Donor–Acceptor Alternating Copolymer Based on Thermally Converted Isothianaphthene Dimer and Thiazolothiazole Subunits

Abstract

A novel donor–acceptor-conjugated polymer PBITT consisting of isothianaphthene (ITN) dimer donor unit and thiazolothiazole acceptor unit was synthesized by thermal conversion method. First, a soluble precursor polymer with an alternating main chain structure of bicyclo[2.2.2]octadiene (BCOD)-fused thiophene dimer and benzodithiophene (PPBITT) was synthesized by palladium(0)-catalyzed Stille coupling reaction. The BCOD moiety underwent the retro-Diels–Alder reaction by the thermal treatment of a red PPBITT film to afford a dark blue film of PBITT that was insoluble in any organic solvents. The optical bandgap of PBITT (1.3 eV) became significantly narrow compared with that of PPBITT (2.1 eV) due to the stabilized quinoid resonance structure of the PBITT main chain. The field-effect hole mobility (μh) of PBITT was determined to be 2.2 × 10–4 cm2 V–1 s–1 with on–off ratio (I on/I off) of 2.5 × 102, whereas the corresponding PPBITT-based device did not show any p- and n-type response. Organic photovoltaic (OPV) devices were fabricated based on the bulk heterojunction film of the polymers and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The device with the PBITT:PCBM film exhibited higher short-circuit current and lower open-circuit voltage than those of the PPBITT:PCBM-based device, resulting in the comparable power conversion efficiency (∼0.3%). These results obtained here will provide fundamental information on the design of thermally induced donor–acceptor alternating polymers for organic electronics.

Effect of Fluorine Substitution on Photovoltaic Properties of Benzothiadiazole–Carbazole Alternating Copolymers

“…The PSC devices were fabricated as follows. − Indium tin oxide (ITO) on a glass substrate with a sheet resistance of 5 Ω/sq (Geomatec) was used. The substrates were sonicated consecutively with acetone and ethanol for 15 min.…”

Design and control of organic semiconductors and their nanostructures for polymer–fullerene-based photovoltaic devices

“…The optical bandgap of P2 (1.3 eV) became signicantly narrow compared to that of P-P2 (2.1 eV) as a result of the stabilized quinoid resonance structure of the P2 main chain. 68 The eld-effect hole mobility (m h ) of P2 was determined to be 2.2 Â 10 À4 cm 2 V À1 s À1 with an on-off ratio (I on /I off ) of 2.5 Â 10 2 , whereas the corresponding P-P2-based device did not show any p-and n-type response. PSC devices were fabricated based on a BHJ lm of the polymers and [60]PCBM.…”

“…The photoresponse of the P2: [60]PCBMbased device ranges widely from 400 nm to 900 nm in the incident photon-to-current efficiency (IPCE) spectrum, reecting the broad absorption band of P2. 68 However, the device performances are still unsatisfactory. To take full advantage of the broad absorption of the low bandgap polymers containing thermally induced ITN structures for high-performance photovoltaic devices, it would be essential to optimize the molecular alignment in the composite lms with [60]PCBM, which could be modulated by altering the side-chain structures and annealing conditions.…”

Photoactive Compounds Based on the Thiazolo[5,4‐d]thiazole Core and Their Application in Organic and Hybrid Photovoltaics

“…Firstly, the polymers synthesized in this fashion are sometimes characterized by low molecular weights and relatively large polydispersities, due to insufficient purity of the starting materials. [43] Secondly, yields are often unsatisfactory, due to difficult-to-optimize reaction condi-tions. Finally, small changes in the reaction stoichiometry or procedure can deeply affect the outcome, giving rise to polymers with very different properties and limiting the reproducibility of the process.…”