Solution-processed polymeric semiconductor films are attracting wide interest for applications in flexible electronics, wherein environmental stability is still a big obstacle. In many polymeric thin-film electronic devices, vertical phase separation has been observed, which leads to film depth dependences of electronic properties. Here, a soft plasma-assisted surface etching method to improve the environmental stability and maintain the electronic properties of organic field-effect transistors (OFETs) is proposed, by which the unwanted thin-film surface (exposed to air) is selectively taken away upon soft plasma etching, and the layer beneath the surface (subsurface) is preserved without any damage to the subsurface’s structure or electronic function. Investigation of frequently used polymeric semiconductors poly(3-hexylthiophene) and poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4b′]dithiophen-2-yl)-alt [1,2,5]thiadiazolo[3,4-c]pyridine] shows that the crystallinity of the surface layer is higher than that of the subsurface layer. However, for p-type polymeric semiconductors, higher crystallinity usually leads to a lower ionization energy and higher doping concentration during exposure to air and thus a higher background conductivity, deteriorating the switching-off capability of the organic field-effect transistors (OFETs). Therefore, by removing this surface layer, the lifetime of OFETs in air is effectively increased by over 50%.
Organic field-effect transistors (OFETs) are attractive for next-generation electronics, while doping plays an important role in their performance optimization. In this work, a soluble molecular dopant with high electron affinity, CN6-CP, is investigated to manipulate the performance of OFETs with a p-type organic semiconductor as the transport layer. The performance of the model 2,7-didodecyl[1]benzothieno[3,2-b][1]benzothiophene (C12-BTBT) bottom-gate top-contact (BGTC) OFETs is greatly optimized upon doping by CN6-CP, and the field-effect mobility is improved from 5.5 to 11.1 cm 2 V −1 s −1 , with a widely tunable threshold voltage from −40 to +5 V. Improvements in performance also appear in CN6-CP doped BGBC OFETs. As compared with commonly used molecular dopant F4-TCNQ, CN6-CP exhibits excellent doping effects and great potential for organic electronic applications.
The preparation of micron- to nanometer-sized functional materials with well-defined shapes and packing is a key process to their applications. There are many ways to control the crystal growth of organic semiconductors. Adding polymer additives has been proven a robust strategy to optimize semiconductor crystal structure and the corresponding optoelectronic properties. We have found that poly(3-hexylthiophene) (P3HT) can effectively regulate the crystallization behavior of N,N′-dioctyl perylene diimide (C8PDI). In this study, we combined P3HT and polyethylene glycol (PEG) to amphiphilic block copolymers and studied the crystallization modification effect of these block copolymers. It is found that the crystallization modification effect of the block copolymers is retained and gradually enhanced with P3HT content. The length of C8PDI crystals were well controlled from 2 to 0.4 μm, and the width from 210 to 35 nm. On the other hand, due to the water solubility of PEG block, crystalline PEG-b-P3HT/C8PDI micelles in water were successfully prepared, and this water phase colloid could be stable for more than 2 weeks, which provides a new way to prepare pollution-free aqueous organic semiconductor inks for printing electronic devices.
Semiconducting polymers inherently exhibit polydispersity in terms of molecular structure and microscopic morphology, which often results in a broad distribution of energy levels for localized electronic states. Therefore, the bulk charge mobility strongly depends on the free charge density. In this study, we propose a method to measure the charge-density-dependent bulk mobility of conjugated polymer films with widely spread localized states using a conventional field-effect transistor configuration. The gate-induced variation of bulk charge density typically ranges within ±1018 cm−3; however, this range depends significantly on the energetic dispersion width of localized states. The field-effect bulk mobility and field-effect mobility near the semiconductor–dielectric interface along with their dependence on charge density can be simultaneously extracted from the transistor characteristics using various gate voltage ranges.
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