Herein, AgInSe2 absorber–based n‐In2S3/p‐AgInSe2/p+‐molybdenum disulfide heterojunction thin‐film solar device is numerically explored with the help of SCAPS‐1D software. The major focus of this numerical study is to inquire the performances of the purported solar cell and hence unearth the highest efficiency of the AgInSe2 (AISe) solar cell. Herein, the functions of different parameters like thicknesses, doping and defect density, working temperature, series, and shunt resistances are investigated. The recommended solar cell parades the short‐circuit current density, open circuit voltage, fill factor, and efficiency of 39.11 mA cm−2, 1.10 V, 82.26%, and 35.44%, respectively. It is noteworthy that the efficiency is comparatively higher than the previously reported AISe‐based solar cell. The AgInSe2 semiconductor is easy to fabricate as well as has good electrical properties, therefore this proposed solar cell is highly efficient and cost effective.