Benzothiadiazole Acceptor Unit Research Articles

Synthesis and characterisation of a new series of 2,6-linked-anthracene–benzothiadiazole based polymers for organic solar cells applications

A series of medium band gap alternating donor-acceptor conjugated polymers based on 2,6-linked anthracene flanked by thienyl donor units and benzothiadiazole acceptor units (BT) are prepared via direct arylation polymerization reactions. The prepared polymers show multiple absorption bands in both solutions and thin films with optical band gaps in the range of 1.75–1.85 eV. Polymers with alkylthienylethynyl substituents on the 9,10-positions of anthracene repeated units show broader absorption spectra compared to a polymer with alkynyl substituents. Photovoltaic studies of poly [9,10-bis [2-ethynyl-5-dodcylthiophene]-anthracene-2,6-diyl-alt-4,7-di(thiophene-2-yl)benzo [c] (Gopalakrishnan et al., 2022; Gokulnath et al., 2021; Bian et al., 2012) [1,2,5]thiadiazole] PATA(D)TBT in this series, blended with phenyl-C70-butyric acid methyl ester PC71BM shows a power conversion efficiency PCE of 0.76% and an open circuit voltage Voc of 0.54 V.

Polymer Additive SBS: More Sensitive to Fluorinated Asymmetric‐Indenothiophene‐Based Polymer Solar Cells

AbstractPolymer solar cells (PSCs) typically suffer from a negative effect of the residual solvent on the performance due to the use of the solvent processing additive. One solution to solve this problem is to use a solid polymer additive that can promote the phase separation of the blend film of the active layers. In this work, two new D−A type photovoltaic polymers, namely PIT‐DTBT and PIT‐DTffBT, based on asymmetric indenothiophene (IT) donor unit and nonfluorinated or difluorinated benzothiadiazole acceptor unit were designed and synthesized, respectively. Then a triblock copolymer, poly(styrene‐block‐butadiene‐block‐styrene) (SBS), was employed as a polymer additive into the active layers of PIT‐DTBT/PC71BM and PIT‐DTffBT/PC71BM based devices, and the SBS effect on the morphology of the blend films of the active layers, and then the performance of the two kinds of devices was investigated. The results demonstrated that the addition of SBS improved the molecule packing and induced the crystallization of PIT‐DTffBT, making the device have higher charge mobilities, more efficient charge dissociation and collection, and less charge recombination. Thus, power conversion efficiency (PCE) was increased from 4.61 % to 6.57 % for PIT‐DTffBT based device. Although almost no improvement in molecule packing and crystallization was observed for SBS‐treated nonfluorinated PIT‐DTBT, the fact of PCE of the PIT‐DTBT based device increased from 2.94 % to 3.13 % can also be attributed to the improved phase separation of the blend film by SBS. These findings indicate that SBS is more sensitive to fluorinated polymers than nonfluorinated polymers in improving molecule packing and inducing crystallization.

Novel Conjugated Polymers Containing 3-(2-Octyldodecyl)thieno[3,2-b]thiophene as a π-Bridge for Organic Photovoltaic Applications.

3-(2-Octyldodecyl)thieno[3,2-b]thiophen was successfully synthesized as a new π-bridge with a long branched side alkyl chain. Two donor-π-bridge-acceptor type copolymers were designed and synthesized by combining this π-bridge structure, a fluorinated benzothiadiazole acceptor unit, and a thiophene or thienothiophene donor unit, (PT-ODTTBT or PTT-ODTTBT respectively) through Stille polymerization. Inverted OPV devices with a structure of ITO/ZnO/polymer:PC71BM/MoO3/Ag were fabricated by spin-coating in ambient atmosphere or N2 within a glovebox to evaluate the photovoltaic performance of the synthesized polymers (effective active area: 0.09 cm2). The PTT-ODTTBT:PC71BM-based structure exhibited the highest organic photovoltaic (OPV) device performance, with a maximum power conversion efficiency (PCE) of 7.05 (6.88 ± 0.12)%, a high short-circuit current (Jsc) of 13.96 mA/cm2, and a fill factor (FF) of 66.94 (66.47 ± 0.63)%; whereas the PT-ODTTBT:PC71BM-based device achieved overall lower device performance. According to GIWAXS analysis, both neat and blend films of PTT-ODTTBT exhibited well-organized lamellar stacking, leading to a higher charge carrier mobility than that of PT-ODTTBT. Compared to PT-ODTTBT containing a thiophene donor unit, PTT-ODTTBT containing a thienothiophene donor unit exhibited higher crystallinity, preferential face-on orientation, and a bicontinuous interpenetrating network in the film, which are responsible for the improved OPV performance in terms of high Jsc, FF, and PCE.

Effect of fluorine substituted benzothiadiazole on electro-optical properties of donor-acceptor-donor type monomers and their polymers

A series of trimeric monomers bearing thiophene donor units and fluorinated analogues of benzothiadiazole acceptor units was synthesized via donor-acceptor-donor approach and polymerized electrochemically in order to investigate the effect of fluorine atom on electro-optical properties of both monomers and their corresponding polymers. All monomers exhibited solvatochromic and fluorescent properties. The introduction of fluorine atom into the conjugated backbone increased the oxidation potentials. Upon moving from nonfluorinated to fully fluorinated analogues, the oxidation potential shifts anodically from 1.30 V to 1.7 V. As in the case of monomers, the fluorine atom substitution also resulted in a decrease in the HOMO energy level of the corresponding polymers, leading to an increase in the electrochemical band gap energy (1.71–1.97 eV). This result can be attributed to deviations from planarity and also to decrease in the effective conjugation length. The polymeric film also exhibited electrochromic properties under various external potentials. Switching time and coloration efficiency values decreased with increasing number of fluorine atom substitution.

Effect of Structure Modification of Benzothiadiazole Acceptor Unit on the D-A-D-A-D Typed Oligothiophene Based Donor Materials for Organic Small Molecules Solar Cells: A Theoretical Study

Effect of Structure Modification of Benzothiadiazole Acceptor Unit on the D-A-D-A-D Typed Oligothiophene Based Donor Materials for Organic Small Molecules Solar Cells: A Theoretical Study

Dopant-free benzothiadiazole bridged hole transport materials for highly stable and efficient perovskite solar cells

D-A-D typed hole transport materials have been designed and synthesized with benzothiadiazole acceptor unit by introducing electron-withdrawing group fluorine atoms and electron-donating group alkoxy as side group. It is found that the three hole transport materials have a low-lying HOMO energy level and higher hole mobility. Furthermore, when these materials are applied in perovskite solar cell, the higher hole mobility (1.02 × 10−3 cm2 V−1 s−1) make the B3, which the fluorine atoms on core acceptor without dopants, get a power conversion efficiency of 12.1%, while spiro-OMeTAD based dopant-free perovskite solar cell only shows a 7.96% efficiency. In addition, the long-term stability of the perovskite solar cells based all the three hole transport materials improved greatly, especially B1-based cells show a favorable long-term stability, which keeps a 90% initial efficiency after 10 days at a relative humidity of 30%. Therefore, the D-A-D typed hole transport materials have a good application prospects in the field of perovskite solar cells with the incorporation of appropriate side group.

Investigation of Fluorine Atom Effect on Benzothiadiazole Acceptor Unit in Donor Acceptor Donor Systems

Synthesis of two new π-conjugated monomers containing fluorine substituted benzothiadiazoles as acceptor units and 3,4-ethylenedioxythiophene (EDOT) as donor unit was accomplished by facilitating Stille cross-coupling reactions (4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-5-fluorobenzo[c][1,2,5]thiadiazole (E2BTD-F) and 4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-5,6-difluorobenzo[c][1,2,5] thiadiazole (E2BTD-2F)). NMR and HRMS spectra of newly synthesized compounds are in agreement with the structures. To compare fluorine substitution effects, non-fluorinated analogue (4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)benzo[c][1,2,5]thiadiazole (E2BTD)) was also synthesized. Besides a blue shift in their absorption spectra, an anodic shift was also noted in the oxidation potentials of both monomers with fluorine atom substitution on the acceptor unit. This was further confirmed by DFT calculations such that upon fluorine substitution EDOT donor units deviate from planarity. Electropolymerization of the monomers were achieved successfully via potentiodynamic polymerization method. A similar trend in optoelectronic properties was also observed for the polymer films as for the monomers.

Donor-acceptor polymers containing thiazole-fused benzothiadiazole acceptor units for organic solar cells.

Two p-type semiconducting donor–acceptor polymers were designed and synthesized for use in organic solar cells. The polymers combine a benzodithiophene (BDT) donor and a thiazole-fused benzothiadiazole (TzBT) acceptor. Two TzBT acceptor units are compared, one with an alkylthio group (P1) and the other with a more strongly electron-withdrawing alkylsulfonyl group (P2) at the fused thiazole ring. The strongly electron-accepting nature of the TzBT unit lowers the lowest unoccupied molecular orbital (LUMO) energy of P1 and P2 relative to that of the BT analog (PBDT-BT), without altering the energy of the highest occupied molecular orbital (HOMO). Despite the smaller optical band gaps, bulk heterojunction organic solar cells fabricated using these polymers in a PC71BM blend showed high open-circuit voltages. The power conversion efficiency (PCE) of the P1-based device reached 6.13%. Though efficiency of the P2-based device was lower, photoelectric conversion extended into the near-IR region up to 950 nm.

An all-small-molecule organic solar cell derived from naphthalimide for solution-processed high-efficiency nonfullerene acceptors

Two small molecules BYG-1 and BYG-2 with fluorene donor and benzothiadiazole acceptor units connected to the terminal naphthamide group via ethyne linker were designed and synthesized.

A 1,1′-vinylene-fused indacenodithiophene-based low bandgap polymer for efficient polymer solar cells

A ladder-type polymer PIDTV-ffBT based on a 1,1′-vinylene-fused indacenodithiophene donor unit and a fluorinated benzothiadiazole acceptor unit was synthesized. The PSCs based on PIDTV-ffBT:PC71BM achieved a PCE of 7.3% with a high Jsc of 17.1 mA cm−2, which is the highest Jsc reported for ladder-type polymer-based PSCs.

Synthesis and characterization of two new benzothiadiazole- and fused bithiophene based low band-gap D–A copolymers: Application as donor bulk heterojunction polymer solar cells

Two new narrow bandgap D–A conjugated copolymers P1 and P2 containing different fused thiophene donor unit and same benzothiadiazole acceptor unit were synthesized by Stille cross-coupling polymerization, and characterized by 1H NMR, elemental analysis and GPC, TGA, DSC. Cyclic voltammetry measurement showed that the HOMO energy level both copolymers is deep lying (−5.10 and −5.35 eV for P1 and P2, respectively) which show that copolymers has good stability in the air and assured a higher open circuit voltage when it photovoltaic application. These copolymer were used as donor along with PC71BM and the BHJ polymer solar cells based on P1:PC71BM and P2:PC71BM processed with chloroform (CF) solvent showed over all PCE of 4.54% and 4.36%, respectively. Additionally, the PCE was improved up to 5.62% and 5.24% for P1:PC71BM and P2:PC71BM active layer processed with DIO (4 v%)/CF solvent. The enhancement in the PCE has been attributed to improved nanoscale morphology and crystalline nature of active layer as well as charge transport in the device with the addition of DIO, due to the higher boiling point of DIO causing slow evaporation rate during the film formation.

Synthesis and characterization of new silafluorene-based copolymers for polymer solar cells.

A series of silafluorene-based copolymers, poly[9-(2-ethylhexyl)-9-dodecyl-silafluorene-2,7-diyl-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (P1), poly[9-(2-ethylhexyl)-9-dodecyl-silafluorene-2,7-diyl-alt-2,5-bis-(thiophene-2-yl)thiazolo [5,4-d]thiazole] (P2), and poly[9-(2-ethylhexyl)-9-dodecyl-silafluorene-2,7-diyl-alt-5,5-(5',8'-di-2-thienyl-2,3-bis(4-octyloxyl)phenyl)quinoxaline] (P3), were synthesized and used as donor materials in polymer solar cells (PSCs). The optical, electrochemical, and photovoltaic properties of the copolymers were investigated. The results indicate that the acceptor units in the copolymers influenced the band gap, electronic energy levels, and photovoltaic properties of the copolymers significantly. The band gaps of the copolymers were in the range 1.82-2.10 eV. Under optimized conditions, the silafluorene-based polymers showed power conversion efficiencies (PCEs) for the PSCs in the range 1.31-1.69% under AM 1.5 illumination (100 mW/cm2). Among the three copolymers, P1, which contained a benzothiadiazole acceptor unit, showed a power conversion efficiency of 1.69% with a short circuit current of 4.59 mA/cm2, open circuit voltage of 0.88 V, and a fill factor of 0.42, under AM 1.5 illumination (100 mW/cm2).

Effect of Nanocrystalline Domains in Photovoltaic Devices with Benzodithiophene-Based Donor–Acceptor Copolymers

We have investigated the effects of thin-film morphology on the photovolatic performance for a series of donor–acceptor copolymers based on benzodithiophene donor and benzothiadiazole acceptor units. Photovoltaic devices incorporating polymer:fullerene blends show highest efficiencies (up to 6%) for those polymers exhibiting the least degree of crystallinity in X-ray diffraction patterns and a corresponding lowest surface roughness in thin films. We find that the existence of such crystalline domains in thin polymer films correlates well with spectral signatures of polymer chain aggregates already present in solution prior to casting of the film. Polymer solubility and casting conditions therefore appear to be crucial factors for enhancing efficiencies of photovoltaic devices based on such donor–acceptor copolymers. To examine why the presence of crystallite domains lowers device efficiencies, we measured exciton diffusion lengths by modeling the time-dependent photoluminescence from thin polymer films de...

Effects of fluorination on the properties of thieno[3,2-b]thiophene-bridged donor–π–acceptor polymer semiconductors

Thieno[3,2-b]thiophene-bridged polymer semiconductors, P(BDT-TT-HBT) and P(BDT-TT-FBT), combining a benzo[1,2-b:4,5-b′]dithiophene donor unit and a benzothiadiazole or fluorinated benzothiadiazole acceptor unit, respectively, were designed and synthesized. The introduction of fluorine substituents remarkably influenced the molecular architecture, optical, electrochemical, and morphological properties of the polymers, as well as the optoelectronic performance of the devices made from these materials. The introduction of fluorine substituents on the benzothiadiazole unit not only down-shifted the HOMO energy level of the organic semiconductor but also enhanced the intra- and intermolecular interactions of the resulting conjugated polymer. As a result, the open-circuit voltage and mobility of corresponding devices based on the fluorinated polymer were enhanced markedly. Power conversion efficiencies of the polymer solar cells based on P(BDT-TT-HBT) and P(BDT-TT-FBT) reached 4.37% and 3.56%, with open circuit voltages of 0.72 and 0.81 V, respectively. The fluorinated polymer exhibited much higher mobilities (4.1 to 6.3 times) than the non-fluorinated polymer, reaching 0.017 cm2 V−1 s−1.

Effects of π-Conjugated Bridges on Photovoltaic Properties of Donor-π-Acceptor Conjugated Copolymers

A series of conjugated donor (D)-π-acceptor (A) copolymers, P(BDT-F-BT), P(BDT-T-BT), and P(BDT-TT-BT), based on benzodithiophene (BDT) donor unit and benzothiadiazole (BT) acceptor unit with different π-bridges, were designed and synthesized via a Pd-catalyzed Stille-coupling method. The π-bridges between the BDT donor unit and BT acceptor unit are furan (F) in P(BDT-F-BT), thiophene (T) in P(BDT-T-BT) and thieno[3,2-b]thiophene (TT) in P(BDT-TT-BT). It was found that the π-bridges significantly affect the molecular architecture and optoelectronic properties of the copolymers. With the π-bridge varied from furan to thiophene, then to thieno[3,2-b]thiophene, the shape of the molecular chains changed from z-shaped to almost straight line gradually. Band gaps of P(BDT-F-BT), P(BDT-T-BT) and P(BDT-TT-BT) were tuned from 1.96 to 1.82 to 1.78 eV with HOMO levels up-shifted from −5.44 to −5.35 to −5.21 eV, respectively. Bulk heterojunction solar cells with the polymers as donor and PC71BM as acceptor demonstrated power conversion efficiency varied from 2.81% for P(BDT-F-BT) to 3.72% for P(BDT-T-BT) and to 4.93% for P(BDT-TT-BT). Compared to furan and thiophene, thieno[3,2-b]thiophene π-bridge in the copolymers shows superior photovoltaic performance. The results indicate that the photovoltaic performance of some high efficiency D–A copolymers reported in literatures could be improved further by inserting suitable π-bridges.

Immobilization of Invertase in DAD Type Polymers: Combination of Benzothiadiazole Acceptor Unit and 3,4-Ethylenedioxythiophene and Thiophene Donor Units

Conductive polymers with donor-acceptor-donor (DAD) type units; benzothiadiazole acceptor unit and 3,4-ethylenedioxythiophene (EDOT) and thiophene (Th) donor units, were investigated for immobilization of invertase. The polymers were prepared potentiodynamically from their monomers, M1 (Th-benzothiadiazole-Th), M2 (EDOT-benzothiadiazole-EDOT), M3 (Th-benzothiadiazole-EDOT) and a copolymer, which is a homolog to homopolymer of M3, was prepared from M1 and M2. Invertase was trapped between a two layer-composite; DAD polymer and polypyrrole. The characterization of immobilized invertase was performed using a spectrophotometric method at 540 nm. Kinetic parameters, V max, maximum reaction rate and Km , Michaelis-Menten constant values of immobilized invertase in DAD type homopolymer (P3), 0.95 μmol min−1 and 22.7 mM, respectively, are found between those of homopolymers P1 and P2 and are better than the copolymer. Polymers and copolymers exhibited a broad optimal temperature profile between 30 and 50°C compared to the free enzyme. Optimum pH (5.0) is the same as for free invertase. The electrodes were found to be stable with 100% activity during one day for 40 consecutive measurements. As to the self-life, 25% of the initial activity was lost in the first ten days, then the electrodes were stable with 75% activity for a 40 day storage at 4°C.