Recently Advanced Polymer Materials Containing Dithieno[3,2‐b:2′,3′‐d]phosphole Oxide for Efficient Charge Transfer in High‐Performance Solar Cells

Two novel semiconducting polymers based on benzodithiophene and dithienophosphole oxide (DTP) units are designed and synthesized. A novel electron‐deficient DTP moiety is developed. Surprisingly, the introduction of DTP units brings highly polarizable characteristics, which is beneficial for the photocurrent in solar cells. Thus, the donor–acceptor type of conjugated polymers based on this novel acceptor has superior charge transfer properties and highly efficient PL quenching efficiencies. As a result, polymer solar cells (PSCs) with high power conversion efficiencies of 6.10% and 7.08% are obtained from poly(3,5‐didodecyl‐4‐phenylphospholo[3,2‐b:4,5‐b']dithiophene–4‐oxide‐alt‐4,8‐bis(5‐decylthiophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene) (PDTP–BDTT) and PDTP–4‐oxide‐alt‐4,8‐bis(5‐decylselenophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene) (PDTP–BDTSe), respectively, when the photoactive layer is processed with the 1,8‐octanedithiol (ODT) additive. The PDTP–BDTSe copolymer is now the best performing DTP‐based material for PSCs. Using the polarizable unit strategy determined in this study for the molecular design of conjugated polymers is expected to greatly advance the development of organic electronic devices.     

A Cruciform Electron Donor–Acceptor Semiconductor with Solid‐State Red Emission: 1D/2D Optical Waveguides and Highly Sensitive/Selective Detection of H2S Gas

In this paper, a new cruciform donor–acceptor molecule 2,2'‐((5,5'‐(3,7‐dicyano‐2,6‐bis(dihexylamino)benzo[1,2‐b:4,5‐b']difuran‐4,8‐diyl)bis(thiophene‐5,2‐diyl))bis (methanylylidene))dimalononitrile ( BDFTM ) is reported. The compound exhibits both remarkable solid‐state red emission and p‐type semiconducting behavior. The dual functions of BDFTM are ascribed to its unique crystal structure, in which there are no intermolecular face‐to‐face π–π interactions, but the molecules are associated by intermolecular CN…π and H‐bonding interactions. Firstly, BDFTM exhibits aggregation‐induced emission; that is, in solution, it is almost non‐emissive but becomes significantly fluorescent after aggregation. The emission quantum yield and average lifetime are measured to be 0.16 and 2.02 ns, respectively. Crystalline microrods and microplates of BDFTM show typical optical waveguiding behaviors with a rather low optical loss coefficient. Moreover, microplates of BDFTM can function as planar optical microcavities which can confine the emitted photons by the reflection at the crystal edges. Thin films show an air‐stable p‐type semiconducting property with a hole mobility up to 0.0015 cm²V^?1s^?1. Notably, an OFET with a thin film of BDFTM is successfully utilized for highly sensitive and selective detection of H₂S gas (down to ppb levels).     

Multifunctional Biomedical Imaging in Physiological and Pathological Conditions Using a NIR‐II Probe

Compared with imaging in the visible (400–650 nm) and near‐infrared window I (NIR‐I, 650–900 nm) regions, imaging in near‐infrared window II (NIR‐II, 1000–1700 nm) is a highly promising in vivo imaging modality with improved resolution and deeper tissue penetration. Here, a small molecule NIR‐II dye,5,5′‐(1H,5H‐benzo[1,2‐c:4,5‐c′] bis[1,2,5]thiadiazole)‐4,8‐diyl)bis(N,N‐bis(4‐(3‐((tert‐butyldimethylsilyl)oxy)propyl)phenyl) thiophen‐2‐amine), is successfully encapsulated into phospholipid vesicles to prepare a probe CQS1000. The novel NIR‐II probe is studied for in vivo multifunctional biological imaging. The results of this study indicate that the NIR‐II vesicle CQS1000 can noninvasively and dynamically visualize and monitor many physiological and pathological conditions of circulatory systems, including lymphatic drainage and routing, angiogenesis of tumor, and vascular deformity such as arterial thrombus formation and ischemia with high spatial and temporal resolution. More importantly, by virtue of the favorable half‐life of blood circulation of CQS1000, NIR‐II imaging is capable of aiding precise resection of tumor such as osteosarcoma and accelerating the process of lymph node dissection to complete sentinel lymph node biopsy for better decision making during the tumor surgery. Overall, CQS1000 is a highly promising NIR‐II probe for multifunctional biomedical imaging in physiological and pathological conditions, surpassing traditional NIR‐I imaging modality and pathologic assessments for clinical diagnosis and treatment.     

Highly Efficient Solid‐State Near‐Infrared Emitting Material Based on Triphenylamine and Diphenylfumaronitrile with an EQE of 2.58% in Nondoped Organic Light‐Emitting Diode

The development of efficient near‐infrared (NIR) emitting material is of current focus. Donor–acceptor (D–A) architecture has been proved to be an effective strategy to obtain narrow energy gap. Herein, a D–A‐type NIR fluorescent compound 2,3‐bis(4′‐(diphenylamino)‐[1,1′‐biphenyl]‐4‐yl)fumaronitrile (TPATCN) is synthesized and fully characterized. As revealed by theoretical calculations and photophysical experiments, TPATCN exerts the advantages of the relatively large dipole moment of the charge transfer state and a certain degree of orbital overlap of the local excited state. A highly mixed or hybrid local and charge transfer excited state might occur to simultaneously achieve both a large fraction of singlet formation and a high quantum efficiency in D–A system. TPATCN exhibits strong NIR fluorescence with the corresponding thin film quantum efficiency of 33% and the crystal efficiency of 72%. Remarkably, the external quantum efficiency of nondoped NIR organic light‐emitting diode (OLED) reaches 2.58% and remains fairly constant over a range of 100–300 mA cm^?2, which is among the best results for NIR OLEDs reported so far.     

An Electron Acceptor with Broad Visible–NIR Absorption and Unique Solid State Packing for As‐Cast High Performance Binary Organic Solar Cells

A novel acceptor–donor–acceptor (A–D–A) type electron acceptor 6TIC‐4F with terthieno[3,2‐b]thiophene (6T) as the core unit is rationally designed and synthesized, which exhibits an extraordinarily narrow bandgap (≈1.24 eV) and strong absorption between 650 and 1000 nm. X‐ray crystallographic analysis reveals that it has unique intermolecular π–π stacking. The solar cells based on the as‐cast poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione))]) (PBDB‐T): 6TIC‐4F binary blends exhibit an excellent power conversion efficiency (PCE) of 11.14% with a high J_SC of 23.00 mA cm^?2, and a high fill factor of 0.67, which represents one of the best PCE values for low bandgap (E_g < 1.3 eV)–based organic solar cells.     

Tunable Förster Resonance Energy Transfer in Colloidal Nanoparticles Composed of Polycaprolactone‐Tethered Donors and Acceptors: Enhanced Near‐Infrared Emission and Compatibility for In Vitro and In Vivo Bioimaging

A near‐infrared (NIR) fluorescent donor/acceptor (D/A) nanoplatform based on Förster resonance energy transfer is important for applications such as deep‐tissue bioimaging and sensing. However, previously reported D/A nanoparticles (NPs) often show limitations such as aggregation‐induced fluorescence quenching and poor interfacial compatibility that reduces the efficiency of the energy transfer and also leads to leaching of the small molecular fluorophores from the NP matrix. Here highly NIR‐fluorescent D/A NPs with a fluorescence quantum yield as high as 46% in the NIR region (700–850 nm) and robust optical stability are reported. The hydrophobic core of each NP is composed of donor and acceptor moieties both of which are tethered with polycaprolactone (PCL), while the hydrophilic corona is composed of poly[oligo(ethylene glycol) methyl ether methacrylate] to offer colloidal stability and “stealthy” effect in aqueous media. The PCL matrix in each colloidal NP not only offers biocompatibility and biodegradability but also minimizes the aggregation‐caused fluorescence quenching of D/A chromophores and prevents the leakage of the NIR fluorophores from the NPs. In vivo imaging using these NIR NPs in live mice shows contrast‐enhanced imaging capability and efficient tumor‐targeting through enhanced permeability and retention effect.     

High Solid‐State Near Infrared Emissive Organic Fluorophores from Thiadiazole[3,4‐c]Pyridine Derivatives for Efficient Simple Solution‐Processed Nondoped Near Infrared OLEDs

Many efforts have been dedicated to developing near infrared (NIR) fluorescent emitters with strong emission especially in the range of 700–1000 nm due to their potential applications in biomedical and optoelectronic fields. However, high solid state NIR emission fluorophores are still rare for applications. Herein, two efficient donor‐π‐acceptor type NIR emitters, C3HTP and C4HTP , are designed and synthesized by end‐capping two isomeric bis(n‐hexylthienyl)thiadiazole[3,4‐c]pyridines as π‐acceptor with structural bulky, electron rich tercarbazole moiety. They exhibit excellent solid state NIR emission with an emission peak at 725 nm, especially C3HTP , reaching a record high photoluminescence quantum yield (Φ_PL) of 34% for NIR organic fluorescent materials. By taking advantage of their Φ_PL values in the film state (Φ_PL = 10–34%), suitable energy levels (highest occupied molecular orbital (HOMO) level ≈ ?5.3 eV), high hole mobility (5.49 × 10^?8 cm² V^?1 s^?1) as well as good amorphous film forming ability by solution casting, they are used to fabricate a nondoped emissive layer (EML) in simple double‐layer solution processed NIR electroluminescent (EL) devices. The device containing C3HTP as the EML shows a NIR emission peaking at 726 nm and excellent EL performance with a high external quantum efficiency of 1.51%, which is the best solution processed nondoped NIR organic light‐emitting diodes reported to date. Importantly, this represents an advance in near infrared organic fluorescent materials and EL devices that meet the requirements of many applications.     

Deep‐Red/Near‐Infrared Electroluminescence from Single‐Component Charge‐Transfer Complex via Thermally Activated Delayed Fluorescence Channel

Formation of a single‐component charge‐transfer complex (SCCTC) is unveiled in solid state of an intermolecular charge‐transfer molecule 2‐(4‐(1‐phenyl‐1H‐phenanthro[9,10‐d]imidazol‐2‐yl)phenyl)anthracene‐9,10‐dione (PIPAQ). Intermolecular donor–acceptor interactions between two PIPAQ molecules is the primary driving force for self‐association and contributes to intermolecular charge transfer. The SCCTC character is fully verified by crystallographic, photophysical, electron spin resonance, and vibrational characterizations. The PIPAQ‐based SCCTC is first applied in light‐emitting devices as an emissive layer to realize efficient deep‐red/near‐infrared electroluminescence. This work provides new insights into SCCTC and represents an important step toward their applications in optoelectronic devices.     

High‐Efficiency Near‐Infrared Fluorescent Organic Light‐Emitting Diodes with Small Efficiency Roll‐Off: A Combined Design from Emitters to Devices

The simultaneous realization of high quantum yield and exciton utilizing efficiency (η_r) is still a formidable challenge in near‐infrared (NIR) fluorescent organic light‐emitting diodes (FOLEDs). Here, to achieve a high quantum yield, a novel NIR dye, 4,9‐bis(4‐(diphenylamino)phenyl)‐naphtho[2,3‐c ][1,2,5]selenadiazole, is designed and synthesized with a large highest occupied molecular orbital/lowest unoccupied molecular orbital overlap and an aggregation‐induced emission property, which demonstrates a high photoluminescence quantum yield of 27% at 743 nm in toluene and 29% at 723 nm in a blend film. For a high η_r, an orange‐emitting thermally activated delayed fluorescent material, 1,2‐bis(9,9‐dimethyl‐9,10‐dihydroacridine)‐4,5‐dicyanobenzene, is chosen as the sensitizing host to harvest triplet excitons in devices. The optimized devices achieve a good η_r of 45.7% and a high external quantum efficiency up to 2.65% at 730 nm, with a very small efficiency roll‐off of 2.41% at 200 mA cm^?2, which are among the most efficient values for NIR‐FOLEDs over 700 nm. The effective utilization of triplet excitons via the thermally activated delayed fluorescence‐sensitizing host will pave a way to realize high‐efficiency NIR‐FOLEDs with small efficiency roll‐off.     

Flexible Near‐Infrared Plastic Phototransistors with Conjugated Polymer Gate‐Sensing Layers

Flexible near‐infrared (NIR) light‐sensing detectors are strongly required in the fast‐growing flexible electronics era, because they can serve as a vision system like eyes in various innovative applications including humanoid robots. Recently, keen interest has been paid to organic phototransistors due to their unique signal amplification and active matrix driving features over organic photodiodes. However, conventional NIR‐sensing organic phototransistors suffer from the limited use of organic materials because the channel layers play a dual role in both charge transport and sensing so that organic semiconducting materials with reasonably high charge mobility can be applied only. Here, it is demonstrated that a conjugated polymer, poly[{2,5‐bis‐(2‐ethylhexyl)‐3,6‐bis‐(thien‐2‐yl)‐pyrrolo[3,4‐c]pyrrole‐1,4‐diyl}‐co‐{2,2′‐(2,1,3‐benzothiadiazole)]‐5,5′‐diyl}] (PEHTPPD‐BT), which exhibits no transistor performance as a channel layer, can stably detect a NIR light (up to 1000 nm) as a gate‐sensing layer (GSL) when it is placed between gate‐insulating layers and gate electrodes. The flexible array (10 × 10) detectors with the PEHTPPD‐BT GSLs could effectively sense NIR light without visible light interference by applying visible light cut films.     

Nonfullerene Small‐Molecule Acceptors for Organic Photovoltaics: Understanding the Impact of Methoxy Substitution Position on Molecular Packing and Electron‐Transfer Properties

Nonfullerene small‐molecule acceptors (SMAs) are considered as a key component of next‐generation organic photovoltaics. Introducing functional groups to the end‐groups of “acceptor‐donor‐acceptor”‐type SMAs is a facile and convenient way to tune their optoelectronic and morphological properties. Here, molecular dynamics simulations are combined with long‐range corrected density functional theory calculations to explore the molecular‐scale impact that the position of methoxy substitution in the end‐group has on the molecular packing and electron‐transfer properties in neat films. The focus here is on 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno [2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene (IT‐OM), where three end‐group methoxy substitution positions are evaluated. Changing the methoxy substitution position is found to influence, to different extents, the planarity of the end‐groups and thus the intermolecular packing density. The effect on the intermolecular electron‐transfer rates is also examined and leads to markedly different sizes of strongly interconnected clusters. Overall, these findings are fully consistent with the experimental evolution of electron mobility in the neat IT‐OM film as a function of methoxy substitution position.     

Optimizing Light‐Harvesting Polymers via Side Chain Engineering

A series of conjugated polymers using naphtho[1,2‐c:5,6‐c]bis[1,2,5]thiadiazole and benzodithiophene alternating backbone is synthesized to investigate the effect of side chain substitution on conjugated donor–acceptor polymer on electronic, morphological, and photovoltaic properties. It is found that light absorption and frontier energy levels of the resultant polymers are strongly affected by the side chains. The thin film morphology, crystal structure, crystallinity, and orientation also depend on the side chains; the side chain type affects more in the π–π stacking direction, while the side chain density plays a significant role in the lamellar packing direction. The thickness of the active layer also influences the performance of the solar cells with some materials showing enhanced performance with thicker active layers. The best solar cell device in this study has power conversion efficiencies of 8.14%, among the highest in materials of similar structure.     

Molecular Imaging in the Second Near‐Infrared Window

In the past decade, noticeable progress has been achieved regarding fluorescence imaging in the second near‐infrared (NIR‐II) window. Fluorescence imaging in the NIR‐II window demonstrates superiorities of deep tissue penetration and high spatial and temporal resolution, which are beneficial for profiling physiological processes. Meanwhile, molecular imaging has emerged as an efficient tool to decipher biological activities on the molecular and cellular level. Extending molecular imaging into the NIR‐II window would enhance the imaging performance, providing more detailed and accurate information of the biological system. In this progress report, selected achievements made in NIR‐II molecular imaging are summarized. The organization of this report is based on strategies underlying rational designs of NIR‐II imaging probes, and their applications in molecular imaging are highlighted. This progress report may provide guidance and reference for further development of functional NIR‐II probes designed for high‐performance molecular imaging.     

Layer‐by‐Layer Conjugated Extension of a Semiconducting Polymer for High‐Performance Organic Field‐Effect Transistor

A donor–acceptor (D–A) semiconducting copolymer, PDPP‐TVT‐29, comprising a diketopyrrolopyrrole (DPP) derivative with long, linear, space‐separated alkyl side‐chains and thiophene vinylene thiophene (TVT) for organic field‐effect transistors (OFETs) can form highly π‐conjugated structures with an edge‐on molecular orientation in an as‐spun film. In particular, the layer‐like conjugated film morphologies can be developed via short‐term thermal annealing above 150 °C for 10 min. The strong intermolecular interaction, originating from the fused DPP and D–A interaction, leads to the spontaneous self‐assembly of polymer chains within close proximity (with π‐overlap distance of 3.55 Å) and forms unexpectedly long‐range π‐conjugation, which is favorable for both intra‐ and intermolecular charge transport. Unlike intergranular nanorods in the as‐spun film, well‐conjugated layers in the 200 °C‐annealed film can yield more efficient charge‐transport pathways. The granular morphology of the as‐spun PDPP‐TVT‐29 film produces a field‐effect mobility (μ _FET) of 1.39 cm² V^?1 s^?1 in an OFET based on a polymer‐treated SiO₂ dielectric, while the 27‐Å‐step layered morphology in the 200 °C‐annealed films shows high μ _FET values of up to 3.7 cm² V^?1 s^?1.     

Highly Efficient Near‐Infrared Electroluminescence up to 800 nm Using Platinum(II) Phosphors

Near‐infrared organic light‐emitting diodes (NIR OLEDs) enable many unique applications ranging from night‐vision displays and photodynamic therapies. However, the development of efficient NIR OLEDs with a low efficiency roll‐off is still challenging. Here, a series of new heteroleptic Pt(II) complexes ( 1 – 4 ) flanked by both pyridyl pyrimidinate and functional azolate chelates are synthesized. The reduced ππ* energy gap of the pyridyl pyrimidinate chelate, and strong intermolecular interaction and high crystallinity in vacuum‐deposited thin films engender strong intermolecular charge transfer transition including metal–metal‐to‐ligand charge transfer; thereby, exhibiting efficient photoluminescence within 776–832 nm and short radiative lifetimes of 0.52–0.79 µs. Consequently, nondoped NIR‐emitting OLEDs based on these Pt(II) complexes are fabricated, to which Pt(II) complexes 2 and 4 give record high maximum external quantum efficiency of 10.61% at 794 nm and 9.58% at 803 nm, respectively. Moreover, low efficiency roll‐off is also observed, among which the device efficiencies of 2 and 4 are at least four times higher than that of the best NIR‐emitting OLEDs recorded at current density of 100 mA cm^?2.     

High‐Performance Organic Light‐Emitting Diodes Based on Intramolecular Charge‐Transfer Emission from Donor–Acceptor Molecules: Significance of Electron‐ Donor Strength and Molecular Geometry

Organic light‐emitting diodes based on intramolecular‐charge‐transfer emission from two related donor–acceptor (D–A) molecules, 3,7‐[bis(4‐phenyl‐2‐quinolyl)]‐10‐methylphenothiazine (BPQ‐MPT) and 3,6‐[bis(4‐phenyl‐2‐quinolyl)]‐9‐methylcarbazole (BPQ‐MCZ), were found to have electroluminescence (EL) efficiencies and device brightnesses that differ by orders of magnitude. High brightness (> 40 000 cd m^–2) and high efficiency (21.9 cd A^–1, 10.8 lm W^–1, 5.78 % external quantum efficiency (EQE) at 1140 cd m^–2) green EL was achieved from the BPQ‐MPT emitter, which has its highest occupied molecular orbital (HOMO) level at 5.09 eV and a nonplanar geometry. In contrast, diodes with much lower brightness (2290 cd m^–2) and efficiency (1.4 cd A^–1, 0.66 lm W^–1, 1.7 % EQE at 405 cd m^–2) were obtained from the BPQ‐MCZ emitter, which has its HOMO level at 5.75 eV and exhibits a planar geometry. Compared to BPQ‐MCZ, the higher‐lying HOMO level of BPQ‐MPT facilitates more efficient hole injection/transport and a higher charge‐recombination rate, while its nonplanar geometry ensures diode color purity. White EL was observed from BPQ‐MCZ diodes owing to a blue intramolecular charge‐transfer emission and a yellow–orange intermolecular excimer emission, enabled by the planar molecular geometry. These results demonstrate that high‐performance light‐emitting devices can be achieved from intramolecular charge‐transfer emission, while highlighting the critical roles of the electron‐donor strength and the molecular geometry of D–A molecules.     

Simultaneous and Dual Emissive Imaging by Micro‐Contact Printing on the Surface of Electrostatically Assembled Water‐Soluble Poly(p‐phenylene) Using FRET

Poly{[2,5‐bis(3‐sulfonatobutoxy)‐1,4‐phenylene sodium salt]‐alt‐(1,4‐phenylene)}, which is an anionically charged, water‐soluble poly(para‐phenylene) derivative with aldehyde groups at both chain ends, is prepared via the Suzuki coupling reaction in order to develop a FRET energy donor, while simultaneously dual‐fluorescence‐patterning the protein. Regardless of the end‐capping, the synthesized polymer exhibits a good solubility in water with an absorption maximum at 338 nm and a photoluminescence maximum at 417 nm, similar to those of the the end‐capped polymer. The emission spectrum of the polymer overlaps the absorption spectrum of fluorescein, and therefore, the polymer can be used as an energy donor with fluorescein as the energy acceptor in the FRET mechanism. This polymer design not only takes advantage of the introduction of biotin at both chain ends (through a reaction with the aldehyde end groups) to realize the facile interaction with streptavidin, but also brings into play the electrostatic features of the anionic sulfonate groups to fabricate an electrostatic self‐assembly with polycation for the pattern substrate. The micropattern of fluorescein‐labeled streptavidin is fabricated on the polymer‐coated substrate through micro‐contact printing using a polydimethylsiloxane mold. As a result, the polymer substrate exhibits a dual fluorescence micropattern, which results from the blue emission color from the energy donor and the FRET‐amplified green emission from the energy acceptor. The high‐resolution patterning is carried out for the application of multiplexing by simultaneously imaging the patterned green‐emitting fluorescein by FRET and the surrounding blue‐emitting polymer according to an optical detection scheme.     

Efficient Near‐Infrared Emission by Adjusting the Guest–Host Interactions in Thermally Activated Delayed Fluorescence Organic Light‐Emitting Diodes

Thermally activated delayed fluorescence materials can effectively achieve high efficiency by harvesting singlet and triplet excitons in organic light‐emitting diodes (OLEDs). However, the choice of host material has a huge impact on the efficiency of the device, especially for the near‐infrared (NIR) luminescent material. In this contribution, a series of host materials are used to match the thermally activated delayed fluorescence emitter, 3,4‐bis(4‐(diphenylamino)phenyl)acenaphtho[1,2‐b]pyrazine‐8,9‐dicarbonitrile (APDC‐DTPA), for fabricating NIR OLEDs. All the host materials have the higher triplet energy than that of APDC‐DTPA. As the organometallic compound of Zn(BTZ)₂ has relatively stronger dipole moment, the electroluminescence spectral peak of doped device shows strong bathochromic shift exceeding 700 nm and changes with doping concentration. Finally, the extremely high external quantum efficiency of 7.8% (with 10 wt% of doping concentration) and 5.1% (with 20 wt% of doping concentration) are achieved with the emission peaks of 710 and 728 nm, respectively, which are superior to that of the device based on the other host materials. The approach is feasible to achieve bathochromic shift and highly efficient fluorescent OLEDs.     

Impact of Nonfullerene Molecular Architecture on Charge Generation,Transport, and Morphology in PTB7‐Th‐Based Organic Solar Cells

Despite the rapid development of nonfullerene acceptors (NFAs), the fundamental understanding on the relationship between NFA molecular architecture, morphology, and device performance is still lacking. Herein, poly[[4,8‐bis[5‐(2‐ethylhexyl)thiophene‐2‐yl]benzo[1,2‐b:4,5‐b0]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]‐thieno[3,4‐b]thiophenediyl]] (PTB7‐Th) is used as the donor polymer to compare an NFA with a 3D architecture (SF‐PDI4) to a well‐studied NFA with a linear acceptor–donor–acceptor (A–D–A) architecture (ITIC). The data suggest that the NFA ITIC with a linear molecular structure shows a better device performance due to an increase in short‐circuit current ( J_sc) and fill factor (FF) compared to the 3D SF‐PDI4. The charge generation dynamics measured by femtosecond transient absorption spectroscopy (TAS) reveals that the exciton dissociation process in the PTB7‐Th:ITIC films is highly efficient. In addition, the PTB7‐Th:ITIC blend shows a higher electron mobility and lower energetic disorder compared to the PTB7‐Th:SF‐PDI4 blend, leading to higher values of J_sc and FF. The compositional sensitive resonant soft X‐ray scattering (R‐SoXS) results indicate that ITIC molecules form more pure domains with reduced domain spacing, resulting in more efficient charge transport compared with the SF‐PDI4 blend. It is proposed that both the molecular structure and the corresponding morphology of ITIC play a vital role for the good solar cell device performance.     

Customized Electronic Coupling in Self‐Assembled Donor–Acceptor Nanostructures

Charge transfer processes between donor–acceptor complexes and metallic electrodes are at the heart of novel organic optoelectronic devices such as solar cells. Here, a combined approach of surface‐sensitive microscopy, synchrotron radiation spectroscopy, and state‐of‐the‐art ab initio calculations is used to demonstrate the delicate balance that exists between intermolecular and molecule–substrate interactions, hybridization, and charge transfer in model donor–acceptor assemblies at metal‐organic interfaces. It is shown that charge transfer and chemical properties of interfaces based on single component layers cannot be naively extrapolated to binary donor–acceptor assemblies. In particular, studying the self‐assembly of supramolecular nanostructures on Cu(111), composed of fluorinated copper‐phthalocyanines (F₁₆CuPc) and diindenoperylene (DIP), it is found that, in reference to the associated single component layers, the donor (DIP) decouples electronically from the metal surface, while the acceptor (F₁₆CuPc) suffers strong hybridization with the substrate.