<p>This work explores the spin-polarized transport properties of [3]triangulene-based molecular junctions, focusing on the pristine and boron/nitrogen (B/N)-doped systems, using density functional theory combined with the nonequilibrium Green’s function (DFT-NEGF) approach. Two types of device geometries, Au | [3]triangulene-dimer|Au and Au | [3]triangulene-nanostar|Au were examined for transport properties and spin filtering capabilities. The pristine systems exhibit an antiferromagnetic (AFM) ground state and yet demonstrate exceptional spin-filtering efficiency (SFE) under external bias due to induced spin-polarization. Furthermore, boron and nitrogen doping switch the ground state to ferromagnetic (FM), resulting in nearly perfect spin filtering efficiencies. Spin-polarized transmission spectra <i>T(E)</i>, density of states (DOS), and current-voltage (<i>I-V</i>) characteristics confirm strong spin transport performance, with all systems showing negative differential resistance (NDR) at higher bias voltages. These findings suggest [3]triangulene-based dimer and nanostar molecular junctions as promising candidates for next-generation spintronic devices, offering critical insights into spin transport and filtering mechanisms in carbon-based systems.</p>