The electronic band structures of PEA (1.34 eV) according to the Shockley-Queisser-efficiency limit for single-junction semiconductor solar cells. For 2D monolayer PEA 2 SnI 4 , the conduction band stems mostly from the 5p orbital of Sn, while the hybrid state between Sn-5s and I-5p orbitals mainly contributes to the valence band (Figure ). Similarly, the valence band and conduction band of The spacer cation impact on the electronic band structure.