Tunable Thermoelectric Performance of the Nanocomposites Formed by Diketopyrrolopyrrole/Isoindigo-Based Donor–Acceptor Random Conjugated Copolymers and Carbon Nanotubes

This paper presents the development of thermoelectric properties in nanocomposites comprising donor–acceptor random conjugated copolymers and single-walled carbon nanotubes (SWCNTs). The composition of the conjugated polymers, specifically the ratio of diketopyrrolopyrrole (DPP) to isoindigo (IID), is manipulated to design a series of random conjugated copolymers (DPP0, DPP5, DPP10, DPP30, DPP50, DPP90, DPP95, and DPP100). The objective is to improve the dispersion of SWCNTs into smaller bundles, leading to enhanced thermoelectric properties of the polymer/SWCNT nanocomposite. This dispersion strategy promotes an interconnected conducting network, which plays a critical role in optimizing the thermoelectric performance. Accordingly, the effects of morphologies on the thermoelectric properties of the nanocomposites are systematically investigated. The DPP95/SWCNT nanocomposite exhibits the strongest interaction, resulting in the highest power factor (PF) of 711.1 μW m–1 K–2, derived from the high electrical conductivity of 1690 S cm–1 and Seebeck coefficient of 64.8 μV K–1. The prototype flexible thermoelectric generators assembled with a DPP95/SWCNT film achieve a maximum power output of 20.4 μW m–2 at a temperature difference of 29.3 K. These findings highlight the potential of manipulating the composition of random conjugated copolymers and incorporating SWCNTs to efficiently harvest low-grade waste heat in wearable thermoelectric devices

Impact of the Heteroatoms on Mobility–Stretchability Properties of <i>n</i>‑Type Semiconducting Polymers with Conjugation Break Spacers

The development of stretchable semiconducting polymers through statistical terpolymerization with conjugation break spacers (CBSs) has gained much attention. In this study, we systematically investigated the effects of incorporating CBSs with thioether units into naphthalenediimide (NDI)-based n-type semiconducting polymers on their semiconductivity and stretchability compared to polymers with the corresponding alkyl- and ether-based CBSs. Indeed, six NDI-based semiconducting polymers with CBSs composed of di(ethylene sulfide), tetra(ethylene sulfide), di(ethylene oxide), tetra(ethylene oxide), octylene, and tetradecylene units were synthesized by statistical terpolymerization based on Migita–Kosugi–Stille cross-coupling reactions of 5,5′-bis(trimethylstannyl)-2,2′-bithiophene (2T), 4,9-dibromo-2,7-bis(2-decyl­tetradecyl)­benzo[lmn][3,8]phenanthroline-1,3,6,8-tetraone (Br-NDI-Br), and CBSs. The experimental results indicate that heteroatom-based CBSs would sufficiently affect solid-state packing, intrinsic stretchability, and mobility retentions of the corresponding polymers. Although all of the polymers demonstrated strong edge-on orientations, those with ether-based CBSs displayed the lowest crystallinity among them. This result was attributed to the phase separation induced by highly polar ethylene oxide moieties, leading to inferior charge transport performances and low crack onset strain. In contrast, the thin film of the polymer with thioether-based CBSs showed delayed crack onset strain and a high dichroic ratio. The narrower bond angle of C–S–C (98.9°) than C–O–C (113.3°) calculated by the DFT method led to a more bent conformation along the polymer backbone, which provided a strain-releasing capability to realign the polymer chains. Consequently, the polymers with thioether-based CBSs displayed higher mobility–stretchability properties than those comprising ether-based CBSs. This is the first report on the design, synthesis, and application to organic field-effect transistors (OFETs) of stretchable n-type semiconducting polymer materials, clarifying the impact of heteroatoms on the mobility–stretchability properties of n-type semiconducting polymers with new CBSs having ethylene oxide and ethylene sulfide units

Tailoring Wavelength-Adaptive Visual Neuroplasticity Transitions of Synaptic Transistors Comprising Rod-Coil Block Copolymers for Dual-Mode Photoswitchable Learning/Forgetting Neural Functions

The vision-inspired artificial neural network based on optical synapses has drawn a tremendous amount of attention for emulating biological senses. Although photoexcitation-induced synaptic functionalities have been widely studied, optical habituation via the photoinhibitory pathway is yet to be demonstrated for sophisticated biomimetic visual adaptive systems. Here, the first optical neuromorphic block copolymer (BCP) phototransistor is demonstrated as an all-optical operation responding to various wavelengths, fulfilling photoassisted dynamic learning/forgetting cycles via optical potentiation without gate bias. The polyfluorene BCPs were precisely designed to enable wavelength-adaptive responses, benefiting from interfacial semiconductor/electret morphology and the crystallinity/electron affinity of the BCPs. Notably, this is the first work to simultaneously exhibit fully light-controlled short- and long-term memory based on organic material systems. The device presents a high current contrast above 100-fold and long-term retention over 104 s. As a proof-of-concept for neural networks, a 6 × 6 array of photosynapses performed outstanding visual pattern learning/forgetting with high accuracy. This study exploits the design strategy of a conjugated BCP electret to unleash the full potential of wavelength-adaptive visual neuroplasticity transitions. It provides an effective architecture for designing high-performance and high-storage capacity required applications in next-generation neuromorphic systems