• 한국진공학회지
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• 제22권1호
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• pp.37-44
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• 2013

본 연구에서는 양자점(quantum dot, QD)에서의 전하트랩이 태양전지의 특성에 미치는 영향을 조사하기 위하여, GaAs 모체 태양전지(MSC)의 활성층에 InAs/GaAs QD을 삽입한 $p^+-QD-n/n^+$ 태양전지(QSC)를 제작하여 그 특성을 비교 조사하였다. Stranski-Krastanow (SK)와 준단층(quasi-monolayer, QML)의 2종류 QD를 도입하였으며, 표준 태양광(AM1.5)에서 얻은 전류-전압 곡선으로부터 태양전지의 특성인자(개방전압($V_{OC}$), 단락전류($I_{SC}$), 충만도(FF), 변환효율(CE))를 결정하였다. SK-QSC의 FF값은 80.0%로 MSC의 값(80.3%)과 비슷한 반면, $V_{OC}$와 $J_{SC}$는 각각 0.03 V와 $2.6mA/cm^2$만큼 감소하였다. $V_{OC}$ 및 $J_{SC}$ 감소 결과로 CE는 2.6% 저하되었는데, QD에 의한 전하트랩이 주요 원인으로 지적되었다. 전하트랩을 완화시키기 위한 구조로서 QML-QD 기반 태양전지를 본 연구에서 처음 시도하였으나, 예측과는 달리 부정적 결과를 보였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.97-97
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• 2010

We demonstrate the hybrid polymer-quantum dot based multi-functional device (Organic bistable devices, Light-emitting diode, and Photovoltaic cell) with a single active-layer structure consisting of CdSe/ZnS semiconductor quantum-dots (QDs) dispersed in a poly N-vinylcarbazole (PVK) and 1,3,5-tirs- (N-phenylbenzimidazol-2-yl) benzene (TPBi) fabricated on indium-tin-oxide (ITO)/glass substrate by using a simple spin coating technique. The multi-functionality of the device as Organic bistable device (OBD), Light Emitting Diode (LED), and Photovoltaic cell can be successfully achieved by adding an electron transport layer (ETL) TPBi to OBD for attaining the functions of LED and Photovoltaic cell in which the lowest unoccupied molecular orbital (LUMO) level of TPBi is positioned at the energy level between the conduction band of CdSe/ZnS and LiF/Al electrode (band-gap engineering). Through transmission electron microscopy (TEM) study, the active layer of the device has a p-i-n structure of a consolidated core-shell structure in which semiconductor QDs are uniformly and isotropically adsorbed on the surface of a p-type polymer core and the n-type small molecular organic materials surround the semiconductor QDs.

• Transactions on Electrical and Electronic Materials
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• 제3권3호
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• pp.8-13
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• 2002

Controlled precipitation of quasi-binary semiconductor system is newly proposed as an effective and reliable technique for the formation of well-defined and crystallographically aligned semiconductor nanostructures. Using HgTe-PbTe quasi-binary semiconductor system, self-aligned HgTe nanocrystallites distributed three dimensionally within PbTe matrix were successfully formed by the simple three step heat treatment process routinely found in age hardening process of metallic alloys. Examination of the resulting nano precipitates using conventional transmission electron microscopy (CTEM) and high resolution TEM (HRTEM) reveals that the coherent HgTe precipitates form as thin discs along the (100) habit planes making a crystallographic relation of {100}$\_$HgTe///{100}$\_$PbTe/ and [100]$\_$HgTe///[100]$\_$PbTe/. It is also found that the precipitate undergoes a gradual thickening and a faceting under isothermal aging up to 500 hours without any noticeable coarsening. These results, combined with the extreme dimension of the precipitates (4-5 nm in length and sub-nanometer in thickness) and the simplicity of the formation process, leads to the conclusion that controlled precipitation is an effective method for preparing desirable quantum-dot nanostructures.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.489-489
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• 2011

The effect of Si quantum dots for solar cell appications was investigated. The 5 ~ 10 nm Si nanoparticle was fabricated on p-type single and poly crystalline wafer by magnetron sputtering and laser irradiation process. Scanning electron microscopy (SEM), atomic force measurement (AFM) and transmission electron microscopy (TEM) images showed that the Si QDs array were clearly embedded in insulating layer ($SiO_2$). Photoluminesence (PL) measurements reliably exhibited bandgap transitions with every size of Si QDs. The photo-current measurements were showed different result with size of QD and number of superlattice.

• 한국산학기술학회논문지
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• 제19권6호
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• pp.646-651
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• 2018

최근 태양전지의 Donor/Acceptor 계면에 그래핀 양자점을 완충 층으로 삽입하여 광 전환 효율을 향상시킨 많은 연구 결과들이 보고되었다. 그래핀 양자점은 그래핀 단일 층이 여러 겹 쌓여서 구성된 수 나노미터 크기의 물질로, 양자 제한 효과에 의한 밴드갭 조절이 가능하다는 장점을 가지고 있다. 하지만 대부분의 그래핀 양자점을 활용한 연구에서 레이저 분쇄나 수열 처리 등과 같은 복잡하고 접근성이 떨어지는 용액 공정들이 박막 형성에 사용되고 있다. 본 연구에서는 Indium tin oxide(ITO)/$TiO_2$/Poly(3-hexylthiophene)(P3HT)/Al 구조로 구성된 태양전지의 Donor/Acceptor 계면에 그래핀 양자점을 단순한 초음파 처리를 통해 용매에 분산시켜 박막 공정에 사용하였음에도 불구하고, 단락 전류를 $1.26{\times}10^{-5}A/cm^2$에서 $7.46{\times}10^{-5}A/cm^2$으로, 곡선인자(Fill factor)를 0.27에서 0.42로 향상된 결과를 확인하였다. 이러한 결과를 트랜지스터 구조의 소자를 활용한 전기적 성질 확인과 순환 전압-전류법을 통한 에너지 레벨 분석 및 가시광 흡수 스펙트럼 분석 등을 통하여 고찰하였다. 본 연구 결과를 통해 그래핀 양자점 용액 공정이 복잡한 처리 공정 없이도, 보다 폭넓게 활용 가능할 것으로 예상된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.221-221
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• 2013

Striving to replace the well known silicon nanocrystals embedded in oxides with solution-processable charge-trapping materials has been debated because of large scale and cost effective demands. Herein, a silicon quantum dot-polystyrene nanocomposite (SiQD-PS NC) was synthesized by postfunctionalization of hydrogen-terminated silicon quantum dots (H-SiQDs) with styrene using a thermally induced surface-initiated polymerization approach. The NC contains two miscible components: PS and SiQD@PS, which respectively are polystyrene and polystyrene chains-capped SiQDs. Spin-coated films of the nanocomposite on various substrate were thermally annealed at different temperatures and subsequently used to construct metal-insulator-semiconductor (MIS) devices and thin film field effect transistors (TFTs) having a structure p-$S^{++}$/$SiO_2$/NC/pentacene/Au source-drain. C-V curves obtained from the MIS devices exhibit a well-defined counterclockwise hysteresis with negative fat band shifts, which was stable over a wide range of curing temperature ($50{\sim}250^{\circ}C$. The positive charge trapping capability of the NC originates from the spherical potential well structure of the SiQD@PS component while the strong chemical bonding between SiQDs and polystyrene chains accounts for the thermal stability of the charge trapping property. The transfer curve of the transistor was controllably shifted to the negative direction by chaining applied gate voltage. Thereby, this newly synthesized and solution processable SiQD-PS nanocomposite is applicable as charge trapping materials for TFT based memory devices.

• Bulletin of the Korean Chemical Society
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• 제32권1호
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• pp.263-272
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• 2011

Highly luminescent and monodisperse InP quantum dots (QDs) were prepared by a non-organometallic approach in a non-coordinating solvent. Fatty acids with well-defined chain lengths as the ligand, a non coordinating solvent, and a thorough degassing process are all important factors for the formation of high quality InP QDs. By varying the molar concentration of indium to ligand, QDs of different size were prepared and their absorption and emission behaviors studied. By spin-coating a colloidal solution of InP QD onto a silicon wafer, InP QD thin films were obtained. The thickness of the thin films cured at 60 and $200^{\circ}C$ were nearly identical (approximately 860 nm), whereas at $300^{\circ}C$, the thickness of the thin film was found to be 760 nm. Different contrast regions (A, B, C) were observed in the TEM images, which were found to be unreacted precursors, InP QDs, and indium-rich phases, respectively, through EDX analysis. The optical properties of the thin films were measured at three different curing temperatures (60, 200, $300^{\circ}C$), which showed a blue shift with an increase in temperature. It was proposed that this blue shift may be due to a decrease in the core diameter of the InP QD by oxidation, as confirmed by the XPS studies. Oxidation also passivates the QD surface by reducing the amount of P dangling bonds, thereby increasing luminescence intensity. The dielectric properties of the thin films were also investigated by capacitance-voltage (C-V) measurements in a metal-insulator-semiconductor (MIS) device. At 60 and $300^{\circ}C$, negative flat band shifts (${\Delta}V_{fb}$) were observed, which were explained by the presence of P dangling bonds on the InP QD surface. At $300^{\circ}C$, clockwise hysteresis was observed due to trapping and detrapping of positive charges on the thin film, which was explained by proposing the existence of deep energy levels due to the indium-rich phases.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2002년도 제23회 학술발표회 초록집
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• pp.45-45
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• 2002

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권1호
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• pp.30-34
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• 2005

This study shows the lasing characteristics of InGaAs/InGaAsP multiple-quantum-well waveguide-type depleted optical thyristor (DOT) using the vertical window. The measured switching voltage and current are 3.36 V and 10 ㎂, respectively. The lasing threshold current is 131 mA at 25 ℃. The output peak wavelength is 1570 nm at a bias current of 1.22 Ith and there is not input signal anymore in the output port. The vertical injection depleted optical thyristor - laser diode (VIDOT-LD) using the vertical-injection structure shows very good isolation between input and output signal.

• 한국재료학회:학술대회논문집
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• 한국재료학회 1998년도 IUMRS-ICEM ABSTRACT BOOK
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• pp.91.3-91
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• 1998