Organic light-emitting diodes (OLEDs) with high-definition displays require narrowband emission from each pixel. Recently, boron-based thermally activated delayed fluorescence (TADF) emitters have gained broad attention in the OLED research field. They can effectively utilize both singlet and triplet excitons for electroluminescence, resulting in a small full width of half maximum (FWHM). The fused nitrogen/boron (N/B) system, known as the multi-resonance TADF (MR-TADF) system, has been making rapid progress. In this review, we summarize the current research progress in both traditional and MR-type boron derivatives with TADF characteristics from a molecular construction perspective. We discuss the molecular design strategy involved in maintaining high device efficiency and simultaneously achieving a narrowband emission profile. This review aims to provide insight and guidance for future developments for improving the stability, color purity, and performance of boron-based materials.