• Applied Chemistry for Engineering
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• v.30 no.4
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• pp.499-503
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• 2019

Characteristics of solar cells employing a lattice matched GaInP/GaAs quantum well (QW) structure in a single N-AlGaInP/p-InGaP heterojunction (HJ) were investigated and compared to those of solar cells without QW structure. The epitaxial layers were grown on a p-GaAs substrate with $6^{\circ}$ off the (100) plane toward the <111>A. The heterojunction of solar cell consisted of a 400 nm N-AlGaInP, a 590 nm p-GaInP and 14 periods of a 10 nm GaInP/5 nm GaAs for QW structure and a 800 nm p-GaInP for the HJ structure (control cell). The solar cells were characterized after the anti-reflection coating. The short-circuit current density for $1{\times}1mm^2$ area was $9.61mA/cm^2$ for the solar cell with QW structure while $7.06mA/cm^2$ for HJ control cells. Secondary ion mass spectrometry and external quantum efficiency results suggested that the significant enhancement of $J_{sc}$ and EQE was caused by the suppression of recombination by QW structure.

• Applied Science and Convergence Technology
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• v.23 no.1
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• pp.27-33
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• 2014

We have studied photovoltaic characteristics of single-junction GaAs solar cells with/without an $MgF_2/ZnS$ anti-reflective coating (ARC) illuminated by low-density concentration (<10 suns). By the ARC deposition, the short-circuit current density ($J_{SC}$) and the fill factor (FF) are increased by $5mA/cm^2$ and 5% at a standard illumination (1 sun), respectively, and the resulted conversion efficiency is enhanced by 45%. In contrast with the cell with no ARC showing a rapid degradation with increasing concentration power, the efficiency of ARC-deposited cell remains almost constant as ($17.7{\pm}0.3$)% regardless of the concentration. It informs that ARC treatment is very effective in GaAs concentrator solar cells.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.347-348
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• 2013

To obtain high conversion efficiency in InGaN-based solar cells, it is critical to grow high indium (In) composed InGaN layer for increasing sun light absorption wavelength rage. At present, most InGaN-based solar cells adopt InGaN/GaN multi-quantum-well (MQW) structure for high crystalline quality of InGaN with high In composition. In this study, we fabricated and compared the performances of two types of InGaN/GaN MQW solar cells which have the 15% (SC 15) and 25% (SC 25) of In composition at quantum well layer. Although both devices showed similar dark current density and leakage current, SC 15 showed better performance under AM 1.5G illumination as shown in Fig. 1. It is interesting to note that SC 25 showed severe current density decrease as increasing voltages. As a result, it lowered short circuit current density and fill factor of the device. However, SC 15 showed steady current density and over 75 % of fill factor. To investigate these differencesmore clearly, we analyzed their photoluminescence (PL) spectra under various applied voltages as shown in Fig. 2. At the same time, photocurrent, which was generated by PL excitation, was also measured as shown in Fig. 3. Further, we investigated the relationship between piezoelectric field and performance of InGaN based solar cell varying indium composition.

• Journal of the Optical Society of Korea
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• v.18 no.2
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• pp.180-183
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• 2014

The surface of semiconductor solar cells, such as a-Si or CIGS (CuInGaSe) solar cells is not flat but textured in the microscopic domain. With textured surfaces, the optical reflectivity of a solar cell is different from that of flat surfaces in the wavelength region. In this paper, the effects of a textured surface on a CIGS solar cell are presented by RCWA (Rigorous Coupled Wave Analysis) method. The effect of incoherent light is also considered by RCWA with a Fourier analysis while conventional optical simulation uses the input light on the solar cell as coherent light. Using experimental results, the author showed that the RCWA method with a Fourier analysis is a proper method to simulate the optical properties of CIGS solar cells.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.196.2-196.2
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• 2013

본 연구에서는 분자선 에피택시 (MBE)법으로 성장된 InAs submonolayer quantum dot (SML-QD)을 태양전지에 응용하여 광학 및 전기적 특성을 평가하였다. 본 연구에서 사용된 양자점 태양전지(quantum dot solar cell, QDSC)의 구조는 n+-GaAs 기판 위에 n+-GaAs buffer와 n-GaAs base layer를 차례로 성장 한 후, 활성영역에 InAs/InGaAs SML-QD와 n-GaAs spacer layer를 8주기 형성하였다. 그 위에 p+-GaAs emitter, p+-AlGaAs window layer를 성장하고 ohmic contact을 위하여 p+-GaAs 를 성장하였다. SML-QD 구조의 두께는 0.3 ML 이며, 이때 SML-QD의 적층수를 4 stacks 으로 고정하였다. SML-QD 와의 비교를 위하여 2.0 ML크기의 InAs자발 형성 양자점 태양전지(SK-QDSC)과 GaAs 단일 접합 태양전지 (reference-SC)를 동일한 성장조건에서 제작하였다. PL 측정 결과, 300 K에서 SML-QD의 발광 피크는 SK-QD 보다 고에너지에서 나타나는데(1.349 eV), 이것은 SML-QD가 SK-QD보다 작은 크기를 가지기 때문으로 사료된다. SML-QD는 single peak를 보이는 반면, SK-QD는 dual peaks (1.112 / 1.056 eV)을 확인하였다. SML-QD의 반치폭(full width at half maximum, FWHM)이 SK-QD에 비하여 작은 것으로 보아 SML-QD가 SK-QD보다 양자점 크기 분포의 균일도가 높은 것으로 해석된다. Illumination I-V 측정 결과, SML-QDSC의 개방 전압(VOC) 과 단락전류밀도(JSC)는 SK-QDSC의 값과 비교해 보면, 각각 47 mV와 0.88 mA/cm2만큼 증가하였다. 이는 SK-QD보다 상대적으로 작은 크기를 가진 SML-QD로 인해 VOC가 증가되었으며, SML-QD가 SK-QD 보다 태양광을 흡수할 수 있는 영역이 비교적 적지만, QD내에 존재하는 energy level에서 탈출 할 수 있는 확률이 더 높음으로써 JSC가 증가한 것으로 분석 된다.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.1
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• pp.46-50
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• 1990

Heteroface AlGaAs/GaAs drift solar cells with an active area conversion efficiency of 15.9% under one sun and AM 1.5 condition have been grown by molecular beam epitaxy(MBE). These drift solar cells have graded doping profiles in the base and emitter regions. The cells have a short circuit current density (Jsc) of 19.00 mA/cm\ulcorner an open circuit voltage(Voc) of 0.93 V, and f fill factor(FF) of 0.78, respectively. Conventional solar cells with fixed doping profiles were also grown by MBE for comparison with the drift solar cells. Even though the fabrication cost of MBE grown solar cell is higher, the expected highest conversion efficiency of the single or multiple cells could compensate for the increased cost, particularly in case of space applications.

• Journal of the Korean Vacuum Society
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• v.22 no.3
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• pp.162-167
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• 2013

An epitaxial layer structure for heterojunction p-InGaP/N-InAlGaP solar cell has proposed. Simulation for current density-voltage characteristics has been performed on p-InGaP/N-InAlGaP structure and the simulation results were compared with p-InGaP/p-GaAs/N-InAlGaP structure and homogeneous InGaP pn junction structure. The simulation result showed that the maximum output power and fill factor have greatly increased by replacing n-InGaP with N-InAlGaP. The thicknesses of p-InGaP and n-InAlGaP were optimized for the epitaxial layer structure of p-InGaP/N-InAlGaP.

• Journal of the Microelectronics and Packaging Society
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• v.26 no.4
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• pp.75-82
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• 2019

Flexible solar cells have attracted enormous attention in recent years due to their wide applications such as portable batteries, wearable devices, robotics, drones, and airplanes. In particular, the demands of the flexible silicon and compound semiconductor solar cells with high efficiency and high reliability keep increasing. In this study, we fabricated a flexible InGaP/GaAs double-junction solar module. Then, the effects of the wind speed and ambient temperature on the operating temperature of the solar cell were analyzed with the numerical simulation. The temperature distributions of the solar modules were analyzed for three different wind speeds of 0 m/s, 2.5 m/s, and 5 m/s, and two different ambient temperature conditions of 25℃ and 33℃. The flexibility of the flexible solar module was also evaluated with the bending tests and numerical bending simulation. When the wind speed was 0 m/s at 25 ℃, the maximum temperature of the solar cell was reached to be 149.7℃. When the wind speed was increased to 2.5 m/s, the temperature of the solar cell was reduced to 66.2℃. In case of the wind speed of 5 m/s, the temperature of the solar cell dropped sharply to 48.3℃. Ambient temperature also influenced the operating temperature of the solar cell. When the ambient temperature increased to 33℃ at 2.5 m/s, the temperature of the solar cell slightly increased to 74.2℃ indicating that the most important parameter affecting the temperature of the solar cell was heat dissipation due to wind speed. Since the maximum temperatures of the solar cell are lower than the glass transition temperatures of the materials used, the chances of thermal deformation and degradation of the module will be very low. The flexible solar module can be bent to a bending radius of 7 mm showing relatively good bending capability. Neutral plane analysis was also indicated that the flexibility of the solar module can be further improved by locating the solar cell in the neutral plane.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.28A no.1
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• pp.30-39
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• 1991

The influence of physical parameters (Al mole fraction, thickness, doping concentration) in the window and emitter on the efficiency characteristics of heteroface p-$Al_{x}Ga_{1-x}As/p-GaAs/n-GaAs/n^{+}$-GaAs solar cell is investigated. The maximum efficiency theoretically calculated in this device is obtained when a thickness of the window is in a range of (400-1000))$\AA$and a thickness/doping concentration of the emitter is in a range of (0.5-0.8)$\mu$m/(1-7)${\times}10^{17}cm^{-3}$, respectively. Also is the efficiency improved according to the increase of Al mole fraction in the indirect gap window(0.41${\le}x{\le}1.0$). The optimum designed heteroface cell with an area of 0.165cm$^2$fabricated using MOCVD exhibits an active area conversion efficiency of 17%, having a short circuit current density of 21.2mA/cm\ulcorner an open circuit voltage of 0.94V, and a fill factor of 0.75 under ELH-100mW/cm$^2$illumination.

• Journal of the Korean Vacuum Society
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• v.18 no.5
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• pp.352-357
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• 2009

The InAs multi-quantum dots (MQDs) solar cell and InGaAs multi-quantum wells (MQWs) solar cell to cover 1.1 eV and 1.3 eV were designed by 1D poisson, respectively. The MQDs and MQWs of 5, 10, 15 layers were grown by molecular beam epitaxy. The photo luminescence results showed that the 5 period stacked MQDs have the highest intensity at around 1.1 eV with 57.6 meV full width at half maximum (FWHM). Also we can observe 10 period stacked MQWs peak position which has highest intensity at 1.31 eV with 12.37 meV FWHM. The density and size of QDs were observed by reflection high energy electron diffraction pattern and atomic force microscope. Futhermore, AlGaAs/GaAs sandwiched tunnel junctions were modified according to the width of GaAs layer on p-type GaAs substrates. The structures with GaAs width of 30 nm and 50 nm have backward diode characteristics. In contrast, tunnel diode characteristics were observed in the 20 nm of that of sample.