• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.4
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• pp.187-191
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• 2004

In this work, we used the PCID simulator for simulation of solar cell and examined the effect of front-back surface recombination velocity, minority carrier diffusion length, junction depth and emitter sheet-resistance. As the effect of base thickness, the efficiency decreased by the increase in series resistance with the increase of the thickness and found decrease in efficiency by decrease of the current as the effect of the recombination. Also, as the effect of base resistivity, the efficiency increased somewhat with the decrease in resistivity, but when the resistivity exceeded certain value, the efficiency decreased as a increase in the recombination ratio. The optimum efficiency was obtained at the resistivity 0.5 $\Omega$-cm, and thickness $100\mu\textrm{m}$. We have successfully achieved 10.8% and 13.7% efficiency large area($103mm{\times}103mm$) mono-crystalline silicon solar cells without and with PECVD silicon nitride antireflection coating.

• Current Applied Physics
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• v.18 no.11
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• pp.1230-1234
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• 2018

We report a new method of measuring the non-radiative recombination rate in bulk Silicon. Synchrotron timeresolved x-ray scattering (TRXS) combines femtometer spatial sensitivity with nanosecond time resolution to record the temporal evolution of a crystal lattice following intense ultrafast laser excitation. Modeling this data requires an Auger recombination time that is considerably slower than previous measurements, which were made at lower laser intensities while probing only a relatively shallow surface depth. We attribute this difference to an enhanced Coulomb interaction that has been predicted to occur in bulk materials with high densities of photoexcited charge carriers.

• Journal of the Korean Vacuum Society
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• v.14 no.4
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• pp.229-237
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• 2005

The degradation phenomena in SiGe hetero-junction bipolar transistors(SiGe HBTs) induced by bias stress are investigated in this review. If SiGe HBTs are stressed over a specific time interval, the device parameters deviate from their nominal values due to the internal changes in the devices. Reverse-bias stress on emitter-base(EB) junctions causes base current increase and current gain decrease because carriers accelerated by the electrical field generate recombination centers. When forward-bias current stress is conducted at an ambient temperature above $140^{\circ}C$ , hot carriers produced by Auger recombination or avalanche multiplication induce current gain fluctuation. Mixed-mode stressing, where high emitter current and high collector-base voltage are simultaneously applied to the device, provokes base current rise as EB reverse-bias stressing does.

• Transactions on Electrical and Electronic Materials
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• v.17 no.1
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• pp.37-40
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• 2016

Performance enhancement of organic light-emitting diodes (OLEDs) is investigated in a device structure of ITO/TPD/Alq₃/LiF/Al and ITO/TPD/Alq₃/BCP/LiF/Al. Here, bathocuproine (BCP) is used as an electron-transport layer. Current density-voltage-luminance characteristics of the OLEDs show that the performance of the device is better with BCP layer than without BCP layer. The current density, luminance, luminous efficiency, and external-quantum efficiency are improved by approximately 22%, 50%, 2%, and 18%, respectively. Since the BCP layer lowers the electron energy barrier, electron transport is facilitated and the movement of hole is blocked as the applied voltage increases. This results in an increased recombination rate of holes and electrons.

• Nuclear Engineering and Technology
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• v.54 no.2
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• pp.501-506
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• 2022

Long turn-off time limits high frequency operation of Bipolar Junction Transistors (BJTs). Turn-off time decreases with increases in the recombination rate of minority carriers at switching transients. Fast neutron irradiation on a Si BJT incurs lattice damages owing to the displacement of silicon atoms. The lattice damages increase the recombination rate of injected holes with electrons, and decrease the hole lifetime in the base region of pnp Si BJT. Fast neutrons generated from a beryllium target with 30 MeV protons by an MC-50 cyclotron were irradiated onto pnp Si BJTs in experiment. The experimental results show that the turn-off time, including the storage time and fall time, decreases with increases in fast neutron fluence. Additionally, it is confirmed that the base current increases, and the collector current and base-to-collector current amplification ratio decrease due to fast neutron irradiation.

• Bulletin of the Korean Chemical Society
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• v.20 no.1
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• pp.7-15
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• 1999

The present paper is a review of the current studies of quantum beats in recombination of spin-correlated radical pairs in solutions as well as of future applications of quantum beats technique for studying these pairs. Examples are given of the use of this method for determining the hfi constants and relaxation times of short-lived radical ions, for finding the rate constants of the reactions of alkane radical cations and for estimating a fraction of singlet-correlated pairs in the pairs in the tracks of ionizing particles. The potentialities of this method, its advantages and limitations are discussed.

• Current Photovoltaic Research
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• v.6 no.2
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• pp.43-48
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• 2018

The traditional silicon heterojunction solar cells consist of intrinsic amorphous silicon to prevent recombination of the silicon surface and doped amorphous silicon to transport the photo-generated electrons and holes to the electrode. Back contact solar cells with silicon heterojunction exhibit very high open-circuit voltages, but the complexity of the process due to form the emitter and base at the backside must be addressed. In order to solve this problem, the structure, manufacturing method, and new materials enabling the carrier selective contact (CSC) solar cell capable of achieving high efficiency without using a complicated structure have recently been actively developed. CSC solar cells minimize carrier recombination on metal contacts and effectively transfer charge. The CSC structure allows very low levels of recombination current (eg, Jo < 9fA/cm2), thereby achieves high open-circuit voltage and high efficiency. This paper summarizes the core technology of CSC solar cell, which has been spotlighted as the next generation technology, and is aiming to speed up the research and development in this field.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.1
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• pp.45-49
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• 2014

We have fabricated white organic light-emitting diodes (OLEDs) using several thicknesses of electron-transport layer. The multi-emission layer structure doped with red and blue phosphorescent guest emitters was used for achieving white emission. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was used as an electron-transport layer. The thickness of BCP layer was varied to be 20, 55, and 120 nm. The current efficiency, emission and recombination characteristics of multi-layer white OLEDs were investigated. The BCP layer thickness variation results in the shift of emission spectrum due to the recombination zone shift. As the BCP layer thickness increases, the recombination zone shifts toward the electron-transport layer/emission-layer interface. The white OLED with a 55 nm thick BCP layer exhibited a maximum current efficiency of 40.9 cd/A.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.230.1-230.1
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• 2016

본 연구에서는 Host-Dopant system 기반 적색 인광 OLED의 Emitting layer(EML)에서 doping 위치에 따른 특성 변화를 분석하였다. EML은 host 물질로 60 nm 두께의 CBP를 사용하고, 적색 발광을 위해 10 %의 $Ir(btp)_2$를 CBP의 Front, Middle, Back side에 각각 20 nm씩 doping하였다. 본 구조의 적색 인광 OLED는 current density, luminance, efficiency, EL spectrum 등을 통해 전기적, 광학적 특성 변화를 확인하였다. Front, Back side에 doping으로 인한 CBP의 Energy level이 3.6 eV에서 1.9 eV로 감소하여 각각 HTL/EML, EML/HBL의 경계에 carrier direct injection이 활성화 되었고, 이로 인한 charge balance의 저하를 확인하였다. EL spectrum결과 각 소자는 CBP의 618 nm 파장 외에도, 추가적으로 TPBi의 398 nm, NPB의 456 nm의 파장을 보였다. 이를 통해 doping 위치에 따라 exciton이 형성되는 recombination zone이 이동하고 있음을 확인하였고, Front side는 6 V의 인가전압에서는 발광 파장이 398 nm에서 높은 값을 보이나 8 V, 10 V, 12 V에서 618 nm에서 높은 값을 보이는 것으로 인가전압에 의해 recombination zone이 HTL쪽으로 이동되는 것 또한 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.484.1-484.1
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• 2014

Bulk hetero junction (BHJ) polymer solar cells (PSCs) are one of the most promising fields as alternative energy source. Especially, the development of new p-type conjugated polymer is one of the main issues to get core technology. In this study, a series of varied ratio of 3,6-carbazole in poly[9-(heptadecan-9-yl)-9H-carbazole-2,7-diyl-alt-(5,6-bis-(octyloxy)-4,7-di(thiophen-2-yl)benzo-[1,2,5]-thia-diazole)-5,5-diyl] were designed and synthesized. These polymers have good solubility and film formability than PCDTBT which is well known promising material. Investigation of the photovoltaic properties of these new polymers indicated that polymer with 2% of 3,6-carbazole provided higher PCE (3.8% to 4.9%) with enhanced JSC, FF, VOC. We found origin of this improvement using several methods, one of which is reduced bimolecular recombination in polymer.