Non-vacuum electroplated al for n-side electrode in Si solar cells

This paper reports Al electroplating on a Si substrate using a room-temperature ionic liquid for the metallization of Si solar cells. The ionic liquid electrolyte was prepared by mixing anhydrous AlCl₃ and 1-ethyl-3-methylimidazolium tetrachloroaluminate ([EMIM]AlCl₄). The plating process was carried out in a dry nitrogen box. A sacrificial Al anode was employed, making the electrolyte reusable for many deposition runs. The sheet resistance of the Al deposits was investigated to reveal the effects of pre-bake conditions, deposition temperature, and post-deposition annealing conditions. It was found that dense and adherent Al deposits with low electrical resistivity can be obtained directly on Si substrates over a wide range of temperatures using galvanostic deposition. The resistivity of the Al deposits was in the high 10^-6 Ω-cm range, similar to that of screen-printed Ag. The maximum process temperature for electroplated Al was 350°C. An all-Al Si solar cell, with an electroplated Al front electrode and a screen-printed Al back electrode, has been demonstrated, and its optimization and characterization will be reported soon.