以昇陳

A novel near‐infrared II (NIR‐II) organic small‐molecule probe CQ‐4T with high quantum yields is synthesized using a simplified procedure. A loading strategy with biocompatible human serum albumin (HSA) is employed to improve the fluorescence intensity and quantum yield of CQL (CQ‐4T/HSA), which enables multifunctional imaging and surgical navigation in circulatory system–related physiological and pathological processes in the NIR‐II window.

Abstract

The dysfunction of the circulatory system leads to various pathological processes with high morbidity. Recently, fluorescence imaging in the near‐infrared II (NIR‐II) window (1000–1700 nm) has attracted immense attention in many biological processes. The rapid metabolism and low toxicity of some NIR‐II organic small molecules indicate their feasibility for use in visualizing the circulatory system. However, most of the reported NIR‐II organic small molecules presently encounter such dilemmas as complicated synthetic procedures and low quantum yields (QY). To address this challenge, a series of facilely prepared NIR‐II organic small molecule CQ‐T (CQ‐1‐4T) are designed and these compounds are loaded with biocompatible human serum albumin (HSA) to improve QY. Among them, CQL (CQ‐4T/HSA) demonstrates superior optical properties and a 6.65‐fold increase in fluorescence compared to the small molecule alone. Further work validates the efficacy and accuracy of CQL in monitoring the real‐time circulatory system‐related physiological and pathological processes in vivo, including thrombosis, peripheral arterial disease, tumor angiogenesis, and lymphatic drainage. Moreover, the excellent optical properties of CQL enable precise tumor resection and sentinel lymph node biopsy under NIR‐II navigation. In conclusion, CQL is a novel and promising NIR‐II organic probe with multifunctional imaging capability. It is highly desirable to accelerate its future translations into the clinic.

A novel benzo[1,2‐b:4,5‐b′]difuran (BDF)‐based copolymer, L2, is designed and synthesized. When blended with a non‐fullerene small molecule acceptor TTPT‐T‐4F, the L2‐based device exhibits an efficiency of 14.0%, which is higher than that (12.72%) of its analogue benzo[1,2‐b:4,5‐b′]dithiophene (BDT) copolymer‐based device. Thus, the performance of the BDF‐based copolymers are equal to or greater than that of the BDT‐based counterparts.

Abstract

The development of high‐performance donor polymers is important for obtaining high power conversion efficiencies (PCEs) of non‐fullerene polymer solar cells (PSCs). Currently, most high‐efficiency PSCs are fabricated with benzo[1,2‐b:4,5‐b′]dithiophene (BDT)‐based conjugated polymers. The photovoltaic performance of benzo[1,2‐b:4,5‐b′]difuran (BDF)‐based copolymers has lagged far behind that of BDT‐based counterparts. In this study, a novel BDF‐based copolymer L2 is designed and synthesized, in which BDF and benzotriazole (BTz) building blocks have been used as the electron‐sufficient and deficient units, respectively. When blending with a non‐fullerene small molecule acceptor (SMA), TTPT‐T‐4F, the L2‐based device exhibits a remarkably high PCE of 14.0%, which is higher than that of the device fabricated by its analogue BDT copolymer (12.72%). Moreover, PSCs based on the L2:TTPT‐T‐4F blend demonstrate excellent ambient stability with 92% of its original PCE remaining after storage in air for 1800 h. Thus, BDF is a promising electron‐donating unit, and the BDF‐based copolymers can be competitive or even surpass the performance of BDT‐based counterparts.

Single‐emissive‐layer all fluorescent white organic light‐emitting diodes yield a record high external quantum efficiency of 19.6%, power efficiency of 52.2 lm W⁻¹, and long half‐lifetime of 2304 h simultaneously, by blending a sterically shielded blue emitter with thermally activated delayed fluorescence and orange conventional fluorescent dopants to modulate exciton interactions.

Abstract

White organic light‐emitting diodes (WOLEDs) with thermally activated delayed fluorophor sensitized fluorescence (TSF) have aroused wide attention, considering their potential for full exciton utilization without noble‐metal containing phosphors. However, performances of TSF‐WOLEDs with a single‐emissive‐layer (SEL) still suffer from low exciton utilization and insufficient blue emission for proper white balance. Here, by modulating Förster and Dexter interactions in SEL‐TSF‐WOLEDs, high efficiencies, balanced white spectra, and extended lifetimes are realized simultaneously. Given the different dependencies of Förster and Dexter interactions on intermolecular distances, sterically shielded blue thermally activated delayed fluorescence (TADF) emitters and orange conventional fluorescent dopants (CFDs) with electronically inert peripheral units are adopted to enlarge distances of electronically active chromophores, not only blocking the Dexter interaction to prevent exciton loss but also finely suppressing the Förster one to guarantee balanced white emission with sufficient blue components. It thus provides the possibility to maximize device performances in a large range of CFD concentrations. A record high maximum external quantum efficiency/power efficiency of 19.6%/52.2 lm W⁻¹, Commission Internationale de L'Eclairage coordinate of (0.33, 0.45), and prolonged half‐lifetime of over 2300 h at an initial luminance of 1000 cd m⁻² are realized simultaneously for SEL‐TSF‐WOLEDs, paving the way toward practical applications.

High‐efficiency, solution‐processed, hybrid tandem photovoltaic devices are demonstrated employing colloidal quantum dot (CQD) and organic bulk heterojunction as an active layer for front‐ and back‐cell, respectively. Notable efficiency of 12.82% is achieved, which is the highest among the reported CQD‐based solar cells, including single‐junction devices and tandem devices.

Abstract

While colloidal quantum dot photovoltaic devices (CQDPVs) can achieve a power conversion efficiency (PCE) of ≈12%, their insufficient optical absorption in the near‐infrared (NIR) regime impairs efficient utilization of the full spectrum of visible light. Here, high‐efficiency, solution‐processed, hybrid series, tandem photovoltaic devices are developed featuring CQDs and organic bulk heterojunction (BHJ) photoactive materials for front‐ and back‐cells, respectively. The organic BHJ back‐cell efficiently harvests the transmitted NIR photons from the CQD front‐cell, which reinforces the photon‐to‐current conversion at 350–1000 nm wavelengths. Optimizing the short‐circuit current density balance of each sub‐cell and creating a near ideal series connection using an intermediate layer achieve a PCE (12.82%) that is superior to that of each single‐junction device (11.17% and 11.02% for the CQD and organic BHJ device, respectively). Notably, the PCE of the hybrid tandem device is the highest among the reported CQDPVs, including single‐junction devices and tandem devices. The hybrid tandem device also exhibits almost negligible degradation after air storage for 3 months. This study suggests a potential route to improve the performance of CQDPVs by proper hybridization with NIR‐absorbing photoactive materials.

A proper vertical phase separation and purer phases of donor and acceptor are finely controlled by sequential blade‐casting strategy in the PTB7‐Th:FOIC‐based organic solar cell, resulting in simultaneous enhancement of efficiency, stability, and mechanical properties.

Abstract

As a predominant fabrication method of organic solar cells (OSCs), casting of a bulk heterojunction (BHJ) structure presents overwhelming advantages for achieving higher power conversion efficiency (PCE). However, long‐term stability and mechanical strength are significantly crucial to realize large‐area and flexible devices. Here, controlling blend film morphology is considered as an effective way toward co‐optimizing device performance, stability, and mechanical properties. A PCE of 12.27% for a P‐i‐N‐structured OSC processed by sequential blade casting (SBC) is reported. The device not only outperforms the as‐cast BHJ devices (11.01%), but also shows impressive stability and mechanical properties. The authors corroborate such enhancements with improved vertical phase separation and purer phases toward more efficient transport and collection of charges. Moreover, adaptation of SBC strategy here will result in thermodynamically favorable nanostructures toward more stable film morphology, and thus improving the stability and mechanical properties of the devices. Such co‐optimization of OSCs will pave ways toward realizing the highly efficient, large‐area, flexible devices for future endeavors.

The dependence of performance on composition in organic solar cells based on PffBT4T‐2DT polymer with O‐IDTBR or O‐IDFBR as a nonfullerene acceptor is investigated. The effect on morphology is discussed in terms of the interplay between immiscibility, inferred from phase behavior, and polymer aggregation. Morphology is optimized when polymer crystallite interconnectivity and size are balanced.

Abstract

The temperature‐dependent aggregation behavior of PffBT4T polymers used in organic solar cells plays a critical role in the formation of a favorable morphology in fullerene‐based devices. However, there is little investigation into the impact of donor/acceptor ratio on morphology tuning, especially for nonfullerene acceptors (NFAs). Herein, the influence of composition on morphology is reported for blends of PffBT4T‐2DT with two NFAs, O‐IDTBR and O‐IDFBR. The monotectic phase behavior inferred from differential scanning calorimetry provides qualitative insight into the interplay between solid–liquid and liquid–liquid demixing. Transient absorption spectroscopy suggests that geminate recombination dominates charge decay and that the decay rate is insensitive to composition, corroborated by negligible changes in open‐circuit voltage. Exciton lifetimes are also insensitive to composition, which is attributed to the signal being dominated by acceptor excitons which are formed and decay in domains of similar size and purity irrespective of composition. A hierarchical morphology is observed, where the composition dependence of size scales and scattering intensity from resonant soft X‐ray scattering (R‐SoXS) is dominated by variations in volume fractions of polymer/polymer‐rich domains. Results suggest an optimal morphology where polymer crystallite size and connectivity are balanced, ensuring a high probability of hole extraction via such domains.

A Lewis acid tris(pentafluorophenyl)borane and nonhygroscopic lithium salt (LiClO₄) codoping strategy is introduced to tailor C₆₀ and fabricate highly efficient inorganic CsPbI₂Br perovskite solar cells with reduced hysteresis. Consequently, square‐centimeter inorganic CsPbI₂Br perovskite solar cells yield a record power conversion efficiency (PCE) of 14.44%. In addition, the first inorganic perovskite solar module with an efficiency exceeding 12% is reported, using a self‐developed quasi‐curved heating method.

Abstract

Although inorganic perovskite solar cells (PSCs) are promising in thermal stability, their large open‐circuit voltage (V _OC) deficit and difficulty in large‐area preparation still limit their development toward commercialization. The present work tailors C₆₀ via a codoping strategy to construct an efficient electron‐transporting layer (ETL), leading to a significant improvement in V _OC of the inverted inorganic CsPbI₂Br PSC. Specifically, tris(pentafluorophenyl)borane (TPFPB) is introduced as a dopant to lower the lowest unoccupied molecular orbital (LUMO) level of the C₆₀ layer by forming a Lewis acidic adduct. The enlarged free energy difference provides a favorable enhancement in electron injection and thereby reduces charge recombination. Subsequently, a nonhygroscopic lithium salt (LiClO₄) is added to increase electron mobility and conductivity of the film, leading to a reduction in the device hysteresis and facilitating the fabrication of a large‐area device. Finally, the as‐optimized inorganic CsPbI₂Br PSCs gain a champion power conversion efficiency (PCE) of 15.19%, with a stabilized power output (SPO) of 14.21% (0.09 cm²). More importantly, this work also demonstrates a record PCE of 14.44% for large‐area inorganic CsPbI₂Br PSCs (1.0 cm²) and reports the first inorganic perovskite solar module with the excellent efficiency exceeding 12% (10.92 cm²) by a self‐developed quasi‐curved heating method.

Color‐selective organic photodiodes are inkjet printed using a novel photoactive material system based on nonfullerene acceptors. This material system simplifies process development and at the same time enables a high degree of color tunability. Energetic and morphological properties are investigated and the color‐selective devices are employed in a multichannel visible‐light‐communication system.

Abstract

Future lightweight, flexible, and wearable electronics will employ visible‐light‐communication schemes to interact within indoor environments. Organic photodiodes are particularly well suited for such technologies as they enable chemically tailored optoelectronic performance and fabrication by printing techniques on thin and flexible substrates. However, previous methods have failed to address versatile functionality regarding wavelength selectivity without increasing fabrication complexity. This work introduces a general solution for printing wavelength‐selective bulk‐heterojunction photodetectors through engineering of the ink formulation. Nonfullerene acceptors are incorporated in a transparent polymer donor matrix to narrow and tune the response in the visible range without optical filters or light‐management techniques. This approach effectively decouples the optical response from the viscoelastic ink properties, simplifying process development. A thorough morphological and spectroscopic investigation finds excellent charge‐carrier dynamics enabling state‐of‐the‐art responsivities >10² mA W⁻¹ and cutoff frequencies >1.5 MHz. Finally, the color selectivity and high performance are demonstrated in a filterless visible‐light‐communication system capable of demultiplexing intermixed optical signals.

While ternary blends for organic solar cells show significant performance improvements, quaternary mixtures typically cannot be fully optimized due to experimental constraints. A robot‐based high‐throughput technology is demonstrated that allows the stability of multicomponent blends to be investigated. Moreover, the use of machine learning algorithms enables an autonomous operation of the self‐driving laboratory with highly efficient optimization routines.

Abstract

Fundamental advances to increase the efficiency as well as stability of organic photovoltaics (OPVs) are achieved by designing ternary blends, which represents a clear trend toward multicomponent active layer blends. The development of high‐throughput and autonomous experimentation methods is reported for the effective optimization of multicomponent polymer blends for OPVs. A method for automated film formation enabling the fabrication of up to 6048 films per day is introduced. Equipping this automated experimentation platform with a Bayesian optimization, a self‐driving laboratory is constructed that autonomously evaluates measurements to design and execute the next experiments. To demonstrate the potential of these methods, a 4D parameter space of quaternary OPV blends is mapped and optimized for photostability. While with conventional approaches, roughly 100 mg of material would be necessary, the robot‐based platform can screen 2000 combinations with less than 10 mg, and machine‐learning‐enabled autonomous experimentation identifies stable compositions with less than 1 mg.

Addition of the n‐type dopant benzyl viologen (BV) into several best‐in‐class organic bulk‐heterojunctions (BHJ) is shown to consistently improve the power conversion efficiency (PCE) of the resulting solar cells. The presence of BV inside the BHJs increases the absorption coefficient, balances charge transport, and enhances the charge‐carrier density. These synergistic effects result in organic photovoltaics with a maximum PCE of 17.1%.

Abstract

Molecular doping is often used in organic semiconductors to tune their (opto)electronic properties. Despite its versatility, however, its application in organic photovoltaics (OPVs) remains limited and restricted to p‐type dopants. In an effort to control the charge transport within the bulk‐heterojunction (BHJ) of OPVs, the n‐type dopant benzyl viologen (BV) is incorporated in a BHJ composed of the donor polymer PM6 and the small‐molecule acceptor IT‐4F. The power conversion efficiency (PCE) of the cells is found to increase from 13.2% to 14.4% upon addition of 0.004 wt% BV. Analysis of the photoactive materials and devices reveals that BV acts simultaneously as n‐type dopant and microstructure modifier for the BHJ. Under optimal BV concentrations, these synergistic effects result in balanced hole and electron mobilities, higher absorption coefficients and increased charge‐carrier density within the BHJ, while significantly extending the cells' shelf‐lifetime. The n‐type doping strategy is applied to five additional BHJ systems, for which similarly remarkable performance improvements are obtained. OPVs of particular interest are based on the ternary PM6:Y6:PC₇₁BM:BV(0.004 wt%) blend for which a maximum PCE of 17.1%, is obtained. The effectiveness of the n‐doping strategy highlights electron transport in NFA‐based OPVs as being a key issue.

Addition of the n‐type dopant benzyl viologen (BV) into several best‐in‐class organic bulk‐heterojunctions (BHJ) is shown to consistently improve the power conversion efficiency (PCE) of the resulting solar cells. The presence of BV inside the BHJs increases the absorption coefficient, balances charge transport, and enhances the charge‐carrier density. These synergistic effects result in organic photovoltaics with a maximum PCE of 17.1%.

Abstract

Molecular doping is often used in organic semiconductors to tune their (opto)electronic properties. Despite its versatility, however, its application in organic photovoltaics (OPVs) remains limited and restricted to p‐type dopants. In an effort to control the charge transport within the bulk‐heterojunction (BHJ) of OPVs, the n‐type dopant benzyl viologen (BV) is incorporated in a BHJ composed of the donor polymer PM6 and the small‐molecule acceptor IT‐4F. The power conversion efficiency (PCE) of the cells is found to increase from 13.2% to 14.4% upon addition of 0.004 wt% BV. Analysis of the photoactive materials and devices reveals that BV acts simultaneously as n‐type dopant and microstructure modifier for the BHJ. Under optimal BV concentrations, these synergistic effects result in balanced hole and electron mobilities, higher absorption coefficients and increased charge‐carrier density within the BHJ, while significantly extending the cells' shelf‐lifetime. The n‐type doping strategy is applied to five additional BHJ systems, for which similarly remarkable performance improvements are obtained. OPVs of particular interest are based on the ternary PM6:Y6:PC₇₁BM:BV(0.004 wt%) blend for which a maximum PCE of 17.1%, is obtained. The effectiveness of the n‐doping strategy highlights electron transport in NFA‐based OPVs as being a key issue.

Through a strategy of embedding cyclohexane‐1,4‐dione into the thieno[3,4‐b]thiophene unit, a highly electron‐deficient core (TTDO) is synthesized, and the corresponding donor polymer (PBTT‐F) is also developed. The nonfullerene photovoltaic device based on this new donor polymer exhibits an outstanding PCE of 16.1% with a very high fill factor of 77.1%, which demonstrates it a very promising donor for high‐performance solar cells.

Abstract

It is of great significance to develop efficient donor polymers during the rapid development of acceptor materials for nonfullerene bulk‐heterojunction (BHJ) polymer solar cells. Herein, a new donor polymer, named PBTT‐F, based on a strongly electron‐deficient core (5,7‐dibromo‐2,3‐bis(2‐ethylhexyl)benzo[1,2‐b:4,5‐c′]dithiophene‐4,8‐dione, TTDO), is developed through the design of cyclohexane‐1,4‐dione embedded into a thieno[3,4‐b]thiophene (TT) unit. When blended with the acceptor Y6, the PBTT‐F‐based photovoltaic device exhibits an outstanding power conversion efficiency (PCE) of 16.1% with a very high fill factor (FF) of 77.1%. This polymer also shows high efficiency for a thick‐film device, with a PCE of ≈14.2% being realized for an active layer thickness of 190 nm. In addition, the PBTT‐F‐based polymer solar cells also show good stability after storage for ≈700 h in a glove box, with a high PCE of ≈14.8%, which obviously shows that this kind of polymer is very promising for future commercial applications. This work provides a unique strategy for the molecular synthesis of donor polymers, and these results demonstrate that PBTT‐F is a very promising donor polymer for use in polymer solar cells, providing an alternative choice for a variety of fullerene‐free acceptor materials for the research community.

Nature Communications, Published online: 12 February 2020; doi:10.1038/s41467-020-14669-3

A novel multi‐(donor/acceptor) thermally activated delayed fluorescence (TADF) molecule with through‐space/‐bond charge transfer is developed. Its nondoped solution‐processed sky‐blue organic light‐emitting diode (OLED) displays high performance with an external quantum efficiency (EQE_max) up to 21.0%, which represents the record‐breaking efficiency among the solution process‐based nondoped sky‐blue OLEDs.

Abstract

Although numerous thermally activated delayed fluorescence (TADF) organic light‐emitting diodes (OLEDs) have been demonstrated, efficient blue or even sky‐blue TADF‐based nondoped solution‐processed devices are still very rare. Herein, through‐space charge transfer (TSCT) and through‐bond charge transfer (TBCT) effects are skillfully incorporated, as well as the multi‐(donor/acceptor) characteristic, into one molecule. The former allows this material to show small singlet–triplet energy splitting (ΔE _ST) and a high transition dipole moment. The latter, on the one hand, further lights up multichannel reverse intersystem crossing (RISC) to increase triplet exciton utilization via degenerating molecular orbitals. On the other hand, the nature of the molecular twisted structure effectively suppresses intermolecular packing to obtain high photoluminescence quantum yield (PLQY) in neat flims. Consequently, using this design strategy, T‐CNDF‐T‐tCz containing three donor and three acceptor units, successfully realizes a small ΔE _ST (≈0.03 eV) and a high PLQY (≈0.76) at the same time; hence the nondoped solution‐processed sky‐blue TADF‐OLED displays record‐breaking efficiency among the solution process‐based nondoped sky‐blue OLEDs, with high brightness over 5200 cd m⁻² and external quantum efficiency up to 21.0%.

Hole transport material (HTM) plays important roles in n–i–p type perovskite solar cells. It affects both efficiency and the stability. After the recognition of its importance, a number of HTMs have been developed. This review summarizes various types of HTMs and discusses their development.

Abstract

With the application of organic–inorganic hybrid perovskites to liquid‐type solar cells, the unprecedented development of perovskite solar cells (Per‐SCs) has been boosted by the introduction of solid‐state hole transport materials (HTMs). The removal of liquid electrolyte has lead to improved efficiency and stability. Supported by high‐quality perovskite films, the certified efficiency of Per‐SCs has reached 25.2%. For Per‐SCs assembled in a conventional structure (n–i–p), the hole transport layer (HTL) plays an extra role in preventing the perovskite layer from external stimuli. In summary, the successful design and fabrication of the HTL must meet various requirements in terms of solubility, hole transport, recombination prevention, stability, and reproducibility, to name but a few. Many research strategies are focused on the development of high‐performance HTMs to meet such requirements. Such strategies for the development of HTMs employed in conventional n–i–p solar cells are reviewed herein. A vision of the future HTMs is proposed in this review based on the already proposed solutions and current trends.