In the past decade, a new family of ternary chalcogenide absorber (TCA) materials MIMIIX2 (where, MI= Cu, Ag, Pb, MII =Sb, Bi, In and X=S, Se, Te) have studied. The Copper family of ternary chalcogenide CuSbS2 CuSbSe2 CuBiS2 and CuBiSe2 are amazing absorber materials for thin film solar cells due to their suitable band gap, high absorption coefficient, inexpensive, nontoxic, sustainable and environment friendly. In this paper, simulated copper vacancies defect density of CuSbS2 (CAS), CuSbSe2 (CASe), CuBiS2 (CBS) and CuBiSe2(CBSe) based heterojunction thin film solar cells (HJTFSC) with buffer CdS, intrinsic i-ZnO, window ZnO: Al and back contact Mo, and set the cell scheming ZnO: Al/i-ZnO/n-CdS/p- TCA/Mo. Major focus of influence of copper vacancies defect density impact on the performance of ternary chalcogenide with various parameters of solar cells i.e., short circuit current density (Jsc), open circuit voltage (Voc), form factor (FF) and efficiency (η). The cell parameter set at constant temperature 300K, thickness 2.5mm, carrier density 5x1016cm-3, front internal transmission coefficient 1, reverses voltage across L-R -1Vand illumination intensity 100 mW/cm2with AM1.5 sun light.