The quest for high-performance solar cell absorbers has garnered significant attention in the field of photovoltaic research in recent years. To overcome the Shockley–Queisser (SQ) limit of ∌31% for single junction solar cell and realize higher power conversion efficiency, the concept of an intermediate band solar cell (IBSC) has been proposed. This involves the incorporation of an intermediate band (IB) to assist the three band-edge absorptions within the single absorber layer. BaSnS2 has an appropriate width of its forbidden gap in order to host an IB. In this work, doping of BaSnS2 was studied based on hybrid functional calculations. The results demonstrated that isolated and half-filled IBs were generated with suitable energy states in the band gap region after group-IIIA element (i.e., Al, Ga, and In) doping at Sn site. The theoretical efficiencies under one sun illumination of 39.0%, 44.3%, and 39.7% were obtained for 25% doping concentration of Al, Ga, and In, respectively; thus, larger than the single-junction SQ-limit. Furthermore, the dopants have lower formation energies when substituting the Sn site compare to occupying the Ba and S sites, and that helps realizing a proper IB with three band-edge absorptions. Therefore, group-IIIA element doped BaSnS2 is proposed as a high-efficiency absorber for IBSC.