A new, well-defined Thermally Activated Delayed Fluorescence (TADF) molecule was designed and synthesized based on a tert-butylcarbazole derivative. Density functional theory (DFT) calculations revealed an extended π-conjugated structure with a small singlet–triplet energy gap (ΔE_ST), facilitating efficient reverse intersystem crossing (RISC). Owing to its bulky tert-butyl substituent, the dye exhibited reduced aggregation and higher photoluminescence quantum yield (PLQY) in spin-coated solid films. Thermal analyses demonstrated excellent stability with decomposition temperatures above 360 °C, consistent with the increased rigidity imparted by the tert-butylcarbazole unit. Photophysical studies further revealed aggregation-induced emission (AIE). When incorporated into light-emitting electrochemical cells (LEECs), the organometallic complex [Ir(buoppy)₂(dmapzpy)]PF₆ acted as an effective host, promoting energy transfer and enabling devices with maximum external quantum efficiencies of 3.38%.