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47 result(s) for "Kang, Yoonmook"
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Unveiling the Hydrogen Diffusion During Degradation of Silicon Solar Cells
We investigated monocrystalline passivated emitter rear contact cells for light- and elevated-temperature-induced degradation. Among the cell performance factors, a short current density results in a significant decrease in the short term. The quantum efficiency is also affected by carrier recombination-active defects, especially in the case of the reference cell, which has a decreased quantum efficiency across the wavelength, unlike the commercial cell. The front side of the cell has a diffuse hydrogen distribution, and it is related to LeTID. We observe how the hydrogen changes during each process and the changes in the profile during the degradation. The hydrogen appears to redistribute within the silicon wafer and saturate at a certain equilibrium state. The hydrogen distribution is correlated with the changes in the lifetime and, finally, short current density. Regeneration occurs depending on the hydrogen concentration within the emitter, and the closer the concentration is to saturation, the less degradation occurs.
Investigation of Thermally Induced Degradation in CH3NH3PbI3 Perovskite Solar Cells using In-situ Synchrotron Radiation Analysis
In this study, we employ a combination of various in-situ surface analysis techniques to investigate the thermally induced degradation processes in MAPbI 3 perovskite solar cells (PeSCs) as a function of temperature under air-free conditions (no moisture and oxygen). Through a comprehensive approach that combines in-situ grazing-incidence wide-angle X-ray diffraction (GIWAXD) and high-resolution X-ray photoelectron spectroscopy (HR-XPS) measurements, we confirm that the surface structure of MAPbI 3 perovskite film changes to an intermediate phase and decomposes to CH 3 I, NH 3 , and PbI 2 after both a short (20 min) exposure to heat stress at 100 °C and a long exposure (>1 hour) at 80 °C. Moreover, we observe clearly the changes in the orientation of CH 3 NH 3 + organic cations with respect to the substrate in the intermediate phase, which might be linked directly to the thermal degradation processes in MAPbI 3 perovskites. These results provide important progress towards improved understanding of the thermal degradation mechanisms in perovskite materials and will facilitate improvements in the design and fabrication of perovskite solar cells with better thermal stability.
UV Degradation and Recovery of Perovskite Solar Cells
Although the power conversion efficiency of perovskite solar cells has increased from 3.81% to 22.1% in just 7 years, they still suffer from stability issues, as they degrade upon exposure to moisture, UV light, heat, and bias voltage. We herein examined the degradation of perovskite solar cells in the presence of UV light alone. The cells were exposed to 365 nm UV light for over 1,000 h under inert gas at <0.5 ppm humidity without encapsulation. 1-sun illumination after UV degradation resulted in recovery of the fill factor and power conversion efficiency. Furthermore, during exposure to consecutive UV light, the diminished short circuit current density (J sc ) and EQE continuously restored. 1-sun light soaking induced recovery is considered to be caused by resolving of stacked charges and defect state neutralization. The J sc and EQE bounce-back phenomenon is attributed to the beneficial effects of PbI 2 which is generated by the decomposition of perovskite material.
Relationship between ion migration and interfacial degradation of CH3NH3PbI3 perovskite solar cells under thermal conditions
Organic-inorganic hybrid perovskite solar cells (PSCs) have been extensively studied because of their outstanding performance: a power conversion efficiency exceeding 22% has been achieved. The most commonly used PSCs consist of CH 3 NH 3 PbI 3 (MAPbI 3 ) with a hole-selective contact, such as 2,2′,7,7′-tetrakis( N , N -di- p -methoxyphenylamine)-9,9-spiro-bifluorene (spiro-OMeTAD), for collecting holes. From the perspective of long-term operation of solar cells, the cell performance and constituent layers (MAPbI 3 , spiro-OMeTAD, etc.) may be influenced by external conditions like temperature, light, etc. Herein, we report the effects of temperature on spiro-OMeTAD and the interface between MAPbI 3 and spiro-OMeTAD in a solar cell. It was confirmed that, at high temperatures (85 °C), I − and CH 3 NH 3 + (MA + ) diffused into the spiro-OMeTAD layer in the form of CH 3 NH 3 I (MAI). The diffused I − ions prevented oxidation of spiro-OMeTAD, thereby degrading the electrical properties of spiro-OMeTAD. Since ion diffusion can occur during outdoor operation, the structural design of PSCs must be considered to achieve long-term stability.
Accelerating High-Entropy Alloy Design via Machine Learning: Predicting Yield Strength from Composition
High-entropy alloys (HEAs) have attracted significant attention due to their exceptional physical, chemical, and mechanical properties. The current development of HEAs primarily depends on time-consuming and costly trial-and-error approaches, which not only hinder the efficient exploration of new compositions but also result in unnecessary resource and energy consumption, thereby negatively affecting sustainable development and production. To address this challenge, this study introduces a machine learning-based methodology for predicting the yield strengths of various HEA compositions. The model was trained using 181 data points and achieved an R2 performance score of 0.85. To further assess its reliability and generalization capability, the model was validated using external data not included in the collected dataset. The validation was performed across four categories: modified Cantor alloys, refractory HEAs, eutectic HEAs, and other HEAs. The predicted yield strength trends were found to align with the actual experimental trends, demonstrating the model’s robust performance across various categories of HEAs. The proposed machine learning approach is expected to facilitate the combinatorial design of HEAs, thereby enabling efficient optimization of compositions and accelerating the development of novel alloys. Moreover, it has the potential to serve as a guideline for sustainable alloy design and environmentally conscious production in future HEA development.
Review on Separation Processes of End-of-Life Silicon Photovoltaic Modules
Solar energy has gained prominence because of the increasing global attention received by renewable energies. This shift can be attributed to advancements and innovations in solar cell technology, which include developments of various photovoltaic materials, such as thin film and tandem solar cells, in addition to silicon-based solar cells. The latter is the most widely commercialized type of solar cell because of its exceptional durability, long-term stability, and high photoconversion efficiency; consequently, the demand for Si solar cells has been consistently increasing. PV modules are designed for an operation lifespan of 25–30 years, which has led to a gradual increase in the number of end-of-life PV modules. The appropriate management of both end-of-life and prematurely failed PV modules is critical for the recovery and separation of valuable and hazardous materials. Effective methods for end-of-life PV waste management are necessary to minimize their environmental impact and facilitate transition to a more sustainable and circular economy. This paper offers a comprehensive overview of the separation processes for silicon PV modules and summarizes the attempts to design easily recyclable modules for sustainable solar module development. Based on the studies summarized in this paper, suggestions are provided for future research.
A Review on Dry Deposition Techniques: Pathways to Enhanced Perovskite Solar Cells
This review discusses the use of evaporation, chemical vapor deposition, and sputtering as the three main dry deposition techniques currently available for fabricating perovskite solar cells. We outline the distinct advantages that each method offers in terms of film quality, control, and scalability. Additionally, recent advancements in process optimization and the integration of dry deposition with other fabrication techniques are highlighted. Thus, this review provides valuable insights into the potential of dry deposition processes to produce high-performance perovskite solar cells and aids researchers and industry professionals in selecting the most suitable technique for the fabrication of efficient and stable devices.
Perovskites fabricated on textured silicon surfaces for tandem solar cells
The silicon surface texture significantly affects the current density and efficiency of perovskite/silicon tandem solar cells. However, only a few studies have explored fabricating perovskite on textured silicon and the effect of texture on perovskite films because of the limitations of solution processes. Here we produce conformal perovskite on textured silicon with a dry two-step conversion process that incorporates lead oxide sputtering and direct contact with methyl ammonium iodide. To separately analyze the influence of each texture structure on perovskite films, patterned texture, high-resolution photoluminescence (μ-PL), and light beam-induced current (μ-LBIC), 3D mapping is used. This work elucidates conformal perovskite on textured surfaces and shows the effects of textured silicon on the perovskite layers with high-resolution 3D mapping. This approach can potentially be applied to any type of layer on any type of substrate. The efficiency of perovskite/silicon tandem solar cells is affected by silicon surface texture, however fabrication processes in solution limit surface studies. Here a perovskite layer on textured silicon is formed through a dry two-step conversion process with lead oxide sputtering and direct contact with methyl ammonium iodide.
The Diagnosis of Shunt Defects in CIGS Modules Using Lock-In Thermography: An Empirical Comparative Study
Shunt defects are often detected in solar panels intended for photovoltaic applications. However, existing nondestructive detection technologies have certain inherent drawbacks depending on the application scenario. In this context, this paper reports a comprehensive empirical investigation into lock-in thermography (LIT) and its applicability to diagnosing shunt defects in copper indium gallium selenide (CIGS) solar modules. LIT was compared with biased thermography, and its distinctive attributes were elucidated. The comparison results demonstrate the superior capabilities of LIT at enhancing the signal-to-noise ratio, improving the visibility, resolution, and quantification of defects, and highlighting the usefulness of LIT for advanced defect analysis. We explored scenarios in which biased thermography could be appropriate despite its inherent limitations and identified conditions under which it might be preferred. The complex thermal behavior of different types of defects under various voltage conditions was analyzed, contributing to a more nuanced understanding of their behavior. Thus, integrating experimental results and theoretical understanding, we provide valuable insights and scientific guidelines for photovoltaic research. Our findings could help enhance the efficiency of defect detection in CIGS modules, highlighting the critical role of optimized thermographic techniques in developing photovoltaic technologies.