Hee-eun Song

A Study on the Optimization of CP Based Low-temperature Tabbing Process for Fabrication of Thin c-Si Solar Cell Module

Thin crystalline silicon (C-Si) solar cell is expected to be a low price energy source by decreasing the consumption of Si. However, thin c-Si solar cell entails the bowing and crack issues in high temperature manufacturing process. Thus, the conventional tabbing process, based on high temperature soldering (> 250°C), has difficulties for applying to thin c-Si solar cell modules. In this paper, a conductive paste (CP) based interconnection process has been proposed to fabricate thin c-Si solar cell modules with high production yield, instead of existing soldering materials. To optimize the process condition for CP based interconnection, we compared the performance and stability of modules fabricated under various lamination temperature (120, 150, and 175°C). The power from CP based module is similar to that with conventional tabbing process, as modules are fabricated. However, the output of CP based module laminated at 120°C decreases significantly (14.1% for Damp heat and 6.1% for thermal cycle) in harsh condition, while the output drops only in 3% in the samples process at 150°C, 175°C. The peel test indicates that the unstable performance of sample laminated at 120°C is attributed to weak adhesion strength (1.7 N) between cell and ribbon compared to other cases (2.7 N). As a result, optimized lamination temperature for CP based module process is 150°C, considering stability and energy consumption during the fabrication.

Control of ghost plating by antireflection coating layer stacking on crystalline silicon solar cells

During the plating process, ghost plating could appear when the quality of the passivation layer is poor, and it causes an increase in the recombination rate. In this paper, light-induced plating was applied, and various passivation layers were investigated to remove ghost plating in crystalline silicon solar cells. These included, (1) SiN_x, (2) double SiN_x layer, (3) double layer with thermal silicon oxide and SiN_x and (4) double layer of SiN_x and SiO_x by PECVD. For the plated solar cells, a laser was used to remove various ARC layers and phosphoric acid was spin-coated onto the doped silicon wafer prior to laser ablation. As a result, a thermal SiO₂/PECVD SiN_x layer showed the lowest pinhole density and its wet vapor transmission rate was characterized. The solar cell with the thermal SiO2/PECVD SiNx layer showed the lowest J₀₂ value, as well as improved V_oc and J_sc.

Electrical and chemical characterization of Al 2 O 3 passivation layer deposited by plasma-assisted atomic layer deposition in c-Si solar cells

Aluminum oxide (Al₂O₃) film by atomic layer deposition (ALD) is known to supply excellent surface passivation properties on crystalline Si surface. In this study, 10 nm Al₂O₃ film was deposited on crystalline silicon by plasma-assisted atomic layer deposition (PAALD). To optimize concentration of hydrogen in Al₂O₃ film, deposited RF power was changed from 100 W to 900 W. Then, annealing and firing process were conducted. After annealing and firing, fixed charge in Al₂O₃ film was calculated by conductance-voltage measurement (C-V) and structure change was analyzed by XPS because the structure is related to fixed charge.

Removal of Laser Damage in Electrode Formed by Plating in Crystalline Silicon Solar Cells

In this paper, we investigated the electrical properties of crystalline silicon solar cell fabricated with Ni/Cu/Ag plating. The laser process was used to ablate silicon nitride layer as well as to form the selective emitter. Phosphoric acid layer was spin-coated to prevent damage caused by laser and formed selective emitter during laser process. As a result, the contact resistance was decreased by lower sheet resistance in electrode region. Low sheet resistance was obtained by increasing laser current, but efficiency and open circuit voltage were decreased by damage on the wafer surface. KOH treatment was used to remove the laser damage on the silicon surface prior to metalization of the front electrode by Ni/Cu/Ag plating. Ni and Cu were plated for each 4 minutes and 16 minutes and very thin layer of Ag with 1 μm thickness was plated onto Ni/Cu electrode for 30 seconds to prevent oxidation of the electrode. The silicon solar cells with KOH treatment showed the 0.2% improved efficiency compared to those without treatment.

Study on Improving Surface Structure with Changing RF Power Conditions in RIE (reactive ion etching)

A textured front surface is required in high efficiency silicon solar cells to reduce reflectance and to improve light trapping. Wet etching with alkaline solution is usually applied for mono crystalline silicon solar cells. However, alkali texturing method is not appropriate for multi-crystalline silicon wafers due to grain boundary of random crystallographic orientation. Accordingly, acid texturing method is generally used for multi-crystalline silicon wafers to reduce the surface reflectance. To reduce reflectivity of multi-crystalline silicon wafers, double texturing method with combination of acid and reactive ion etching is an attractive technical solution. In this paper, we have studied to optimize RIE condition by different RF power condition (100, 150, 200, 250, 300 W).

A Simulation of Photocurrent Loss by Reflectance of the Front Glass and EVA in the Photovoltaic Module

The solar cell is a device to convert light energy into electric, which supplies power to the external load when exposed to the incident light. The photocurrent and voltage occurred in the device are significant factors to decide the output power of solar cells. The crystalline silicon solar cell module has photocurrent loss due to light reflections on the glass and EVA(Ethylene Vinyl Acetate). These photocurrent loss would be a hinderance for high-efficiency solar cell module. In this paper, the quantitative analysis for the photocurrent losses in the 300-1200 wavelength region was performed. The simulation method with MATLAB was used to analyze the reflection on a front glass and EVA layer. To investigate the intensity of light that reached solar cells in PV(Photovoltaic) module, the reflectance and transmittance of PV modules was calculated using the Fresnel equations. The simulated photocurrent in each wavelength was compared with the output of real solar cells and the manufactured PV module to evaluate the reliability of simulation. As a result of the simulation, We proved that the optical loss largely occurred in wavelengths between 300 and 400 nm.

Compatative analysis of system economics for the Korean and German photovoltaic sypport program

Recently the photovoltaic markets are rapidly changing to renovate the PV support system by government in Korea. This situation is due to changing Korean PV support system to the Renewable portfolio standard (RPS) in 2012, so PV market in Korea meets the confused stage. Actual state is demanded an objective analysis for governments support system because existing system (Feed-in Tariff) and RPS pilot project for 2011 coexist in 2011 now. And especially as Germany has retained the greatest PV market share for a long time globally, it is necessary that Korea checks their present conditions on policy for stable and continuous growth like German PV area. Therefore we compared and analyzed the PV support system (FIT) of Korea and Germany from an economical point of view.