• Current Optics and Photonics
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• 제2권6호
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• pp.514-518
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• 2018

Carrier diffusion length in the light-sensitive material is one of the key elements in improving the light-current conversion efficiency of solar-cell devices. In this paper, we measured the carrier diffusion length in lead-halide perovskite ($MAPbI_3$) and mixed lead-halide ($MAPbI_{3-x}Cl_x$) perovskite devices using scanning photocurrent microscopy (SPCM). The SPCM signal decreased as we moved the focused laser spot away from the metal contact. By fitting the data with a simple exponential curve, we extracted the carrier diffusion length of each perovskite film. Importantly, the diffusion length of the mixed-halide perovskite was higher than that of the halide perovskite film by a factor of 3 to 6; this is consistent with the general expectation that the carrier mobility will be higher in the case of the mixed lead-halide perovskites. Finally, the diffusion length was investigated as a function of applied bias for both samples, and analyzed successfully in terms of the drift-diffusion model.

• 한국재료학회지
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• 제32권11호
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• pp.449-457
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• 2022

Halide perovskites are emerging materials for next-generation display applications, thanks to their narrow emission linewidth and band gap tunability, capable of covering the entire range of visible light. Despite their short period of research, perovskite light emitting diodes (PeLEDs) have shown rapid progress in device external quantum efficiency (EQE) in the near-infrared (NIR), red, and green emission wavelengths, and the record EQE has exceeded over 20 %. However there has been limited progress with blue emission compared to the red and green counterparts. In this review, the current status and challenges of blue PeLEDs are introduced, and strategies to produce spectrally stable blue PeLEDs are discussed. The strategies include 1) a mixed halide system in the form of 3-dimensional (3D) perovskites, 2) colloidal perovskite nanocrystals and 3) low dimensional perovskites, known as quasi-2D perovskites. In the mixed halide system, previous reports based on the compositional engineering of 3D perovskites to reduce spectral instability (i.e., halide segregation) will be discussed. Since spectral instability issue originate from the mixed halide composition in perovskites, the two other strategies are based on enlarging the band gap with a single halide composition. Finally, the prospects for each strategy are discussed, for further improvement in spectrally stable blue PeLEDs.

• Electronic Materials Letters
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• 제14권6호
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• pp.700-711
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• 2018

CdS synthesized by the chemical bath method at $70^{\circ}C$, has been used as an electron transport layer in the planar structure of the perovskite solar cells. A two-step spin process produced a mixed halide perovskite of $CH_3NH_3PbI_{3-x}Cl_x$ and a mixture of $PbCl_2$ and $PbI_2$ was deposited on CdS, followed by a sub-sequential reaction with MAI ($CH_3NH_3I$). The added $PbCl_2$ to $PbI_2$ in the first spin-step affected the structure, orientation, and shape of lead halides, which varied depending on the content of Cl. A small amount of Cl enhanced the surface morphology and the preferred orientation of $PbI_2$, which led to large and uniform grains of perovskite thin films. In contrast, the high content of Cl produces a new phase PbICl in addition to $PbI_2$, which leads to the small and highly uniform grains of perovskites. An improved surface coverage of perovskite films with the large and uniform grains maximized the performance of perovskite solar cells at 0.1 molar ratio of $PbCl_2$ to $PbI_2$. The depth profiling of elements in both lead halide films and mixed halide perovskite films were measured by Rutherford backscattering spectroscopy, revealing the distribution of chlorine along with the thickness, and providing the basis for the mechanism for enhanced preferred orientation of lead halide and the microstructure of perovskites.

• 전기화학회지
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• 제21권2호
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• pp.21-27
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• 2018

본 총설에서는 최근 전세계적으로 각광 받고 있는 유기 금속 할라이드 페로브스카이트 소재에서 일어나는 이온 이동 현상에 대한 최신 연구에 대해 정리하였다. 페로브스카이트 물질 조성, 인가전압에 따라 다른 결과들이 보고되었지만, 실제 태양전지 작동 조건에서 iodide 가 이동하는 것으로 보이며, 때로는 methylammonium의 이동도 관찰된다. 페로브스카이트는 상온에서 전자와 이온이 동시에 이동하는 이른바 mixed conductor이고, 이는 페로브스카이트 태양전지 전류-전압곡선의 hysteresis, 장시간 작동에 따른 성능 저하 등에 지대한 영향을 미친다.

• Applied Science and Convergence Technology
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• 제27권2호
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• pp.42-45
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• 2018

Photovoltaic and optoelectronic devices based on hybrid metal halide perovskites ($MAPbX_3$; $MA=CH_3NH_3{^+}$, $X=Cl^-$, $Br^-$, or $I^-$) are rapidly improving in power conversion efficiency. Also, during recent years, perovskite single crystals have emerged as promising materials for high-efficiency photovoltaic and optoelectronic devices because of their low defect density. Here we show that the light soaking effect of mixed halide perovskite ($MAPbBr_{3-x}I_x$) single crystals can be explained using photoluminescence, time-resolved photoluminescence, and Raman scattering measurements. Unlike Br-based single crystal, Br/I mixed single crystal show a strong light soaking effect under laser irradiation condition that was related to the existence of multiple phases.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.429-429
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• 2016

Organolead halide perovskite have attracted much attention over the past three years as the third generation photovoltaic due to simple fabrication process via solution process and their great photovoltaic properties. Many structures such as mesoporous scaffold, planar heterojunction or 1-D TiO2 or ZnO nanorod array structures have been studied to enhance performances. And the photovoltaic performances and carrier transport properties were studied depending on the cell structures and shape of perovskite film. For example, the perovskite cell based on TiO2/ZnO nanorod electron transport materials showed higher electron mobility than the mesoporous structured semiconductor layer due to 1-D direct pathway for electron transport. However, the reason for enhanced performance was not fully understood whether either the shape of perovskite or the structure of TiO2/ZnO nanorod scaffold play a dominant role. In this regard, for a clear understanding of the shape/structure of perovskite layer, we applied anodized aluminum oxide material which is good candidate as the inactive scaffold that does not influence the charge transport. We fabricated vertical one dimensional (1-D) nanostructured methylammonium lead mixed halide perovskite (CH3NH3PbI3-xClx) solar cell by infiltrating perovskite in the pore of anodized aluminum oxide (AAO). AAO template, one of the common nanostructured materials with one dimensional pore and controllable pore diameters, was successfully fabricated by anodizing and widening of the thermally evaporated Al film on the compact TiO2 layer. Using AAO as a scaffold for perovskite, we obtained 1-D shaped perovskite absorber, and over 15% photo conversion efficiency was obtained. I-V measurement, photoluminescence, impedance, and time-limited current collection were performed to determine vertically arrayed 1-D perovskite solar cells shaped in comparison with planar heterojunction and mesoporous alumina structured solar cells. Our findings lead to reveal the influence of the shape of perovskite layer on photoelectrical properties.

• EDISON SW 활용 경진대회 논문집
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• 제4회(2015년)
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• pp.378-381
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• 2015

To produce low cost and efficient photovoltaic cells, inorganic-organic lead halide perovskite materials appear promising for most suitable solar cells owing to their high power conversion efficiency. Most recent research showes that formamidinium lead iodide ($FAPbI_3$) with methylammonium lead bromide ($MAPbBr_3$) improves the power conversion efficiency of the solar cell to more than 18 per cent under a standard illumination because incorporated $MAPbBr_3$ makes $FAPbI_3$-relatively unstable but comparatively narrow band gap-more stable composition. In respect to first principle study, we investigated band gap of $MAPbI_3$, $FAPbI_3$, $MAPbBr_3$, $(FAPbI_3)_{0.89}-(MAPbBr_3)_{0.11}$ and 0.615(eV), 0.466, 1.197, 0.518 respectively through EDISON DFT software. These results emphasize enhancing structure stability is important factor as well as finding narrow band gap.

• 마이크로전자및패키징학회지
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• 제30권2호
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• pp.71-75
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• 2023

본 연구에서는 열화학기상증착법을 이용한 세슘계 무기 페로브스카이트의 성장기판에 따른 결정 구조의 변화 및 광학적 특성을 비교 분석하였다. 무기 페로브스카이트 결정은 CsBr과 PbBr₂를 전구체로 사용하여 SiO₂/Si와 c-Al₂O₃ 기판 위에 동일한 조건으로 CsPbBr₃를 성장하였다. 비정질 구조를 가진 SiO₂ 표면에서는 Cs₄PbBr₆-CsPbBr₃ 혼합상의 결정 입자가 성장하였으며, 단결정 구조인 c-Al₂O₃ 기판에서는 CsPbBr₃ (100) 결정 면방향이 우세한 단일상의 박막이 형성되었다. 광학적 분석 결과 CsPbBr₃는 약 91 meV의 반치폭을 갖고 약 534 nm 중심의 발광특성을 보였으며, Cs₄PbBr₆-CsPbBr₃ 혼합구조에서는 청색 변이에 의해 523 nm의 발광 및 6.88 ns의 빠른 광 소결시간을 확인하였다. 열화학기상증착법을 이용한 페로브스카이트의 결정구조의 제어 및 광특성의 변화는 디스플레이, 태양 전지, 광센서 등 다양한 광전 소자에 적용할 수 있을 것으로 기대된다.