Enhanced Performance of Polymer Solar Cells Comprising Diketopyrrolopyrrole-Based Regular Terpolymer Bearing Two Different π‑Extended Donor Units

New regular and random diketopyrrolopyrrole (DPP)-based terpolymers (i.e., Reg-PBDPPT and Ran-PBDPPT, respectively) bearing DPP as an electron deficient unit and 2,2′-bithiophene and (<i>E</i>)-1,2-di­(thiophen-2-yl)­ethene as electron donating units were designed and synthesized, and their performance in photovoltaic cells was investigated precisely. The absorption properties and highest occupied molecular orbital (HOMO) of Reg-PBDPPT were found to be different from those of Ran-PBDPPT. The results of grazing incidence X-ray diffraction experiments revealed that Ran-PBDPPT typically had a predominantly edge-on chain orientation on the substrate, whereas Reg-PBDPPT showed mixed chain orientation both in pristine and thermally annealed films. Although Reg-PBDPPT exhibited a lower degree of edge-on chain orientation on the substrate, the corresponding TFTs showed a high hole mobility of 0.42–0.96 cm² V^–1 s^–1 and maintained a high current on/off ratio (>10⁶). A polymer solar cell (PSC) composed of Reg-PBDPPT and PC₇₁BM exhibited power conversion efficiencies (PCE) of 5.24–5.45%, which were higher than those of the Ran-PBDPPT-based PSCs. The enhanced efficiency was supported by an increase in the short circuit current, which is strongly related to the unique internal crystalline morphology and pronounced nanophase segregation behavior in the blend films. These results obviously manifested that this synthetic strategy for regular conjugated terpolymers could be employed to control morphological properties to obtain high-performance PSCs

Enhanced Efficiency and Stability of Novel Pseudo-ternary Polymer Solar Cells Enabled by a Conjugated Donor Block Copolymer

The recent breakthrough in power conversion efficiencies (PCEs) of polymer solar cells (PSCs) that contain an active layer of a ternary system has achieved values of 18–19%; this has sparked interest for further research. However, this system has difficulties in optimizing the composition and controlling the interaction between the three active materials. In this study, we investigated the use of a donor1 (D1)–donor2 (D2) conjugated block copolymer (CBP), PM6-b-TT, to replace the physical blend of two donors. PM6-b-TT, which exhibits an extended absorption range, was synthesized by covalently bonding PM6, a medium-band gap polymer, with PBDT-TT, a wide-band gap polymer. The blend films containing PM6-b-TT and Y6-BO acceptor, demonstrated excellent crystallinity and a film morphology favorable for PSCs. The corresponding pseudo-ternary PSC exhibited significantly higher PCE and thermal stability than the PM6:PBDT-TT-based ternary device. This study unambiguously demonstrates that the novel D1–D2 CBP strategy, combined with the conventional binary and ternary system advantages, is a promising material production strategy that can boost the performance of future PSCs

Bis(thienothiophenyl) Diketopyrrolopyrrole-Based Conjugated Polymers with Various Branched Alkyl Side Chains and Their Applications in Thin-Film Transistors and Polymer Solar Cells

New thienothiophene-flanked diketopyrrolopyrrole and thiophene-containing π-extended conjugated polymers with various branched alkyl side-chains were successfully synthesized. 2-Octyldodecyl, 2-decyltetradecyl, 2-tetradecylhexadecyl, 2-hexadecyloctadecyl, and 2-octadecyldocosyl groups were selected as the side-chain moieties and were anchored to the N-positions of the thienothiophene-flanked diketopyrrolopyrrole unit. All five polymers were found to be soluble owing to the bulkiness of the side chains. The thin-film transistor based on the 2-tetradecylhexadecyl-substituted polymer showed the highest hole mobility of 1.92 cm² V^–1 s^–1 due to it having the smallest π–π stacking distance between the polymer chains, which was determined by grazing incidence X-ray diffraction. Bulk heterojunction polymer solar cells incorporating [6,6]-phenyl-C71-butyric acid methyl ester as the n-type molecule and the additive 1,8-diiodooctane (1 vol %) were also constructed from the synthesized polymers without thermal annealing; the device containing the 2-octyldodecyl-substituted polymer exhibited the highest power conversion efficiency of 5.8%. Although all the polymers showed similar physical properties, their device performance was clearly influenced by the sizes of the branched alkyl side-chain groups

High-Performance Polymer Solar Cell with Single Active Material of Fully Conjugated Block Copolymer Composed of Wide-Band gap Donor and Narrow-Band gap Acceptor Blocks

We synthesized a novel fully conjugated block copolymer, <b>P3</b>, in which a wide-band gap donor block (<b>P1</b>) was connected to a narrow-band gap acceptor block (<b>P2</b>). As <b>P3</b> contains <b>P1</b> block with a wide bandgap and <b>P2</b> block with a narrow bandgap, it exhibits a very wide complementary absorption. Transient photoluminescence measurement using <b>P3</b> dilute solution demonstrated intramolecular charge transfer between the <b>P1</b> block and the <b>P2</b> block, which was not observed in a <b>P1</b>/<b>P2</b> blend solution. A <b>P3</b> thin film showed complete PL quenching because the photoinduced inter-/intramolecular charge transfer states were effectively formed. This phenomenon can play an important role in the photovoltaic properties of <b>P3</b>-based polymer solar cells. A single active material polymer solar cell (SAMPSC) fabricated from <b>P3</b> alone exhibited a high power conversion efficiency (PCE) of 3.87% with a high open-circuit voltage of 0.93 V and a short-circuit current of 8.26 mA/cm², demonstrating a much better performance than a binary <b>P1</b>-/<b>P2</b>-based polymer solar cell (PCE = 1.14%). This result facilitates the possible improvement of the photovoltaic performance of SAMPSCs by inducing favorable nanophase segregation between p- and n blocks. In addition, owing to the high morphological stability of the block copolymer, excellent shelf-life was observed in a <b>P3</b>-based SAMPSC compared with a <b>P1</b>/<b>P2</b>-based PSC

Acene-Containing Donor–Acceptor Conjugated Polymers: Correlation between the Structure of Donor Moiety, Charge Carrier Mobility, and Charge Transport Dynamics in Electronic Devices

We synthesized five different donor–acceptor (D–A) conjugated polymers bearing diketopyrrolopyrrole (DPP) acceptors and acene donors in the repeating groups via the Suzuki and Stille coupling methods. To investigate the effect of acene donor moieties on static and dynamic charge transport properties, pyrene, naphthodithiophene, benzodithiophene, dithieno­[3,2-<i>b</i>:2′,3′-<i>d</i>]­thiophene (DTT), and thieno­[3,2-<i>b</i>]­thieno­[2′,3′:4,5]­thieno­[2,3-<i>d</i>]­thiophene (TTTT) were selected and introduced into the structure of the polymer repeating group. Among the five polymers, the polymer PDPPTTTT bearing TTTT donor units exhibited the highest hole mobility, ∼3.2 cm² V^–1 s^–1 (<i>I</i>_on/<i>I</i>_off > 10⁶) in the thin film transistors. The five polymers had different mobilities and exhibited different charge transport dynamic responses. The response was investigated by applying a pulsed bias to thin film transistors loaded with a resistor. The resistor loaded (RL) inverter made of PDPPTTTT operates well, maintaining a fairly high switching voltage ratio at a relatively high frequency. The PDPPTTTT-based RL inverter also had the fastest switching behavior with a relatively small decay time of 1.86 ms. From this study, the structure of the donor moiety in the D–A conjugated polymer was found to strongly affect the optical property, internal morphology of the polymer film, charge carrier mobility, and charge transport dynamics in electronic devices

High-Performing Thin-Film Transistors in Large Spherulites of Conjugated Polymer Formed by Epitaxial Growth on Removable Organic Crystalline Templates

Diketopyrrolopyrrole (DPP)-based conjugated polymer <b>PDTDPPQT</b> was synthesized and was used to perform epitaxial polymer crystal growth on removable 1,3,5-trichlorobenzene crystallite templates. A thin-film transistor (TFT) was successfully fabricated in well-grown large spherulites of <b>PDTDPPQT</b>. The charge carrier mobility along the radial direction of the spherulites was measured to be 5.46–12.04 cm² V^–1 s^–1, which is significantly higher than that in the direction perpendicular to the radial direction. The dynamic response of charge transport was also investigated by applying a pulsed bias to TFTs loaded with a resistor (∼20 MΩ). The charge-transport behaviors along the radial direction and perpendicular to the radial direction were investigated by static and dynamic experiments through a resistor-loaded (RL) inverter. The RL inverter made of <b>PDTDPPQT</b>-based TFT operates well, maintaining a fairly high switching voltage ratio (<i>V</i>_out^ON/<i>V</i>_out^OFF) at a relatively high frequency when the source-drain electrodes are aligned parallel to the radial direction

Excellent Long-Term Stability of Power Conversion Efficiency in Non-Fullerene-Based Polymer Solar Cells Bearing Tricyanovinylene-Functionalized n‑Type Small Molecules

New small molecules having modified acceptor strength and π-conjugation length and containing dicyanovinylene (DCV) and tricyanovinylene (TCV) as a strongly electron-accepting unit with indacenodithiophene, IDT­(DCV)₂, IDT­(TCV)₂, and IDTT­(TCV)₂, were synthesized and studied in terms of their applicability to polymer solar cells with PTB7-Th as an electron-donating polymer. Intriguingly, the blended films containing IDT­(TCV)₂ and IDTT­(TCV)₂ exhibited superior shelf life stabilities of more than 1000 h without any reduction in the initial power conversion efficiency. The low-lying lowest unoccupied molecular orbital energy levels and robust internal morphologies of small TCV-containing molecules could afford excellent shelf life stability

Unconventional Three-Armed Luminogens Exhibiting Both Aggregation-Induced Emission and Thermally Activated Delayed Fluorescence Resulting in High-Performing Solution-Processed Organic Light-Emitting Diodes

In this work, three-armed luminogens <b>IAcTr-out</b> and <b>IAcTr-in</b> were synthesized and used as emitters bearing triazine and indenoacridine moieties in thermally activated delayed fluorescence organic light-emitting diodes (OLEDs). These molecules could form a uniform thin film via the solution process and also allowed the subsequent deposition of an electron transporting layer either by vacuum deposition or by an all-solution coating method. Intriguingly, the new luminogens displayed aggregation-induced emission (AIE), which is a unique photophysical phenomenon. As a nondoped emitting layer (EML), <b>IAcTr-in</b> showed external quantum efficiencies (EQEs) of 11.8% for the hybrid-solution processed OLED and 10.9% for the all-solution processed OLED with a low efficiency roll-off. This was evident by the higher photoluminescence quantum yield and higher rate constant of reverse intersystem crossing of <b>IAcTr-in</b>, as compared to <b>IAcTr-out</b>. These AIE luminogens were used as dopants and mixed with the well-known host material 1,3-bis­(<i>N</i>-carbazolyl)­benzene (mCP) to produce a high-efficiency OLED with a two-component EML. The maximum EQE of 17.5% was obtained when using EML with <b>IAcTr-out</b> doping (25 wt %) into mCP, and the OLED with EML bearing <b>IAcTr-in</b> and mCP showed a higher maximum EQE of 18.4% as in the case of the nondoped EML-based device

Manipulating Magneto-Optic Properties of a Chiral Polymer by Doping with Stable Organic Biradicals

We report the first example of tuning the large magneto-optic activity of a chiral polymer by addition of stable organic biradicals. The spectral dispersion of Verdet constant, which quantifies magneto-optic response, differs substantially between the base polymer and the nanocomposite. We employed a microscopic model, supported by atomistic calculations, to rationalize the behavior of this nanocomposite system. The suggested mechanism involves magnetic coupling between helical conjugated polymer fibrils, with spatially delocalized helical π-electron density, and the high density of spin states provided by the biradical dopants, which leads to synergistic enhancement of magneto-optic response. Our combined experimental and theoretical studies reveal that the manipulation of magnetic coupling in this new class of magneto-optic materials offers an opportunity to tailor the magnitude, sign, and spectral dispersion of the Verdet constant over a broad range of wavelengths, from the UV to the near-IR. This provides a new strategy for creating conformable materials with extraordinary magneto-optic activity, which can ultimately enable new applications requiring spatially and temporally resolved measurement of extremely weak magnetic fields. In particular, magneto-optic materials, presently employed in technologies like optical isolators and optical circulators, could be used in ultrasensitive optical magnetometers. This, in turn, could open a path toward mapping of brain activity via optical magnetoencephalography

New Bipolar Host Materials for Realizing Blue Phosphorescent Organic Light-Emitting Diodes with High Efficiency at 1000 cd/m²

New host molecules such as 9-(6-(9<i>H</i>-carbazol-9-yl)­pyridin-3-yl)-6-(9<i>H</i>-carbazol-9-yl)-9<i>H</i>-pyrido­[2,3-<i>b</i>]­indole (pPCB2CZ) and 9-(6-(9<i>H</i>-carbazol-9-yl)­pyridin-2-yl)-6-(9<i>H</i>-carbazol-9-yl)-9<i>H</i>-pyrido­[2,3-<i>b</i>]­indole (mPCB2CZ) were designed and synthesized for blue phosphorescent organic light-emitting diodes (PhOLEDs). The glass transition temperatures of two host molecules were measured higher than 120 °C, and the identical triplet energies were determined to be 2.92 eV for both molecules. The bis­(3,5-difluoro-2-(2-pyridyl)­phenyl-(2-carboxypyridyl)­iridium­(III) (FIrpic)-doped mPCB2CZ-based PhOLED exhibited practically useful driving voltage of 4.8 V in a simple organic three layer device configuration which has a smaller number of interfaces in conventional multilayer PhOLEDs. Also, the high quantum efficiency of 23.7% is reported at the practically useful brightness value of 1000 cd/m²