Role of PbO-based glass frit in Ag thick-film contact formation for crystalline Si solar cells

Abstract

The reactions between Ag pastes containing two types of PbO-based glass frits and an n-type (100) Si wafer during firing in air at 800°C were investigated in order to understand the mechanism for the formation of inverted pyramidal Ag crystallites at the Si interface as well as the effect of the PbO content of the glass frit on Ag crystallite formation. Inverted pyramidal Ag crystallites were formed by the precipitation of Ag atoms dissolved in fluidized glass during the subsequent cooling process after firing. PbO in the glass frit did not participate directly in the reaction with the Si wafer. However, its content had a strong influence on the reaction rate at the glass/Si interface and, thus, on the size and distribution of the Ag crystallites. The effect of the PbO content in the glass could be understood from the higher Ag solubility and lower viscosity of the glass at the firing temperature with increasing PbO content. Based on the experimental results, a model was proposed for the formation of Ag crystallites at the glass/Si interface during the firing process of screen-printed thick-film Ag metallization.

Effect of Pb–Te–O glasses on Ag thick-film contact in crystalline silicon solar cells

“…Numerous SEM top-view images have shown that Ag crystallites were grown all over Ag/Si interface ( Fig. 13(a) and (b)), indicating a complete etching of SiN x :H antireflective (ARC) layer ( $70 nm thick) through the redox reaction (2) [4]. However, Ag crystallites attached to the silicon surface of the cells were found to be different by using different PTO glasses.…”

“…Low-melting glass frit must be able to etch through the SiN x :H layer without damaging the emitter layer, thereby exposing the emitter surface and establishing electrical contact between the silicon and the silver contact [2,3]. In the metallization procedure, the glass frit melts could wet and dissolve the Ag powder at elevated temperature to generate a liquid glassy-phase, which would facilitate the sintering of Ag powder [2,4,5]. The flow behavior of the glassy-phase, to a degree, is associated with the capillary attraction force caused by the tiny spacing between Ag particles, and it also depends on the wetting ability of the glassy-phase itself to the anti-reflection layer [5].…”

“…The first model is based on the fact that Ag crystallites directly grow on the silicon emitter surface [7]. So it is suggested that the Ag crystallites, including those directly connected to Ag fingers and a multi-step tunneling process through the modified glass layer, have created a possible current transport paths from Si emitter to Ag finger [3][4][5]. Another model, the tunneling conduction mechanism, has been established on the discovery of nano-Ag colloids (Ag precipitates) in the thin glass layer between Ag finger and Si emitter [8,9].…”

Effects of precursors of glass material on the characteristics of silver-glass composite powders prepared by spray pyrolysis

“…The silver electrode is generally fabricated by the firing of a printed layer formed by a screen printing method using silver paste containing a silver powder, a glass frit, and a resin binder [1][2][3][4][5][6][7][8][9][10][11]. In order to improve the power generation characteristics of Si solar cells, it is important to examine the characteristics of the silver electrode.…”

Characteristics of silver–glass composite powders as the silver electrode for Si solar cells

“…A micron-sized glass frit with irregular morphology prepared by a conventional melting process is mainly used as a sintering agent in silver paste [4][5][6][7]. The characteristics of silver conducting films are affected by the composition of glass frits [8][9][10]. Glass frit with a softening point of 450-550 • C is generally used as the inorganic binder.…”