The impact of the chemical structure and molecular order on the charge transport properties of two donor-acceptor copolymers in their neutral and doped states is investigated. Both polymers comprise 3,7-bis((E)-7-fluoro-1-(2-octyl-dodecyl)-2-oxoindolin-3-ylidene)-3,7-dihydrobenzo[1,2-b:4,5-b′] difuran-2,6-dione (FBDOPV) as electron-accepting unit, copolymerized with 9,9-dioctyl-fluorene (P(FBDOPV-F)) or with 3-dodecyl-2,2′-bithiophene (P(FBDOPV-2T-C 12 )). These copolymers possess an amorphous and semicrystalline nature, respectively, and exhibit remarkable electron mobilities of 0.065 and 0.25 cm 2 V -1 s -1 in field effect transistors. However, after chemical n-doping with 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl) dimethylamine (N-DMBI), electrical conductivities four orders of magnitude higher can be achieved for P(FBDOPV-2T-C 12 ) (σ = 0.042 S cm −1 ). More charge-transfer complexes are formed between P(FBDOPV-F) and N-DMBI, but the highly localized polaronic states poorly contribute to the charge transport. Doped P(FBDOPV-2T-C 12 ) exhibits a negative Seebeck coefficient of -265 µV K −1 and a thermoelectric power factor (PF) of 0.30 µW m −1 K −2 at 303 K which increases to 0.72 µW m −1 K −2 at 388 K. The in-plane thermal conductivity (κ || = 0.53 W m −1 K −1 ) on the same micrometer-thick solution-processed film is measured, resulting in a figure of merit (ZT) of 5.0 × 10 −4 at 388 K. The results provide important design guidelines to improve the doping efficiency and thermoelectric properties of n-type organic semiconductors.
Mechanical durability is one of the main obstacles of flexible organic electronic devices. In this work, the fatigue behavior of flexible field‐effect transistors based on a diketopyrrolo‐pyrrole‐dithienylthieno[3,2‐b]thiophene polymer is reported. An especially for that purpose designed bending setup allows to perform precise multiple deformation cycles of the transistor channel area while monitoring the device behavior. The transistors show high operational stability upon 100 bending cycles at a radius of 500 µm. Bending at smaller radius of 100 µm leaves the functionality of the parylene dielectric intact but induces serious mechanical fractures in the semiconducting film. Despite macroscopic defects, the transistors still reveal good reliability including high charge carrier mobility, due to presence of sufficient pathways for the charge carrier transport and to a low gate leakage. It is also observed that thinner polymer films are more sensitive to the deformation‐induced defects leading to a larger decrease in device performance, especially during the initial bending cycles. In thicker DPP‐DTT films, the crack propagation less affects the semiconductor/dielectric interface, at which the main charge carrier transport take place, resulting in a more stable device operation. Therefore, the work provides fundamental understanding of the fatigue behavior of flexible transistors based on semiconducting polymers.
This article presents an ablative method of cutting masks from ultra-thin metal foils using nanosecond laser pulses. As a source of laser radiation, a pulsed fiber laser with a wavelength of 1062 nm with the duration of pulses from 15 to 220 nanoseconds (ns), was used in the research. The masks were made of stainless-steel foil with thicknesses of 30 µm, 35 µm, and 120 µm. Channels of different lengths from 50 to 300 µm were tested. The possibilities and limitations of the presented method are described. The optimization of the cutting process parameters was performed using the experiment planning techniques. A static, determined complete two-level plan (SP/DC 24) was used. On the basis of the analysis of the test structures, we designed and produced precise shading masks used in the process of organic field effect transistor (OFET) electrode evaporation. The ablative method proved suitable to produce masks with canals of minimum lengths of 70 µm. It offers facile, fast, and economically viable shadow mask fabrication for organic electronics applications, which moreover might enable fast prototyping and circuit design.
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