• Current Photovoltaic Research
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• v.6 no.1
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• pp.12-16
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• 2018

The interest in perovskite solar cells has been skyrocketed owing to their rapid progress in efficiency in recent years. Here, we report the effect of non-stoichiometry in the methylammonium lead trihalide ($MAPbI_3$) precursors used in a solution process with different MAI : $PbI_2$ ratios of 1 : 0.96, 1 : 1.10, 1 : 1.15, and 1:1.20. With an increase in the $PbI_2$ content, the $PbI_2$ secondary phase was found to form at grain boundary region of perovskite thin films, as evidenced by X-ray diffraction (XRD) and scanning electron microscopy (SEM). In terms of device performance, open-circuit voltage in particular is significantly improved with increasing the molar ratio of $PbI_2$, which is possibly ascribed to the reduction in recombination sites at grain boundary of perovskite and hence the prolonged life time of light-generated carriers according to the reported. As a result, the $PbI_2-excess$ devices exhibited a higher power conversion efficiency compared to the MAI-excess ones.

• Journal of the Korean Ceramic Society
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• v.37 no.5
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• pp.418-424
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• 2000

Effects of Ar ion damage prior to the phase transformation from pyrochlore to perovskite structure of PZT thin films have been investigated. As the degree of damage increased by increasing the acceleration voltage in the ion mass doping system, the phase transformation temperature decreased such that the temperature could be lowered down to 550$^{\circ}C$ when the film was damaged at 15 kV for 5 minutes. When the film was damaged prior to the heat treatment grain size of the perovskite thin films became less than 300${\AA}$. It turned out that relatively high value of the remanent polarization (about 30${\mu}$C/$\textrm{cm}^2$) as well as improvement of the fatigue characteristics to a large extent is closely related to the fine grain size of thus obtained PZT films.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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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.

• Journal of the Korean Ceramic Society
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• v.30 no.5
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• pp.365-372
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• 1993

Variation of dielectric constant in PMN-Pyrochlore diphasic mixtures were investigated with grain size of pyrochlore phase. Size of pyrochlore phase was controlled by the numbers of calcining and sedimentation method during powder processing. When grain size of pyrochlore phase is large in the sintered specimen, dielectric constant slowly decreased with increase of amount of pyrochlore phase. On the contary, grain size of pyrochlore phase is small, dielectric constant drastically decreased. It was thought that small sized pyrochlore grains more easily surrounded high dielectric phase (perovskite PMN) than large ones with addition of pyrochlore phase.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.26-32
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• 2021

The photovoltaic properties and microstructure changes were observed while perovskite solar cells (PSCs) with a fabricated carbon electrode were formed using the following annealing processes: hot-plate, oven, and rapid thermal annealing (RTA). Perovskite solar cells with a glass/FTO/compact TiO2/meso TiO2/meso ZrO2/carbon structure were prepared. The photovoltaic properties and microstructure changes in the PSCs were analyzed using a solar simulator, optical microscopy, and field emission scanning electron microscopy. An analysis of the photovoltaic properties revealed outstanding properties when RTA was applied to the cells. Microstructure analysis showed that perovskite was formed locally on the carbon electrode surface when hot-plate and oven annealing were applied. On the other hand, PSC with RTA showed a flat surface without extra perovskite agglomeration. Denser perovskite formed on the porous carbon electrode layer with RTA showed superior photovoltaic properties. These results suggest that the RTA process might be appropriate for the massive production of carbon electrode PSCs considering the processing time.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.3
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• pp.286-291
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• 2023

Perovskite materials are promising candidates for next-generation optoelectronic devices owing to their outstanding external quantum efficiency, high color purity, and ability to tune the light emission wavelength. However, conventional thermal annealing processes caused the degradation of perovskite, resulting in poor optoelectronic properties and a short lifetime. Herein, we propose a laser-induced recrystallization of perovskite thin film to enhance its light-emitting properties. Laser-induced recrystallization process was performed using rapid and instantaneous laser heating, which successfully induced grain growth of the perovskite material. The laser processing conditions were thoroughly optimized based on theoretical calculations and various material analyses such as x-ray diffraction, scanning electron microscope, and photoluminescence spectroscopy.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.2
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• pp.60-66
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• 2001

($Ba_x$$Sr_{1-x}$)$TiO_3$ (x=0.9, 0.7, 0.5) thin films were prepared on ITO-coated glass by sol-gel method. Perovskite phase formation temperature of BST thin films seemed to be higher than $600^{\circ}C$. Peaks of perovskite phase shift to high diffraction angles as the Sr/(Ba+Sr) ratio was increased, due to the smaller ionic size of $Sr^{2+}$ than $Ba^{2+}$ . As a heating temperature was increased, the grain became coarser. And as Sr/(Ba + Sr) ratio was increased, the grain became finer. Dielectric constants of the BST(50/50) thin film are higher and dielectric losses of that are lower than those of the others. Dielectric constant and dielectric loss of the BST(50/50) thin film were 652 and 0.042 at 1kHz, respectively.

• The Korean Journal of Ceramics
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• v.6 no.1
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• pp.74-77
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• 2000

Ta-doped PZT thin films prepared by reactive co-sputtering method could be transformed into single grained perovskite structure utilizing physical etching of Pt bottom electrode. It is found that PZT perovskite phase on damaged (111) Pt electrode by IMD was more easily crystallized than random oriented Pt electrode and less crystallized than (111) Pt electrode. This shows that amorphized Pt electrode surface by IMD process has an effect on crystallization of PZT perovskite phase. 40$\mu\textrm{m}\times40\mu\textrm{m}$ square shape single grain PZT array could be obtained utilizing the difference of incubation time for nucleation of rosettes between ion damaged Pt and (111) oriented Pt electrode. Single grained PZT thin films show low leakage current density of $1\times10^{-7}$ A/$\textrm{cm}^2$ and high break down field of 440kV/cm. The loss of remanent polarization after $10^{11}$ cycles was less than 15% of initial value.

• Journal of the Korean Ceramic Society
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• v.37 no.6
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• pp.530-536
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• 2000

During the grain growth of the PZT thin films by selective nucleation method using PZT seed, it was found that the grain size was saturated with the annealing temperature. The saturation of grain size was analyzed by the interfacial energy which appeared during the crystallization. The factors affecting the saturation of grain size were found to be the interfacial energy between perovskite phase and pyrochlore phase, and PZT thin film and the bottom Pt electrode. When the ion damage was introduced to the grain-size saturated PZT thin films, further lateral growth was observed. Pt bottom electrode thickness was changed to control the interfacial energy between the PZT thin film and the Pt bottom electrode. When Pt thickness was increased, the grain size was also increased, because the lattice parameter of Pt films was increased with the thickness of the Pt films. The incubation time of nucleation was increased with the amount of the ion damage on the Pt films.

• Journal of the Korean Ceramic Society
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• v.29 no.3
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• pp.216-222
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• 1992

PLZT thin films were prepared using sol-gel spin coating. The films mainly consisted of perovskite phase when heat treated at 600$^{\circ}C$ and in O2 or air atmosphere for 2 hours after 7 coating cycles. Cracks were formed when smaller than after 9 coating cycles. When ITO interlayer existed between Corning 7059 glass substrate and the film, cracks were not formed after 9 coating cycles, but cracks were formed after 11 coating cycles because of large volume change of the film contracting on the substrate during the heat treatment. In the observation of microstructure, the thin films have perovskite phase of about 2 $\mu\textrm{m}$ grain size and pyrochlore phase of 100∼200${\AA}$ grain size.