal target for cancer detection due to their abundance in tumoral tissues. Among the tested, SH1 provides ubiquitous tumor targetability and a high tumor-to-background ratio (TBR) ranging from 9.5 to 47 in pancreatic, breast, and lung cancer mouse models upon a single bolus intravenous injection. Furthermore, SH1 can be used to detect small cancerous tissues smaller than 2 mm in diameter in orthotopic lung cancer models. Thus, SH1 could be a promising cancer-targeting agent and have a bright future for intraoperative optical imaging and image-guided cancer surgery.

The hyperfine interaction is an important spin quantum property in organic semiconductors. Exploiting the electroluminescence response of organic light-emitting diodes to magnetic fields, large intra-device variations of this property exceeding ≈30% are resolved which are spatially correlated over characteristic lengths of 7 µm. This has implications for the reproducibility and integration of organic devices which rely on spin for their functionality.

Abstract

Devices that exploit the quantum properties of materials are widespread, with quantum information processors and quantum sensors showing significant progress. Organic materials offer interesting opportunities for quantum technologies owing to their engineerable spin properties, with spintronic operation and spin resonance magnetic-field sensing demonstrated in research grade devices, as well as proven compatibility with large-scale fabrication techniques. Yet several important challenges remain as moving toward scaling these proof-of-principle quantum devices to larger integrated logic systems or spatially smaller sensing elements, particularly those associated with the variation of quantum properties both within and between devices. Here, spatially resolved magnetoluminescence is used to provide the first 2D map of a hyperfine spin property—the Overhauser field—in traditional organic light-emitting diodes (OLEDs). Intra-device variabilities are found to exceed ≈30% while spatially correlated behavior is exhibited on lengths beyond 7 µm, similar in size to pixels in state-of-the-art active-matrix OLED arrays, which has implications for the reproducibility and integration of organic quantum devices.

A new metal–organic framework (MOF) termed Spiro-MOF-1 is successfully constructed by using a spiro-bi-acridine unit, exhibiting high thermally activated delayed fluorescence persistence under various biological environments. This highly rigid MOF structure is first designed and solved exhibiting long lifetime of fluorescence. Combing the analysis of time-dependent transient photoluminescence spectra, Spiro-MOF-1 will offer a new option for the time-resolved, MOF-based luminophores in cell imaging.

Abstract

To achieve better resolution and contrast in fluorescence techniques, time-resolved fluorophores are promising constituents for probes in imaging and sensing, allowing for the elimination of background signals from scattering and short-lived autofluorescence. Here a metal–organic framework (MOF) named Spiro-MOF-1 is designed with high thermally activated delayed fluorescence (TADF) persistence using a strategy of high rigidity to achieve a lifetime more than two times longer than that of pure linker. The rigid structure originated from spiro-bi-acridine unit is unambiguously revealed through 3D electron diffraction tomography (3D-EDT). Furthermore, nanocrystals of Spiro-MOF-1 are successfully developed and modified with polyethylene glycol (PEG) as a biocompatible, time-resolved fluorescent fluorophore with high TADF persistence, which exhibits a lifetime around 1 μs with no obvious decay under various bio-mimicking environments, which has not been achieved by any other MOF-based TADF emitter and small organic molecules. In further cell experiments, PEG-modified nanocrystals exhibit a fluorescent signal that is more than 30 times longer than that of autofluorescence background in BGC823 cell line.

Triplet management of host is quantitatively correlated with the device lifetime of blue phosphorescent organic light-emitting diodes (OLEDs). Exciton dynamics in the electroplex hosts is explored by comprehensively analyzing transient electroluminescence characteristics. It is revealed that the minimization of triplet excitons in the host during operation leads to enhanced device stability of OLEDs.

Abstract

The improvement of the device stability of blue phosphorescent organic light-emitting diodes (PhOLEDs) has proven to be a challenging issue in terms of enhancing the efficiency of blue organic light-emitting diodes in practical applications. This work comprehensively investigates the exciton dynamics of electroplex hosts and quantitatively correlates the steady-state triplet excitons in the host with the device lifetime of state-of-the-art blue PhOLEDs. The kinetic processes of electrically generated singlet excitons, triplet excitons, and polarons explored via transient electroluminescence and numerical modeling reveal that the triplet exciton density in the host is governed by reverse intersystem crossing and the triplet–triplet annihilation rates. A degradation modeling that takes into account the simultaneous material degradation due to the triplet excitons in the host and the dopant is newly established. The results indicate that the suppressed host degradation due to the reduction (1.5×) in host triplet excitons leads to enhanced operational stability. The characterization method and the numerical modeling in this work facilitate the determination of the exciton and polaron behavior of the host and allow for predicting the host-dependent device lifetime of PhOLEDs for specific host materials.

Two molecules mBDPA-TOAT and pBDPA-TOAT that show hybridization of multiple resonance and intersegmental charge-transfer features in their apparent excited states are obtained by considering their excited state alignment. The mBDPA-TOAT-based organic light-emitting diode exhibits an external quantum efficiency of 17.3% with a full width at half maximum of 45 nm and Commission Internationale de l'Eclairage coordinate of (0.61, 0.39).

Abstract

Thermally activated delayed fluorescence (TADF) emitters induced by the multiple resonance (MR) effect have garnered considerable attention. However, it is difficult to develop MR-TADF emitters that maintain high color purities in the red region. In this work, the importance of excited state alignments of MR-based donor-acceptor (D-A) molecules in determining their preferring characteristics is clarified. By using the newly designed molecule mBDPA-TOAT whose apparent excited states show hybridization of MR and intersegmental charge-transfer features as an emitter in an organic light-emitting diode (OLED), a high external quantum efficiency of 17.3% is achieved with a full width at half-maximum of 45 nm (154 meV) and Commission Internationale de L'Éclairage coordinate of (0.61, 0.39). This work demonstrates when introducing D-A typed structures, features, and alignments of molecular excited states determine ultimate material properties. This could help to develop high efficiency and high color purity TADF emitters toward long wavelength range.

The fast advances in both polycyclic arenes chemistry and their crystal engineering have greatly promoted the development of crystal photonic materials. In this review, a survey of the contribution of polycyclic arenes on crystal optical waveguides is summarized; several proof-of-concept devices are shown, and some of the most prospective future directions are highlighted.

Abstract

Organic crystals which can confine and guide optical waves on command are currently of considerable interest because of their tremendous potentials in broadband communications, optoelectronic devices, high-capacity information storage, etc. Polycyclic arenes, with tunable molecular structures, packing modes, and photophysical properties, are a highly versatile class of organic materials, applicable as optical waveguide crystals. In this review, the optical waveguides of polycyclic arene-based crystals are discussed, focusing on the molecular design, packing structures, crystal engineering, and the corresponding photonic properties. Moreover, several proof-of-concept devices are also shown. This review summarizes the current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of optical waveguiding materials.

Thermally activated delayed fluorescence (TADF) has received increasing attention in recent years and shows rapid development due to the excellent applications in designing optical materials of organic light-emitting diodes (OLEDs). In this Review, the advances of TADF-active crystalline metal-organic materials in recent years are summarized. Some problems and challenges of TADF materials concerning the properties and applications in OLEDs are also presented.

Abstract

Thermally activated delayed fluorescence (TADF) properties of crystalline metal-organic materials, mainly including small-molecule metal–organic complexes, organic ligand-protected metal clusters, and metal-organic coordination polymers are summarized here. The characteristics of TADF of each type of materials are discussed. Thermally activated delayed photoluminescence (TADPL) in quantum dots grafted organic chromophores is also briefly presented to highlight the difference from TADF. Finally, the perspectives of crystalline metal-containing TADF emitters are discussed. Therefore, a panoramic view of recent advances in metal-organic materials for TADF emitters is provided.

Accurate kinetic modeling of the photoluminescence (PL) decay of a thermally activated delayed fluorescence (TADF) emitter is important to extract intrinsic parameters like the(reverse) intersystem crossing rate. Here, the PL decay of the TADF emitter 9,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylphenyl)-9,10-diboraanthracene is modeled, taking annihilation processes into account. The authors find that triplet–triplet annihilation and singlet–triplet annihilation are the dominant exciton annihilation processes.

Abstract

Important parameters for the design and performance of thermally activated delayed fluorescence (TADF) emitters are the forward and reverse intersystem crossing rates between singlet and triplet states. The magnitude of these rates is determined from the prompt and delayed transient photoluminescence decay. It is demonstrated that this photoluminescence decay strongly depends on the initial photoexcited population density due to exciton–exciton annihilation processes. By kinetic modeling of the power-dependent time-resolved photoluminescence of the TADF emitter 9,10-bis(4-(9H-carbazol-9-yl)-2,6-dimethylphenyl)-9,10-diboraanthracene (CzDBA), singlet–triplet annihilation and triplet–triplet annihilation are identified as the main loss processes with rate constants in the order of 10⁻¹⁷ m³ s⁻¹. Neglecting these quenching processes leads to erroneous estimates of the (reverse) intersystem crossing rates.

A multifunctional deep-blue fluorophor is used to develop monochromatic and hybrid white organic light-emitting diodes (OLEDs), realizing the external quantum efficiency (EQE) of 8.98% and Commission Internationale de l'Eclairage coordinates of (0.15, 0.07) for nondoped OLED, and the EQEs exceeding 20% at 1000 cd m⁻² for good color stability, high efficiency, and low roll-off white OLEDs.

Abstract

High-performance deep-blue fluorescent materials matching the required Commission Internationale de l'Eclairage y coordinate value (CIEy) of < 0.08 are much-needed in organic light-emitting diodes (OLEDs) for realizing the perfect application of full-color displays. However, deep-blue fluorophors commonly show unsatisfactory performance due to the intrinsic large bandgap characteristic. Here, the deep-blue nondoped OLED with the good CIE coordinates of (0.15, 0.07) and external quantum efficiency (EQE) of ≈9% is achieved based on a multifunctional and efficient anthracene-based fluorophor (2M-ph-3CzAnBzt). Using it as a host, the sky-blue fluorescent OLED realizes the maximum EQE of 9.50%, and keeps as high as 9.27% and 8.56% at 1000 and 5000 cd m⁻². More surprisingly, high-performance hybrid white OLEDs (WOLEDs) with good color stability and low roll-off are achieved by using it as the blue emitter. Two-color WOLED shows the forward-viewing efficiencies of 20.46%, and 76.80 lm W⁻¹. The three-color WOLED emitting a candlelight with the color rendering index of ≥ 82 realizes the maximum EQE of 21.49% and remains 20.80% at 1000 cd m⁻². Such superior electroluminescence performance achieved in these OLEDs ranks among the highest values based on deep-blue fluorophors with CIEy < 0.08.

PM6:AQx-2-based organic photovoltaics (OPV) featuring a lower temperature coefficient for power conversion efficiency (PCE) is utilized for PV–thermoelectric generator (TEG) integration. A lower dT _c for OPV–TEG integration than those of the traditional c-SiPV–TEG counterpart is observed, broadening application scenarios. Under AM 1.5G illumination, a 1-cm² OPV device integrated with a TEG delivers a record PCE of 18.2%.

Abstract

Photovoltaics (PVs, light to electricity) integrated with a thermoelectric generator (TEG, heat to electricity) has been viewed as a promising technique that can achieve high power gain and extend device lifetime, but which have rarely been applied in organic PVs. The critical temperature difference (dT _c) is a key parameter because only if the temperature difference (dT) is higher than dT _c a power gain can be realized, and dT _c is closely associated with device performance and application scenarios. By examining the performance of a simulated PV–TEG integrated device comprising a state-of-the-art organic solar cell and a commercial TEG at various dT _s, this dT _c is witnessed. An effective numerical simulation method is established to study the PV–TEG integration based on, the dT _c can be perfectly reproduced and corresponding optimal p–n leg density for the TEG module to generate the highest power output at a certain dT. Integrated organic PV–TEG (OPV–TEG) devices show a lower dT _c than c-SiPV–TEG devices, which, together with the lower temperature coefficient, are intrinsic advantages of OPVs for future applications. Under AM 1.5G illumination, the 1-cm² optimized OPV–TEG integrated device achieves a record energy conversion efficiency of 18.2%.

A poly(methyl methacrylate) (PMMA) interlayer between the perovskite and CuPc improves the insufficient electron blocking due to the low LUMO energy level of CuPc. In addition, the PMMA layer strongly interacts with the perovskite, greatly reducing the defect density responsible for non-radiative recombination. Eventually, PMMA significantly improves the efficiency of PSCs fabricated using CuPc as a hole conductor.

Abstract

The use of inexpensive, highly efficient, and long-term stable hole-transporting layers (HTLs) while facilitating the fabrication process has become a critical issue for PSC commercialization. Among organic HTLs, copper phthalocyanine (CuPc) has been increasingly studied owing to its low cost and excellent thermal stability. Nevertheless, CuPc has a low energy level in the conduction band, resulting in low efficiency due to a poor electron barrier. In this study, an efficient and stable PSC is fabricated by combining CuPc with an ultrathin poly(methyl methacrylate) (PMMA) interlayer, which is deposited on a [(FAPbI₃)_0.95(MAPbBr₃)_0.05] absorption layer (here, FAPbI₃ and MAPbBr₃ denote formamidinium lead triiodide and methylammonium lead tribromide, respectively). PMMA in perovskite has been found to reduce perovskite surface defects and series resistance as well as the electronic barrier to HTL. The optimum concentration of PMMA allows for the fabrication of the PSC with a PCE of 21.3%, which is the highest PCE for PSCs featuring metal phthalocyanines as the HTL reported to date. The stability of the encapsulated PSC exceeds 80% after 760 h at 85 °C under 85% RH conditions.

Two small-molecule donors, SM-BF1 and SM-BF2, are synthesized by a low-cost synthesis route utilizing cheap raw materials. The champion device based on SM-BF1:Y6 shows a power conversion efficiency (PCE) of 15.71%, benefitted from its better miscible morphology and more balanced charge-carrier transport characteristics. Furthermore, through the figure of merit (FOM) analysis, SM-BF1 also shows a good prospect for commercial application.

Abstract

Low cost, high efficiency, and high stability are the three key issues of organic solar cells (OSCs) that should be carefully considered to meet the requirement of future commercial applications. Therefore, the development of high-performance organic photovoltaic materials with low synthetic cost has been becoming a crucial challenge in the field of OSCs. Herein, two new low-cost small-molecule donors (SM-BF1 and SM-BF2) are designed and synthesized with a facile synthetic route by replacing 4-bromo-2-fluorobenzenethiol and 4-bromo-3-fluorobenzenethiol with low-cost 4-bromo-2-fluoro-1-iodobenzene and 4-bromo-3-fluoro-1-iodobenzene as key raw materials. Besides, the influence of the chemical steric effect of the phenyl conjugated side chains of the benzodithiophene (BDT) unit on photophysical properties, charge transfer, and photovoltaic properties are deeply investigated by the modulation of fluorine atom substituted position. As a result, SM-BF1 with ortho-fluorinated substituent has outstanding crystallization properties and better miscibility with acceptor Y6 and exhibits more desirable morphology and more balanced charge-carrier transport properties, leading to a superior power conversion efficiency (PCE) to 15.71%. More encouragingly, according to the figure of merit (FOM) and the industrial figure of merit (i-FOM) to evaluate the small-molecule donors, the SM-BF1-based device has excellent potential for future commercial applications.

High-efficiency ultrapure blue delayed-fluorescence materials are produced by the strategic doping of multiple boron, nitrogen, oxygen, and sulfur atoms into the fused polycyclo-heteraborin π-system. These new fluorophores allow organic light-emitting diodes to demonstrate ideal narrowband and ultrapure blue electroluminescence, meeting the requirements for modern ultrahigh-definition displays.

Abstract

To achieve an ultimate wide color gamut for ultrahigh-definition displays, there is great demand for the development of organic light-emitting diodes (OLEDs) enabling monochromatic, ultrapure blue electroluminescence (EL). Herein, high-efficiency and ultrapure blue OLEDs based on polycyclo-heteraborin multi-resonance thermally activated delayed fluorescence (MR-TADF) materials, BOBO-Z, BOBS-Z, and BSBS-Z, are reported. The key to the design of the present luminophores is the exquisite combination and interplay of multiple boron, nitrogen, oxygen, and sulfur heteroatoms embedded in a fused polycyclic π-system. Comprehensive photophysical and computational investigations of this family of MR-TADF materials reveal that the systematic implementation of chalcogen (oxygen and sulfur) atoms can finely modulate the emission color while maintaining a narrow bandwidth, as well as the spin-flipping rates between the excited singlet and triplet states. Consequently, OLEDs based on BOBO-Z, BOBS-Z, and BSBS-Z demonstrate narrowband and ultrapure blue EL emission, with peaks at 445–463 nm and full width at half maxima of 18–23 nm, leading to Commission Internationale de l'Éclairage-y coordinates in the range of 0.04–0.08. Particularly, for OLEDs incorporating sulfur-doped BOBS-Z and BSBS-Z, notably high maximum external EL quantum efficiencies of 26.9% and 26.8%, respectively, and small efficiency roll-offs are achieved concurrently.

Exploiting norbornenyl modified terminals endows the fused ring acceptor (SM16) with an unprecedentedly high photoluminescence quantum yield of 8.61%, thus leading to a very low nonradiative voltage loss of 0.145 V when blended with PBDB-T. A power conversion efficiency of 17.1% is achieved by using SM16 as the third component due to the boosting of open-circuit voltage and fill factor.

Abstract

Increasing the photoluminescence quantum yield (PLQY) of narrow bandgap acceptors is of critical importance to suppress the nonradiative voltage loss (ΔV _nr) in organic solar cells (OSCs). Herein, two acceptors, SM16 and SM16-R, with an identical backbone but different terminal groups (norbornenyl modified 1,1-dicyanomethylene-3-indanone and dimethyl substituted 1,1-dicyanomethylene-3-indanone) are designed and synthesized. Compared with SM16-R, SM16 displays better solubility, higher PLQY, and more favorable nanomorphology when blended with polymer donor PBDB-T. PBDB-T:SM16-based OSCs yield a ΔV _nr as low as 0.145 V. Using SM16 as the third component, a high power conversion efficiency of 17.1% is achieved in the ternary OSCs based on PBDB-T:Y14:SM16, considerably higher than that of the binary devices based on PBDB-T:Y14 or PBDB-T:SM16. These results highlight that enhancing the PLQY of low bandgap acceptor via terminal group engineering strategy is highly effective to reduce ΔV _nr of OSCs.

Significant extension of the direct charge-transfer absorption to longer wavelengths of the well-known PBTTT:PC₆₁BM blend through polymer side chain engineering is demonstrated. When applied into an optical cavity device, the novel intercalating blend extends its employability for near-infrared detection by more than 300 nm.

Abstract

Incorporation of compact spectroscopic near-infrared (NIR) light detectors into various wearable and handheld devices opens up new applications, such as on-the-spot medical diagnostics. To extend beyond the detection window of silicon, i.e., past 1000 nm, organic semiconductors are highly attractive because of their tunable absorption. In particular, organic NIR wavelength-selective detectors have been realized by incorporating donor:acceptor thin films, exhibiting weak intermolecular charge-transfer (CT) absorption, into an optical microcavity architecture. In this work, the alkyl side chains of the well-known PBTTT donor polymer are replaced by alkoxy substituents, hereby redshifting the CT absorption of the polymer:PC₆₁BM blend. It is shown that the unique fullerene intercalation features of the PBTTT polymer are retained when half of the side chains are altered, hereby maximizing the polymer:fullerene interfacial area and thus the CT absorption strength. This is exploited to extend the detection range of organic narrow-band photodetectors with a full-width-at-half-maximum of 30–38 nm to wavelengths between 840 and 1340 nm, yielding detectivities in the range of 5 × 10¹¹ to 1.75 × 10¹⁰ Jones, despite the low CT state energy of 0.98 eV. The broad wavelength tuning range achieved using a single polymer:fullerene blend renders this system an ideal candidate for miniature NIR spectrophotometers.

A new wide-bandgap nonfused nonfullerene acceptor named GS-ISO is designed and synthesized. GS-ISO exhibits a very flat molecular backbone and stable molecular conformation. Based on GS-ISO, outstanding power conversion efficiencies of over 19% (AM 1.5G, 100 mW cm⁻²) for a tandem organic photovoltaic (OPV) cell and over 28% (500 lux, 2700 K LED) for an indoor OPV cell are achieved.

Abstract

Wide-bandgap (WBG) nonfullerene acceptors (NFAs) with nonfused conjugated structures play a critical role in organic photovoltaic (OPV) cells. Here, NFAs named GS-OEH, GS-OC6, and GS-ISO, with optical bandgaps larger than 1.70 eV, are synthesized without using the fused ring structures. Compared with GS-OEH and GS-OC6, GS-ISO exhibits much stronger crystallinity, leading to a smaller energetic disorder and a larger exciton diffusion coefficient. GS-ISO also possesses a higher electroluminescence external quantum efficiency of 1.0 × 10⁻². The OPV cell based on PBDB-TF:GS-ISO demonstrates a power conversion efficiency (PCE) of 11.62% under the standard one sun illumination. Besides, the PBDB-TF:GS-ISO-based cell with effective area of 1.0 cm² exhibits a PCE of 28.37% under 2700 K illumination of 500 lux. A tandem OPV cell using PBDB-TF:GS-ISO as the front subcell shows an outstanding efficiency of 19.10%. Importantly, the GS-ISO-based OPV cell exhibits promising stability under the continuous illumination of simulated sunlight. This study indicates that the molecular design strategy demonstrated in this work has great superiority in developing nonfused NFAs and also that GS-ISO is a promising WBG acceptor for versatile photovoltaic applications.

The influence of the first three-component metal-free photon upconversion system on the upconversion efficiency and threshold light intensity is studied herein. While the efficiency is doubled, the threshold light intensity is also increased. The performance enhancement can be attributed to more efficient energy transfer from the sensitizer to the intermediate acceptor in combination with a high quantum yield emitter molecule.

Abstract

As in many fields, the most exciting endeavors in photon upconversion research focus on increasing the efficiency (upconversion quantum yield) and performance (anti-Stokes shift) while diminishing the cost of production. In this vein, studies employing metal-free thermally activated delayed fluorescence (TADF) sensitizers have garnered increased interest. Here, for the first time, the strategy of ternary photon upconversion is utilized with the TADF sensitizer 2,4,5,6-tetrakis(carbazol-9-yl)isophthalonitrile (4CzIPN), resulting in a doubling of the upconversion quantum yield in comparison to the binary system employing p-terphenyl as the emitter. In this ternary blend, the sensitizer 4CzIPN is paired with an intermediate acceptor, 1-methylnaphthalene, in addition to the emitter molecule, p-terphenyl, yielding a normalized upconversion quantum yield of 7.6% while maintaining the 0.83 eV anti-Stokes shift. These results illustrate the potential benefits of utilizing this strategy of energy-funneling, previously used only with heavy-metal based sensitizers, to increase the performance of these photon upconversion systems.

This review briefly introduces the solubility and miscibility parameters that affect the morphology of ternary blends and then summarizes the recent processes of morphology study on ternary blends from the aspects of molecular crystallinity, molecular packing orientation, domain size and purity, vertical phase separation, direct observation of the morphology as well as morphological stability.

Abstract

Ternary blend organic solar cells (TB-OSCs) incorporating multiple donor and/or acceptor materials into the active layer have emerged as a promising strategy to simultaneously improve the overall device parameters for realizing higher performances than binary devices. Whereas introducing multiple materials also results in a more complicated morphology than their binary blend counterparts. Understanding the morphology is crucially important for further improving the device performance of TB-OSC. This review introduces the solubility and miscibility parameters that affect the morphology of ternary blends. Then, this review summarizes the recent processes of morphology study on ternary blends from the aspects of molecular crystallinity, molecular packing orientation, domain size and purity, directly observation of morphology, vertical phase separation as well as morphological stability. Finally, summary and prospects of TB-OSCs are concluded.

Nature Photonics, Published online: 18 November 2021; doi:10.1038/s41566-021-00904-w

Highly efficient upconversion of light by organic semiconductor heterojunction interfaces is demonstrated. This process is enabled by charge separation- and recombination-mediated charge transfer states at the interface.