• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.400.1-400.1
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• 2016

Interfacial engineering approaches as an efficient strategy for improving the power conversion efficiencies (PCEs) of inverted polymer solar cells (iPSCs) has attracted considerable attention. Recently, polymer surface modifiers, such as poly(ethyleneimine) (PEI) and polyethylenimine ethoxylated (PEIE), were introduced to produce low WF electrodes and were reported to have good electron selectivity for inverted polymer solar cells (iPSCs) without an n-type metal oxide layer. To obtain more efficient solar cells, quantum dots (QDs) are used as effective sensitizers across a broad spectral range from visible to near IR. Additionally, they have the ability to efficiently generate multiple excitons from a single photon via a process called carrier multiplication (CM) or multiple exciton generation (MEG). However, in general, it is very difficult to prepare a bilayer structure with an organic layer and a QD interlayer through a solution process, because most solvents can dissolve and destroy the organic layer and QD interlayer. To present a more effective strategy for surpassing the limitations of traditional methods, we studied and fabricated the highly efficient iPSCs with mono-layered QDs as an effective multi-functional layer, to enhance the quantum yield caused by various effects of QDs monolayer. The mono-layered QDs play the multi-functional role as surface modifier, sub-photosensitizer and electron transport layer. Using this effective approach, we achieve the highest conversion efficiency of ~10.3% resulting from improved interfacial properties and efficient charge transfer, which is verified by various analysis tools.

• Current Photovoltaic Research
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• v.7 no.4
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• pp.103-110
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• 2019

Cu(In,Ga)₃Se₅ (β-CIGS) has a band gap of 1.35 eV, which is an optimum value for high solar-energy conversion efficiency. The effects of Cu and Ga content on the cell performance were investigated previously. However, the effect of Se content on the cell performance is not well understood yet. In this work, β-CIGS films were fabricated by three-stage co-evaporation of elemental sources with various Se fluxes at the third stage instead of at all stages. The average composition of five samples was Cu_1.05(In_0.59,Ga_0.41)3Se_y, where the stoichiometric y value is 5.03 and the stoichiometric Se/metal (Se/M) ratio is 1.24. We varied the Se/metal ratio in a range from 1.18 to 1.28. We found that the best efficiency was achieved when the Se/M ratio was 1.24, which is exactly the stoichiometric value where the CIGS grains on the CIGS surface were tightly connected and faceted. With the optimum Se/M ratio, we were able to enhance the cell efficiency of a β-CIGS solar cell from 9.6% to 12.0% by employing a Na₂S post deposition treatment. Our results indicate that Na₂S post deposition treatment is very effective to enhance the cell efficiency to a level on par with that in α-CIGS cell.

• Current Photovoltaic Research
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• v.4 no.2
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• pp.54-58
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• 2016

Laser-doped selective emitter process requires dopant source deposition, spin-on-glass, and is able to form selective emitter through SiNx layer by laser irradiation on desired locations. However, after laser doping process, the remaining dopant layer needs to be washed out. Laser-induced melting of pre-deposited impurity doping is a precise selective doping method minimizing addition of process steps. In this study, we introduce a novel scheme for fabricating highly efficient selective emitter solar cell by laser doping. During this process, laser induced damage induces front contact destabilization due to the hindrance of silver nucleation even though laser doping has a potential of commercialization with simple process concept. When the laser induced damage is effectively removed using solution etch back process, the disadvantage of laser doping was effectively removed. The devices fabricated using laser doping scheme power conversion efficiency was significantly improved about 1% abs. after removal the laser damages.

• Korean Journal of Materials Research
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• v.21 no.8
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• pp.432-438
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• 2011

In this study, chemical bath deposited (CBD) indium sulfide buffer layers were investigated as a possible substitution for the cadmium sulfide buffer layer in CIGS thin film solar cells. The performance of the $In_2S_3$/CIGS solar cell dramatically improved when the films were annealed at $300^{\circ}C$ in inert gas after the buffer layer was grown on the CIGS film. The thickness of the indium sulfide buffer layer was 80 nm, but decreased to 60 nm after annealing. From the X-ray photoelectron spectroscopy it was found that the chemical composition of the layer changed to indium oxide and indium sulfide from the as-deposited indium hydroxide and sulfate states. Furthermore, the overall atomic concentration of the oxygen in the buffer layer decreased because deoxidation occurred during annealing. In addition, an In-thin layer was inserted between the indium sulfide buffer and CIGS in order to modify the $In_2S_3$/CIGS interface. The $In_2S_3$/CIGS solar cell with the In interlayer showed improved photovoltaic properties in the $J_{sc}$ and FF values. Furthermore, the $In_2S_3$/CIGS solar cells showed higher quantum efficiency in the short wavelength region. However, the quantum efficiency in the long wavelength region was still poor due to the thick buffer layer.

• Current Photovoltaic Research
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• v.2 no.3
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• pp.95-102
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• 2014

Light trapping techniques can change the propagation direction of incident light and keep the light longer in the absorption layers of solar cells to enhance the power conversion efficiency. In thin film silicon (Si) solar cells, the thickness of absorption layer is generally not enough to absorb entire available photons because of short carrier life time, and light induced degradation effect, which can be compensated by the light trapping techniques. These techniques have been adopted as textured transparent conduction oxide (TCO) layers randomly or periodically textured, intermediate reflection layers of tandem and triple junction, and glass substrates etched by various patterning methods. We reviewed the light trapping techniques for thin film Si solar cells and mainly focused on the commercially available techniques applicable to textured TCO on patterned glass substrates. We described the characterization methods representing the light trapping effects, texturing of TCO and showed the results of multi-scale textured TCO on etched glass substrates. These methods can be used tandem and triple thin film Si solar cells to enhance photo-current and power conversion efficiency of long term stability.

• Current Photovoltaic Research
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• v.3 no.4
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• pp.135-139
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• 2015

$Cu_2SnS_3$ (CTS) based thin film solar cells (TFSCs) are of great interest because of its earth abundant, low-toxic and eco-friendly material with high optical absorption coefficient of $10^4cm^{-1}$. In this study, the DC sputtered precursor thin films have been sulfurized using rapid thermal annealing (RTA) system in the graphite box under Ar gas atmosphere for 10 minute. The systematic variation of sulfur powder during annealing process has been carried out and their effects on the structural, morphological and optical properties of CTS thin films have been investigated. The preliminary power conversion efficiency of 1.47% with a short circuit current density of $33.9mA/cm^2$, an open circuit voltage of 159.7 mV, and a fill factor of 27% were obtained for CTS thin film annealed with 0.05g of S powder, although the processing parameter s have not yet been optimized.

• Current Photovoltaic Research
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• v.3 no.4
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• pp.130-134
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• 2015

The high efficiency cell research processes through the KF post deposition treatment (PDT) of the $Cu(In,Ga)Se_2(CIGS)$ thin film has been very actively progress. In this study, it CIGS thin film deposition process when KF PDT 300 to the processing temperature, 350, $400^{\circ}C$ changed to soda-lime glass (SLG) efficiency of the CIGS thin film characteristics, and solar cell according to Na presence of diffusion from the substrate the effects were analyzed. As a result, the lower the temperature of KF PDT and serves to interrupt the flow of current K-CIGS layer is not removed from the reaction surface, FF and photocurrent is decreased significantly. Blocking of the Na diffusion from the glass substrate is significantly increased while the optical voltage, photocurrent and FF is a low temperature (300, $350^{\circ}C$) in the greatly reduced, and in $400^{\circ}C$ tend to reduce fine. It is the presence of Na in CIGS thin film by electron-induced degradation of the microstructure of CIGS thin film is expected to have a significant impact on increasing the hole recombination rate a reaction layer is formed of the K elements in the CIGS thin film surface.

• New & Renewable Energy
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• v.16 no.4
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• pp.65-75
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• 2020

The value of tangible assets depreciates over their useful life and this depreciation should be adequately reflected in any tax or financial reports. However, the method used to calculate depreciation can impact the financial performance of solar projects due to the time value of money. Korean tax law stipulates only one method for calculating the depreciation of solar photovoltaic facilities: the straight-line method. Conversely, USA's tax law accepts other depreciation methods as solar incentives, including the modified accelerated cost recovery system (MACRS) and Bonus depreciation method. This paper compares different depreciation methods in the financial analysis of a 10 MW solar system to determine their effect on the financial results. When depreciation was calculated utilizing the MACRS and Bonus depreciation method, the internal rate of return (IRR) was 10.9% and 16.4% higher, respectively, than when the Korean straight-line depreciation method was used. Additionally, the increased IRR resulting from the use of the two US methods resulted in a 20.5% and 27.4% higher net present value, respectively. This shows that changing the depreciation calculation method can redistribute the tax amount during the project period, thereby increasing the discounted cash flow of the solar project. In addition to increasing profitability, USA's depreciation methods alleviate the uncertainty of solar projects and provide more flexibility in project financing than the Korean method. These results strongly suggest that Korean tax law could greatly benefit from adopting USA's depreciation methods as an effective incentive scheme.

• Current Photovoltaic Research
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• v.9 no.1
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• pp.17-21
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• 2021

In this study, the effect of water level and temperature on the power generation was investigated in a water tank with an aquavoltaic PV module to perform feasibility research for the development of salt farm aquavoltaic system. The silicon solar cell attached to the bottom of each water tank is a 1-cell mini module, and the underwater effects of the crystal phase (19.0~19.9% of single- & 17.9~19.9% of poly-crystalline) of the PV module were investigated, and power generation characteristics for water level (0~10 cm) and temperature (10~40℃) were analyzed. The deterioration coefficients according to the water level and temperature of each single- and poly-crystalline module were investigated at very similar levels such as, -2.01 %/cm and -2.02 %/cm, -0.50 %/℃ and -0.48 %/℃, respectively. Therefore, in salt farm aquavoltaic system, water levels need to maintain as low as possible, and heat-induced degradation is similar to those shown in general land, and no factors have been found to be affected by the underwater environment depending on the determination.

• Current Photovoltaic Research
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• v.10 no.4
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• pp.95-100
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• 2022

Solar cell is a device that converts photon energy into electrical energy. Therefore, absorption of solar spectrum light is one of the most important characteristics to design the solar cell structures. Various methods have emerged to reduce optical losses, such as textured surfaces, back contact solar cells, anti-reflection layers. Here, the anti-reflection coating (ARC) layer is typically utilized whose refractive index value is between air (~1) and silicon (~4) such as SiN_x layer (~1.9). This research is to print a material called polydimethylsiloxane (PDMS) to form a double anti-reflection layer. Light with wavelength in the range of 0.3 to 1.2 micrometers does not share a wavelength with solar cells. It is confirmed that the refractive index of PDMS (~1.4) is an ARC layer which decreases the reflectance of light absorption region on typical p-type solar cells with SiN_x layer surface. Optimized PDMS printing with analyzing optical property for cell structure can be the effective way against outer effects by encapsulation.