Small molecule BODIPY dyes as non-fullerene acceptors in bulk heterojunction organic photovoltaics

Rational Synthesis of Highly Stable Dithienopyrrole-Embedded BODIPYs Exhibiting Large Stokes Shift

A series of dithienopyrrole (DTP) embedded BODIPYs were synthesized and structurally characterized. These BODIPYs have strong absorption in the green region and broad emission in the red region with a large Stokes shift ranging from 3100 to 4200 cm-1. Interestingly, all three BODIPYs show intramolecular charge transfer interaction (ICT). Intriguingly, both BODIPYs (bis- and tris-BOD) also exhibit excited state symmetry breaking (ES-SB). Single-crystal X-ray analysis unambiguously confirmed the exact structures of all three structurally distinct BODIPYs.

Highly crystalline and fluorescent BODIPY-labelled phenyl-triazole-coumarins as n-type semiconducting materials for OFET devices

In this work, the synthesis of BODIPY-phenyl-triazole labelled coumarins (BPhTCs) using a two-step approach is described. The influence of the BODIPY appending on the photophysical, electrochemical and thermal properties of the phenyl-triazole-coumarin precursors (PhTCs) was investigated. Band gap energies were measured by absorption spectroscopy (2.20 ± 0.02 eV in the solid and 2.35 ± 0.01 eV in solution) and cyclic voltammetry (2.10 ± 0.05 eV). The results are supported by DFT calculations confirming the presence of lowest LUMO levels that facilitate the electron injection and stabilize the electron transport. Their charge-transport parameters were measured in Organic Field-Effect Transistor (OFET) devices. BPhTCs showed an ambipolar transistor behavior with good n-type charge mobilities (10-2 cm2V-1s-1) allowing these derivatives to be employed as promising semiconducting crystalline and fluorescent materials with good thermal and air stability up to 250 °C.

Small-molecule ambipolar transistors

Ambipolar transistor properties have been observed in various small-molecule materials. Since a small energy gap is necessary, many types of molecular designs including extended π-skeletons as well as the incorporation of donor and acceptor units have been attempted. In addition to the energy levels, an inert passivation layer is important to observe ambipolar transistor properties. Ambipolar transport has been observed in extraordinary π-electron systems such as antiaromatic compounds, biradicals, radicals, metal complexes, and hydrogen-bonded materials. Several donor/acceptor cocrystals show ambipolar transport as well.

BODIPY Cored A-D-A'-D-A Type Nonfused-Ring Electron Acceptor for Efficient Polymer Solar Cells

In this work, boron dipyrromethene (BODIPY) is for the first time employed as electron-deficient core (A') to construct an A-D-A'-D-A type nonfused-ring electron acceptor (NFREA) for polymer solar cells (PSCs). Among, cyclopentadithiophene (CPDT) and fluorinated dicyanoindanone (DFIC) are involved as electron-donating (D) bridges and terminal A groups, respectively. Bearing with the steric BODIPY core, tMBCIC exhibits twisted configuration with dihedral angles >45^o  between BODIPY and CPDT bridges. Thus, compared with the BODIPY-free planar A-D-D-A structured bCIC, reduced aggregation, weakened intramolecular D-A interactions with up-shifted LUMO by 0.4 eV as well as blue-shifted absorption by up to 150 nm is observed in tMBCIC. Moreover, owing to the intrinsic large molar extinction coefficient from BODIPY, promoted light-harvest ability is achieved for tMBCIC, particularly in its blend films. Therefore, PSCs by using PBDB-T as donor, tMBCIC as NFREA afford superior power conversion efficiency (PCE) of 9.22% and higher open-circuit voltage (V_oc ) of 0.954 V compared to 4.47% and 0.739 V from bCIC-devices. Moreover, compared to other BODIPY-flanked electron acceptors (<5%) reported so far, BODIPY-cored tMBCIC realizes a remarkable progress in PCE. This article is protected by copyright. All rights reserved.

Organoboron molecules and polymers for organic solar cell applications

Organic solar cells (OSCs) are emerging as a new photovoltaic technology with the great advantages of low cost, light-weight, flexibility and semi-transparency. They are promising for portable energy-conversion products and building-integrated photovoltaics. Organoboron chemistry offers an important toolbox to design novel organic/polymer optoelectronic materials and to tune their optoelectronic properties for OSC applications. At present, organoboron small molecules and polymers have become an important class of organic photovoltaic materials. Power conversion efficiencies (PCEs) of 16% and 14% have been realized with organoboron polymer electron donors and electron acceptors, respectively. In this review, we summarize the research progress in various kinds of organoboron photovoltaic materials for OSC applications, including organoboron small molecular electron donors, organoboron small molecular electron acceptors, organoboron polymer electron donors and organoboron polymer electron acceptors. This review also discusses how to tune their opto-electronic properties and active layer morphology for enhancing OSC device performance. We also offer our insight into the opportunities and challenges in improving the OSC device performance of organoboron photovoltaic materials.

Panchromatic aza-Bodipy based π-conjugates

A series of three aza-Bodipy donor molecules namely Aza-Bthp, Aza-Sty, and Aza-Fhdt have been synthesized.

BODIPY-Based Molecules, a Platform for Photonic and Solar Cells

The 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based molecules have emerged as interesting material for optoelectronic applications. The facile structural modification of BODIPY core provides an opportunity to fine-tune its photophysical and optoelectronic properties thanks to the presence of eight reactive sites which allows for the developing of a large number of functionalized derivatives for various applications. This review will focus on BODIPY application as solid-state active material in solar cells and in photonic devices. It has been divided into two sections dedicated to the two different applications. This review provides a concise and precise description of the experimental results, their interpretation as well as the conclusions that can be drawn. The main current research outcomes are summarized to guide the readers towards the full exploitation of the use of this material in optoelectronic applications.

Panchromatic Organoboron Molecules with Tunable Absorption Spectra

Panchromatic molecules, e. g. organic small molecules with wide absorption spectra, are very desirable for solar energy-related applications. Here, we report the development of a series of organoboron compounds composed of an organoboron core unit, two π-bridging units and two electron-withdrawing end-capping units. All seven molecules have the HOMO localized on the core unit and the LUMO delocalized on the whole conjugated backbone. They exhibit wide absorption spectra consisting of two strong absorption bands with the full width at half maximum of ca. 280 nm. These panchromatic compounds can be used as electron acceptors in organic solar cells. We elucidate the relationship between the chemical structures and opto-electronic properties of these organoboron panchromatic compounds. Increasing the electron-withdrawing capability of the core units results in a downshifted HOMO level as well as blueshifted long-wavelength absorption band with increased extinction coefficient. Extending the π-bridging units causes an increased HOMO level and blueshifted long-wavelength absorption band with increased extinction coefficients. Weakening the electron-withdrawing capability of the end-capping units leads to an upshifted LUMO level and blueshifted long-wavelength absorption peak with decreased extinction coefficient. This work provides insight into the absorption spectrum manipulation of panchromatic molecules and would pave the way for the development of solar energy-related applications.

Boron(iii) β-diketonate-based small molecules for functional non-fullerene polymer solar cells and organic resistive memory devices

A class of acceptor-donor-acceptor chromophoric small-molecule non-fullerene acceptors, 1-4, with difluoroboron(iii) β-diketonate (BF2bdk) as the electron-accepting moiety has been developed. Through the variation of the central donor unit and the modification on the peripheral substituents of the terminal BF2bdk acceptor unit, their photophysical and electrochemical properties have been systematically studied. Taking advantage of their low-lying lowest unoccupied molecular orbital energy levels (from -3.65 to -3.72 eV) and relatively high electron mobility (7.49 × 10-4 cm2 V-1 s-1), these BF2bdk-based compounds have been employed as non-fullerene acceptors in organic solar cells with maximum power conversion efficiencies of up to 4.31%. Moreover, bistable resistive memory characteristics with charge-trapping mechanisms have been demonstrated in these BF2bdk-based compounds. This work not only demonstrates for the first time the use of a boron(iii) β-diketonate unit in constructing non-fullerene acceptors, but also provides more insights into designing organic materials with multi-functional properties.

Synthesis and Photovoltaic Properties of Boron β-Ketoiminate Dyes Forming a Linear Donor-π-Acceptor Structure

Organoboron complexes are of interest as chromophores for dye sensitizers owing to their light-harvesting and carrier-transporting properties. In this study, compounds containing boron β-ketoiminate (BKI) as a chromophore were synthesized and used as dye sensitizers in dye-sensitized solar cells. The new dyes were orange or red crystals and showed maximum absorptions in the 410-450 nm wavelength region on titanium dioxide substrates. These electrodes exhibited maximum efficiencies of over 80% in incident photon-to-current conversion efficiency spectra, suggesting that the continuous process of light absorption-excitation-electron injection was effectively performed. Open-circuit photovoltages were relatively high owing to the large dipole moments of the BKI dyes with a linear molecular structure. Thus, a maximum power conversion efficiency of 5.3% was successfully observed. Comparison of BKI dyes with boron β-diketonate dyes revealed certain differences in solution stability, spectral properties, and photovoltaic characteristics.

Selective Soxhlets extraction to enhance solubility of newly-synthesized poly(indoloindole-selenophene vinylene selenophene) donor for photovoltaic applications

An electron-rich fused indoloindole-based poly(indoloindole-selenophene vinylene selenophene) was synthesized and characterized. Soxhlet can be obtained by continuously purifying the product with a specific solvent and obtaining a pure polymer with a high concentration. Molecular weight is affected by the vapor pressure of marginal solvent, and the polymer was fractionated using tetrahydrofuran, chloroform, and chlorobenzene. Solubility is closely related to the morphology of bulk heterojunction and device parameters. In the solution process of fabricating the organic solar cell, securement of solubility has a great effect on the performance of the device, because morphology and orientation of a photo-active layer which significantly affect charge transport in the device. Since tetrahydrofuran (THF) Soxhlet solvents have high vapor pressure and appropriate solubility parameters, THF induced the best solubility of P-IDI-SVS materials for organic solvents. And through additive optimization, the performance of the device based on P-IDI-SVS from THF-Soxhlet extraction was enhanced. This is expected to be a meaningful study because the effect on solubility of Soxhlet solvent suggests factors to be considered in the solution process in organic solar cell research. In addition, surface modified bulk heterojunction was observed using atomic force microscopy, photoluminescence, time-correlated single photon counting and Raman spectroscopy analysis.

A Solution-Processable meso-Phenyl-BODIPY-Based n-Channel Semiconductor with Enhanced Fluorescence Emission

The molecular design, synthesis, and characterization of an acceptor-donor-acceptor (A-D-A) semiconductor BDY-Ph-2T-Ph-BDY comprising a central phenyl-bithiophene-phenyl π-donor and BODIPY π-acceptor end-units is reported. The semiconductor shows an optical band gap of 2.32 eV with a highly stabilized HOMO/LUMO (-5.74 eV/-3.42 eV). Single-crystal X-ray diffraction (XRD) reveals D-A dihedral angle of ca. 66° and strong intermolecular "C-H ⋅⋅⋅ π (3.31 Å)" interactions. Reduced π-donor strength, increased D-A dihedral angle, and restricted intramolecular D-A rotations allows for both good fluorescence efficiency (Φ_F =0.30) and n-channel OFET transport (μ_e =0.005 cm² /V ⋅ s; I_on /I_off =10⁴ -10⁵ ). This indicates a much improved (6-fold) fluorescence quantum yield compared to the meso-thienyl BODIPY semiconductor BDY-4T-BDY. Photophysical studies reveal important transitions between locally excited (LE) and twisted intramolecular charge-transfer (TICT) states in solution and the solid state, which could be controlled by solvent polarity and nano-aggregation. This is the first report of such high emissive characteristics for a BODIPY-based n-channel semiconductor.

Enhanced Organic and Perovskite Solar Cell Performance through Modification of the Electron-Selective Contact with a Bodipy-Porphyrin Dyad

Photovoltaic devices based on organic semiconductors and organo-metal halide perovskites have not yet reached the theoretically predicted power conversion efficiencies while they still exhibit poor environmental stability. Interfacial engineering using suitable materials has been recognized as an attractive approach to tackle the above issues. We introduce here a zinc porphyrin-triazine-bodipy donor-π bridge-acceptor dye as a universal electron transfer mediator in both organic and perovskite solar cells. Thanks to its "push-pull" character, this dye enhances electron transfer from the absorber layer toward the electron-selective contact, thus improving the device's photocurrent and efficiency. The direct result is more than 10% average power conversion efficiency enhancement in both fullerene-based (from 8.65 to 9.80%) and non-fullerene-based (from 7.71 to 8.73%) organic solar cells as well as in perovskite ones (from 14.56 to 15.67%), proving the universality of our approach. Concurrently, by forming a hydrophobic network on the surface of metal oxide substrates, it improves the nanomorphology of the photoactive overlayer and contributes to efficiency stabilization. The fabricated devices of both kinds preserved more than 85% of their efficiency upon exposure to ambient conditions for more than 600 h without any encapsulation.

Boron-nitrogen substituted dihydroindeno[1,2-b]fluorene derivatives as acceptors in organic solar cells

The electrophilic borylation of 2,5-diarylpyrazines results in the formation of boron-nitrogen doped dihydroindeno[1,2-b]fluorene which can be synthesized using standard Schlenk techniques and worked up and handled readily under atmospheric conditions. Through transmetallation via diarylzinc reagents a series of derivatives were synthesized which show broad visible to near-IR light absorption profiles that highlight the versatility of this BN substituted core for use in optoelectronic devices. The synthesis is efficient, scalable and allows for tuning through changes in substituents on the planar heterocyclic core and at boron. Exploratory evaluation in organic solar cell devices as non-fullerene acceptors gave power conversion efficiencies of 2%.

Tunable Low-LUMO Boron-Doped Polycyclic Aromatic Hydrocarbons by General One-Pot C-H Borylations

Boron-doping has long been recognized as a promising LUMO energy-lowering modification of graphene and related polycyclic aromatic hydrocarbons (PAHs). Unfortunately, synthetic difficulties have been a significant bottleneck for the understanding, optimization, and application of precisely boron-doped PAHs for optoelectronic purposes. Herein, a facile one-pot hydroboration electrophilic borylation cascade/dehydrogenation approach from simple alkene precursors is coupled with postsynthetic B-substitution to give access to ten ambient-stable core- and periphery-tuned boron-doped PAHs. These include large hitherto unknown doubly boron-doped analogues of anthanthrene and triangulene. Crystallographic, optical, electrochemical, and computational studies were performed to clarify the effect of boron-doped PAH shape, size, and structure on optoelectronic properties. Our molecular tuning allowed the synthesis of molecules exhibiting visible-range absorption, near-unity fluorescence quantum yields, and, to our knowledge, the most facile electrochemical reductions of any reported ambient-stable boron-doped PAHs (corresponding to LUMO energy levels as low as fullerenes). Finally, our study describes the first implementation of a precise three-coordinate boron-substituted PAH as an acceptor material in organic solar cells with power conversion efficiencies (PCEs) of up to 3%.

New dithienosilole- and dithienogermole-based BODIPY for solar cell applications

We report two efficient donor materials for organic solar cells, namely Si-BDP and Ge-BDP, composed by the novel union of thienyl Bodipy wings and a dithienosilole/dithienogermole core.

BODIPY-Based Semiconducting Materials for Organic Bulk Heterojunction Photovoltaics and Thin-Film Transistors

The rapid emergence of organic (opto)electronics as a promising alternative to conventional (opto)electronics has been achieved through the design and development of novel π-conjugated systems. Among various semiconducting structural platforms, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) π-systems have recently attracted attention for use in organic thin-films transistors (OTFTs) and organic photovoltaics (OPVs). This Review article provides an overview of the developments in the past 10 years on the structural design and synthesis of BODIPY-based organic semiconductors and their application in OTFT/OPV devices. The findings summarized and discussed here include the most recent breakthroughs in BODIPYs with record-high charge carrier mobilities and power conversion efficiencies (PCEs). The most up-to-date design rationales and discussions providing a strong understanding of structure-property-function relationships in BODIPY-based semiconductors are presented. Thus, this review is expected to inspire new research for future materials developments/applications in this family of molecules.

BN Embedded Polycyclic π-Conjugated Systems: Synthesis, Optoelectronic Properties, and Photovoltaic Applications

In the periodic table of elements, boron (B, atomic number, 5) and nitrogen (N, atomic number, 7) are neighboring to the carbon (C, atomic number, 6). Thus, the total electronic number of two carbons (12) is equal to the electronic sum of one boron (5) and one nitrogen (7). Accordingly, replacing two carbons with one boron and one nitrogen in a π-conjugated structure gives an isoelectronic system, i.e., the BN perturbed π-conjugated system, comparing to their all-carbon analogs. The BN embedded π-conjugated systems have unique properties, e.g., optical absorption, emission, energy levels, bandgaps, and packing order in contrast to their all-carbon analogs and have been intensively studied in terms of novel synthesis, photophysical characterizations, and electronic applications in recent years. In this review, we try to summarize the synthesis methods, optoelectronic properties, and progress in organic photovoltaic (OPV) applications of the representative BN embedded polycyclic π-conjugated systems. Firstly, the narrative will be commenced with a general introduction to the BN units, i.e., B←N coordination bond, B-N covalent bond, and N-B←N group. Then, the representative synthesis strategies toward π-conjugated systems containing B←N coordination bond, B-N covalent bond, and N-B←N group will be summarized. Afterwards, the frontier orbital energy levels, optical absorption, packing order in solid state, charge transportation ability, and photovoltaic performances of typical BN embedded π-conjugated systems will be discussed. Finally, a prospect will be proposed on the OPV materials of BN doped π-conjugated systems, especially their potential applications to the small molecules organic solar cells.

BODIPY dyads and triads: synthesis, optical, electrochemical and transistor properties

A series of D–A dyads and D–A–D triads molecular systems based on triphenylamine and 9-ethyl-carbarzole as donor (D) and BODIPY as acceptor (A) has been designed and synthesized. The optoelectronic properties including optical, electrochemical, and charge carrier mobility of these molecules have been investigated. We found that the D–A–D triads exhibited broader absorption, raising the HOMO energy levels and increase hole carrier mobilities. Analysis surface morphology revealed that BODIPY containing carbazole demonstrated smooth film and no macro phase aggregation was observed upon thermal annealing.

An organoboron compound with a wide absorption spectrum for solar cell applications

Organoboron compounds offer new approaches to tune the electronic structures of π-conjugated molecules. In this work, an electron acceptor (M-BNBP4P-1) is developed by endcapping an organoboron core unit with two strong electron-withdrawing groups. M-BNBP4P-1 exhibits a unique wide absorption spectrum with two strong absorption bands in the long wavelength region (λ_max = 771 nm) and the short wavelength region (λ_max = 502 nm), which indicate superior sunlight harvesting capability. This is due to its special electronic structure, i.e. a delocalized LUMO and a localized HOMO. Prototype solution-processed organic solar cells based on M-BNBP4P-1 show a power conversion efficiency of 7.06% and a wide photoresponse from 350 nm to 880 nm.

Benzothiadiazole-oligothiophene flanked dicyanomethylenated quinacridone for non-fullerene acceptors in polymer solar cells

A new class of benzothiadiazole-oligo(3-hexylthiophene) flanked dicyanomethylenated quinacridone derivatives DCNQA-BT-Tn (n = 1–3) has been designed and synthesized in good yield by iterative bromination and Suzuki coupling reactions, followed by Knoevenagel condensation.

A triptycene-cored perylenediimide derivative and its application in organic solar cells as a non-fullerene acceptor

A triptycene-cored PDI derivative with a 3D molecular structure was designed and synthesized as a promising acceptor in OSCs.

A new rod-shaped BODIPY-acetylene molecule for solution-processed semiconducting microribbons in n-channel organic field-effect transistors

A novel solution-processable BODIPY-based small molecule (BDY-PhAc-BDY) yields highly-crystalline, one-dimensional (1-D) microribbon semiconductors for organic field-effect transistors (OFETs).

Novel Dual BODIPY-Carbazole Conjugates with Various Linkers

Four dual BODIPY-carbazole conjugates (BDPa–d, BODIPY is 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene), with various π bridges, including none, phenyl, thiophene, and furan, were designed and synthesized. The results suggest that the π bridges have significant effect on the thermal, photophysical, and electrochemical properties of the conjugates. BDPc and BDPd, with a five-membered heterocycle as a π bridge possessing more coplanar molecular geometry, exhibit broader and red-shifted absorption with an obvious charge transfer shoulder peak, as well as red-shifted emission. UV-visible absorption spectroscopy and cyclic voltammetry results show that the extension of the π-conjugated system leads to a reduction in the optical gap with a decrease of the LUMO level. All conjugates display remarkable Stokes shifts (107–216 nm) and low fluorescence quantum yields. BDPc and BDPd, which essentially possess broad and intense absorption, and suitable HOMO–LUMO energy levels, are potential candidates for light-harvesting and photovoltaic applications.

Molecular electron acceptors for efficient fullerene-free organic solar cells

Small molecule electron acceptors pairing with wide bandgap or narrow bandgap electron donors are reviewed and discussed for fullerene-free organic solar cells.

Photophysical and Electrochemical Characterization of BODIPY-Containing Dyads Comparing the Influence of an A-D-A versus D-A Motif on Excited-State Photophysics

A complete photophysical characterization of organic molecules designed for use as molecular materials is critical in the design and construction of devices such as organic photovoltaics (OPV). The nature of a molecule's excited state will be altered in molecules employing the same chromophoric units but possessing different molecular architectures. For this reason, we examine the photophysical reactions of two BODIPY-based D-A and A-D-A molecules, where D is the donor and A is the acceptor. A BODIPY (4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene) moiety serves as the A component and is connected through the meso position using a 3-hexylthiophene linker to a N-(2-ethylhexyl)dithieno[3,2-b:2',3'-d]pyrrole (DTP), which serves as the D component. An A-D-A motif is compared to its corresponding D-A dyad counterpart. We show a potential advantage to the A-D-A motif over the D-A motif in creating longer-lived excited states. Transient absorption (TA) spectroscopy is used to characterize the photophysical evolution of each molecule's excited state. Global analysis of TA data using singular value decomposition and target analysis is performed to identify decay-associated difference spectra (DADS). The DADS reveal the spectral features associated with charge-transfer excited states that evolve with different dynamics. A-D-A possess slightly longer excited-state lifetimes, 42 ps nonradiative decay, and 4.64 ns radiative decay compared to those of D-A, 24 ps nonradiative decay, and 3.95 ns radiative decay. A longer lived A-D-A component is observed with microsecond lifetimes, representing a small fraction of the total photophyscial product. Steady-state and time-resolved photoluminescence augment the insights from TA, while electrochemistry and spectroelectrochemistry are employed to identify the nature of the excited state. Density functional theory supports the observed electronic and electrochemical properties of the D-A and A-D-A molecules. These results form a complete picture of the electronic and photophysical properties of D-A and A-D-A and provide contextualization for structure-function relationships between molecules and OPV devices.

Solution-Processable BODIPY-Based Small Molecules for Semiconducting Microfibers in Organic Thin-Film Transistors

Electron-deficient π-conjugated small molecules can function as electron-transporting semiconductors in various optoelectronic applications. Despite their unique structural, optical, and electronic properties, the development of BODIPY-based organic semiconductors has lagged behind that of other π-deficient units. Here, we report the design and synthesis of two novel solution-proccessable BODIPY-based small molecules (BDY-3T-BDY and BDY-4T-BDY) for organic thin-film transistors (OTFTs). The new semiconductors were fully characterized by (1)H/(13)C NMR, mass spectrometry, cyclic voltammetry, UV-vis spectroscopy, photoluminescence, differential scanning calorimetry, and thermogravimetric analysis. The single-crystal X-ray diffraction (XRD) characterization of a key intermediate reveals crucial structural properties. Solution-sheared top-contact/bottom-gate OTFTs exhibited electron mobilities up to 0.01 cm(2)/V·s and current on/off ratios of >10(8). Film microstructural and morphological characterizations indicate the formation of relatively long (∼0.1 mm) and micrometer-sized (1-2 μm) crystalline fibers for BDY-4T-BDY-based films along the shearing direction. Fiber-alignment-induced charge-transport anisotropy (μ∥/μ⊥ ≈ 10) was observed, and higher mobilities were achieved when the microfibers were aligned along the conduction channel, which allows for efficient long-range charge-transport between source and drain electrodes. These OTFT performances are the highest reported to date for a BODIPY-based molecular semiconductor, and demonstrate that BODIPY is a promising building block for enabling solution-processed, electron-transporting semiconductor films.

Regioisomeric donor–acceptor–donor triads based on benzodithiophene and BODIPY with distinct optical properties and mobilities

Two regioisomeric donor–acceptor–donor triads composed of benzodithiophene and BODIPY exhibit distinct optical and charge transfer properties, and mobilities of ∼10⁻⁴ cm² V⁻¹ s⁻¹.

Non-symmetric benzo[b]-fused BODIPYs as a versatile fluorophore platform reaching the NIR: a systematic study of the underlying structure–property relationship

Ten newly synthesized non-symmetric benzo[b]-fused BODIPYs are compared with an extended series of nine related families (23 compounds) to gain insights into their structure–property relationship.

Dye Encapsulation in Polynorbornene Micelles

The encapsulation efficiency of high-Tg polynorbornene micelles was probed with a hydrophobic dye 2,6-diiodoboron-dipyrromethene (BODIPY). Changes in the visible absorption spectra of aggregated versus monomeric dye molecules provided a probe for assessing encapsulation. Polynorbornene micelles are found to be capable of loading up to one BODIPY dye per ten polymers. As the hydrophilic block size increased in the polymeric amphiphiles, more of the dye was incorporated within the micelles. This result is consistent with the dye associating with the polymer backbone in the shell of the micelles. The encapsulation rate varied significantly with temperature, and a slight dependence on micellar morphology was also noted. Additionally, we report a 740 μs triplet lifetime for the encapsulated BODIPY dye. The lifetime is the longest ever recorded for a BODIPY triplet excited state at room temperature and is attributed to hindered triplet-triplet annihilation in the high-viscosity micellar shell.

High-efficiency BODIPY-based organic photovoltaics

A benzannulated boron dipyrromethene (BODIPY, bDIP) molecule exhibiting strong absorption at 640 nm was synthesized. The organic dye was used in an organic solar cell as the electron donor with C60 as the acceptor. The BODIPY dye demonstrated the best performance in lamellar architecture (indium tin oxide (ITO)/bDIP/C60/bathocuproine/Al), giving power conversion efficiency up to 4.5% with short-circuit current (JSC) of 8.7 mA/cm(2) and an open-circuit voltage (VOC) of 0.81 V. Neutron reflectivity experiments were performed on the bilayer film to investigate the thickness dependence of JSC. A 13 nm mixed layer was found to be present at the donor/acceptor interface in the bilayer device, formed when the C60 was deposited onto a room temperature bDIP film. Planar-mixed heterojunction devices were fabricated to understand the extent of spontaneous mixing between the donor and acceptor materials. The native mixed region in the bilayer device was shown to most resemble 1:3 bDIP:C60 layer in the structure: (ITO/bDIP/bDIP:C60 blend/C60/bathocuproine/Al).

Synthesis of 3-aminoBODIPY dyes via copper-catalyzed vicarious nucleophilic substitution of 2-halogeno derivatives

Copper catalysed vicarious nucleophilic substitution of 2-halogeno BODIPYs with alkyl amines, anilines and an amide produces the corresponding 3-aminoBODIPY derivatives.

Solution processable diketopyrrolopyrrole (DPP) cored small molecules with BODIPY end groups as novel donors for organic solar cells

Two novel triads based on a diketopyrrolopyrrole (DPP) central core and two 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) units attached by thiophene rings have been synthesised having high molar extinction coefficients. These triads were characterised and used as donor materials in small molecule, solution processable organic solar cells. Both triads were blended with PC71BM as an acceptor in different ratios by wt % and their photovoltaic properties were studied. For both the triads a modest photovoltaic performance was observed, having an efficiency of 0.65%. Moreover, in order to understand the ground and excited state properties and vertical absorption profile of DPP and BODIPY units within the triads, theoretical DFT and TDDFT calculations were performed.

Integrated molecular, interfacial, and device engineering towards high-performance non-fullerene based organic solar cells

High-performance non-fullerene OSCs with PCEs of up to ca. 6.0% are demonstrated based on PBDTT-F-TT polymer and a molecular di-PBI acceptor through comprehensive molecular, interfacial, and device engineering. Impressive PCEs can also be retained in devices with relatively thick BHJ layer and processed through non-halogenated solvents, indicating these high-performance non-fullerene OSCs are promising for large-area printing applications.