Benzothiadiazole Units Research Articles

Optimization of porphyrin dyes with a bulky triphenylamine donor for developing efficient dye-sensitized solar cells

To fabricate efficient dye-sensitized solar cells (DSSCs), three porphyrin dyes XW65−XW67 have been designed and synthesized using a bulky triphenylamine donor. Based on our previously reported dyes with a carbazole donor, a bulky triphenylamine unit was employed as the donor to synthesize XW65 with the aim to enhance the electron donating ability and suppress dye aggregation. As a result, XW65 shows enhanced photocurrent density (Jsc) and open circuit voltage (Voc), affording a high efficiency of 9.02%. On this basis, XW66 was synthesized with a methyl group introduced into the carboxyphenyl acceptor to further suppress dye aggregation and improve the Voc, achieving an enhanced efficiency of 9.23% with improved Voc of 849 mV and Jsc of 14.87 mA cm−2, which can be ascribed to the further suppressed dye aggregation and enhanced adsorption amount on the TiO2 film induced by the additional methyl group. To further improve the Jsc, a benzothiadiazole (BTD) unit has been introduced as the auxiliary acceptor to afford XW67, which exhibits a strikingly red-shifted monochromatic photon-to-electron conversion efficiency (IPCE) onset wavelength of 830 nm, obtaining the highest Jsc value of 15.83 mA cm−2 among the three dyes. Consequently, despite the sacrifice of Voc caused by the severe dye aggregation associated the extended conjugation framework, XW67 exhibits the highest efficiency of 9.43%. On this basis, cosensitization with WS-5 afforded elevated efficiencies of 10.07%, 10.38% and 10.13% for XW65−XW67, respectively, owing to the simultaneously enhanced Jsc and Voc. These results indicate that it is effective to develop efficient DSSCs based on cosensitization of optimized porphyrin dyes containing a bulky triphenylamine donor, a methyl group on the carboxyphenyl acceptor, and an auxiliary electron acceptor.

Near‐Infrared Organic Phototransistors with p‐Channel Photosensitive Layers of Conjugated Polymer Composed of bis‐Octyldodecyl‐Diketopyrrolopyrrole and Benzothiadiazole Units

AbstractA near‐infrared (NIR)‐absorbing conjugated polymer, poly[{2,5‐bis‐(2‐octyldodecyl)‐3,6‐bis‐(thien‐2‐yl)‐pyrrolo[3,4‐c]pyrrole‐1,4‐diyl}‐co‐{2,2′‐(2,1,3‐benzothiadiazole)‐5,5′‐diyl}] (PODTPPD‐BT), which is synthesized via a Stille coupling reaction, can play a dual role (charge transport and sensing) in NIR‐sensing organic phototransistors (OPTRs). The PODTPPD‐BT films, which feature two strong optical absorption peaks at wavelengths (λ) of 830 and 935 nm, possess a highly ordered crystalline state as evidenced by the synchrotron radiation grazing incidence X‐ray diffraction (GIXD) method. The OPTRs with the PODTPPD‐BT layers show typical p‐channel transistor behaviors in the dark, while their best dark performance is measured at a PODTPPD‐BT thickness (t) of 85 nm. The highest overall photocurrent is measured at t = 85 nm under illumination with three monochromatic NIR lights, while the highest photoresponsivity (RC) is obtained for the thickest PODTPPD‐BT layers (t = 145 nm). The flexible OPTRs with the PODTPPD‐BT layers demonstrate stable sensing characteristics upon optical on/off modulations using a high‐power NIR laser diode (λ = 905 nm) used for actual light detection and ranging (LiDAR) systems.

Self-Assembled Pd12 Coordination Cage as Photoregulated Oxidase-Like Nanozyme.

Designing supramolecular architectures with uncommon geometries embedded with functional building units is of immense importance in contemporary research. In this report, we present a new water-soluble Pd12L6 supramolecular coordination nanocage (1) that was synthesized via self-assembly of a tetradentate donor (L) with ditopic acceptor cis-[(en)Pd(NO3)2] [en = ethylenediamine]. Self-assembly of a tetratopic donor with a cis-blocked 90° acceptor commonly produces tri/tetra- or hexagonal barrel-type structures. However, the resulting cage 1 has an uncommon geometry consisting of two triangular cupolas conjoined through an irregular common hexagonal base. Incorporation of the benzothiadiazole unit in the structure helped in the photogeneration of reactive oxygen species (ROS) in water. Many nanomaterials have shown to have the ability to mimic the catalytic activity of natural enzymes (nanozymes). Majority of such nanozymes are water insoluble metal/metal-oxide nanoparticles or extended metal organic frameworks (MOFs)/metal-carbon composites, etc. The present water-soluble Pd12 nanocage 1 has shown excellent oxidase-like activity upon irradiation with white light. The enzymatic activity of 1 is photoregulated which offers other obvious advantages, such as external control of enzymatic activity and noninvasiveness. The oxidase-like activity and exogenous ROS generation have been further exploited in photocatalytic antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) bacterial strain.

Impact of the acceptor units on optoelectronic and photovoltaic properties of (XDADAD)n-type copolymers: Computational and experimental study

A series of ten conjugated polymers incorporating in their molecular frameworks extended DADAD building blocks with thiophene donor (D) and either benzotriazole, benzoxadiazole, benzothiadiazole, difluorobenzothiadiazole or quinoxaline acceptor (A) units were synthesized and characterized. The optoelectronic properties of new polymers were computed and experimentally investigated revealing a good relationship, which can guide further rational design of materials with tailored properties for organic photovoltaics using in-silico approaches. The performance of all polymers in organic bulk heterojunction solar cells was compared and some important empirical rules were formulated for reaching the best photovoltaic performance from (X-DADAD)n family of polymers.

The improvement of photovoltaic performance of quinoline-based dye-sensitized solar cells by modification of the auxiliary acceptors

Three new dyes containing diphenylamine as electron donor, benzene (BIM1), benzothiadiazole (BTD) (BIM2) and N-ethylhexylbenzotriazole (BTZ) (BIM3) as auxiliary electron acceptors, quinoline as π-bridge and cyanoacrylic acid as anchoring group were synthesized in D-A-π-A structure for use in dye-sensitized solar cells (DSSCs). The optical, electrochemical, theoretical and photovoltaic methods were performed to understand the auxiliary acceptor influence on the performance of these dyes. Compared to the other dyes, the DSSC with dye BIM3 slightly increases the open circuit voltage (Voc) owing to the retardation of charge recombination by BTZ. However, replacement of benzene or BTZ by BTD unit causes a large red shift of the absorption spectra, leading BIM2 cell to produce the highest short circuit current density (Jsc). Thus, among the three D-A-π-A dyes, BIM2 is determined to be the most efficient dye, which reached a Voc of 0.627 V and Jsc of 11.53 mA cm–2, corresponding to an overall power conversion efficiency of 5.21 % in the presence of chenodeoxycholic acid (CDCA) as the coadsorbent. These results suggest that the insertion of benzothiadiazole as auxiliary acceptor into quinoline-based D-A-π-A dyes can effectively improve photovoltaic performance of DSSCs.

Effect of auxiliary donors and position of benzothiadiazole on the optical and photovoltaic properties of dithieno[3,2-b:2′,3′-d]pyrrole-based sensitizers

Organic dyes used as sensitizers in dye-sensitized solar cells offer endless opportunities for modulation of cell efficiency through structural diversifications. Despite the countless number of dyes developed, structure-property analysis by varying chromophores and their topology in dyes is useful to formulate design principles. Herein, we report six new organic dyes featuring dithienopyrrole (DTP), benzothiadiazole (BTD) and cyanoacrylic acid units. The effect of auxiliary donors such as triphenylamine or diphenylaminofluorene and the position of benzothiadiazole on the optical and photovoltaic properties were evaluated by appropriate design of dyes. Incorporation of additional donor enhanced the spectral response of the dyes by elongating the conjugation length and supplementing the donor-acceptor interaction. Moving the BTD unit from the position between DTP and acceptor (D-D-A-π-A) to a position between the auxiliary donor and DTP (D-A-D-A) altered the absorption as well as electrochemical properties. Theoretical calculations revealed that the later molecular configuration ensures sufficient overlap of HOMO and LUMO and facilitate the charge transfer propensity from arylamine donor to acceptor which is beneficial for light harvesting. Among the dyes, a D-A-D-A dye possessing triphenylamine exhibited highest power conversion efficiency (η = 7.57%). The structure-property relationship is supported by electron transfer kinetics elucidated by electrochemical impedance spectroscopic studies. The best performing dye displayed high charge recombination and sufficiently low charge transfer resistance in the device.

Design of novel thiazolothiazole-based conjugated polymer for efficient fullerene and non-fullerene organic solar cells

We report the synthesis of novel low bandgap conjugated polymer P1 comprising thiazolothiazole, benzothiadiazole and thiophene units and investigation its photovoltaic properties in organic solar cells with [70]PCBM ([6,6]-phenyl-C71-butyric acid methyl ester) and high-performing non-fullerene IT-4F acceptor (9-bis(2-methylene-((3-(1,1-dicyanomethylene)-6,7-difluoro)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2’,3’-d’]-s-indaceno [1,2-b:5,6-b’]dithiophene). Polymer P1 showed promising results in both fullerene and non-fullerene organic solar cells. In particular, P1/IT-4F blends demonstrated enhanced charge carrier mobilities and suppressed trap-assisted recombination, which resulted in impressive short-circuit current densities and decent power conversion efficiency of 8.8 % in solar cells. The fullerene-based devices delivered efficiency of 8.2 % with remarkably high open-circuit voltages. The obtained results feature conjugated polymers based on thiazolothiazole as promising absorber materials for organic solar cells.

Simulation of time-resolved x-ray absorption spectroscopy of ultrafast dynamics in particle-hole-excited 4-(2-thienyl)-2,1,3-benzothiadiazole.

To date, alternating co-polymers based on electron-rich and electron-poor units are the most attractive materials to control functionality of organic semiconductor layers in which ultrafast excited-state processes play a key role. We present a computational study of the photoinduced excited-state dynamics of the 4-(2-thienyl)-2,1,3-benzothiadiazole (BT-1T) molecule, which is a common building block in the backbone of π-conjugated polymers used for organic electronics. In contrast to homo-polymer materials, such as oligothiophene, BT-1T has two non-identical units, namely, thiophene and benzothiadiazole, making it attractive for intramolecular charge transfer studies. To gain a thorough understanding of the coupling of excited-state dynamics with nuclear motion, we consider a scenario based on femtosecond time-resolved x-ray absorption spectroscopy using an x-ray free-electron laser in combination with a synchronized ultraviolet femtosecond laser. Using Tully's fewest switches surface hopping approach in combination with excited-state calculations at the level of configuration interaction singles, we calculate the gas-phase x-ray absorption spectrum at the carbon and nitrogen K edges as a function of time after excitation to the lowest electronically excited state. The results of our time-resolved calculations exhibit the charge transfer driven by non-Born-Oppenheimer physics from the benzothiadiazole to thiophene units during relaxation to the ground state. Furthermore, our ab initio molecular dynamics simulations indicate that the excited-state relaxation processes involve bond elongation in the benzothiadiazole unit as well as thiophene ring puckering at a time scale of 100 fs. We show that these dynamical trends can be identified from the time-dependent x-ray absorption spectrum.

Highly Efficient Luminescent Solar Concentrators Based on Benzoheterodiazole Dyes with Large Stokes Shifts.

Five extended π-conjugated systems with electron donor (D) and acceptor (A) moieties have been synthesized. Their basic D-A-D structural motif is a benzothiadiazole unit symmetrically equipped with two thiophene rings (S2T). Its variants include 1) the same molecular framework in which sulfur is replaced by selenium (Se2T), also with four thiophene units (Se4T) and 2) a D'-D-A-D system having a N-carbazole donor moiety at one end (CS2T) and a D'-D-A-D-A' array with a further acceptor carbonyl unit at the other extremity (CS2TCHO). The goal is taking advantage of the intense luminescence and large Stokes shifts of the five molecules for use in luminescent solar concentrators (LSCs). All of them exhibit intense absorption spectra in the UV/Vis region down to 630 nm, which are fully rationalized by DFT. Emission properties have been studied in CH2 Cl2 (298 and 77 K) as well as in PMMA and PDMS matrices, measuring photoluminescence quantum yields (up to 98 %) and other key optical parameters. The dye-PMMA systems show performances comparable to the present state-of-the-art, in terms of optical and external quantum efficiencies (OQE=47.6 % and EQE=31.3 %, respectively) and flux gain (F=10.3), with geometric gain close to 90. LSC devices have been fabricated and tested in which the five emitters are embedded in PDMS and their wave-guided VIS luminescence feeds crystalline silicon solar cells.

Crystals of Phenylene–Oxazole Oligomer with a Central Benzothiadiazole Fragment

The results of growth from solutions of organic crystals of a new π-conjugated linear oligomer (Hex-O-Ph)2-BTD consisting of benzothiadiazole (BTD), phenyl (Ph) and oxazole (O) units and n-hexyl terminal substituents are presented. Well soluble at 20°C in n-hexane (1.7 g/L) and acetone (1.9 g/L), (Hex-O-Ph)2-BTD crystals are formed in the shape of films or plates up to 8 mm long and about 10 μm thick at the liquid–air interface within five days. The polymorphism and melting parameters of the new compound are determined by the method of differential scanning calorimetry. The structure of the single-crystal film is analyzed by Х-ray diffraction. The crystal structure of (Hex-O-Ph)2-BTD is found to be formed from close-packed (001) layers with a thickness of d001 = 2.39 nm.

Synthesis, properties, and charge transport characteristics of the conjugated copolymers containing the azaisoindigo and benzothiadiazole units

We report two novel azaisoindigo and benzothiadiazole-containing ternary copolymers PAZDTBT and PAZDTBTF. The thermal, optical and electrochemical properties, conjugated backbone planarity, film morphology and molecular packing mode, as well as charge transport characteristics of two copolymers, were studied systematically through either experimental evaluations or theoretical modellings. The copolymer PAZDTBTF containing fluorine atoms on benzothiadiazole units owns an energy level of the lowest unoccupied molecular orbital (LUMO) (−3.56 eV) similar to that of non-fluorinated copolymer PAZDTBT (−3.53 eV). Both ternary copolymers PAZDTBT and PAZDTBTF exhibited ambipolar charge carrier transport characteristics. When compared with the averaged hole/electron mobilities of 0.377 and 0.092 cm2 V−1 s−1 for PAZDTBT, the polymer PAZDTBTF has an enhanced electron mobility of 0.126 cm2 V−1 s−1, though its hole mobility of 0.358 cm2 V−1 s−1 was a little bit lower than that of PAZDTBT. Our work demonstrates the great potentials of ternary π-conjugated system with two different acceptor units in fine-tuning the optoelectronic properties of polymer semiconductors.

A thiophene-fused benzotriazole unit as a “π-bridge” in A-π-D-π-A type acceptor to achieve more balanced JSC and VOC for OSCs

As known, to balance the open-circuit voltage (VOC) and short-circuit current density (JSC) is one of the effective strategies to improve the photovoltaic performances of OSCs. In this work, a thiophene-fused benzotriazole (BTAZT) unit acts as a “π-bridge” to build an acceptor (A3) with A-π-D-π-A structure for OSCs. Compared with a thiophene-fused benzothiadiazole (BTT) unit as a “π-bridge” in our previous acceptor (A2), BTAZT unit exhibits relatively weak electron-withdrawing ability that results in a significant uplift of LUMO energy level to favor for enhancement of VOC. Also, the fusion of a thiophene ring onto BTAZ unit strengthens the intramolecular charge transfer to maintain the relatively high JSC. Therefore, the PTB7-Th:A3 OSC device shows higher PCE of 11.0% with more balanced device parameters (VOC = 0.959 V, JSC = 17.30 mA cm−2, FF = 66.2%) as well as smaller energy loss (Eloss) of 0.63 eV than the PTB7-Th:A2 device with PCE of 8.20% (VOC = 0.701 V, JSC = 19.47 mA cm−2, FF = 60.1% and Eloss = 0.67 eV). This work indicates that the rational structural modification of a “π-bridge” for A-π-D-π-A type acceptor is an effective approach to achieve the balanced VOC and JSC for the OSCs.

Small molecule donor based on alkoxylated benzothiadiazole unit: Synthesis and photovoltaics properties

Two small molecule donors (namely BTRO and BTCN) based on the benzothiadiazole unit were synthesized in this study. In comparison to BTRO, BTCN has a narrower absorption spectrum, however, BTCN has better crystallinity, higher carrier mobility, and better light absorption that is complementary to IDIC-4F. Non-fullerene all small molecule organic solar cells (SM-OSCs) based on BTCN: IDIC-4F exhibited a power conversion efficiency (PCE) of 4.62% with short circuit current density (Jsc) of 11.46 mA/cm2, open-circuit voltage (Voc) of 0.89 V, and fill factor (FF) of 0.45. In contrast, non-fullerene SM-OSCs based on BTRO: IDIC-4F showed PCE, Jsc, Voc, and FF values of 4.08%, 11.04 mA/cm2, 0.91 V, and 0.41, respectively. Our results show that benzothiadiazole is a very good acceptor unit for regulating the absorption and energy levels of non-fullerene SM-OSCs.

Structure evolution of azo-fused conjugated microporous polymers for high performance lithium-ion batteries anodes

Redox polymers as electrodes for rechargeable batteries have gained much attention because of their tunable chemical structures and designable electrochemical performance. Herein, a class of azo-fused conjugated microporous polymers with distinct electronic structures is reported as anode materials of rechargeable lithium-ion batteries. The structure-performance correlation revealed by the comparative study in this work demonstrates that the lowest unoccupied molecular orbital energy level and the band gap play significant roles in enhancing the capability of Li ions storage for the azo-fused conjugated microporous polymer electrodes. The polymer of AzoBT comprising azo and benzothiadiazole units delivers a high reversible capacity up to 1543 mAh g−1 at 50 mA g−1, outstanding rate capability (366 mAh g−1 at 3 A g−1) and stable cycling performance of 1000 cycles at 2 A g−1, demonstrating that the newly developed azo-fused conjugated microporous polymers are potential candidate anodes for energy storage. The result underlines the key role of electronic structures in the structure design of high-performance organic electrodes for rechargeable lithium-ion batteries.

A2-D-A1-D-A2-type small molecule acceptors incorporated with electron-deficient core for non-fullerene organic solar cells

Two A2-D-A1-D-A2-type small molecule acceptors (SMAs), DFB-dIDT and BT-dIDT with 2,5-difluorobenzene (DFB) or benzothiadiazole (BT) as electron-withdrawing core (A1) and a derivative of indanone as A2 units, were prepared for applications in organic solar cells (OSCs). The results indicate that BT unit is more beneficial to forming multiple noncovalent conformational locks of N⋯S and N⋯H between BT and IDT unit than DFB in the core, so BT-dIDT showed better molecular coplanarity, higher-lying HOMO energy level, more red-shifted spectrum, superior molar absorption coefficient (1.60 × 105 M−1 cm−1 at 696 nm), more complementary absorption spectrum with PBDB-T and better photovoltaic performance than DFB-dIDT. As a result, the BT-dIDT-based OSCs blending with PBDB-T exhibited higher power conversion efficiency (PCE) value of 10.52% with higher Jsc of 18.59 mA cm−2 than that of the DFB-dIDT-based devices (PCE of 6.71% with Jsc of 15.58 mA cm−2). These results demonstrate that the A2-D-A1-D-A2-type SMAs incorporated with a suitable electron-deficient core are promising candidates for high performance OSCs.

Boosting the performance of D–A–D type hole-transporting materials for perovskite solar cells via tuning the acceptor group

Phenanthrothiadiazole (PT) and triphenylenobisthiadiazole (TBT) are proposed as the acceptor groups of D–A–D-type HTMs, and compared with the benzothiadiazole (BT) unit, three small molecule HTMs are investigated theoretically.

Synthesis and Photovoltaic Property of Acceptor-Acceptor Conjugated Polymers Based on 4,7-Dithiophene Benzothiadiazole and Isoindigo Units

Synthesis and Photovoltaic Property of Acceptor-Acceptor Conjugated Polymers Based on 4,7-Dithiophene Benzothiadiazole and Isoindigo Units

Correction: A new non-fullerene acceptor based on the combination of a heptacyclic benzothiadiazole unit and a thiophene-fused end group achieving over 13% efficiency.

Correction for 'A new non-fullerene acceptor based on the combination of a heptacyclic benzothiadiazole unit and a thiophene-fused end group achieving over 13% efficiency' by Yunqiang Zhang et al., Phys. Chem. Chem. Phys., 2019, DOI: .

One-step synthesis of an acceptor–donor–acceptor small molecule based on indacenodithieno[3,2-b]thiophene and benzothiadiazole units for high-performance solution-processed organic field-effect transistors

We reported a one-step synthesis of a high-performance acceptor–donor–acceptor small molecule based on indacenodithieno[3,2-b]thiophene (IDTT) as the donor unit and benzothiadiazole (BT) as the acceptor unit.

Solar cells sensitized by porphyrin dyes containing a substituted carbazole donor with synergistically extended absorption and suppressed the dye aggregation

To achieve high power conversion efficiency (PCE), three porphyrin sensitizers have been synthesized and explored to simultaneously enhance the photocurrent (Jsc) and photovoltage (Voc). On basis of the XW4, a benzothiadiazole (BTD) unit has been introduced to afford XW57 with the aim to extend the absorption wavelength and enhance the light harvesting ability. As a result, a Jsc of 13.72 mA/cm2 has been obtained for XW57, higher than that of XW4. On this basis, XW58 has been prepared by modifying the carbazole-based donor with two bulky dihexyloxyphenyl groups, and the superior anti-aggregation character raises the Voc from 781 mV (XW4) to 844 mV. When both the BTD unit and the bulky groups are introduced to the acceptor and donor units, respectively, the resulting sensitizer XW59 exhibits a highest PCE value of 7.34% with synergistically enhanced Jsc of 13.19 mA/cm2 and Voc of 793 mV. These results provide further insight into developing high performance dye-sensitized solar cells