Takuya Aoyagi

A Crystalline Metallic Copper Network Application Film Produced by High-Temperature Atmospheric Sintering

We show the first production of a copper (Cu) application film (AF) consisting of a novel network of crystalline metallic Cu embedded with copper-phosphorus-oxygen glasses (Cu 2(PO4) and Cu 2P2O 7) to provide new feedstock materials for crystalline silicon (Si) photovoltaics (PVs). The Cu crystal network was preferentially grown in AF, and thus, a Cu AF with low-electrical resistivity was formed in air at elevated temperatures of ≥ 450°C by using a copper-phosphorus (Cu-P) alloy paste as a starting material for the sintering. The Cu-P alloy had the role that governed deoxidization of a cuprous oxide, which was formed on heating during the sintering, by virtue of a concurrent oxidation of the Cu phosphide at elevated temperatures. Our results may open the way to the widespread use of atmospherically sintered Cu AFs for mass-production of next-generation crystalline Si PVs.

Lead-Free Low-Melting and Semiconductive Vanadate Glass Applicable to Low-Temperature Sealing

We optimized the fundamental composition and additives in a semiconducting V2O5–P2O5–TeO2 glass system to develop lead-free low-melting glass suitable for low-temperature sealing below 400 °C. Glass with a composition of 55.7V2O5–19.8P2O5–23.5TeO2 (mol %) has a low glass transformation temperature (Tg < 300 °C) as well as hard crystallization, and it is desired as a low-temperature sealing material. The effects of adding BaO, Sb2O3, MnO2, or Fe2O3 to the fundamental composition of 55.7V2O5–19.8P2O5–23.5TeO2 (mol %) on the thermal properties and water-vapor resistance were then characterized. Adding 11.7 mol % Fe2O3 improved the water-vapor resistance drastically and decreased the thermal expansion coefficient without increasing Tg. Sealing at 360 °C with our lead-free Fe2O3-added vanadate glass enabled practical airtight packaging on an electronic device.

Development of Innovative Application Films for Silicon Solar Cells Using a Copper–Phosphorus Alloy by an Atmospheric Sintering Process

In this paper we aim to develop copper (Cu)-based backside soldering tabs/pads for crystalline silicon (Si) solar cells using atmospheric sintering. In our previous study, we found that a Cu network can be formed in an application film (AF) by self-deoxidization when the AF consisting of copper-phosphorus (Cu-P) alloy paste is sintered in an atmospheric environment, and the Cu AF showed low electrical resistivity that satisfied the criteria for backside soldering tabs/pads. In this study, Si solar cells using Cu AF for front-side contacts were evaluated to confirm that Cu AF is applicable to Si solar cells in principle. The Cu-P alloy paste using Cu-7 mass%P particles was printed on an Si wafer and, finally, sintered at 640 °C in atmosphere. The resulting AF showed low electrical resistivity of 2.96 × 10 -5 Ωcm. The solar cell using the Cu AF and conductive glass layer had conversion efficiency (η) of 6.6%. We demonstrated the need for a barrier layer to prevent the formation of Cu 3Si compound on the Si wafer surface when applying it to Cu AF on the solar cells. Our results may improve the potential for the widespread use of an atmospheric sintered Cu AF as backside soldering tabs/pads for Si solar cells.