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Cross-sectional TEM images of interlayer between Ag electrode and Si cell formed (a) without and (b) with Ag acetate. Inset shows low-magnification images of cross-sectional view of Ag electrode, and (a) is the high-magnification image of the box area. EDX line profiles were obtained from the dotted lines. Ag acetate in the Ag paste reduced the interlayer thickness from 22 ± 6 nm to 8 ± 3 nm. The EDX profile in (a) shows that Ag was present within the interlayer, as indicated by the contrast difference between the center and the edge of the interlayer.
Schematic diagram showing the mechanism of contact formation [(a-i)–(a-iv)] without Ag acetate and (b-i)–(b-v)] with Ag acetate. Without Ag acetate, (i) Ag paste after printing (ii) thermoplastically formed Al MG frit sandwiched between Ag powders and Si emitter. In the area indicated by a black box in Fig. ??? , this (iii) Al MG frit interdiffused with Ag powder on one side, and with Si emitter on the other side, thus forming Ag/Al and Si/Al solid solutions below the eutectic temperature. (iv) The Ag–A1 or Al–Si eutectic melting was followed by cooling, leading to the formation of a Ag–Al alloy on the surface of the Ag powders and a thick interlayer on Si emitter. With Ag acetate, (i) after printing the Ag paste, Ag acetate was randomly distributed in paste, and (ii) thermal decomposition of Ag acetate formed Ag nanocrystallites. The (iii) thermoplastically formed Al MG frit (iv) interdiffused with both the Ag powders and the Si emitter covered in Ag nanocrystallites below the eutectic temperature. Fig. ??? is an enlarged image of the area indicated by a black box in Fig. ??? . (v) Ag–Al and Al(Ag)–Si eutectic melting was followed by cooling, leading to the formation of a Ag–Al alloy and a thinner interlayer in comparison to the one formed without Ag acetate. (ii-1) SEM image showing Ag nanocrystallites formed from thermally decomposed Ag acetate on the surface of powders and Si emitters. The image was obtained after Ag paste was annealed up to 300 °C.
EELS profiles of Al, Al2O3, and interlayer formed with Ag acetate showing the presence of Al as Al2O3 in the interlayer.
I–V curve and summary of cell parameters correspond to the interdigitated back contact cell fabricated. A photovoltaic conversion efficiency of 20.3% was achieved at 1-sun concentration and AM 1.5G. The area and thickness of the cell were 154.8 cm2 and 130 μm, respectively.
Comparisons of both specific contact resistance and electrical resistivity of Ag electrode fabricated with using the Ag/Al MG paste with and without Ag acetate.
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