Preparation of size-controlled fine Al particles for application to rear electrode of Si solar cells

Micron-sized aluminum (Al) particles are widely used in the fabrication of rear electrodes of Si solar cells. Moreover, the rear electrode of Si solar cells can be fabricated at relatively low electrode firing temperature using submicron Al particles whose sizes can be easily controlled, but there have not been any clear methods to obtain submicron Al particles yet. In this study, we first successfully prepared size-controlled Al submicron particles via a wet chemical process using dibutyl ether solvent and then to fabricate rear electrodes of Si solar cells; to our knowledge, this is the first such application of submicron Al particles. The geometric mean diameter (Dp) of the Al particles could be controlled from 139 to 614 nm by adjusting the reaction temperature, and the prepared Al particles showed geometric standard deviations (σg) of 1.25–1.30. The Al particle size was reduced to ∼35 nm by adding an organic surfactant to the precursor solution for Al particle preparation. Rear electrodes were fabricated by firing the screen printed Al paste films comprising Al particles with geometric mean diameters of ∼379 nm from 600 to 900° C. The electrode fired at 750 °C showed the minimum electrical sheet resistivity of 77.9 mΩ/□ (specific resistivity: 97.3 μΩ cm) and contained a BSF (back surface field) with a thickness of ∼3 μm. Our results indicate that the reported method can be used to minimize the thermal defects in the rear electrode of Si solar cells by lowering the electrode firing temperature.