Perovskite light-emitting diodes (PeLEDs) based on three-dimensional (3D) polycrystalline perovskites suffer from ion migration, which causes overshoot of luminance over time during operation and reduces its operational lifetime. Here, we demonstrate 3D/2D hybrid PeLEDs with extremely reduced luminance overshoot and 21 times longer operational lifetime than 3D PeLEDs. The luminance overshoot ratio of 3D/2D hybrid PeLED is only 7.4% which is greatly lower than that of 3D PeLED (150.4%). The 3D/2D hybrid perovskite is obtained by adding a small amount of neutral benzylamine to methylammonium lead bromide, which induces a proton transfer from methylammonium to benzylamine and enables crystallization of 2D perovskite without destroying the 3D phase. Benzylammonium in the perovskite lattice suppresses formation of deep-trap states and ion migration, thereby enhances both operating stability and luminous efficiency based on its retardation effect in reorientation.

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Recently, perovskite solar cells (PSC) with high power-conversion efficiency (PCE) and long-term stability have been achieved by employing 2D perovskite layers on 3D perovskite light absorbers. However, in-depth studies on the material and the interface between the two perovskite layers are still required to understand the role of the 2D perovskite in PSCs. Self-crystallization of 2D perovskite is successfully induced by deposition of benzyl ammonium iodide (BnAI) on top of a 3D perovskite light absorber. The self-crystallized 2D perovskite can perform a multifunctional role in facilitating hole transfer, owing to its random crystalline orientation and passivating traps in the 3D perovskite. The use of the multifunctional 2D perovskite (M2P) leads to improvement in PCE and long-term stability of PSCs both with and without organic hole transporting material (HTM), 2,2′,7,7′-tetrakis-(N,N-di-pmethoxyphenyl-amine)-9,9′-spirobifluorene (spiro-OMeTAD) compared to the devices without the M2P.light absorbers have suffered from high defect density at the surfaces and grain boundaries, which can lead to nonradiative recombination and decrease PCEs of PSC. [6,8] Also, the volatile organic cation in the 3D perovskite lattice such as methylammonium (MA + ) and formamidinium (FA + ) degrades the stability of the perovskite itself and lifetime of PSCs. [9,10] In this regard, 2D perovskites have recently received substantial attention as they contain less-volatile bulkier organic cations, which can trigger passivation effect and lead to better water resistance, resulting in higher PCE and extended long-term stability of PSCs. Therefore, the deposition of 2D perovskite on top of the 3D perovskite has presented significant enhancement both in PCEs and stability of PSCs because the 3D/2D perovskite can take advantage of features of 2D perovskite while it can maintain the excellent optoelectronic properties of 3D perovskites. [11][12][13][14][15][16][17][18][19] In this study, we present the incorporation of self-crystallized multifunctional 2D perovskite (M2P) on top of a 3D perovskite (Cs 0.08 FA 0.77 MA 0.12 PbI 2.62 Br 0.35 ) light absorber. The self-crystallized M2P can facilitate hole transfer due to its randomly oriented crystalline structure and reduce the trap density in underlying 3D perovskite through a trap passivation effect. Therefore, the introduction of the M2P layer between 3D perovskite light absorber and hole transport material (HTM) in a PSC led to improvement in the PCE from 19.75% to 20.79% and long-term stability under simulated continuous sunlight, compared to the device without the M2P layer. Furthermore, we demonstrated the use of M2P as a hole-transporting layer (HTL) in a PSC without using the organic HTM, 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-OMeTAD), which resulted in PCE of 15.17%, which was greatly higher than PCE of the device without M2P (6.22%). Results and DiscussionWe developed layer-by-layer deposited self-crystallized 2D perovskite grown on top of 3D per...

Despite organic/inorganic lead halide perovskite solar cells becoming one of the most promising next-generation photovoltaic materials, instability under heat and light soaking remains unsolved. In this work, a highly hydrophobic cation, perfluorobenzylammonium iodide (5FBzAI), is designed and a 2D perovskite with reinforced intermolecular interactions is engineered, providing improved passivation at the interface that reduces charge recombination and enhances cell stability compared with benchmark 2D systems. Motivated by the strong halogen bond interaction, (5FBzAI) 2 PbI 4 used as a capping layer aligns in in-plane crystal orientation, inducing a reproducible increase of ≈60 mV in the V oc , a twofold improvement compared with its analogous monofluorinated phenylethylammonium iodide (PEAI) recently reported. This endows the system with high power conversion efficiency of 21.65% and extended operational stability after 1100 h of continuous illumination, outlining directions for future work. Lead halide perovskite solar cells (PSCs) have demonstrated unprecedented progress in device performance, allowing remarkable power conversion efficiency (PCE) of 25.2% in only one decade. With their unique combination of electrical and optical properties, [1-4] perovskites have the potential to overcome the energy-intensive manufacturing process associated with silicon photovoltaics while ensuring low-cost. Yet, hybrid 3D

Organic synaptic transistors using intrinsic (i.e., non‐doped) organic semiconductors have demonstrated various synaptic functions to mimic biological synapses, but the devices show limited long‐term retention behaviors although long‐term memory is essential for neuromorphic computing. To achieve long‐term retention time, correlating the synaptic responses with the microstructures of polymer semiconductor is an imperative step. It is shown that synaptic plasticity in ion‐gel‐gated organic synaptic transistors (IGOSTs) can be modulated by controlling the microstructure of organic semiconductors and that long‐term memory retention can be significantly prolonged by increasing their crystallinity. The crystallinity of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) films that are spun‐cast on bare and self‐assembled monolayer is systematically controlled, before and after thermal treatments. Long‐term retention tends to extend, as the crystallinity increases. To evaluate synaptic current decay behaviors, it is suggested that the relaxation is a result of de‐doping of the polymer semiconductor over time. The recognition of handwritten digits is simulated and a high classification accuracy (>92%) is achieved with IGOSTs including high crystalline P3HT film. The study provides fundamental information about the effects of polymer microstructure on synaptic plasticity of IGOSTs, which may be applicable in neuromorphic electronics.