No abstract

Thus far, there is still no study systematically investigating the influence of asymmetric side-chain design on a polymer’s stretchability and its associated stretchable device applications. Herein, three kinds of asymmetric side chains consisting of carbosilane side chain (Si-C8), siloxane-terminated side chain (SiO-C8), and decyltetradecane side chain (DT) are engineered in isoindigo-bithiophene (PII2T, P1–P3) and isoindigo-difluorobithiophene (PII2TF, P4–P6) conjugated polymers, and their structure–stretchability correlation is explored in field-effect transistor characterization. It is revealed that owing to the geometric difference between the side chains, different asymmetric side-chain combinations impose distinct influences on the molecular stacking and orientation of the derived polymers. Surprisingly, the combination of asymmetric side chains and backbone fluorination is shown to deliver the best stretchability and mechanical durability of the derived polymer. Consequently, P6 consisting of asymmetric Si-C8/DT side chains and fluorinated backbone possesses the best mobility preservation of 81% at 100% strain with the stretching force perpendicular to the charge-transporting direction. Moreover, it presents 90% mobility retention after 400 stretching–releasing cycles with 60% strain, greatly exceeding the value (36%) of the non-fluorinated counterpart (P3). Our results suggest that the rational design of asymmetric side chains and backbone fluorination provides an efficient way to enhance the intrinsic stretchability of conjugated polymers.

Polymers with an abundant amorphous domain should facilitate energy dissipation upon stretching, making near amorphous π-conjugated polymers have immense potential in realizing intrinsically stretchable field-effect transistor (FET) devices. In this study, high mobility preservation under the stretched state is attempted by replacing typical alkyl-monothienyl (T-R) on a benzo­[1,2-b:4,5-b’]­dithiophene-difluorobenzothiadiazole backbone with three other biaxially extended side-chains, including alkyl-dithienyl (2T-R), branching alkyl-trithienyl (3T-R), and alkyl-benzotrithienyl (B3T-R) groups. Despite showing near amorphous features, the semi-2D BDT-based polymers with bulkier biaxially extended side chains (PBDT-2T, PBDT-3T, and PBDT-B3T) still present comparable mobility to the reference semicrystalline polymer (PBDT-T). Although these four polymers yield comparable mobility, they show distinctly different mobility retention in the stretched state. From the study of their mobility-stretchability relationship, the interdigitating and/or entanglement of these biaxially extended conjugated side chains are shown to play a nontrivial role in the resultant mechanical robustness against the stretching force. Owing to the proper spatial mobility and geometry, the branched 3T-R side chain possesses a more intense interdigitating and/or entanglement capability than the linear 2T-R one and the fused B3T-R one, providing better mechanical strength under stretched states. Meanwhile, it maintains sufficient interchain connectivity for intermittent interchain hopping to compensate for the 1D charge transport along the backbone, ensuring good charge transport even in the stretched state. As a result, the printed PBDT-3T film is demonstrated to deliver a high mobility retention of 73% at a 60% strain exerted parallel to the charge-transporting direction and a very stable mobility retention of 88% after 1000 stretching-releasing cycles at a 60% strain, being one of the best stretchable near amorphous conjugated polymers reported thus far. Our result underlines the effectiveness of using biaxially extended conjugated side chains to realize high-performance stretchable polymers.

Photonic data storage has diverse optoelectronic applications such as optical sensing and recording, integrated image circuits, and multibit-storage flash memory. In this study, we employ conjugated/insulated polymer blends as the charge storage electret for photonic field-effect transistor memory devices by exploring the blend composition, energy level alignment, and morphology on the memory characteristics. The studied conjugated polymers included poly­(9,9-di-n-octylfluorenyl-2,7-diyl) (PF), poly­[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), poly­[{2,5-di­(3′,7′-dimethyloctyloxy)-1,4-phenylene-vinylene}-co-{3-(4′-(3″,7″-dimethyloctyloxy)­phenyl)-1,4-phenylenevinylene}-co-{3-(3′-(3′,7′-dimethyloctyloxy)­phenyl)-1,4-phenylenevinylene}] (SY-PPV), and poly­[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo­[2,1,3]­thiadiazol-4,8-diyl)] (F8BT), and the insulated polymers were polystyrene (PS) and poly­(methyl methacrylate) (PMMA). The photonic memory device using the PF/PS blend electret exhibited a dynamic switching behavior with light-writing and voltage-erasing processes both within only 1 s, along with a high contrast on the current on/off ratio between “Photo-On” and “Electrical-OFF” over 106 and the decent retention time for more than 3 months. In addition, the multilevel memory behavior could be observed using different light sources of 405, 450, and 520 nm or energy intensity, which was supported by surface potential analysis. The characteristics were superior to those of the devices using PF/PMMA blend due to the higher charge storage behavior of PS supported by fluorescence analysis. The PF/PS blend film prepared from the chlorobenzene solvent exhibited mesh-like and aggregated PF domains in the PS matrix and enhanced the contact surface area between the semiconductor and blend electret, leading to a higher memory window. The photonic memory behavior was also observed in the blend electrets of PS with the low band gap polymer, MEH-PPV, SY-PPV, or F8BT, by changing the photoresponsive light sources. Our study demonstrated a new electret system to apply on the multilevel photonic memory devices.

A novel approach for using conjugated rod–coil materials as a floating gate in the fabrication of nonvolatile photonic transistor memory devices, consisting of n‐type Sol‐PDI and p‐type C10‐DNTT, is presented. Sol‐PDI and C10‐DNTT are used as dual functions of charge‐trapping (conjugated rod) and tunneling (insulating coil), while n‐type BPE‐PDI and p‐type DNTT are employed as the corresponding transporting layers. By using the same conjugated rod in the memory layer and transporting channel with a self‐assembled structure, both n‐type and p‐type memory devices exhibit a fast response, a high current contrast between “Photo‐On” and “Electrical‐Off” bistable states over 105, and an extremely low programing driving force of 0.1 V. The fabricated photon‐driven memory devices exhibit a quick response to different wavelengths of light and a broadband light response that highlight their promising potential for light‐recorder and synaptic device applications.

We report the synthesis, morphology and photo-memory device applications of a block copolymer (BCP) consisting of poly(9,9-dioctylfluorene) (PFO) and polystyrene (PS).

Intrinsically stretchable isoindigo–bithiophene conjugated copolymers for organic field-effect transistors with high carrier mobility were achieved using hydrogen-bonded poly(acrylate amide) side chains.

No abstract