以昇陳

Organic field‐effect transistors based on thin films of a benzothieno[3,2‐b][1]benzothiophene derivative and blends of it with polystyrene are fabricated. In the films based on only the organic semiconductor a phase transformation from the metastable surface‐induced polymorph (SIP) to the bulk polymorph is found. In contrast, the blended films show an improved performance and, remarkably, stabilize the SIP polymorph.

Abstract

The lack of long‐term stability in thin films of organic semiconductors can often be caused by the low structural stability of metastable phases that are frequently formed upon deposition on a substrate surface. Here, thin films of 2,7‐dioctyloxy[1]benzothieno[3,2‐b]benzothiophene (C₈O‐BTBT‐OC₈) and blends of this material with polystyrene by solution shearing are fabricated. Both types of films exhibit the metastable surface‐induced herringbone phase (SIP) in all the tested coating conditions. The blended films reveal a higher device performance with a field‐effect mobility close to 1 cm² V⁻¹ s⁻¹, a threshold voltage close to 0 V, and an on/off current ratio above 10⁷. In situ lattice phonon Raman microscopy is used to study the stability of the SIP polymorph. It is found that films based on only C₈O‐BTBT‐OC₈ slowly evolve to the Bulk cofacial phase, significantly impacting device electrical performance. In contrast, the blended films stabilize the SIP phase, leading to devices that maintain a high performance over 1.5 years. This work demonstrates that blending small‐molecule organic semiconductors with insulating binding polymers can trap metastable polymorphs, which can lead to devices with both improved performance and long‐term stability.

The presented combined computational and experimental approach provides a detailed description of the hyperfluorescence processes in organic blue‐emitting thin films with an 87% photoluminescence quantum yield.

Abstract

Hyperfluorescence is emerging as a powerful strategy to develop optoelectronic devices with high‐color purity and enhanced stability. It requires appropriate integration of a sensitizer displaying efficient thermally activated delayed fluorescence (TADF) and an emitter displaying strong, narrow‐band fluorescence. Here, through a joint computational and experimental approach, an unprecedented, end‐to‐end systems level description of the electronic and optical processes that take place in a hyperfluorescent emissive layer composed of a TADF sensitizer, 2,5‐bis(2,6‐di(9H‐carbazol‐9‐yl)phenyl)‐1,3,4‐oxadiazole (4CzDPO), and a fluorescent emitter, 2,5,8,11‐tetra‐tert‐butylperylene (TBPe) is provided. The photophysical properties measurement of the emissive layer is combined with the computational determination of the electronic properties, film morphology, and excitation transfer phenomena. The Förster resonance energy transfer rates from 4CzDPO to TBPe are on the order of 10¹¹ s⁻¹, considerably higher than the radiative and nonradiative recombination rates for 4CzDPO. These features ensure nearly complete energy transfer to TBPe, leading to a five‐fold increase in the photoluminescence quantum yields in the 4CzDPO:TBPe system in comparison to neat films of 4CzDPO. This approach highlights the factors that can provide efficient energy transfer from TADF molecules to fluorescent emitters, suppress energy transfer among TADF molecules, and avoid the need for a host material within the emissive layer.

A donor‐acceptor‐donor structure‐based iridium(III) complex is synthesized for synergistic photodynamic and photothermal therapy of cancer. The complex can be triggered with 808 nm light, generate O₂ ^−• to relieve the oxygen‐dependence, and exbibit efficient reactive oxygen species (ROS) and heat generation with ROS quantum yield of 14.6% and photothermal conversion efficiency of 27.5%.

Abstract

Iridium(III) complexes are an important group of photosensitizers for photodynamic therapy (PDT). This work constructs a donor–acceptor–donor structure‐based iridium(III) complex (IrDAD) with high reactive oxygen species (ROS) generation efficiency, negligible dark toxicity, and synergistic PDT and photothermal therapy (PTT) effect under near‐infrared (NIR) stimulation. This complex self‐assembles into metallosupramolecular aggregates with a unique aggregation‐induced PDT behavior. Compared with conventional iridium(III) photosensitizers, IrDAD not only achieves NIR light deep tissue penetration but also shows highly efficient ROS and heat generation with ROS quantum yield of 14.6% and photothermal conversion efficiency of 27.5%. After conjugation with polyethylene glycol (PEG), IrDAD is formulated to a nanoparticulate system (IrDAD‐NPs) with good solubility. In cancer phototherapy, IrDAD‐NPs preferentially accumulate in tumor area and display a significant tumor inhibition in vivo, with 96% reduction in tumor volume, and even tumor elimination.

The rational design of StyPy enables a push–pull system that undergoes a twisted intramolecular charge transfer (TICT) in its excited state and is applied to sense local viscosities and polarities in DNA hybrid mesostructures. The enormous Stokes shift of 250 nm enables to concurrently detect StyPy and conventional dyes with a single laser excitation.

Abstract

There exists a critical need in biomedical molecular imaging and diagnostics for molecular sensors that report on slight changes to their local microenvironment with high spatial fidelity. Herein, a modular fluorescent probe, termed StyPy, is rationally designed which features i) an enormous and tunable Stokes shift based on twisted intramolecular charge transfer (TICT) processes with no overlap, a broad emission in the far‐red/near‐infrared (NIR) region of light and extraordinary quantum yields of fluorescence, ii) a modular applicability via facile para‐fluoro‐thiol reaction (PFTR), and iii) a polarity‐ and viscosity‐dependent emission. This renders StyPy as a particularly promising molecular sensor. Based on the thorough characterization on the molecular level, StyPy reports on the viscosity change in all‐DNA microspheres and indicates the hydrophilic and hydrophobic compartments of hybrid DNA‐based mesostructures consisting of latex beads embedded in DNA microspheres. Moreover, the enormous Stokes shift of StyPy enables one to detect multiple fluorophores, while using only a single laser line for excitation in DNA protocells. The authors anticipate that the presented results for multiplexing information are of direct importance for advanced imaging in complex soft matter and biological systems.

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Minsoo P. Kim, Chang Won Ahn, Youngsu Lee, Kyoungho Kim, Jonghwa Park, Hyunhyub Ko

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Jingnan Wu, Qunping Fan, Minghai Xiong, Qiutang Wang, Kai Chen, Haiqin Liu, Mengyuan Gao, Long Ye, Xia Guo, Jin Fang, Qing Guo, Wenyan Su, Zaifei Ma, Zheng Tang, Ergang Wang, Harald Ade, Maojie Zhang

Molecular packing and thermodynamic properties of D18‐based fullerene‐free organic solar cells are studied. The D18 polymer exhibits strong chain extension in films, which is beneficial to charge transport. Miscibility and other characterizations explain the disparate performance of three systems and the processing procedures.

Abstract

Organic solar cells (OSCs) based on D18:Y6 have recently exhibited a record power conversion efficiency of over 18%. The initial work is extended and the device performance of D18‐based OSCs is compared with three non‐fullerene acceptors, Y6, IT‐4F, and IEICO‐4Cl, and their molecular packing characteristics and miscibility are studied. The D18 polymer shows unusually strong chain extension and excellent backbone ordering in all films, which likely contributes to the excellent hole‐transporting properties. Thermodynamic characterization indicates a room‐temperature miscibility for D18:Y6 and D18:IT‐4F near the percolation threshold. This corresponds to an ideal quench depth and explains the use of solvent vapor annealing rather than thermal annealing. In contrast, D18:IEICO‐4Cl is a low‐miscibility system with a deep quench depth during casting and poor morphology control and low performance. A failure of ternary blends with PC₇₁BM is likely due to the near‐ideal miscibility of Y6 to begin with and indicates that strategies for developing successful ternary or quaternary solar cells are likely very different for D18 than for other high‐performing donors. This work reveals several unique property–performance relations of D18‐based photovoltaic devices and helps guide design or fabrication of yet higher efficiency OSCs.

Recent advances in organic photovoltaic (OPV) materials and processing technologies are promising for transitioning of OPV devices from laboratory‐scale to large‐area industrial scale modules. Recent breakthroughs attained by development of nonfullerene acceptors have led to significant enhancement in power conversion efficiency. It is essential to elucidate degradation mechanisms of OPV devices for improving device long‐term stability.

Abstract

Organic solar cells based on bulk heterojunctions (BHJs) are attractive energy‐conversion devices that can generate electricity from absorbed sunlight by dissociating excitons and collecting charge carriers. Recent breakthroughs attained by development of nonfullerene acceptors result in significant enhancement in power conversion efficiency (PCEs) exceeding 17%. However, most of researches have focused on pursuing high efficiency of small‐area (<1 cm²) unit cells fabricated usually with spin coating. For practical application of organic photovoltaics (OPVs) from lab‐scale unit cells to industrial products, it is essential to develop efficient technologies that can extend active area of devices with minimized loss of performance and ensured operational stability. In this progress report, an overview of recent advancements in materials and processing technologies is provided for transitioning from small‐area laboratory‐scale devices to large‐area industrial scale modules. First, development of materials that satisfy requirements of high tolerability in active layer thickness and large‐area adaptability is introduced. Second, morphology control using various coating techniques in a large active area is discussed. Third, the recent research progress is also underlined for understanding mechanisms of OPV degradation and studies for improving device long‐term stability along with reliable evaluation procedures.

The energy level alignment between the two materials in an inorganic/organic semiconductor heterojunction significantly influences device functionality and performance. Here, a method that allows one to change the energy level alignment at such a heterojunction almost at will is demonstrated.

Abstract

The combination of inorganic and organic semiconductors in a heterojunction is considered a promising approach to overcome limitations of each individual material class. However, to date only few examples of improved (opto‐)electronic functionality have been realized with such hybrid heterojunctions. The key to unraveling the full potential offered by inorganic/organic semiconductor heterojunctions is the ability to deliberately control the interfacial electronic energy levels. Here, a universal approach to adjust the offset between the energy levels at inorganic/organic semiconductor interfaces is demonstrated: the interlayer method. A monolayer‐thick interlayer comprising strong electron donor or acceptor molecules is inserted between the two semiconductors and alters the energy level alignment due to charge transfer with the inorganic semiconductor. The general applicability of this method by tuning the energy levels of hydrogenated silicon relative to those of vacuum‐processed films of a molecular semiconductor as well as solution‐processed films of a polymer semiconductor is exemplified, and is shown that the energy level offset can be changed by up to 1.8 eV. This approach can be used to adjust the energy levels at the junction of a desired material pair at will, and thus paves the way for novel functionalities of optoelectronic devices.

Efficient red‐emitting aggregation‐induced emission luminogens with tunable organelle‐specific anchoring of PIZ‐CN and PID‐CN are designed and synthesized. By virtue of their large Stokes shift, excellent photostability, and low stimulated emission depletion (STED) saturation intensity, the dynamic motions of lysosomes and mitochondria are recorded with high resolution under low STED power.

Abstract

Lysosomes and mitochondria play an important role in maintaining cell homeostasis. Visualizing the long‐term activities of lysosomes and mitochondria on the nanometer scale in live cells is essential for further understanding their functions but remains challenging due to the limitations of existing fluorescent probes, such as aggregation‐caused quenching (ACQ) effect, limited signal‐to‐noise ratio from fluorescence “always on” in the process of targeting organelle and poor photobleaching resistance. Herein, two efficient red‐emitting aggregation‐induced emission (AIE) luminogens are reported, which showed “off‐on” fluorescence characteristic and specific lysosomes as well as mitochondria targeting capability. Owing to their AIE characteristics, a Stokes’ shift larger than 100 nm, good biocompatibility, and excellent photostability, the AIE luminogens have been successfully utilized for high fidelity imaging of lysosomes and mitochondria. By virtue of these two probes, stimulated emission depletion (STED) images of dynamic lysosomal fusion and mitochondrial fission with a high resolution of 65.6 nm are obtained. Furthermore, the interactions between lysosomes and mitochondria in the process of mitophagy are recorded. This study also provides practical guidance for designing specific organelle targeting probes to support live cell dynamic super‐resolution imaging.

Through investigation of the underlying thermodynamic and kinetic aspects of non‐fullerene acceptor crystallization, the importance of diffusion coefficients and melting enthalpies in controlling the crystal growth rates is demonstrated, and it is revealed and that differences in halogenation can drastically change crystallization kinetics and device stability.

Abstract

With power conversion efficiency now over 17%, a long operational lifetime is essential for the successful application of organic solar cells. However, most non‐fullerene acceptors can crystallize and destroy devices, yet the fundamental underlying thermodynamic and kinetic aspects of acceptor crystallization have received limited attention. Here, room‐temperature (RT) diffusion coefficients of 3.4 × 10⁻²³ and 2.0 × 10⁻²² are measured for ITIC‐2Cl and ITIC‐2F, two state‐of‐the‐art non‐fullerene acceptors. The low coefficients are enough to provide for kinetic stabilization of the morphology against demixing at RT. Additionally profound differences in crystallization characteristics are discovered between ITIC‐2F and ITIC‐2Cl. The differences as observed by secondary‐ion mass spectrometry, differential scanning calorimetry (DSC), grazing‐incidence wide‐angle X‐ray scattering, and microscopy can be related directly to device degradation and are attributed to the significantly different nucleation and growth rates, with a difference in the growth rate of a factor of 12 at RT. ITIC‐4F and ITIC‐4Cl exhibit similar characteristics. The results reveal the importance of diffusion coefficients and melting enthalpies in controlling the growth rates, and that differences in halogenation can drastically change crystallization kinetics and device stability. It is furthermore delineated how low nucleation density and large growth rates can be inferred from DSC and microscopy experiments which could be used to guide molecular design for stability.

With synergistic optimization of the active layer morphology, flexible substrate properties, and processing temperature, large‐area flexible organic solar cells with high performance are achieved by the slot‐die coating process. The 1 cm² flexible devices produce an excellent power conversion efficiency (PCE) of 12.16%, and, for modules with an area of 25 cm², an extraordinary PCE of 10.09% is observed.

Abstract

Slot‐die coating is generally regarded as the most effective large‐scale methodology for the fabrication of organic solar cells (OSCs). However, the corresponding device performance significantly lags behind spin‐coated devices. Herein, the active layer morphology, flexible substrate properties, and the processing temperature are optimized synergistically to obtain high power conversion efficiency (PCE) for both the flexible single cells and the modules. As a result, the 1 cm² flexible devices produce an excellent PCE of 12.16% as compared to 12.37% for the spin‐coated small‐area (0.04 cm²) rigid devices. Likewise, for modules with an area of 25 cm², an extraordinary PCE of 10.09% is observed. Hence, efficiency losses associated with the upscaling are significantly reduced by the synergistic optimization. Moreover, after 1000 bending cycles at a bending radius of 10 mm, the flexible devices still produce over 99% of their initial PCE, whereas after being stored for over 6000 h in a glove box, the PCE reaches 103% of its initial value, indicating excellent device flexibility as well as superior shelf stability. These results, thus, are a promising confirmation the great potential for upscaling of large‐area OSCs in the near future.

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Claudia Caddeo, Alessio Filippetti, Andrea Bosin, Christine Videlot-Ackermann, Jörg Ackermann, Alessandro Mattoni

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Narges Yaghoobi Nia, Mahmoud Zendehdel, Mojtaba Abdi-Jalebi, Luigi Angelo Castriotta, Felix U. Kosasih, Enrico Lamanna, Mohammad Mahdi Abolhasani, Zhaoxiang Zheng, Zahra Andaji-Garmaroudi, Kamal Asadi, Giorgio Divitini, Caterina Ducati, Richard H. Friend, Aldo Di Carlo

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Dongwoo Lee, Inkyum Kim, Daewon Kim

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Yue Yu, Defei Xu, Chenchao Huang, Xiongwei He, Jingrui Li, Chenjing Zhao, Bo Jiao, Man-Keung Fung, Liangsheng Liao, Zhaoxin Wu

Nature Photonics, Published online: 21 December 2020; doi:10.1038/s41566-020-00743-1

Nature Photonics, Published online: 21 December 2020; doi:10.1038/s41566-020-00734-2

This work is the first to integrate the multimechanism recombination parameters with the density of states (DOS) distribution and effective bandgap in the framework of a semiempirical analytical model of temperature and light intensity dependent V _oc. The proposed approach is expected to be a useful tool for quantifying the full spectrum of recombination‐ and DOS‐related parameters of nonfullerene organic solar cells.

Abstract

The relationship of the temperature–light intensity dependence of open‐circuit voltage V _oc in nonfullerene‐based organic solar cells with their material characteristics and multimechanism recombination parameters is described. The systematic variation of the effective bandgap E _g,eff and the electrode layers allows the observation of different relative contributions of bimolecular, bulk, and surface trap‐assisted recombination mechanisms. The complementary advantages of the analytical model and the established voltage‐impedance spectroscopy technique provide a useful tool to quantify multimechanism recombination parameters, effective density of states N _c, and energetic disorder σ in organic solar cells under operating conditions. The validity of the proposed model to understand the temperature and light intensity dependent of V _oc is shown by applying it to four different donor:nonfullerene acceptor blend systems with conventional or inverted device architectures.

A narrow bandgap polymer acceptor PYF‐T with fluorinated end groups on monomer sub‐units is synthesized, showing stronger and red‐shifted absorption, lower‐lying frontier molecular orbitals, higher electron mobility, enhanced intermolecular packing, and without sacrificing photovoltage compared to its non‐fluorinated counterpart (PY‐T). When employed in all‐polymer solar cells, PYF‐T yields an outstanding efficiency of 14.10%.

Abstract

Fluorination of end groups has been a great success in developing efficient small molecule acceptors. However, this strategy has not been applied to the development of polymer acceptors. Here, a dihalogenated end group modified by fluorine and bromine atoms simultaneously, namely IC‐FBr, is first developed, then employed to construct a new polymer acceptor (named PYF‐T) for all‐polymer solar cells (all‐PSCs). In comparison with its non‐fluorinated counterpart (PY‐T), PYF‐T exhibits stronger and red‐shifted absorption spectra, stronger molecular packing and higher electron mobility. Meanwhile, the fluorination on the end groups down‐shifts the energy levels of PYF‐T, which matches better with the donor polymer PM6, leading to efficient charge transfer and small voltage loss. As a result, an all‐PSC based on PM6:PYF‐T yields a higher power conversion efficiency (PCE) of 14.1% than that of PM6:PY‐T (11.1%), which is among the highest values for all‐PSCs reported to date. This work demonstrates the effectiveness of fluorination of end‐groups in designing high‐performance polymer acceptors, which paves the way toward developing more efficient and stable all‐PSCs.