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Orthogonal integration of holographic and fluorescent dual-mode optical images with facile tunable emission colors has been achieved by precisely controlling the Förster resonance energy transfer and photocleavage reaction of an AIEgen.

This perspective summarizes the recently encouraging progress of asymmetric fused ring electron acceptors and tries to show a picture of the relationship between the asymmetric molecular structure, energy loss and device performance.

Flexible manufacturing of holographic polymer nanocomposites has been realized by the synergy of hydrogen bonding networks with thiol–ene click reaction, which allows for the reconstruction of polarization-sensitive 3D images for advanced security.

Long-term stability is critical for organic solar cells (OSCs) for practical applications. Several factors affect the stability of OSCs, including materials stability, morphology stability of bulk-heterojunctions and interface stability. In this perspective, we focus on interface stability due to interfacial reactions between the emerging acceptor-donor-acceptor (A-D-A) type nonfullerene active layers and interfacial layers. The description covers the initial phenomena of interfacial instability, mechanism of interfacial reactions, and strategies adopted to suppress interfacial reactions between the nonfullerene active layers and interfacial layers. Methods to test and analyze the chemical instability of nonfullerene acceptors are also included. The C[double bond, length as m-dash]C vinyl linker between the donor moiety and acceptor moiety is chemically or photochemically reactive and is a weak point for interface stability. The interface stability of OSCs could be enhanced by reducing the reactivity of the C[double bond, length as m-dash]C vinyl linker or removing it directly, modifying the surface of interfacial layers, and developing other novel interfacial materials.

In order to artificially regulate cell behaviors, intracellular polymerization as an emerging chemical technique has attracted much attention. Yet, it is still a challenge to achieve effective intracellular polymerization to conquer tumors in the complex cellular environment. Herein, this work develops a tumor-targeting and caspase-3 responsive nanoparticle composed of a diacetylene-containing lipidated peptide amphiphile and mitochondria-targeting photosensitizer (C3), which undergoes nanoparticle-to-nanofiber transformation and efficient in situ polymerization triggered by photodynamic treatment and activation of caspase-3. The locational nanofibers on the mitochondria membranes lead to mitochondrial reactive oxygen species (mtROS) burst and self-amplified circulation, offering persistent high oxidative stress to induce cell apoptosis. This study provides a strategy for greatly enhanced antitumor therapeutic efficacy through mtROS burst and self-amplified circulation induced by intracellular transformation and in situ polymerization.

Solar-driven photocatalysis offers an environmentally friendly and sustainable approach for the degradation of organic pollutants in water without chemical additives, but the low specific surface area and adsorption capacity of common photocatalysts restricts the surface reactions with the contaminants. Herein, we hypercrosslinked polymer layers on TiO

Currently, the performance improvement for inverted perovskite solar cells (PVSCs) is mainly limited by the high open circuit voltage (VOC ) loss caused by detrimental non-radiative recombination (NRR) processes. Herein, we report a simple and efficient way to simultaneously reduce the NRR processes inside perovskites and at the interface by rationally designing a new pyridine-based polymer hole-transporting material (HTM), PPY2, which exhibits suitable energy levels with perovskites, high hole mobility, effective passivation of the uncoordinated Pb2+ and iodide defects, as well as the capability of promoting the formation of high-quality polycrystalline perovskite films. In absence of any dopants, the inverted PVSCs using PPY2 as the HTM deliver an encouraging PCE up to 22.41 % with a small VOC loss (0.40 V), among the best device performances for inverted PVSCs reported so far. Furthermore, PPY2-based unencapsulated devices show an excellent long-term photostability, and over 97 % of its initial PCE can be maintained after one sun constant illumination for 500 h.

Development of charge-transporting molecules that can simultaneously passivate multiple surface defects of perovskites is highly desirable for further performance increase of perovskite solar cells...

Aggregation-induced emission (AIE) has attracted great attention during the past two decades, and preventing strong π–π interactions in the aggregate state has been widely accepted as a strategy that brings an AIE effect. However, the relationship among the molecular structure, molecular packing, and emission properties of AIE-active molecules remains unclear. Herein, we have systematically investigated the emission properties of four fluorenone derivatives and have found that changing the substituents and substitution positions results in significantly different emission characteristics. 27-DPA exhibits a nearly quenched emission in both the solution and the aggregated states, while its regioisomer, 36-DPA, is a typical AIE molecule. In addition, two-color polymorph-dependent emission can be found for 36-TPA. X-ray single-crystal analysis was then conducted to understand these distinct emission properties. Our results emphasize the importance of molecular packing modes on the AIE effect, in particular for molecules containing molecular rotors, and further show that the formation of a three-dimensional molecular packing network is an effective way to suppress molecular motions to achieve AIE properties.

Recently, the power conversion efficiencies (PCEs) of bulk-heterojunction organic solar cells (BHJ-OSCs) based on non-fullerene acceptors (NFAs) have made a very impressive progress in the research field. However, less attention has been paid to the intrinsic chemical and photochemical stability of NFAs, although they are correlated greatly with the resulting device stability. Herein, we describe a new molecular design strategy to enhance the intrinsic chemical and photochemical stability of acceptor–donor–acceptor (A–D–A)-type NFAs by introducing ring-locked carbon–carbon double bonds between D–A conjugation, attributed to increased steric hindrance of nucleophilic attack and the formation of intramolecular C–H⋯O interactions. Based on this strategy, two types of NFAs were successfully prepared, 2-(1,1-dicyanomethylene)rhodanine-based IDT-CR and IDTT-CR and thiobarbituric acid-based IDT-CT and IDTT-CT. When blended with a wide-bandgap polymer donor (P3HT), the IDTT-CR-based solar cells can exhibit a PCE of 2.86%. Moreover, a much enhanced PCE of 6.13% was realized by adopting a low-bandgap polymer donor PTB7-Th to pair with IDTT-CT. The fabricated PTB7-Th:IDTT-CT-based OSCs showed very encouraging photostability, the PCE of which could retain >80% of the initial values after 200 h one sun irradiation in air without a UV filter. Such photostability performance has greatly outperformed those from conventional NFAs like ITIC, IT-4F, and IT-M, suggesting the effectiveness of our ring-locking design strategy. Moreover, PTB7-Th:IDTT-CT-based OSCs could retain ∼70% of its initial PCE after heating at 85 °C for 100 h. Furthermore, we reported an inferior device stability for P3HT:IDTT-CR based OSCs, which is primarily attributed to the evolution of BHJ film morphology under light illumination.

This study reports the facile synthesis, characterization and quantitative structure-property relationship analysis of molecular and material properties of tricyanofuran-based (TCF) dipolar heptamethines with different electron donors of indoline ( F1 ), benzo[ e ]- indoline ( F2 ), benz[ cd ]indoline ( F3 ), and Michler’s base derivatives ( M1 and M2 ). The linear and nonlinear optical (NLO) properties of these chromophores have been thoroughly investigated, and the relationship between molecular and bulk response has been analyzed and compared with dipolar tetraene AJLZ53 as one of the best chromophores for electro-optic (EO) devices. In particular, we provide responsible data collection and analysis of optical and EO properties for poled thin films using a widely-recognized and accredited methodology of prism coupling system with the help of rigid oriented gas model. We found that these push-pull heptamethines with synthetic efficacy exhibit high near-infrared absorption, excellent chemical stability and large hyperpolarizabilities ( β ) varied from 1,023×10−30 esu for F1 , 3,047×10−30 esu for M1 , and 3,547×10−30 esu for F3 at 1,304 nm in poled films, respectively. The β values of these molecules are among the highest ones for TCF-based dipolar chromophores, and also agree well with reported analytical results in the solutions. In poled polymers with a modest chromophoric loading density of 1.3× 1020 cm−3, M1 and M2 give a high poled-induced noncentrosymmetric order and relatively large r 33 values around 40 pm V−1 at 1,304 nm, indicative of large μβ values and suitable structural modification for high poling efficiency. Furthermore, a binary EO polymer based on the co-loading of M1 and AJLZ53 achieve a large r 33 value of 143.3 pm V−1 at 1,304 nm. Our studies suggest that concise synthesis and molecular design of push-pull polymethines can be well guided by the tabulation of their linear and NLO properties in bulk materials, and streamline future development of high performance organic EO materials for photonic applications.

Perovskite solar cells (PVSCs) have achieved incredible progress in power conversion efficiency (PCE) from 3.8% to 25.2% in the past decade. With the requirement of commercial applications, the sta...

Non-fullerene acceptors with fused-ring structures have rapidly improved the performance of organic solar cells over the past five years, but they still suffer from synthetic complexity and thus high material costs, one of the major obstacles of hindering their commercialization process. The construction of non-fused ring acceptors (NFRAs) has recently been regarded as a feasible solution due to their facile synthesis and satisfactory device performances. Thus in this concept, we highlight the important progress of NFRAs in recent years, and discuss the key relationship between molecular design strategies and device performance. Finally, we provide some potential molecular insights for the future design of high-performance NFRAs.

Cyanines have been widely used as the photosensitizers (PSs) in the biomedical field, but controlling their molecular aggregates in nanoparticles (NPs) remains a major challenge. Moreover, the impact of aggregate behaviors of cyanines on the photosensitization is still unclear. Herein, the first anionic cyanine PSs based on a tricyanofuran end group have been designed by achieving supramolecular J-type aggregates in NPs via counterion engineering. Our results indicate that J-type aggregates in NPs can not only bring significantly red-shifted emission, negatively charged surface, and high photostability, but also enable a significant 5-fold increase in singlet oxygen generation efficiency compared to that in the nonaggregate state, providing strong experimental evidence for the superiority of J-aggregates in enhancing photosensitization. Thus, combined with the mitochondria-targeting ability, the J-type aggregate NPs show remarkable in vivo antitumor phototheranostic efficacy, making them have a potential for clinical use.

Dendronized hyperbranched polymers (DHPs) can provide advantages for both hyperbranched polymers and dendrimers, making them a promising structure platform for high-performance second-order nonlinear optical (NLO) materials. Herein, a new A

Two challenges remain for organic thermoresponsive materials; one is to develop high-performance red-emissive thermoresponsive materials, while another is to simultaneously achieve high contrast ratio (CR), fast and reversible thermoresponse in a single element. Herein, we not only develop a new deep-red emissive squaraine-based AIEgen (TPE-SQ12) based on a pyrylium end group, which is suitable for fabricating high-performance thermoresponsive materials, but also show an effective approach to improve both CR (∼ten times increase) and response time (less than 3 seconds), that is, molecularly dispersing AIEgen into an elastomer, attributed to the significantly expanded free volume of elastomer upon increasing the temperature that can activate the AIEgen intramolecular movements more pronouncedly. Double encryption and temperature mapping systems have been separately established by using our designed elastomer/TPE-SQ12 film, showing the great potential for anti-counterfeiting and temperature sensing. Finally, white emission is further achieved by co-doping TPE-SQ12 with cyan dye into elastomer, which enables fluorescent thermochromism for improving the temperature mapping ability.

Currently, the two exocyclic vinyl bridges in the acceptor–donor–acceptor (A–D–A)-type nonfullerene acceptors (NFAs) have been widely recognized as one of the most vulnerable sites under external stresses. Embedding the exocyclic vinyl bridges into an aromatic ring could be a feasible solution to stabilize them. Herein, we successfully develop a phenalene-locked vinyl bridge via a titanium tetrachloride—pyridine catalytic Knoevenagel condensation, to synthesize two new A–D–A-type unfused NFAs, EH-FPCN and O-CPCN, wherein malononitrile is used as the electron-deficient terminal group while fluorene and carbazole rings are used as the electron-rich cores, respectively. These two NFAs possess wide bandgaps associated with deep energy levels, and significantly enhanced chemical and photochemical stabilities compared to the analogue molecule O-CzCN with normal exocyclic vinyl bridges. When pairing with a narrow bandgap polymer donor PTB7-Th, the fabricated EH-FPCN- and O-CPCN-based organic solar cells achieved power conversion efficiencies of 0.91 and 1.62%, respectively. The higher efficiencies for O-CPCN is attributed to its better film morphology and higher electron mobility in the blend film. Overall, this work provides a new design strategy to stabilize the vulnerable vinyl bridges of A–D–A-type NFAs.

For organic semiconductors, the development of electron-deficient building blocks has lagged far behind that of the electron-rich ones. Moreover, it remains a significant challenge to design organic molecules with efficient charge transport and strong solid-state emission simultaneously. Herein, we describe a facile synthetic route toward a new π-acceptor imide building block, namely 2,3-fluoranthene imide, based on which four regioregular small molecules (F1-F4) are synthesized by tuning the imide orientations and the central linkage bridges. All molecules exhibit attractive aggregation-induced emission (AIE) characteristics with strong far-red emission in the powder state, and F3 shows the highest photoluminescence quantum yield of 5.9%. F1 and F3 with a thiophene bridge present an obvious p-type characteristic, while for F3 with an outward imide orientation, the maximum hole mobility from a solution-processed field-effect transistor (FET) device reaches 0.026 cm

The interface and crystallinity of perovskite films play a decisive role in determining the device performance, which is significantly influenced by the bottom hole-transporting material (HTM) of inverted perovskite solar cells (PVSCs). Herein, this work reports a simple design strategy of polymer HTMs, which can modulate the wettability and promote the anchoring by introducing pyridine units into the polyarylamine backbone, so as to realize efficient and stable inverted PVSCs. The HTM properties can be effectively modified by varying the linkage sites of pyridine units, and 3,5-linked PTAA-P1 particularly demonstrates a more regulated molecular configuration for interacting with perovskites, leading to highly crystalline perovskite films with uniform back contact and reduced defect density. Dopant-free PTAA-P1-based inverted PVSCs have realized remarkable efficiencies of 24.89% (certified value: 24.50%) for small-area (0.08 cm

Patterning multiple images within a single element without crosstalk can significantly increase the information capacity and security, but it is challenging to enable the response capability in each image. Now, the patterning of crosstalk-free yet cooperative-thermoresponse images (holographic and fluorescent images) is successfully achieved by designing a liquid crystal (LC)/AIEgen system with a unique synergy. The AIEgen's fluorescence intensity is controlled by the LC, while the LC's phase transition is in turn promoted by the AIEgen. The fluorescent image contrast is significantly boosted by efficient energy transfer (ΦET : 96 %) from the LC to the AIEgen. The AIEgen's photocyclization for fluorescent patterning occurs in a zero-order kinetic manner and can be completed within several minutes when assisted by the LC. The photocyclization conversion is quantitatively dependent on the aggregation size: α∼exp(-d), and able to reach as high as 98 %.

Organic nonlinear optical (NLO) materials are very important for high-speed information processing in addressing the challenges of reduced energy consumption and enhanced speed and bandwidth. In particular, organic second-order NLO materials are very promising for meeting the combined requirements of ultra-low energy and ultra-high bandwidth in electro-optic (EO) modulation, while organic third-order NLO materials have good potential for applications in ultra-speed all-optical signal processing (AOSP). This review highlights the recent significant progress made in organic second- and third-order NLO materials. For second-order NLO materials, the recent advances in the efficient and cost-effective synthesis of dipolar polyene chromophores and thin-film engineering for efficient electric field poling are summarized. The applications and prospects of these high-performance EO materials are also discussed. For third-order NLO materials, we discuss the molecular design strategies of cyanine dyes for AOSP applications, particularly focusing on anionic tricyanofuran (TCF)-based cyanines. We aim to provide a better understanding of the structure–property relationships for cyanine-based AOSP materials. Finally, a summary and outlook for advancing high-performance organic NLO materials are provided.

So far, second-order nonlinear optical (NLO) hyperbranched polymers have been widely reported; however, introduction of highly polarizable NLO chromophores into them remains a challenge. In this work, we have successfully prepared a tetracyanobutadienyl (TCBD)-based AB2-type hyperbranched polymer HP3 by integrating double click-type postfunctionalization reactions including Cu(I)-catalyzed Huisgen's 1,3-dipolar cycloaddition and alkyne-TCNE [2 + 2] cycloaddition. The NLO property of HP3 was carefully studied based on the second-harmonic generation (SHG) measurement, showing a SHG coefficient of 55.6 pm V−1 and good alignment stability with a depoling temperature of 125 °C.

Herein, a new electropolymerized (EP) film named poly-triphenylcarbazole fluoranthene (p-TPCF) has been in situ synthesized by an electrochemical cyclic voltammetry method and applied to tune the work-function (WF) of the PEDOT:PSS hole-transporting layer (HTL) in organic solar cells (OSCs). Multiple techniques, including Kelvin probe force microscopy (KPFM), light intensity dependent solar cell characterization, Mott–Schottky analysis, and transient photovoltage (TPV) and transient photocurrent (TPC) measurements, have been explored to provide insights into the mechanism. Benefiting from the deeper work-function (WF), larger built-in voltage (Vbi), decreased recombination, and longer carrier lifetime, the devices with EP films exhibited superior device performance with simultaneously enhanced Voc, Jsc and FF.

In this work, three new squaraine-based aggregation induced emission luminogens (AIEgens), TPE-SQ1–3, have been successfully developed with different functions by using TPE-functionalized diarylamine derivatives as the critical end-capping subunits. In particular, the powders of symmetric TPE-SQ1 and TPE-SQ2 exhibit reversible mechanochromic (MC) characteristics with a clear emission color change from yellow to orange-red, due to the morphology change from the loose crystalline state to the tight amorphous state. Differently, using indolenine as another end-capping subunit, the resulting asymmetric TPE-SQ3 can exhibit intense far-red solid state emission, but does not show any mechanochromic characteristics, attributed to its amorphous nature in the pristine state. However, it can encouragingly serve as a reaction-based fluorescent probe to detect hypochlorite sensitively and selectively, and the detection limit is as low as 105 nM. The sensing mechanism is based on the oxidation cleavage of electron-deficient CC double bonds connecting to the indolenine side. Furthermore, amphiphilic polymer encapsulated TPE-SQ3 nanoparticles have further proven to be good live-cell imaging agents, providing bright intracellular far-red fluorescence with high photostability. Thus, our work has shown that integrating AIE characteristics into squaraines is an efficient design strategy to afford new functional materials for optoelectric and biological applications.

Development of high-performance dopant-free hole-transporting materials (HTMs) with comprehensive passivation effects is highly desirable for all-inorganic perovskite solar cells (PVSCs). Squaraines (SQs) could be a candidate for dopant-free HTMs as they are natural passivators for perovskites. One major limitation of SQs is their relatively low hole mobility. Herein we demonstrate that polymerizing SQs into pseudo two dimensional (2D) p-π conjugated polymers could overcome this problem. By rationally using N,N-diarylanilinosquaraines as the comonomers, the resulting polysquaraine HTMs not only exhibit suitable energy levels and efficient passivation effects, but also achieve very high hole mobility close to 0.01 cm-2 V-1 s-1 . Thus as dopant-free HTMs for α-CsPbI2 Br-based all-inorganic PVSCs, the best PCE reached is 15.5 %, outperforming those of the doped-Spiro-OMeTAD (14.4 %) based control devices and among the best for all-inorganic PVSCs.

Significant progress on the development of non-fullerene acceptors (NFAs) for organic solar cells (OSCs) has been made in the past several years, and the power conversion efficiency (PCE) exceeding 17% has been already realized based on a tandem non-fullerene device. To date, NFAs with a linearly fused acceptor-donor-acceptor (A-D-A) structure are of great interest, due to their attracting synthetic flexibility and high photovoltaic performance. Rhodanine is one of the most studied electron-withdrawing moieties to construct such A-D-A type NFAs, and the resulting single-junction OSCs have produced PCEs of ~10%. More interestingly, those rhodanine-based NFAs have demonstrated a particularly excellent compatibility with well-known P3HT donor, enabling respectable PCEs over 7%. Thus in this review, we summarize the important advances on rhodanine-based NFAs with a main focus on discussing the molecular design strategies, providing a better understanding of the structure-property relationship for those rhodanine-based NFAs.

Photopolymerization-based three-dimensional (3D) printing can enable customized manufacturing that is difficult to achieve through other traditional means. Nevertheless, it remains challenging to achieve efficient 3D printing due to the compromise between print speed and resolution. Herein, we report an efficient 3D printing approach based on the photooxidation of ketocoumarin that functions as the photosensitizer during photopolymerization, which can simultaneously deliver high print speed (5.1 cm h−1) and high print resolution (23 μm) on a common 3D printer. Mechanistically, the initiating radical and deethylated ketocoumarin are both generated upon visible light exposure, with the former giving rise to rapid photopolymerization and high print speed while the latter ensuring high print resolution by confining the light penetration. By comparison, the printed feature is hard to identify when the ketocoumarin encounters photoreduction due to the increased lateral photopolymerization. The proposed approach here provides a viable solution towards efficient additive manufacturing by controlling the photoreaction of photosensitizers during photopolymerization., 3D printing enables customized manufacturing that is difficult to achieve through traditional material processing but 3D printing with high resolution and high speed is challenging to realize. Here, the authors demonstrate that photooxidation of a ketocoumarin photosensitizer can simultaneously deliver high print speed and high print resolution on a common 3D printer.

The development of wide-bandgap polymer donors having complementary absorption and compatible energy levels with near-infrared (NIR) absorbing nonfullerene acceptors is highly important for realizing high-performance organic solar cells (OSCs). Herein, a new thiophene-fused diazabenzo[k]fluoranthene derivative is successfully synthesized as the electron-deficient unit to construct an efficient donor-acceptor (D-A) type alternating copolymer donor, namely, PABF-Cl, using the chlorinated benzo[1,2-b:4,5-b']dithiophene as the copolymerization unit. PABF-Cl exhibits a wide optical bandgap of 1.93 eV, a deep highest occupied molecular level of -5.36 eV, and efficient hole transport. As a result, OSCs with the best power conversion efficiency of 11.8% are successfully obtained by using PABF-Cl as the donor to blend with a NIR absorbing BTP-eC9 acceptor. This work provides a new design of electron-deficient unit for constructing high-performance D-A type polymer donors.

In this paper, we synthesized a new class of thiopyranylidene-based NIR absorbing asymmetrical squaraines (IPSQ 1–4), and carefully investigated their photophysical, thermal, electrochemical and semiconducting properties. A high hole mobility close to 10−4 cm2/Vs can be realized for IPSQ-3 based organic field effect transistors (OFETs), attributed to the strong intermolecular π-π interactions induced by pyranylidene-type end-groups with large π-system. More interestingly, we find through subtle structural variation, totally different molecular arrangements, herringbone and “brick-wall” -type, can be achieved for IPSQ-1 and -4, respectively, which therefore enables us to study the influence of molecular packing structure on semiconducting properties. For IPSQ-1, the hole mobility was found to be ∼50 times that of IPSQ-4, indicating herringbone-type arrangement is more beneficial to charge carrier transport here. Furthermore, IPSQ-1 also showed a better photovoltaic performance than IPSQ-4. Thus, our findings in this work can help us to understand the implications of tuning structural properties of squaraines, which will be very useful for designing high-performance squaraine-based semiconductors.

Continuous success has been achieved for solution-processed inorganic-organic hybrid perovskite solar cells (PVSCs) in the past several years, in which organic charge transporting materials play an important role. At present, most of the commonly used hole-transporting materials (HTMs) such as spiro-OMeTAD derivatives for PVSCs require additional chemical doping process to ensure sufficient conductivity and shift the Fermi level towards the HOMO level for efficient hole transport and collection. However, this doping process not only increases the complexity and cost of device fabrication, but also decreases the device stability. Thus development of efficient dopant-free HTMs for PVSCs is highly desirable and remains as a major challenge in this field. In this review, we will summarize the recent advances in the molecular design of dopant-free HTMs for PVSCs.

Squaraines have been demonstrated as one class of effective low-bandgap donor materials in bulk-heterojunction organic solar cells (BHJ-OSCs). However, they often suffer from low hole mobility, thereby limiting their photovoltaic performance. Herein, we designed and synthesized three new butterfly-shaped dimeric squaraines (DSQ1–3) with an extended π-conjugated system for BHJ-OSCs. Our results reveal that the modification of connecting bridges between two asymmetric dyes has a minimal effect on their absorption, energy levels and charge transport properties, however, subtle side chain modifications can efficiently improve the charge transport ability in the BHJ films due to enhanced miscibility with fullerene acceptors. By simply replacing the hexyl chains in the fluorene core of DSQ1 by branched 2-ethylhexyl chains, the resulting DSQ3 could possess a hole mobility of 1.10 × 10−4 cm2 V−1 s−1, providing an ∼6 times enhancement of that of DSQ1. Thus, as donor materials in single-junction BHJ-OSCs, DSQ3 afforded a power conversion efficiency (PCE) of 4.02%, while that of DSQ1 was only 2.26%. Moreover, the 2-hexyldecyl substituted carbazole cored DSQ2 showed slightly higher hole mobility than DSQ3, and thus generated the highest PCE of 4.38% among the three dimers. Our work strengthens the importance of side chain engineering for designing high-performance squaraine-based donor materials, even for those already having a large π-conjugated system.

Two novel second order nonlinear optical (NLO) chromophores based on N,N-diethylaniline as a donor, verbenone based tetraene as a bridge, and tricyanofuran (TCF) or tricyanofuran derivatives with a dendritic moiety as an acceptor have been synthesized in good overall yields and systematically characterized. Besides, a facile applicable synthetic approach for a NLO dendritic acceptor was developed. Compared with C7, after introducing dendritic derivative steric hindrance groups into the acceptor, chromophore C8 had good thermal stabilities with high thermal decomposition temperatures which were 33 °C higher than that of chromophore C7. At the same time, cyclic voltammetry (CV) experiments were performed to determine the different redox properties. The conjugated verbenone tetraene segments in two chromophores could significantly improve the glass-forming ability and molecular polarization of chromophores as revealed by UV-vis-NIR absorption measurements. The bulky dendritic moiety linked by a short C–C bond is closer to the TCF acceptor, which is the most polar part in the chromophore, compared to conventional isolation groups. The results obtained from electro-optic (EO) coefficients indicate that this TCF acceptor with a unique dendritic structure can prevent antiparallel packing between chromophores, improving the poling efficiency and enhancing the EO performance. These properties, together with the good solubility, suggest the potential use of these new chromophores as materials for advanced photonic devices.

Summary Despite the demonstrated high power conversion efficiency (PCE) of perovskite solar cells (PVSC), long-term stability of the device operated in humid environments under photo- and thermal stresses is still a serious concern prior to any commercialization. To provide possible solutions to overcome this hurdle, we have synthesized an n-type conjugated molecule, c -HATNA, that can be crosslinked as an electron-transporting layer (ETL) on top of the desired perovskites. By proper doping to increase its electron-transporting property, a high PCE of 18.21% can be obtained with respectable moisture and thermal stability without encapsulation. Moreover, this c -HATNA ETL can be used in conjunction with another crosslinkable hole-transporting layer, c -TCTA-BVP, to fabricate all-crosslinked charge-transporting layers (CTLs) for PVSCs and achieve 16.08% and 13.42% PCEs on rigid and flexible substrates, respectively. More importantly, the device with all-crosslinked CTLs showed impressive thermal stability in ambient environment: almost 70% of its initial PCE after being heated at 70°C for 300 hr.

Significant efforts have been devoted to developing new dopant-free hole transporting materials (HTMs) for perovskite solar cells (PVSCs). Fluoranthene is one typical cyclopentene-fused polycyclic aromatic hydrocarbon with a rigid planarized structure, and thus could be an ideal building block to construct dopant-free HTMs, which have not been reported yet. Here, we report a new and simple synthetic method to prepare unreported 2,3-dicyano-fluoranthene through a Diels-Alder reaction between dibenzofulvene and tetracyanoethylene, and demonstrate that it can serve as an efficient electron-withdrawing unit for constructing donor-acceptor (D-A) type HTMs. This novel building block not only endows the resulting molecules with suitable energy levels, but also enables highly ordered and strong molecular packing in solid states, both of which could facilitate hole extraction and transport. Thus with dopant-free HTMs, impressive efficiencies of 18.03% and 17.01% which are associated with enhanced stability can be achieved based on conventional n-i-p and inverted p-i-n PVSCs respectively, outperforming most organic dopant-free HTMs reported so far.

In this paper, an efficient p-type polymer semiconductor (PASQ-IDT) is first developed by integrating a two-dimensional (2D) structure concept into the design of squaraine-based π-conjugated polymers, and it shows multiple applications in both bulk-heterojunction polymer solar cells (BHJ-PSCs) and perovskite solar cells (PVSCs) with high performance. As the polymer-donor blended with a fullerene acceptor, PASQ-IDT can endow the derived additive-free single-junction PSCs and semi-transparent PSCs with impressive efficiencies of 6.35% and 4.03%, respectively, both of which are the highest values reported for polysquaraines. More encouragingly, PASQ-IDT not only exhibits good hole extraction/transport ability, but also shows very good surface wettability to the perovskite precursor solution to enable the growth of perovskites with high film quality, making it suitable as an efficient hole transporting material (HTM) for inverted PVSCs. Thus, a very promising efficiency of 18.29% with negligible hysteresis and good device stability can be delivered by PASQ-IDT-based inverted PVSCs in the absence of dopants, outperforming the PEDOT:PSS-based control devices (16.14%) and most dopant-free HTMs reported so far.

Squaraines (SQs) have been demonstrated as one of potential low-cost donor materials for organic solar cells (OSCs), for which the performances however are limited by low open circuit voltage (VOC). Herein, we show a new molecular design strategy that can achieve SQ-based OSCs with high Vocs exceeding 1.0 V by constructing butterfly-shaped SQ dimers. Through using branched-alkyl substituted carbazole as the bridge unit and fluorinated indole derivatives as the end-groups, the resulting dimers DSQ4-5 show deep-lying HOMO levels, enhanced photostability, high hole mobility and good compatibility with fullerene acceptors. Impressively, the resulting device VOCs for both dimers can reach 1.0 V through blending with PC71BM acceptor, together with rather low energy losses (Elosss) of ~0.6 eV, outperforming most of SQ-based donors reported so far. In addition, we found that the processing solvents have a pronounced effect on the blend film morphology and the device performance, while DSQ4-based devices processed by chlorobenzene can deliver the best efficiency of ~3%.

In this work, a new phosphonium-containing cationic polyelectrolyte (PE1) has been rationally designed and developed via a facile click-chemistry type postfunctionalization, which can form complexe...