Using the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional approach in the DFT calculations, a bandgap of 1.43 eV and 1.52 eV bandgap is determined under the HSE06+SOC and HSE06 conditions, respectively (refer to Figure ). The electronic band dispersion, illustrated in Figure , reveals a direct bandgap at 1.43 eV at the Y point in reciprocal space (0.5 0.5 0 in the reduced reciprocal lattice). The omission of spin-orbit coupling yields a higher band gap (1.63 eV; Figure ). The Kane effective masses of 0.23 and 1.52 are determined at the HSE06+SOC and HSE06 levels, respectively. Spin-orbital coupling is introduced to the HSE06 model to elevate the conduction band minimum (CBM), reducing the bandgap and Kane effective masses by 0.09 eV and 1.29, respectively. The transition probability between the VB and CB is reasonable high at the band edge; thus, the expected absorption scales with the joint density of states (Figure ). The (NH 3 (CH 2 ) 7 NH 3 ) 2 Sn 3 I 10 exhibits a unique perovskite-derived crystal structure compared to other structures with large organic cations, such as (NH 3 (CH 2 ) 6 NH 3 )SnI 4 and (NH 3 (CH 2 ) 8 NH 3 )SnI 4 . The comparison between these structures is shown in Figure .