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The hysteretic behavior of organic–inorganic halide perovskites (OHPs) are exploited for application in neuromorphic electronics. Artificial synapses with 2D and quasi‐2D perovskite are demonstrated that have a bulky organic cation (phenethylammonium (PEA)) to form structures of (PEA)2MAn‐1PbnBr3n+1. The OHP films have morphological properties that depend on their structure dimensionality (i.e., n value), and artificial synapses fabricated from them show synaptic responses such as short‐term plasticity, paired‐pulse facilitation, and long‐term plasticity. The operation mechanism of OHP artificial synapses are also analyzed depending on the dimensionality and it is found that quasi‐2D (n = 3–5) OHP artificial synapses show much longer retention than 2D and 3D OHP counterparts. The calculated energy consumption of a 2D OHP artificial synapse (≈0.7 fJ per synaptic event) is comparable to that of biological synapses (1–10 fJ per synaptic event). These OHP artificial synapses may enable development of neuromorphic electronics that use very little energy. [ABSTRACT FROM AUTHOR]

Highlights from the article: In article number 1901225, Tae-Woo Lee and co-workers suggest a strategy to improve the electroluminescence efficiency of Ruddlesden-Popper (RP) phase perovskite light-emitting diodes by introducing structurally modulated RP-phase perovskite emitters, which can improve the charge transport ability without hampering the confinement of the electron-hole pair. The randomly oriented RP-phase perovskite forces contact between inorganic layers and thereby improves charge transport ability and radiative recombination. Carrier transport, nanocrystal orientation, nanocrystal pinning, quasi-2D perovskite, structural modulation.

Ruddlesden–Popper phase (RP‐phase) perovskites that consist of 2D perovskite slabs interleaved with bulky organic ammonium (OA) are favorable for light‐emitting diodes (LEDs). The critical limitation of LED applications is that the insulating OA arranged in a preferred orientation limits charge transport. Therefore, the ideal solution is to achieve a randomly connected structure that can improve charge transport without hampering the confinement of the electron–hole pair. Here, a structurally modulated RP‐phase metal halide perovskite (MHP), (PEA)2(CH3NH3)m−1PbmBr3m+1 is introduced to make the randomly oriented RP‐phase unit and ensure good connection between them by applying modified nanocrystal pinning, which leads to an increase in the efficiency of perovskite LEDs (PeLEDs). The randomly connected RP‐phase MHP forces contact between inorganic layers and thereby yields efficient charge transport and radiative recombination. Combined with an optimal dimensionality, (PEA)2(CH3NH3)2Pb3Br10, the structurally modulated RP‐phase MHP exhibits increased photoluminescence quantum efficiency, from 0.35% to 30.3%, and their PeLEDs show a 2,018 times higher current efficiency (20.18 cd A−1) than in the 2D PeLED (0.01 cd A−1) and 673 times than in the 3D PeLED (0.03 cd A−1) using the same film formation process. This approach provides insight on how to solve the limitation of RP‐phase MHP for efficient PeLEDs. [ABSTRACT FROM AUTHOR]