Switching from electron to hole transport in solution-processed organic blend field-effect transistors

Organic electronics became an attractive alternative for practical applications in complementary logic circuits due to the unique features of organic semiconductors such as solution processability and ease of large-area manufacturing. Bulk heterojunctions (BHJ), consisting of a blend of two organic semiconductors of different electronic affinities, allow fabrication of a broad range of devices such as light-emitting transistors, light-emitting diodes, photovoltaics, photodetectors, ambipolar transistors and sensors. In this work, the charge carrier transport of BHJ films in field-effect transistors is switched from electron to hole domination upon processing and post-treatment. Low molecular weight n-type N,N′-bis(n-octyl)-(1,7&1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI8-CN2) was blended with p-type poly[2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14) and deposited by spin-coating to form BHJ films. Systematic investigation of the role of rotation speed, solution temperature, and thermal annealing on thin film morphology was performed using atomic force microscopy, scanning electron microscopy, and grazing incidence wide-angle X-ray scattering. It has been determined that upon thermal annealing the BHJ morphology is modified from small interconnected PDI8-CN2 crystals uniformly distributed in the polymer fraction to large planar PDI8-CN2 crystal domains on top of the blend film, leading to the switch from electron to hole transport in field-effect transistors

Optimization of the Ablative Laser Cutting of Shadow Mask for Organic FET Electrode Fabrication

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

Molecular Ordering of Dithieno[2,3‑<i>d</i>;2′,3′‑<i>d</i>]benzo[2,1‑<i>b</i>:3,4‑<i>b</i>′]dithiophenes for Field-Effect Transistors

Four derivatives of dithieno­[2,3-<i>d</i>;2′,3′-<i>d</i>′]­benzo­[1,2-<i>b</i>;3,4-<i>b</i>′]­dithiophene (<b>DT<i>m</i>BDT</b>) have been synthesized to investigate the correlation between molecular structure, thin-film organization, and charge-carrier transport. Phenyl or thiophene end-capped derivatives at alpha positions of the outer thiophenes of <b>DT<i>m</i>BDT</b> present vastly different optoelectronic properties in comparison with bay-position alkyl-chain-substituted <b>DT<i>m</i>BDT</b>, which was additionally confirmed by density functional theory simulations. The film morphology of the derivatives strongly depends on alkyl substituents, aromatic end-caps, and substrate temperature. Field-effect transistors based on <b>DT<i>m</i>BDT</b> derivatives with bay-substituted alkyl chains show the best performance within this studied series with a hole mobility up to 0.75 cm²/V s. Attachment of aromatic end-caps disturbs the ordering, limiting the charge-carrier transport. Higher substrate temperature during deposition of the <b>DT<i>m</i>BDT</b> derivatives with aromatic end-caps results in larger domains and improved the transistor mobilities but not beyond the alkylated <b>DT<i>m</i>BDT</b>

Zygmunt Charzyński. Selected Paper

The volume is published on the occasion of the 70th anniversary of the establishment in 1945 the University of Łódź. Professor Zygmunt Charzyński was employed in the University since 1952 until 1995