All-Small-Molecule Solar Cells Incorporating NDI-Based Acceptors: Synthesis and Full Characterization

Amplifying the photovoltaic properties of tetrathiafulvalenes based materials by incorporation of small acceptors: a density functional theory approach

Currently, polycyclic aromatic compounds in organic solar cells (OSCs) have gained substantial consideration in research communities due to their promising characteristics. Herein, polycyclic aromatic hydrocarbons (PAHs) core-based chromophores (TTFD1-TTFD6) were designed by structural modifications of peripheral acceptor groups into TTFR. The density functional theory (DFT) and time dependent density functional theory (TD-DFT) calculations were carried out at B3LYP/6-311G (d, p) functional to explore insights for their structural, electronic, and photonic characteristics. The structural modulation unveiled notable electronic impact on the HOMO and LUMO levels across all derivatives, leading to decreased band gaps. All the designed compounds exhibited band gap ranging from 2.246 to 1.957 eV, along with wide absorption spectra of 897.071-492.274 nm. An elevated exciton dissociation rate was observed due to the lower binding energy values (Eb = 0.381 to 0.365 eV) calculated in the derivatives compared to the reference (Eb = 0.394 eV). Furthermore, data from the transition density matrix (TDM) and density of states (DOS) also corroborated the effective charge transfer process. Comparable results of Voc for reference and designed chromophores were obtained via HOMOdonor-LUMOPC71BM. The declining Voc order values was noted as TTFD5 > TTFD6 > TTFD4 > TTFD3 > TTFD2 > TTFD1 > TTFR. Interestingly, TTFD5 was found with the smallest energy gap and highest absorption value, resulting in better charge transference among all the derivatives. The results illustrated that the modification in indenofluorene based chromophores with end-capped small acceptors proved to be a significant approach in achieving favorable photovoltaic properties.

Naphthalene diimide-Annulated Heterocyclic Acenes: Synthesis, Electrochemical and Semiconductor Properties and their Multifaceted Applications

Acenes and Naphthalene Diimides (NDIs) stand as distinguished classes of organic compounds, each possessing unique and intriguing properties that have garnered significant attention across various scientific disciplines. Acenes, characterized by linearly fused aromatic rings, have captivated researchers due to their diverse electronic structures and promising applications in materials science. On the other hand, NDIs, known for their distinctive electron-accepting properties, exhibit remarkable versatility in fields ranging from organic electronics, supramolecular to spin chemistry. In this review, we navigate through the fascinating realms of both acenes and NDIs before converging our focus on the highly diverse and distinctive subgroup of NDI-annulated heterocyclic acenes. This potentially important subgroup, has emerged as a subject of intense investigation, encapsulating their fascinating synthesis, optical and electrochemical characteristics, and multifaceted applications that span the realms of chemistry, physics, and biology. Through the exploration of their synthetic strategies, unique properties, and diverse applications, this review aims to offer a comprehensive understanding of the pivotal role played by NDI-based heterocyclic acenes in contemporary multidisciplinary research and technological innovation.

Solvent‐Free Synthesis of Core‐Functionalised Naphthalene Diimides by Using a Vibratory Ball Mill: Suzuki, Sonogashira and Buchwald–Hartwig Reactions

Solvent‐free synthesis by using a vibratory ball mill (VBM) offers the chance to access new chemical reactivity, whilst reducing solvent waste and minimising reaction times. Herein, we report the core functionalisation of N,N’‐bis(2‐ethylhexyl)‐2,6‐dibromo‐1,4,5,8‐naphthalenetetracarboxylic acid (Br₂‐NDI) by using Suzuki, Sonogashira and Buchwald–Hartwig coupling reactions. The products of these reactions are important building blocks in many areas of organic electronics including organic light‐emitting diodes (OLEDs), organic field‐effect transistors (OFETs) and organic photovoltaic cells (OPVCs). The reactions proceed in as little as 1 h, use commercially available palladium sources (frequently Pd(OAc)₂) and are tolerant to air and atmospheric moisture. Furthermore, the real‐world potential of this green VBM protocol is demonstrated by the double Suzuki coupling of a monobromo(NDI) residue to a bis(thiophene) pinacol ester. The resulting dimeric NDI species has been demonstrated to behave as an electron acceptor in functioning OPVCs.

Synthesis, optical properties and cation mediated tuning of reduction potentials of core-annulated naphthalene diimide derivatives

Napthalene diimides (NDIs) are attractive candidates for electrical energy storage owing to the stabilisation of complexes between eletrogenerated dianions and cations. However, stability of such complexes are often compromised due...

Fine-Tuning Miscibility and π-π Stacking by Alkylthio Side Chains of Donor Molecules Enables High-Performance All-Small-Molecule Organic Solar Cells

Optimization of morphology and precise control of miscibility between donors and acceptors play an important role in improving the power conversion efficiencies (PCEs) of all-small-molecule organic solar cells (SM-OSCs). Besides device optimization, methods such as additives and thermal annealing are applied for finely tuning bulk-heterojunction morphology; strategies of molecular design are also the key to achieve efficient phase separation. Here, a series of A-D-A-type small-molecule donors (SM4, SM8, and SM12) based on benzodithiophene units were synthesized with different lengths of alkylthio side chains to regulate crystallinity, and their miscibility with the acceptor (BO-4Cl) was investigated. Consequently, SM4 with a short alkylthio substituent had a high crystallization propensity, leading to the oversized molecular domains and the poor morphology of the active layer. Meanwhile, SM12 with a longer alkylthio substituent showed weak crystallinity, causing a relatively looser π-π stacking and thus adversely affecting charge-carrier transport. The SM-OSC based on the small-molecule donor SM8 with a mid-length alkylthio substituent achieved a better PCE over 13%, which was attributed to a more harmonious blend miscibility without sacrificing carrier-charge transport. Eventually, the modulation of phase separation and miscibility via controlling the lateral side chains has proven its potential in optimizing the blend morphology to aid the development of highly efficient SM-OSCs.

Naphthalene diimides: perspectives and promise

In this review, we describe the developments in the field of naphthalene diimides (NDIs) from 2016 to the presentday. NDIs are shown to be an increasingly interesting class of molecules due to their electronic properties, large electron deficient aromatic cores and tendency to self-assemble into functional structures. Almost all NDIs possess high electron affinity, good charge carrier mobility, and excellent thermal and oxidative stability, making them promising candidates for applications in organic electronics, photovoltaic devices, and flexible displays. NDIs have also been extensively studied due to their potential real-world uses across a wide variety of applications including supramolecular chemistry, sensing, host-guest complexes for molecular switching devices, such as catenanes and rotaxanes, ion-channels, catalysis, and medicine and as non-fullerene accepters in solar cells. In recent years, NDI research with respect to supramolecular assemblies and mechanoluminescent properties has also gained considerable traction. Thus, this review will assist a wide range of readers and researchers including chemists, physicists, biologists, medicinal chemists and materials scientists in understanding the scope for development and applicability of NDI dyes in their respective fields through a discussion of the main properties of NDI derivatives and of the status of emerging applications.

Facile Photo-cross-linking System for Polymeric Gate Dielectric Materials toward Solution-Processed Organic Field-Effect Transistors: Role of a Cross-linker in Various Polymer Types

Energy-efficient solution-processed organic field-effect transistors (OFETs) are highly sought after in the low-cost printing industry as well as for the manufacture of flexible and other next-generation devices. The fabrication of such electronic devices requires high-functioning insulating materials that are chemically and mechanically robust to avoid lowering insulating properties during the device fabrication process or utilization of devices. In this study, we report a facile, fluorinated, UV-assisted cross-linker series using a fluorophenyl azide (FPA), which reacts with the C-H groups of a conventional polymer. This demonstrates the application of the cross-linked films in OFET gate dielectrics. The effects of the cross-linkable chemical structure of the FPA series on the cross-linking chemistry, photopatternability, and dielectric properties of the resulting films are investigated for low/high-k or amorphous/crystalline polymeric gate dielectric materials. The characteristics of insulating layers and behavior of OFETs containing these cross-linked gate dielectrics (for example, leakage current density (J), hysteresis, and charge trap density) depend on the polymer type. Furthermore, an organic-based complementary inverter and various printable OFETs with excellent electrical characteristics are successfully fabricated. Thus, these reported cross-linkers that enable the solution process and patterning of well-developed conventional polymer dielectric materials are promising for the realization of a more sustainable next-generation industrial technology for flexible and printable devices.

Side chain engineering in DTBDT-based small molecules for efficient organic photovoltaics

A new small-molecule donor with a dithieno[2,3-d:2',3'-d']-benzo[1,2-b:4,5-b']-dithiophene (DTBDT) core and both alkyl and alkylthio substituents is designed and synthesized to improve the miscibility between DTBDT-based small molecules and [6,6]-phenyl-C71-butyric acid methyl ester (PC₇₁BM). The alkyl substituent on the 4-position and the alkylthio substituent on the 5-position of the substituted thiophene are expected to improve intermolecular interactions and prevent severe aggregation of the small molecules. The new small molecule, DTBDT-S-C8-TTR, exhibits a homogenous blend morphology with small domains and edge-on-oriented crystalline structures in blends with PC₇₁BM, and give a maximum power conversion efficiency (PCE) of 8.43%. To recover the crystallinity of the DTBDT-S-C8-TTR small molecules weakened after being blended with PC₇₁BM, a solvent vapor annealing (SVA) treatment is performed. The SVA-treated blend films reveal well-developed crystalline domains with interconnected fibrillar structures. This blend morphology allows efficient charge carrier transport in blends and leads to increased PCEs. The maximum PCE of 9.18% achieved using DTBDT-S-C8-TTR suggests that substituting both alkylthio and alkyl groups into DTBDT can yield small-molecule-based organic photovoltaics (OPVs) displaying improved photovoltaic performances.

New Fused Pyrrolopyridine-Based Copolymers for Organic Solar Cell

A fused pyrrolopyridine core having substituents on the nitrogen atom instead of the carbon atom of the indoloindole unit is developed as a new donor unit for organic electronics. The new donor-acceptor copolymers, PDHPHBT, PDHPFBT, and PDHP2FBT, are synthesized using the new donor unit, well-known benzothiadiazole derivatives containing fluorine atoms as the acceptor. The thermal, optical, and electrochemical properties of these novel copolymers are reported. A solar cell using PDHPFBT with diphenyl ether has an open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of 0.86 V, 11.32 mA cm^-2 , 0.59%, and 5.68%, respectively, under AM 1.5G illumination (100 mW cm^-2 ) in the absence of annealing.

Understanding Structure-Property Relationships in All-Small-Molecule Solar Cells Incorporating a Fullerene or Nonfullerene Acceptor

To investigate the influence of donor molecule crystallinity on photovoltaic performance in all-small-molecule solar cells, two dithieno[2,3- d:2',3'- d']-benzo[1,2- b:4,5- b']dithiophene (DTBDT)-based small molecules, denoted as DTBDT-Rho and DTBDT-S-Rho and incorporating different side chains, are synthesized and characterized. The photovoltaic properties of solar cells made of these DTBDT-based donor molecules are systemically studied with the [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) fullerene acceptor and the O-IDTBR nonfullerene acceptor to study the aggregation behavior and crystallinity of the donor molecules in both blends. Morphological analyses and a charge carrier dynamics study are carried out simultaneously to derive structure-property relationships and address the requirements of all-small-molecule solar cells. This study reveals exciton decay loss driven by large-scale phase separation of the DTBDT molecules to be a crucial factor limiting photocurrent generation in the all-small-molecule solar cells incorporating O-IDTBR. In the all-small-molecule blends, DTBDT domains with dimensions greater than 100 nm limit the exciton migration to the donor-acceptor interface, whereas blends with PC₇₁BM exhibit homogeneous phase separation with smaller domains than in the O-IDTBR blends. The significant energy losses in nonfullerene-based devices lead to decreased J_sc and fill factor values and unusual decrease in V_oc values. These results indicate the modulation of phase separation to be important for improving the photovoltaic performances of all-small-molecule blends. In addition, the enhanced molecular aggregation of DTBDT-S-Rho with the alkylthio side chain leads to higher degrees of phase separation and unfavorable charge transfer, which are mainly responsible for the relatively low photocurrent when using DTBDT-S-Rho compared with that when using DTBDT-Rho. On the other hand, this enhanced molecular aggregation improves the crystallinity of DTBDT-S-Rho and results in its increased hole mobility.

Novel Star-Shaped Helical Perylene Diimide Electron Acceptors for Efficient Additive-Free Nonfullerene Organic Solar Cells

Two star-shaped helical perylene diimide (PDI) electron acceptors TPDI2 and FTPDI2 were designed and synthesized for nonfullerene organic solar cells (OSCs). The integration of helical PDIs into a three-dimensional structure provides a new strategy to tune the intermolecular interactions, and the as-cast blend films with PTB7-Th show favorable morphology as well as efficient charge transfer and separation, as evidenced by the morphology and femtosecond transient absorption (fs-TA) spectroscopy studies. A trade-off between suppressing the self-aggregation and maintaining the charge-transfer properties was achieved by FTPDI2. Using PTB7-Th as the electron donor, the FTPDI2-based nonfullerene OSCs show a high power conversion efficiency of 8.28%, without the assistance of any additives.

Electron-poor arylenediimides

This review article highlights the emergence of eclectic molecular design principles to realize remarkably strong electron deficient arylenediimide molecules, aspects of their stability and associated applications.