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

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

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

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