Sintesis dan Karakterisasi BiOBr/TiO2 Nanotubes serta Penerapannya pada Sistem Tandem Dye Sensitized Solar Cell-Photoelectrochemistry (DSSC-PEC) untuk Konversi Nitrogen Menjadi Amonia = Synthesis and Characterization of BiOBr/TiO2 Nanotubes and Its Application in the Tandem System of Dye Sensitized Solar Cell-Photoelectrochemistry (DSSC-PEC) for Conversion of Nitrogen to Ammonia