In this paper, the Silvaco TCAD simulation tool is utilized for modeling of ternary chalcostibite copper antimony sulfide (CuSbS2) thin film solar cells (TFSCs). The earth-abundant CuSbS2 is a promising material as a solar absorber and hole transport layer due to its high optical absorption coefficient, and low cost. CuSbS2 based solar cell can be fabricated in vacuum-free environment. Mostly CdS is used as electron transport layer (ETL) in CuSbS2 based solar cell but the efficiency is low due to creation of Schottky barrier at the back-contact and substantial carrier recombination at the CuSbS2/CdS interface. Hence, a (ITO/n-TiO2/p-CuSbS2/Au) np heterojunction-based solar cell has been developed. The observed maximum power conversion efficiency (PCE) of 15.26% (open circuit voltage (Voc) = 823 mV, short circuit current (Jsc) = 28.48 mA/cm2, fill factor (FF) = 65.1%) is achieved by optimizing the absorber thickness (400 nm) of the solar cell. Different parameters like effect of absorber thickness, back contact, bandgap, carrier concentration, temperature, and defect density are optimized to find the best possible efficiency of the solar cell. The device also exhibits good performance stability at high temperatures. Based on results, a (ITO/n-TiO2/p-CuSbS2/Au) np heterojunction-based fabricated solar cell device is possible in future.