• 한국재료학회지
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• 제30권10호
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• pp.515-521
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• 2020

Organic-inorganic hybrid perovskite nanocrystals have attracted a lot of attention owing to their excellent optical properties such as high absorption coefficient, high diffusion length, and photoluminescence quantum yield in optoelectronic applications. Despite the many advantages of optoelectronic materials, understanding on how these materials interact with their environments is still lacking. In this study, the fluorescence properties of methylammonium lead bromide (CH₃NH₃PbBr₃, MAPbBr₃) nanoparticles are investigated for the detection of volatile organic compounds (VOCs) and aliphatic amines (monoethylamine, diethylamine, and trimethylamine). In particular, colloidal MAPbBr₃ nanoparticles demonstrate a high selectivity in response to diethylamine, in which a significant photoluminescence (PL) quenching (~ 100 %) is observed at a concentration of 100 ppm. This selectivity to the aliphatic amines may originate from the relative size of the amine molecules that must be accommodated in the perovskite crystals structure with a narrow range of tolerance factor. Sensitive PL response of MAPbBr₃ nanocrystals suggests a simple and effective strategy for colorimetric and fluorescence sensing of aliphatic amines in organic solution phase.

• 한국전기전자재료학회논문지
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• 제33권2호
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• pp.118-122
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• 2020

Inorganic-organic hybrid perovskite solar cells have demonstrated a significant achievement by reaching a certified power conversion efficiency of 25.2% in 2019 as compared to that of 3.8% in 2009. However, organic hole conductors such as PTAA and spiro-OMeTAD are known to be expensive and unstable when they are exposed to operational conditions. In this study, the inorganic hole conductor CuSCN was used to overcome such concerns. The influence of dipropyl sulfide (DPS) and diethyl sulfide (DES) as CuSCN deposition solvents on the underlying perovskite active layer was investigated. DES solvent was observed to be advantageous in terms of CuSCN solubility and mild for the perovskite layer, thereby resulting in a power conversion efficiency of 16.9%.

• Electronic Materials Letters
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• 제14권6호
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• pp.657-668
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• 2018

Organic-inorganic hybrid lead halide perovskites have been extensively investigated for various optoelectronic applications. Particularly, owing to their ability to form highly crystalline and homogeneous films utilizing low-temperature solution processes (< $150^{\circ}C$), perovskites have become promising photoactive materials for realizing high-performance flexible solar cells. However, the current use of mesoporous $TiO_2$ scaff olds, which require high-temperature sintering processes (> $400^{\circ}C$), has limited the fabrication of perovskite solar cells on flexible substrates. Therefore, the development of a low-temperature processable charge-transporting layer has emerged as an urgent task for achieving flexible perovskite solar cells. This review summarizes the recent progress in low-temperature processable electron- and hole-transporting layer materials, which contribute to improved device performance in flexible perovskite solar cells.

• 한국재료학회지
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• 제31권9호
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• pp.496-501
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• 2021

Metal halide perovskite nanocrystals, due to their high absorption coefficient, high diffusion length, and photoluminescence quantum yield, have received significant attention in the fields of optoelectronic applications such as highly efficient photovoltaic cells and narrow-line-width light emitting diodes. Their energy band structure can be controlled via chemical exchange of the halide anion or monovalent cations in the perovskite nanocrystals. Recently, it has been demonstrated that chemical exfoliation of the halide perovskite crystal structure can be achieved by addition of organic ligands such as n-octylamine during the synthetic process. In this study, we systematically investigated the quantum confinement effect of methylammonium lead bromide (CH₃NH₃PbBr₃, MAPbBr₃) nanocrystals by precise control of the crystal thickness via chemical exfoliation using n-octylammonium bromide (OABr). We found that the crystalline thickness consistently decreases with increasing amounts of OABr, which has a larger ionic radius than that of CH₃NH₃⁺ ions. In particular, a significant quantum confinement effect is observed when the amounts of OABr are higher than 60 %, which exhibited a blue-shifted PL emission (~ 100 nm) as well as an increase of energy bandgap (~ 1.53 eV).

• 한국전기전자재료학회논문지
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• 제34권1호
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• pp.73-77
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• 2021

Inorganic-organic hybrid perovskite solar cells have demonstrated considerable improvements, reaching 25.5% of certified power conversion efficiency in 2020 from 3.8% in 2009. In normal structured perovskite solar cells, TiO2 electron-transporting materials require heat treatment process at a high temperature over 450℃ to induce crystallinity. Inverted perovskite solar cells have also been studied to exclude the additional thermal process by using [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as a non-oxide electron-transporting layer. However, the drawback of the PCBM layer is a charge accumulation at the interface between PCBM and a metal electrode. The impact of bathocuproin (BCP) buffer layer on photovoltaic performance has been investigated herein to solve the problem of PCBM. 2-mM BCP-modified perovskite solar cells were observed to exhibit a maximum efficiency of 12.03% compared with BCP-free counterparts (5.82%) due to the suppression of the charge accumulation at the PCBM-Au interface and the resulting reduction of the charge recombination between perovskite and the PCBM layer.

• 공업화학
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• 제33권1호
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• pp.78-82
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• 2022

무-유기 페로브스카이트 태양전지는 2009년 3.8%에서 2020년 25.5%로 급격한 광전변환효율 상승으로 실리콘 태양전지의 효율과 경쟁할 수준이 되었다. 하지만, 페로브스카이트의 구성성분 중 유기양이온인 메틸암모늄의 열화에 대한 취약성으로 인해 태양전지 소자의 안정성은 여전히 부족하여 상업화에 걸림돌이 되고 있다. 본 연구에서는 태양전지 소자의 광전변환효율의 감소를 최소화하면서 수분 안정성 향상을 위해 열화에 취약한 메틸암모늄의 일부를 소수성의 알킬 사슬이 긴 옥틸암모늄으로 소량 부분 도입하였다. 퓨리에 변환 적외선 흡수분광법과 자외선-가시광선 흡수분광법을 이용하여 옥틸암모늄이 페로브스카이트 결정 내에 도입되었을 확인하였다. 또한, 옥틸암모늄이 소량 부분 도입된 페로브스카이트 태양전지의 광전변환효율은 16.6%로 기존 페로브스카이트 태양전지(18.5%)에 비해 소폭 감소하였지만, 수분 안정성을 나타내는 접촉각은 57.0°에서 72.2°로 크게 향상되었음을 확인하였다. 본 연구는 소수성의 알킬사슬이 긴 유기 양이온을 도입하여 페로브스카이트 태양전지의 광전변환효율과 수분 안정성을 동시에 만족시키는 페로브스카이트 조성 기술 전략을 제공하고 있다.

• Current Photovoltaic Research
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• 제10권2호
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• pp.49-55
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• 2022

With rapid growth in light-harvesting efficiency from 3.8 to 25.8%, organic-inorganic hybrid perovskite solar cells (PSCs) have attracted great attention as promising photovoltaic devices. However, despite of their outstanding performance, the commercialization of PSCs has been suffered from severe stability issues, especially for UV and humidity: (i) UV irradiation towards PSCs is able to lead UV-induced decomposition of perovskite films or catalytic reactions of charge-transporting layers, and (ii) exposure to surrounding humidity causes irreversible hydration of perovskite layers by the penetration of water molecules, resulting considerable decrease in their power-conversion efficiency (PCE). This review investigates current status of strategies to enhance UV and humidity stability of PSCs in terms of UV-management and moisture protection, respectively. Furthermore, the multifunctional approach to increase long-term stability as well as performance is discussed as advanced research directions for the commercialization of PSCs.

• Current Photovoltaic Research
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• 제4권2호
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• pp.68-79
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• 2016

The power conversion efficiency of perovskite solar cells has remarkably increased from 3.81% to 22.1% in the past 6 years. Perovskite solar cells, which are based on the perovskite crystal structure, are fabricated using organic-inorganic hybrid materials. The advantages of these solar cells are their low cost and simple fabrication procedure. Also, they have a band gap of about 1.6 eV and effectively absorb light in the visible region. For the commercialization of perovskite solar cells in the field of photovoltaics, the issue of their long term stability cannot be overlooked. Although the development of perovskite solar cells is unprecedented, their main drawback is the degradation of the perovskite structure by moisture. This degradation is accelerated by exposure to UV light, temperature, and external bias. This paper reviews the aforesaid reasons for perovskite solar cell degradation. We also discuss the research directions that can lead to the development of perovskite solar cells with high stability.

• 한국재료학회지
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• 제29권6호
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• pp.371-377
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• 2019

A flexible piezoelectric energy harvester(f-PEH) that converts tiny mechanical and vibrational energy resources into electric signals without any restraints is drawing attention as a self-powered source to operate flexible electronic systems. In particular, the nanocomposites-based f-PEHs fabricated by a simple and low-cost spin-coating method show a mechanically stable and high output performance compared to only piezoelectric polymers or perovskite thin films. Here, the non-piezoelectric polymer matrix of the nanocomposite-based f-PEH is replaced by a P(VDF-TrFE) piezoelectric polymer to improve the output performance generated from the f-PEH. The piezoelectric hybrid nanocomposite is produced by distributing the perovskite PZT nanoparticles inside the piezoelectric elastomer; subsequently, the piezoelectric hybrid material is spin-coated onto a thin metal substrate to achieve a nanocomposite-based f-PEH. A fabricated energy device after a two-step poling process shows a maximum output voltage of 9.4 V and a current of 160 nA under repeated mechanical bending. Finite element analysis(FEA) simulation results support the experimental results.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.427-427
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• 2016

Organic-inorganic hybrid perovskite have attracted significant attention as a new revolutionary light absorber for photovoltaic device due to its remarkable characteristics such as long charge diffusion lengths (100-1000nm), low recombination rate, and high extinction coefficient. Recently, power conversion efficiency of perovskite solar cell is above 20% that is approached to crystalline silicon solar cells. Planar heterojunction perovskite solar cells have simple device structure and can be fabricated low temperature process due to absence of mesoporous scaffold that should be annealed over 500 oC. However, in the planar structure, controlling perovskite film qualities such as crystallinity and coverage is important for high performances. Those controlling methods in one-step deposition have been reported such as adding additive, solvent-engineering, using anti-solvent, for pin-hole free perovskite layer to reduce shunting paths connecting between electron transport layer and hole transport layer. Here, we studied the effect of alkali metal halide to control the fabrication process of perovskite film. During the morphology determination step, alkali metal halides can affect film morphologies by intercalating with PbI2 layer and reducing $CH3NH3PbI3{\cdot}DMF$ intermediate phase resulting in needle shape morphology. As types of alkali metal ions, the diverse grain sizes of film were observed due to different crystallization rate depending on the size of alkali metal ions. The pin-hole free perovskite film was obtained with this method, and the resulting perovskite solar cells showed higher performance as > 10% of power conversion efficiency in large size perovskite solar cell as $5{\times}5cm$. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectrometry (ICP-OES) are analyzed to prove the mechanism of perovskite film formation with alkali metal halides.