Metal Halide Perovskite/Electrode Contacts in Charge-Transporting-Layer-Free Devices

Microscale Lateral Perovskite Light Emitting Diode Realized by Self-Doping Phenomenon

High-definition near-eye display technology has extremely close sight distance, placing a higher demand on the size, performance, and array of light-emitting pixel devices. Based on the excellent photoelectric performance of metal halide perovskite materials, perovskite light-emitting diodes (PeLEDs) have high photoelectric conversion efficiency, adjustable emission spectra, and excellent charge transfer characteristics, demonstrating great prospects as next-generation light sources. Despite their potential, the solubility of perovskite in photoresist presents a hurdle for conventional micro/nano processing techniques, resulting in device sizes typically exceeding 50 μm. This limitation impedes the further downsizing of perovskite-based components. Herein, we propose a plane-structured PeLED device that can achieve microscale light-emitting diodes with a single pixel device size < 2 μm and a luminescence lifetime of approximately 3 s. This is accomplished by fabricating a patterned substrate and regulating ion distribution in the perovskite through self-doping effects to form a PN junction. This breakthrough overcomes the technical challenge of perovskite-photoresist incompatibility, which has hindered the development of perovskite materials in micro/nano optoelectronic devices. The strides made in this study open up promising avenues for the advancement of PeLEDs within the realm of micro/nano optoelectronic devices.

Investigation of the Role of K2SO4 Electrolyte in Hole Transport Layer for Efficient Quasi-2D Perovskite Light-Emitting Diodes

Quasi-two-dimensional (2D) perovskite light-emitting diodes are promising light sources for color display and lighting. However, poor carrier injection and transport between the bottom hole transport layer (HTL) and perovskite limit the device performance. Here we demonstrate a simple and effective way to modify the HTL for enhancing the performance of perovskite light-emitting diodes (PeLEDs). An electrolyte K2SO4 is used to mix with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as the hole transport layer. The K+ doping helped the quasi-2D perovskite phases grow vertically along the interface of the PEDOT:PSS, fine-modulate the phase distribution, and simultaneously reduce the defect density of quasi-2D perovskites. It also significantly reduced the exciton quenching and injection barrier at PEDOT:PSS and quasi-2D perovskite interface. The optimized green PeLEDs with the K2SO4 doped PEDOT:PSS HTL showed a maximum luminance of 17185 cd/m2 which is almost 4.7 times brighter than the control one, with a maximum external quantum efficiency of 18.64%.

Quantum Topological Neuristors for Advanced Neuromorphic Intelligent Systems

Neuromorphic artificial intelligence systems are the future of ultrahigh performance computing clusters to overcome complex scientific and economical challenges. Despite their importance, the advancement in quantum neuromorphic systems is slow without specific device design. To elucidate biomimicking mammalian brain synapses, a new class of quantum topological neuristors (QTN) with ultralow energy consumption (pJ) and higher switching speed (µs) is introduced. Bioinspired neural network characteristics of QTNs are the effects of edge state transport and tunable energy gap in the quantum topological insulator (QTI) materials. With augmented device and QTI material design, top notch neuromorphic behavior with effective learning-relearning-forgetting stages is demonstrated. Critically, to emulate the real-time neuromorphic efficiency, training of the QTNs is demonstrated with simple hand gesture game by interfacing them with artificial neural networks to perform decision-making operations. Strategically, the QTNs prove the possession of incomparable potential to realize next-gen neuromorphic computing for the development of intelligent machines and humanoids.

Quantifying and Reducing Ion Migration in Metal Halide Perovskites through Control of Mobile Ions

The presence of intrinsic ion migration in metal halide perovskites (MHPs) is one of the main reasons that perovskite solar cells (PSCs) are not stable under operation. In this work, we quantify the ion migration of PSCs and MHP thin films in terms of mobile ion concentration (N_o) and ionic mobility (µ) and demonstrate that N_o has a larger impact on device stability. We study the effect of small alkali metal A-site cation additives (e.g., Na⁺, K⁺, and Rb⁺) on ion migration. We show that the influence of moisture and cation additive on N_o is less significant than the choice of top electrode in PSCs. We also show that N_o in PSCs remains constant with an increase in temperature but μ increases with temperature because the activation energy is lower than that of ion formation. This work gives design principles regarding the importance of passivation and the effects of operational conditions on ion migration.