In this article, AgGaTe2-based n-CdS/p-AgGaTe2/p+-SnS double-heterojunction solar cells have been designed and explored utilizing a solar cell capacitance simulator (SCAPS-1D). This design manifested n-type CdS and p+-type SnS as window and back surface field (BSF) layer, respectively with the AgGaTe2 absorber. The major contributing parameters of these layers such as thickness, doping concentration level, and bulk flaws have been adjusted to reach the optimum computation. This introduced n-CdS/p-AgGaTe2/p+-SnS double-heterostructure solar cell demonstrates the significant power conversion efficiency (PCE) of 32.48% with the open circuit voltage, VOC of 0.96 V, short circuit current, JSC of 38.64 mA/cm2, and the Fill factor, FF of 87.31%. This remarkable efficiency is originated by the formation of a higher built-in potential at the p-AgGaTe2/p+-SnS heterostructure and a decrease in the surface recombination velocity brought on by the SnS BSF layer. This computational study demonstrates the potential of AgGaTe2 as an absorber and SnS as a BSF layer, and pave the way for the AgGaTe2-based experimental research in the era of solar cells.