Joo‐Hong Lee

In recent years, surface defect passivation has become essential in the fabrication of perovskite solar cells (PSCs) with record-high efficiencies. However, the exact mechanism and all possible effects of surface passivation on the performance and stability of the PSCs have not been elucidated clearly. In this Perspective, we summarize the status of the current research on halide perovskite surfaces and their passivation, followed by a discussion of the important issues yet to be resolved. The m

Abstract For resolving toxicity issues of Pb‐based perovskites, Sn‐based perovskites have been widely studied as a promising alternative due to similar valence electron configuration between Sn 2+ and Pb 2+ . However, desired Sn 2+ in the precursor solution and film is easily oxidized to Sn 4+ , causing detrimental Sn vacancies and impurities in the films. Unfortunately, dimethyl sulfoxide, a ubiquitously used Lewis base for the fabrication of high‐quality perovskite thin films via the adduct ap

Metal halide perovskite solar cells (PSCs) are infamous for their batch-to-batch and lab-to-lab irreproducibility in terms of stability and performance. Reproducible fabrication of PSCs is a critical requirement for market viability and practical commercialization. PSC irreproducibility plagues all levels of the community; from institutional research laboratories, start-up companies, to large established corporations. In this work, the critical function of atmospheric humidity to regulate the cr

The metal contacts on metal halide perovskite thin films are often formed through physical vapor deposition (PVD) processes for investigation of the film properties or construction of optoelectronic devices. However, the PVD processes generate high-energy metal atoms, directly bombarding the film surface, potentially causing unintended damage in the film. In this study, we performed systematic investigation on the impact of a PVD-processed metal contact on the optoelectronic properties of underl

Excess charge carriers in metal halide perovskite layer have been known to accelerate degradation of the film and devices to cause poor operational stability of perovskite solar cells (PSCs). While mechanisms for such degradation have been predominantly studied for methylammonium‐based perovskites, effects of excess charge carriers and their interplays with other degradation causes are barely studied for widely used formamidinium‐based perovskites. Herein, a possible decomposition mechanism of t

Abstract Organic–inorganic or inorganic metal halide materials have emerged as a promising candidate for a resistive switching material owing to their ability to achieve low operating voltage, high on–off ratio, and multi‐level switching. However, the high switching variation, limited endurance, and poor reproducibility of the device hinder practical use of the memristors. In this study, a universal approach to address the issues using a van der Waals metal contact (vdWC) is reported. By transfe

Low-dimensional perovskites with large organic cations have shown great potential for boosting the luminescence efficiency of metal halide perovskite light-emitting diodes (PeLEDs). Although numerous successful results have been obtained for mixed two-dimensional (2D)/three-dimensional (3D) perovskite films, the correlation of the optoelectronic properties with the crystallographic properties and film composition remains elusive. Herein, we investigated the optoelectronic quality of thin films a

For the fabrication of thin-film electronics, conventional physical vapor deposition (PVD) processes have been widely used to form metal contacts on various thin films. However, the PVD process, involving thermally activated high-energy metal atoms, damages the underlying thin films, severely deteriorating the performance and stability of the device. The van der Waals (vdW) metal-contact approach has recently emerged to avoid this issue. By transferring predeposited metal contacts using vdW inte

Sn-based perovskite light-emitting diodes (PeLEDs) have emerged as promising alternatives to Pb-based PeLEDs with their rapid increase in performance owing to the various research studies on inhibiting Sn oxidation. However, the absence of defect passivation strategies for Sn-based perovskite LEDs necessitates further research in this field. We performed systematic studies to investigate the design rules for defect passivation agents for Sn-based perovskites by incorporating alkali/multivalent m

The organic-based memristive devices are widely studied as a next-generation electronics for eco-friendly wearable applications, thanks to materials` flexibility and biocompatibility. However, poor operational reliability and stability of the devices remain a critical challenge. Here, the study demonstrates a crystalline organohalide, Dabconium ammonium triiodide (DABCO-NH₄-I₃, DABCO is 1,4-diazabicyclo[2.2.2] octonium)-based memristive device with exceptionally high reliab

제조 로봇에 사용되는 감속기는 정밀한 반복운동을 하는 로봇에 있어 핵심적인 역할을 하기 때문에 감속기의 성능과 내구성은 로봇의 신뢰성에 매우 중요하다. 이에 본 논문은 로봇용으로 개발된 RV감속기의 신뢰성 검증을 위해 수명시험 모드와 가속수명시험법을 제안한다. 이를 위해 토크를 가속인자로 하는 계단형 스트레스 시험을 사전 시험으로 수행하여 가장 높은 가속 수준을 정한 후, 교정가속수명시험 방법에 따라 3개의 각기 다른 스트레스 수준에서 RV 감속기의 가속수명시험을 진행한다. 그리고 각각의 가속시험에서 얻어진 데이터를 외삽하여 정격 조건에서의 RV 감속기 수명을 추정하고, 통계적 분석법을 활용하여 다양한 수명 추정치와 신뢰성 정보를 확보하는 방법에 대하여 논하고자 한다.

Abstract Organic-inorganic or inorganic metal halide materials have emerged as a promising candidate for a resistive switching material owing to its capability to achieve low operating voltage, high on/off ratio and multi-level switching. However, the high switching variation, limited endurance and poor reproducibility of the device hinder practical use of the memristors. Here, we report a universal approach to relieve the issues by using a van der Waals metal contacts (vdWC). By transferring th

Crack fracture in large rotating shaft results in catastrophic failure in many industrial plants. To prevent this, a health index model is developed to diagnose the crack severity by the vibration sensor. A full-scale test rig was constructed with a similar configuration to the field conditions to reduce the associated uncertainties. Vibration signals were collected under various operating conditions for artificial cracks with different severities and locations. After identifying useful features