Dongsun Kim

Electrical Properties of Screen Printed Silicon Solar Cell Dependent upon Thermophysical Behavior of Glass Frits in Ag Pastes

Ag pastes consist of Ag powder, vehicles, glass frits and additives, such as bismuth, aluminum and zinc. Pb–Bi oxide glass frits have been used in Ag pastes of silicon solar cells. The glass frit plays important roles in Ag paste. However, there are few studies of glass frit in Ag paste for silicon solar cell. In this study, the screen-printed silicon solar cell was investigated with Pb–Bi oxide glass frits in Ag pastes. The electrical properties of fabricated silicon solar cell were correlated to the viscous flow of glass frits in the Ag pastes during the fast firing. The glass particles were spread perfectly over the Ag and SiNx substrates with decreasing contact angle at approximately 700 °C. Based on our results, the thermophysical properties of Pb–Bi oxide glass frits can be helpful for understanding the contact formation of silicon solar cell and improving the solar cell performance.

Highly efficient and stable dye-sensitized solar cells from adding low melting point glass frits

TiO2 films were modified by adding a low melting point glass frit as a light scattering particle and applied to an anode electrode in dye-sensitized solar cells (DSSCs) to enhance the interconnection between TiO2 and fluorine doped transparent oxide. The optical properties, photovoltaic properties and microstructures of the photo electrodes were examined to determine the role of the low glass transition temperature (Tg) glass frit. Electrochemical impedance spectroscopy, the Brunauer-Emmett-Teller method and a scratch test were conducted to support the results. The DSSC with the TiO2 film containing 3 wt% low Tg frit showed optimal performance (5.1%, efficiency) compared to the TiO2-based one. The photocurrent density slightly decreased by adding 3 wt% low Tg frit due to its large size and non-conductivity. However, the decrease of current density was compensated for by the scattering effect, high surface area and low electron transfer impedance at the electrolyte-dye-TiO2 interface.

Interface Structures of Ag-Si Contacts with Thermal Properties of Frits in Ag Pastes

Ag pastes added to Bi-oxide frits have been applied to the electrode material of Si solar cells. It has been reported that frits induce contacts between the Ag electrodes and the Si wafer after firing. During firing, the control of interfaces among Ag, the glass layer, and Si is one of the key factors for improving cell performance. Specifically, the thermo-physical properties of frits considerably influence Ag-Si contact. Therefore, the thermal properties of frits should be carefully controlled to enhance the efficiency of cells. In this study, the interface structures among Ag electrodes, glass layers, and recrystallites on an n+ emitter were carefully analyzed with the thermal properties of lead-free frits. First, a cross-section of the area between the Ag electrodes and the Si wafer was studied in order to understand the interface structures in light of the thermal properties of the frits. The depth and area of the pits formed in the Si wafer were quantitatively calculated with the thermal properties of frits. The area of the glass layers between the Ag electrodes and Si, and the distribution of recrystallites on the n+ emitter, were measured from a macroscopic point of view with the characteristics of the frits. Our studies suggest that the thermophysical properties should be controlled for the optimal performance of Si solar cells; our studies also show why cell performance deteriorated due to the high viscosity of frits in Ag pastes.

Effects of the Physical Properties of Bismate Frits on Contact Formation Between Ag Electrodes and Si Emitter in Si Solar Cells

To improve the performance of Si solar cells after firing, it is necessary to control the thickness of the glass layers between the Ag and Si, and the formation of Ag when it recrystallizes into the Si emitter, both of which decisively influence the performance of the cell. In this study, the effect of the physical properties of the frits on the contacts between Ag and Si is verified. Interfaces of Ag electrodes/glass layers/Ag recrystallized into n+ emitter are formed when using high-fluidity frits. On the other hand, as the viscous flow of the frits slows as the temperature increases, an interface structure formed of Ag/thin glass/SiNx layers results, with the formation of Ag nanoprecipitates in the glass layers. Our results suggest that the viscous behavior of frits under increasing temperatures leads to the formation of distinct interfaces between Ag electrodes and Si.

Characteristics of Si Solar Cells with the Addition of Frits and Additives to Al Pastes

Thick Al films are used widely as the backside electrode material of Si solar cells. The formation of Al and a back surface field reduce the back-surface recombination and improve the cell performance. This study examined the characteristics of Si solar cells with the addition of frits and additives to Al pastes after firing. The reactions among Al powders, frits and additives were studied. The wetting behavior between each powder (Al powder, frit, additive) and Si, Al substrates was also measured as a function of the temperature. These preliminary studies show that the frits affect the adhesion between Al and Si. In addition, the proper additives prevent the bowing of Si wafer.

Wettability Between Vehicle and Lead/Bismuth Oxide Glasses

Lead and bismuth glass systems have different wettability, which affects the mixture of the paste (vehicle and frits) and the burn-out of the vehicle within a thick film. This study examined the reaction between the vehicle (ethyl cellulose (EC) with α-terpineol) and oxide glasses (PbO and Bi2O3 glasses). The contact angle with the vehicle on the Bi2O3 glass was found to be higher than that on the PbO glass. This suggests that Bi2O3 glass has lower driving force and work of adhesion than PbO glass.