The present study was concentrated on the synthesis of four coordinate mixed ligand copper(I) complexes containing 1,10-phenanthroline derivatives, which were produced from 1,10-phenanthroline-5,6-dione, substituted 1,2-aminobenzene and 1-(1-methyl-1H-pyrazol-4-yl) butane-1,3-di (acacp). The [CuL1-5(acacp)] produced complexes were evaluated using FT-IR, UV-Vis, Raman, mass, molar conductance, and elemental analyses. The 1,10-Phenanthroline derivative coordinates to the copper(I) ion in a bidentate fashion via the N(imine) atoms which along with 3-hydroxy-1-(1-methyl-1H-pyrazol-4-yl)but-2-en-1-one form a tetracoordinate complex. The complex has a distorted square planar coordination environment. Complexes with non-electrolyte composition are visible in the molar conductance measurements. The metal complexes mentioned above can be prepared for OLED devices using the solution approach since they are soluble in organic solvents. Based on emissive compounds as the dopants, effective solution-processed green, yellow, and red emitting OLEDs are created. The mixed ligand copper complexes achieved a high external quantum efficiency (EQE) of 26.8% with an extremely low efficiency roll-off of 10% at the high luminance of 10 000 nits, but also provides 18 times longer operational lifetime than that of the non-sensitized reference device. This finding firstly demonstrates the use of Cu(I) complex as an efficient TADF sensitizer and paves the way for practical applications of TADF sensitized OLEDs. The observed results suggested that the Cu(I) complex with a 1,10-Phenanthroline backbone coated on the OLED device achieved good performances due to the copper complex as emitter contain an imidazole moiety at the backbone of the diimine ligand and other heterocyclic cores, which increases the aromatic π-system compared to other ligand systems