Halogenated 9H-Indeno[1,2-b]Pyrazine-2,3-Dicarbonitrile End Groups Based Asymmetric Non-Fullerene Acceptors for Green Solvent-Processable, Additive-Free, and Stable Organic Solar Cells.

Non-fullerene acceptors (NFAs) significantly enhance photovoltaic performance in organic solar cells (OSCs) using halogenated solvents and additives. However, these solvents are environmentally detrimental and unsuitable for industrial-scale production, and the issue of OSCs' poor long-term stability persists. This report introduces eight asymmetric NFAs (IPCnF-BBO-IC2F, IPCnF-BBO-IC2Cl, IPCnCl-BBO-IC2F, and IPCnCl-BBO-IC2Cl, where n = 1 and 2). These NFAs comprise a 12,13-bis(2-butyloctyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo[3,4-e]thieno[2'',3'':4',5']thieno[2',3':4,5]pyrrolo[3,2-g]thieno[2',3':4,5]thieno-[3,2-b]indole (BBO) core. One end of the core attaches to a mono- or di-halogenated 9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile (IPC) end group (IPC1F, IPC1Cl, IPC2F, or IPC2Cl), while the other end connects to a 2-(5,6-dihalo-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC) end group (IC2F or IC2Cl). The optical and electronic properties of these NFAs can be finely tuned by controlling the number of halogen atoms. Crucially, these NFAs demonstrate excellent compatibility with PM6 even in o-xylene, facilitating the production of additive-free OSCs. The di-halogenated IPC-based NFAs outperform their mono-halogenated counterparts in photovoltaic performance within OSCs. Remarkably, the di-halogenated IPC-based NFAs maintain 94‒98% of their initial PCEs over 2000 h in air without encapsulation, indicating superior long-term device stability. These findings imply that the integration of di-halogenated IPCs in asymmetric NFA design offers a promising route to efficient, stable OSCs manufactured through environmentally friendly processes.

Alkyl Chain Engineering of Low Bandgap Non-Fullerene Acceptors for High-Performance Organic Solar Cells: Branched vs. Linear Alkyl Side Chains.

In this work, we report the synthesis and photovoltaic properties of IEBICO-4F, IEHICO-4F, IOICO-4F, and IDICO-4F non-fullerene acceptors (NFAs) bearing different types of alkyl chains (2-ehtylhexyl (EH), 2-ethylbutyl (EB), n-octyl (O), and n-decyl (D), respectively). These NFAs are based on the central indacenodithiophene (IDT) donor core and the same terminal group of 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC-2F), albeit with different side chains appended to the thiophene bridge unit. Although the side chains induced negligible differences between the NFAs in terms of optical band gaps and molecular energy levels, they did lead to changes in their melting points and crystallinity. The NFAs with branched alkyl chains exhibited weaker intermolecular interactions and crystallinity than those with linear alkyl chains. Organic solar cells (OSCs) were fabricated by blending these NFAs with the p-type polymer PTB7-Th. The NFAs with appended branched alkyl chains (IEHICO-4F and IEBICO-4F) possessed superior photovoltaic properties than those with appended linear alkyl chains (IOICO-4F and IDICO-4F). This result can be ascribed mainly to the thin-film morphology. Furthermore, the NFA-based blend films with appended branched alkyl chains exhibited the optimal degree of aggregation and miscibility, whereas the NFA-based blend films with appended linear alkyl chains exhibited higher levels of self-aggregation and lower miscibility between the NFA molecule and the PTB7-Th polymer. We demonstrate that changing the alkyl chain on the π-bridging unit in fused-ring-based NFAs is an effective strategy for improving their photovoltaic performance in bulk heterojunction-type OSCs.

Impact of symmetry-breaking of non-fullerene acceptors for efficient and stable organic solar cells.

The concurrent enhancement of short-circuit current (J SC) and open-circuit voltage (V OC) is a key problem in the preparation of efficient organic solar cells (OSCs). In this paper, we report efficient and stable OSCs based on an asymmetric non-fullerene acceptor (NFA) IPC-BEH-IC2F. The NFA consists of a weak electron-donor core dithienothiophen[3,2-b]-pyrrolobenzothiadiazole (BEH) and two kinds of strong electron-acceptor (A) units [9H-indeno[1,2-b]pyrazine-2,3-dicarbonitrile (IPC) with a tricyclic fused system and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC2F)]. For comparison, the symmetric NFAs IPC-BEH-IPC and IC2F-BEH-IC2F were characterised. The kind of flanking A unit significantly affects the light absorption features and electronic structures of the NFAs. The asymmetric IPC-BEH-IC2F has the highest extinction coefficient among the three NFAs owing to its strong dipole moment and highly crystalline feature. Its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels lie between those of the IPC-BEH-IPC and IC2F-BEH-IC2F molecules. The IPC group also promotes molecular packing through the tricyclic π-conjugated system and achieves increased crystallinity compared to that of the IC2F group. Inverted-type photovoltaic devices based on p-type polymer:NFA blends with PBDB-T and PM6 polymers as p-type polymers were fabricated. Among all these devices, the PBDB-T:IPC-BEH-IC2F blend device displayed the best photovoltaic properties because the IPC unit provides balanced electronic and morphological characteristics. More importantly, the PBDB-T:IPC-BEH-IC2F-based device exhibited the best long-term stability owing to the strongly interacting IPC moiety and the densely packed PBDB-T:IPC-BEH-IC2F film. These results demonstrate that asymmetric structural modifications of NFAs are an effective way for simultaneously improving the photovoltaic performance and stability of OSCs.

Stimuli-Responsive Trimorphs and Charge-Transfer Complexes of a Twisted Molecular Donor.

Supramolecular self-assemblies and co-assemblies possess multiple noncovalent interactions, highly ordered structures, and multifunctional properties. Yet, the fundamental understanding of their "structure-property relationship" remains very challenging. Herein, two kinetically controlled supramolecular charge transfer (CT) complexes were conceptualized from a trimorphic molecular donor denoted as "twisted aromatic hydrocarbon" (TAH), with p-fluoranil (TFQ) and p-chloranil (TCQ) in water, organic solvent, and solvent-free methods. Elucidating their co-assembling mechanism revealed that segmentation of the TAH with molecules having planar deficient cores spontaneously formed a distinct "H-type mixed stack" and "J-type segregated stack", regulated by blue/red-shifted charge-transfer and π-π stacking including weak C-H···F and C-H···O noncovalent interactions. By utilizing the structural transformational ability of the self-assembled TAH, the mechanistic aspects for the rapid nanoscopic co-assembly formation were precisely demonstrated experimentally and theoretically. The trimorphs and co-crystals of TAH could be disassembled resulting in turn-on emission by applying various external stimuli and being repeatedly reconfigured, thus providing a unique structure-property relationship and new TAH-based materials. This unique concept offers color-specific polymorphism and CT-complex formation strategy involving a simple class of functional materials having cooperative network forming ability using the twisted molecular donor.

White light emitting diode based on purely organic fluorescent to modern thermally activated delayed fluorescence (TADF) and perovskite materials.

White organic/polymer light emitting diode (WOLED/WPLED) processed from solution has attracted significant research interest in recent years due to their low device production cost, device flexibility, easy fabrication over large area including roll to roll and ability to print in various designs and shapes providing enormous design possibilities. Although WOLEDs fabricated using solution process lack their thermally evaporated counterparts in terms of device efficiency, remarkable progress has been made in this regard in recent years by utilizing new materials and device structures. In the present review, we have summarized and extrapolated an excellent association of old and modern concept of cost-effective materials and device structure for realization of white light. In particular, this article demonstrated and focused on design, and development of novel synthesis strategy, mechanistic insights and device engineering for solution process low cost WOLEDs device. Herein, an overview of the prevailing routes towards white light emitting devices (WLEDs) and corresponding materials used, including polymer based WLED, small molecules emitters based thermally activated delayed fluorescence (TADF), perovskite light-emitting diodes (PeLEDs) and hybrid materials based LEDs, color down-converting coatings with corresponding best efficiencies ever realized. We presume that this exhaustive review on WLEDs will offer a broad overview of the latest developments on white SSL and stonework the approach en route for innovations in the immediate future.

Receptor-Free Detection of Picric Acid: A New Structural Approach for Designing Aggregation-Induced Emission Probes.

A pristine aggregation-induced enhanced emission (AIEE) active monomer 2,5-bis(( E)-4-bromostyryl)-3,4-diphenylthiophene (TPBZ) and its copolymer (PFTPBZ) with 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propandiol) ester have been synthesized via Suzuki coupling polymerization. PFTPBZ that is devoid of any receptor showed AIEE property and demonstrated excellent and selective fluorometric recognition of 2,4,6-trinitrotoluene (TNT) in aggregated state (aqueous medium) and picric acid (PA) in aggregated state and solution state (organic solvent) as well as in vapor phase via PFTPBZ dip-coated Whatman filter paper on a solid-phase platform in 1.86 ng level (naked eye). Limit of detection (LOD) for TNT in 95% water fraction ( fw) was 53.74 × 10-6 M, and at 40% fw, it was 14.26 × 10-7 M. PA detection in tetrahydrofuran solution was possible with a LOD of 28.16 × 10-7 M, 95% fw with LOD of 10.47 × 10-6 M, and in 40% fw with LOD of 47.39 × 10-8 M. As a unique example of structural design, the probe PFTPBZ surprisingly possesses no receptor, yet remarkably high selectivity was achieved via Förster resonance energy transfer (FRET) and photoinduced electron transfer from the copolymer PFTPBZ to PA and TNT. Detection of PA in the presence of various metal analytes and inorganic acids in real water samples (lakes, rivers, and sea water) was also demonstrated using this concept of receptor-free conjugated polymer probe.

Functional 1,8-Naphthalimide AIE/AIEEgens: Recent Advances and Prospects.

This comprehensive review surveys the up-to-date development of aggregation-induced emission/aggregation-induced emission enhancement (AIE/AIEE) active naphthalimide (NI)-based smart materials with potential for wide and real-world applications and that serves as a highly versatile building block with tunable absorption and emission in the complete visible region. The review article commences with a precise description of the importance of NI moiety and its several restricted area of applications owing to its aggregation caused quenching (ACQ) properties, followed by the discovery and importance of AIE/AIEE-active NIs. The introduction section tracked an overview of the state of the art in NI luminogens in multiple applications. It also includes a few mechanistic studies on the structure-property correlation of NIs and provides more insights into the condensed-state photophysical properties of small aggregation-prone systems. The review aims to ultimately accomplish current and forthcoming views comprising the use of the NIs for the detection of biologically active molecules, such as amino acids and proteins, recognition of toxic analytes, fabrication of light emitting diodes, and their potential in therapeutics and diagnostics.

White polymer light emitting diodes based on PVK: the effect of the electron injection barrier on transport properties, electroluminescence and controlling the electroplex formation.

The effects of the electron injection barrier on the charge transport, brightness and the electroluminescence (EL) properties of polymer light emitting diodes (PLEDs) with poly(9-vinylcarbazole) (PVK) as an emissive layer have been studied. By using Al and LiF/Al as the cathode in single layer PLEDs and diverse electron transporting layers (ETLs) such as 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 4,7-diphenyl-1,10-phenanthroline (BPhen) and 2,2',2''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) in the case of multilayer PLEDs, the charge transport, brightness, color tuning and the EL properties of the devices were drastically modified. The energy barrier for electrons affects the electron current flowing through the device, thereby affecting the operating voltage and the brightness of the PLEDs. The PLEDs with TPBi as the ETL possess the lowest injection barrier and give the maximum brightness of 426.24 cd m-2. The electron injection barrier is also found to play a major role in defining the EL spectra of the PLEDs. A larger injection barrier gives rise to electroplex formation in the EML-ETL interface of the PLEDs and an additional peak at ∼605 nm was observed in the EL spectrum. As a result, a near white emission with CIE coordinates of (0.30, 0.30) and (0.25, 0.23) at 20 V was obtained from devices with BCP and BPhen as ETLs. Furthermore, PVK doped with 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) at 10, 20 and 30 wt% ratios modified the electron transport nature of PVK and had a remarkable influence on the aforesaid properties, especially on the electroplex formation.

Efficient blue and white polymer light emitting diodes based on a well charge balanced, core modified polyfluorene derivative.

Fabrication of efficient blue and white polymer light-emitting diodes (PLEDs) using a well charge balanced, core modified polyfluorene derivative, poly[2,7-(9,9'-dioctylfluorene)-co-N-phenyl-1,8-naphthalimide (99:01)] (PFONPN01), is presented. The excellent film forming properties as observed from the morphological study and the enhanced electron transport properties due to the inclusion of the NPN unit in the PFO main chain resulted in improved device properties. Bright blue light was observed from single layer PLEDs with PFONPN01 as an emissive layer (EML) as well as from double layer PLEDs using tris-(8-hydroxyquinoline) aluminum (Alq3) as an electron transporting layer (ETL) and LiF/Al as a cathode. The effect of ETL thickness on the device performance was studied by varying the Alq3 thickness (5 nm, 10 nm and 20 nm) and the device with an ETL thickness of 20 nm was found to exhibit the maximum brightness value of 11 662 cd m(-2) with a maximum luminous efficiency of 4.87 cd A(-1). Further, by using this highly electroluminescent blue PFONPN01 as a host and a narrow band gap, yellow emitting small molecule, dithiophene benzothiadiazole (DBT), as a guest at three different concentrations (0.2%, 0.4% and 0.6%), WPLEDs with the ITO/PEDOT:PSS/emissive layer/Alq3(20 nm)/LiF/Al configuration were fabricated and maximum brightness values of 8025 cd m(-2), 9565 cd m(-2) and 10 180 cd m(-2) were achieved respectively. 0.4% DBT in PFONPN01 was found to give white light with Commission International de l'Echairage (CIE) coordinates of (0.31, 0.38), a maximum luminous efficiency of 6.54 cd A(-1) and a color-rendering index (CRI) value of 70.