Neuromorphic vision is reaching an important transition from proof-of-concept device demonstrations toward quantitative energy benchmarks and scalable hardware integration. Yet, a chemistry-centered understanding of what attojoule-scale neuromorphic vision requires from materials and interfaces remains underdeveloped. Two-terminal (2T) photoelectric synapses are particularly well positioned for this transition by integrating sensing, memory, and computation within compact device architectures, while their performance, stability, scalability, and sustainability are fundamentally governed by materials selection and interfacial chemistry. This review therefore examines 2T photoelectric synapses from a coupled materials-device-system perspective. Starting from biological synapses and the human visual pathway, key biological concepts are translated into measurable device metrics and learning rules, followed by a comparison of the structural and operational characteristics of 2T and three-terminal (3T) architectures. The principal physical mechanisms governing photoelectric synaptic plasticity are then systematically discussed. Building on this mechanistic framework, materials-by-design strategies are examined across oxides, organic semiconductors, halide perovskites, and two-dimensional materials, with particular attention to their roles in device performance, stability, and energy efficiency. Representative neuromorphic vision functions, ranging from retina-inspired preprocessing to image recognition, are further reviewed together with device- and system-level energy considerations. Finally, safe-and-sustainable-by-design (SSbD) principles are incorporated to connect materials development with long-term technological and environmental requirements. Overall, this review highlights how coordinated materials, device, and system design can guide the development of energy-efficient, scalable, stable, and sustainable 2T photoelectric synapses for next-generation neuromorphic vision.
Perovskite nanocrystals (PNCs) are promising active materials because of their outstanding optoelectronic properties, which are finely tunable via size and shape. However, previous synthetic methods such as hot-injection and ligand-assisted reprecipitation require a high synthesis temperature or provide limited access to homogeneous PNCs, leading to the present lack of commercial value and real-world applications of PNCs. Here, we report a room-temperature approach to synthesize PNCs within a liquid crystalline antisolvent, enabling access to PNCs with a precisely defined size and shape and with reduced surface defects. We demonstrate that elastic strains and long-range molecular ordering of the liquid crystals play a key role in not only regulating the growth of PNCs but also promoting high surface passivation of PNCs with ligands. The approach is a simple, rapid, and room-temperature process, yet it enables access to highly homogeneous PNCs on a mass scale with substantially reduced surface defect states leading to significantly enhanced optoelectronic features. Our results provide a versatile and generalizable strategy to be broadly compatible with a range of nanomaterials and other synthetic methods such as ligand exchange and microfluidic processes.
Organo-metal halide perovskite field-effect transistors present serious challenges in terms of device stability and hysteresis in the current-voltage characteristics. Migration of ions located at grain boundaries and surface defects in the perovskite film are the main reasons for instability and hysteresis issues. Here, we introduce a perovskite grain molecular cross-linking approach combined with amine-based surface passivation to address these issues. Molecular cross-linking was achieved through hydrogen bond interactions between perovskite halogens and dangling bonds present at grain boundaries and a hydrophobic cross-linker, namely diethyl-(12-phosphonododecyl)phosphonate, added to the precursor solution. With our approach, we obtained smooth and compact perovskite layers composed of tightly bound grains hence significantly suppressing the generation and migration of ions. Moreover, we achieved efficient surface passivation of the perovskite films upon surface treatment with an amine-bearing polymer, namely polyethylenimine ethoxylated. With our synergistic grain and surface passivation approach, we were able to demonstrate the first perovskite transistor with a complete lack of hysteresis and unprecedented stability upon continuous operation under ambient conditions. Added to the merits are its ambipolar transport of opposite carriers with balanced hole and electron mobilities of 4.02 and 3.35 cm2 V-1 s-1, respectively, its high Ion/Ioff ratio >104 and the lowest sub-threshold swing of 267 mV dec-1 reported to date for any perovskite transistor. These remarkable achievements obtained through a cost-effective molecular cross-linking of grains combined with amine-based surface passivation of the perovskite films open a new era and pave the way for the practical application of perovskite transistors in low-cost electronic circuits.
Expression of concern for 'A hysteresis-free perovskite transistor with exceptional stability through molecular cross-linking and amine-based surface passivation' by Hyeong Pil Kim et al., Nanoscale, 2020, 12, 7641-7650, https://doi.org/10.1039/C9NR10745B.
Correction and removal of expression of concern for 'A hysteresis-free perovskite transistor with exceptional stability through molecular cross-linking and amine-based surface passivation' by Hyeong Pil Kim et al., Nanoscale, 2020, 12, 7641-7650, https://doi.org/10.1039/C9NR10745B.