• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.458.1-458.1
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• 2014

An effective light-managing structure has been achieved by using a nano-imprint method. A transparent conductor of indium-tin-oxide (ITO) was periodically nanodome-shaped to have a height of 200 nm with a diameter of 340 nm on a p-type Si substrate. This spontaneously formed a heterojunction between the ITO layer and Si substrate and effectively reduced the light-reflection. The ITO nanodome device response was significantly enhanced to 6010 from the value of 72.9 of a planar ITO film. The transparent conducting ITO nanodome structure efficiently manipulates the incident light driving into the light-absorber and can be applied in various photoelectric applications.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.250-253
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• 2007

An evaporated Ti/Pd/Ag contact system is most widely used to make high-efficiency silicon solar cells, however, the system is not cost effective due to expensive materials and vacuum techniques. Commercial solar cells with screen-printed contacts formed by using Ag paste suffer from a low fill factor and a high shading loss because of high contact resistance and low aspect ratio. Low-cost Ni and Cu metal contacts have been formed by using electroless plating and electroplating techniques to replace the Ti/Pd/Ag and screen-printed Ag contacts. Ni/Cu alloy is plated on a silicon substrate by electro-deposition of the alloy from an acetate electrolyte solution, and nickel-silicide formation at the interface between the silicon and the nickel enhances stability and reduces the contact resistance. It was, therefore, found that nickel-silicide was suitable for high-efficiency solar cell applications. The Ni contact was formed on the front grid pattern by electroless plating followed by anneal ing at $380{\sim}400^{\circ}C$ for $15{\sim}30$ min at $N_{2}$ gas to allow formation of a nickel-silicide in a tube furnace or a rapid thermal processing(RTP) chamber because nickel is transformed to NiSi at $380{\sim}400^{\circ}C$. The Ni plating solution is composed of a mixture of $NiCl_{2}$ as a main nickel source. Cu was electroplated on the Ni layer by using a light induced plating method. The Cu electroplating solution was made up of a commercially available acid sulfate bath and additives to reduce the stress of the copper layer. The Ni/Cu contact was found to be well suited for high-efficiency solar cells and was successfully formed by using electroless plating and electroplating, which are more cost effective than vacuum evaporation. In this paper, we investigated low-cost Ni/Cu contact formation by electroless and electroplating for crystalline silicon solar cells.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.688-688
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• 2013

Al-doped ZnO (AZO) thin films have attracted a lot of attention as a cheap transparent conducting oxide (TCO) material that can replace the expensive Sn-doped In2O3. In particular, AZO thin films are widely used as a window layer of chalcogenide-based thin film solar cells such as Cu(In,Ga)Se2 and Cu2ZnSnS4 (CZTS). Mostly important requirements for the window layer material of the thin film solar cells are the high transparency and the low sheet resistance, because they influence the light absorption by the activelayer and the electron collection from the active layer, respectively. In this study, we prepared the AZO thin films by RF magnetron sputtering using a ZnO/Al2O3 (98：2wt%) ceramic target, and the effect of the sputtering condition such as the working pressure, RF power, and the working distance on the optical, electrical, and crystallographic properties of the AZO thin films was investigated. The AZO thin films with optimized properties were used as a window layer of CZTS thin film solar cells. The CZTS active layers were prepared by the electrochemical deposition and the subsequent sulfurization process, which is also one of the cost-effective synthetic approaches. In addition, the solar cell properties of the CZTS thin film solar cells, such as the photocurrent density-voltage (J-V) characteristics and the external quantum efficiency (EQE) were investigated.

• Advances in nano research
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• v.3 no.3
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• pp.133-141
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• 2015

Influence of Ag nanoparticles on optical and photovoltaic properties of, silicon substrates, silicon solar cells and glass have been investigated. Silver nanoparticles have been fabricated by evaporation of thin Ag layers followed by the thermal annealing. The surface plasmon resonance peak was observed in the absorbance spectrum at 470 nm of glass with deposited silver nanoparticles. It is demonstrated that deposition of silver nanoparticles on silicon substrates was accompanied with a significant decrease in reflectance at the wavelength 360-1100 nm and increase of the absorption at wavelengths close to the band gap for Si substrates. We studied influence of Ag nanoparticles on photovoltaic characteristics of silicon solar cells without and with common use antireflection coating (ARC). It is shown that silver nanoparticles deposited onto the front surface of the solar cells without ARC led to increase in the photocurrent density by 39% comparing to cells without Ag nanoparticles. Contrary to this, solar cells with Ag nanoparticles deposited on front surface with ARC discovered decrease in photocurrent density. The improved performance of investigated cells was attributed to Ag-plasmonic excitations that reduce the reflectance from the silicon surface and ultimately leads to the enhanced light absorption in the cell. This study showed possibility of application of Ag nanoparticles for the improvement of the conversion efficiency of waferbased silicon solar cells instead of usual ARC.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.466.2-466.2
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• 2014

The Quantum dot (QD) solar cells have been under active research due to their high light harvesting efficiencies and low fabrication cost. In spite of these advantages, there have been some problems on the charge collection due to the limitation of the diffusion length. The modification of advanced nanostructure is capable of solving the charge collection problem by increasing diffusion length of electron. One dimensional nanomaterials such as nanorods, nanowires, and nanotubes may enhance charge collection efficiency in QD solar cells. In this study, we synthesized $TiO_2$ anatase nanorod arrays with length of 200 nm by two-step sol-gel method. The morphology and crystal structure for the nanorod were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The anatase nanorods are single-crystalline and possess preferred orientation along with (001) direction. The photovoltaic properties for the heterojunction structure QD solar cells based on the anatase nanorod were also characterized. Compared with conventional $TiO_2$ nanoparticle based QD solar cells, these nanostructure solar cells exhibited better charge collection properties due to long life time measured by transient open circuit studies. Our findings demonstrate that the single crystalline anatase nanorod arrays are promising charge transport semiconductors for heterojunction QD solar cells.

• Korean Journal of Materials Research
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• v.28 no.1
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• pp.38-42
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• 2018

Continuous efforts are being made to improve the efficiency of Si solar cells, which is the prevailing technology at this time. As opposed to the standard front-lit solar cell design, the back-lit design suffers no shading loss because all the metal electrodes are placed on one side close to the pn junction, which is referred to as the front side, and the incoming light enters the denuded back side. In this study, a systematic comparison between the two designs was conducted by means of computer simulation. Medici, a two-dimensional semiconductor device simulation tool, was utilized for this purpose. The $0.6{\mu}m$ wavelength, the peak value for the AM-1.5 illumination, was chosen for the incident photons, and the minority-carrier recombination lifetime (${\tau}$), a key indicator of the Si substrate quality, was the main variable in the simulation on a p-type $150{\mu}m$ thick Si substrate. Qualitatively, minority-carrier recombination affected the short circuit current (Isc) but not the opencircuit voltage (Voc). The latter was most affected by series resistance associated with the electrode locations. Quantitatively, when ${\tau}{\leq}500{\mu}s$, the simulation yielded the solar cell power outputs of $20.7mW{\cdot}cm^{-2}$ and $18.6mW{\cdot}cm^{-2}$, respectively, for the front-lit and back-lit cells, a reasonable 10 % difference. However, when ${\tau}$ < $500{\mu}s$, the difference was 20 % or more, making the back-lit design less than competitive. We concluded that the back-lit design, despite its inherent benefits, is not suitable for a broad range of Si solar cells but may only be applicable in the high-end cells where float-zone (FZ) or magnetic Czochralski (MCZ) Si crystals of the highest quality are used as the substrate.

• Korean Chemical Engineering Research
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• v.58 no.1
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• pp.1-20
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• 2020

Development of efficient methods for clean energy production became a critical issue to improve the quality of human lives. Solar cells is considered as one of the alternative solutions to resolve the issue. Although Si-based solar cells are only popularly utilized for practical applications, high manufacturing cost is considered as a serious drawback for further versatile applications. Thus, different types of are being investigated aiming to replace the Si-based solar cells. Recently, perovskite solar cells (PSC) are considered as a potential replacement for Si-based solar cells due to their low production cost, high power conversion efficiency, light weight and possibility of flexible device fabrication. Thus, we have reviewed the challenges of PSC faced with practical application, particularly on stability.

• Journal of the Korean Solar Energy Society
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• v.34 no.6
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• pp.75-83
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• 2014

Heat loss through windows and doors occupies 20 to 45% of the total heat loss in building. It accounts for a large proportion of the total heat loss in building. In order to suppress the amount of heat flow through the windows and doors were considered actions such as reinforcement of insulation performance of window, adoption of low-e glass, and installation of solar heat shading device. The Purpose of this study is to compare solar heat shading performances of 3 types of internal blinds in the summer. In order to verify the solar heat shading performances of the blinds, a roll blind, blind A(Venetian blind) and blind B(Daylight guiding venetian blind)were installed in the four rooms with the same environmental conditions. As a result of the experiment, the blind B, blind A, roll blind showed an excellent performance in that order. Its because the blind B is made of aluminum materials coated with special paints on surface. It doesn't converted to long wave by short wave light. and it is reflected to short wave to outside.

• 한국태양에너지학회:학술대회논문집
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• 2011.11a
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• pp.34-39
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• 2011

Screen printing method is a common way to fabricate the crystalline silicon solar cell with low-cost and high-efficiency. The screen printing metallization use silver paste and aluminum paste for front and rear contact, respectively. Especially the rear contact between aluminum and silicon is important to form the back surface filed (Al-BSF) after firing process. BSF plays an important role to reduces the surface recombination due to $p^+$ doping of back surface. However, Al electrode on back surface leads to bow occurring by differences in coefficient of thermal expansion of the aluminum and silicon. In this paper, we studied the properties of mono crystalline silicon solar cell for rear electrode with aluminum and aluminum-boron in order to characterize bow and BSF of each paste. The 156*156 $m^2$ p-type silicon wafers with $200{\mu}m$ thickness and 0.5-3 ${\Omega}\;cm$ resistivity were used after texturing, diffusion, and antireflection coating. The characteristics of solar cells was obtained by measuring vernier callipers, scanning electron microscope and light current-voltage. Solar cells with aluminum paste on the back surface were achieved with $V_{OC}$ = 0.618V, JSC = 35.49$mA/cm^2$, FF(Fill factor) = 78%, Efficiency = 17.13%.

• 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.