Unveiling the Role of Side Chain for Improving Nonvolatile Characteristics of Conjugated Polymers-Based Artificial Synapse.

Interest has grown in services that consume a significant amount of energy, such as large language models (LLMs), and research is being conducted worldwide on synaptic devices for neuromorphic hardware. However, various complex processes are problematic for the implementation of synaptic properties. Here, synaptic characteristics are implemented through a novel method, namely side chain control of conjugated polymers. The developed devices exhibit the characteristics of the biological brain, especially spike-timing-dependent plasticity (STDP), high-pass filtering, and long-term potentiation/depression (LTP/D). Moreover, the fabricated synaptic devices show enhanced nonvolatile characteristics, such as long retention time (≈102 s), high ratio of Gmax/Gmin, high linearity, and reliable cyclic endurance (≈103 pulses). This study presents a new pathway for next-generation neuromorphic computing by modulating conjugated polymers with side chain control, thereby achieving high-performance synaptic properties.

Revisiting the Classical Wide-Bandgap HOMO and Random Copolymers for Indoor Artificial Light Photovoltaics.

Organic indoor photovoltaics (IPVs) are attractive energy harvesting devices for low-power consumption electronic devices and the Internet of Things (IoTs) owing to their properties such as being lightweight, semitransparent, having multicoloring capability, and flexibility. It is important to match the absorption range of photoactive materials with the emission spectra of indoor light sources that have a visible range of 400-700 nm for IPVs to provide sustainable, high-power density. To this end, benzo[1,2-b:4,5-b']dithiophene-based homopolymer (PBDTT) is synthesized as a polymer donor, which is a classical material that has a wide bandgap with a deep highest occupied molecular orbitals (HOMO) level, and a series of random copolymers by incorporating thieno[3,4-c]pyrrole-4,6,-dione (TPD) as a weak electron acceptor unit in PBDTT. The composition of the TPD unit is varied to fine tune the absorption range of the polymers; the polymer containing 70% TPD (B30T70) perfectly covers the entire range of indoor lamps such as light-emitting diodes (LEDs) and fluorescent lamp (FL). Consequently, B30T70 shows a dramatic enhancement of the power conversion efficiency (PCE) from 1-sun (PCE: 6.0%) to the indoor environment (PCE: 18.3%) when fabricating organic IPVs by blending with PC71 BM. The simple, easy molecular design guidelines are suggested to develop photoactive materials for efficient organic IPVs.