Electronic and\nOptical Properties of Sn/Ge-Substituted\n2D Dion-Jacobson Phase (3-AMPY)<sub>4</sub>Pb<sub>4</sub>I<sub>16</sub> Perovskite for Photovoltaic Applications: A First Principle Study

The\nstructural, electronic, optical, and photovoltaic properties\nof Sn/Ge-substituted 2D slightly shifted DJ phase (3-AMPY)<sub>4</sub>Pb<sub>4</sub>I<sub>16</sub> perovskite were investigated using first\nprinciple calculations. The toxic Pb was substituted in the primary\ngeometry by less toxic Sn/Ge. We found that Ge/Sn doping is energetically\nfavorable for decreasing and eliminating the Pb content in pristine\n(3-AMPY)<sub>4</sub>Pb<sub>4</sub>I<sub>16</sub>. On both Ge/Sn doping\ncritical characteristics for perovskite, strong optical absorption,\np–p/s-p couplings, and direct band gap are observed. The strong\np–p/s-p couplings in both Ge/Sn-substituted conformers decrease\nthe band gap of the pristine (3-AMPY)<sub>4</sub>Pb<sub>4</sub>I<sub>16</sub> to the value suitable for photovoltaic applications. This\nfurther helps us get good optical absorption coefficient and high-power\nconversion efficiency in (3-AMPY)<sub>4</sub>Pb<sub>4–<i>x</i></sub>Ge<sub><i>x</i></sub>I<sub>16</sub> (<i>x</i> = 1, 2, 3, 4) and (3-AMPY)<sub>4</sub>Ge<sub>4–<i>x</i></sub>Sn<sub><i>x</i></sub>I<sub>16</sub> conformers.\nThe partial density of states and band structure plots show significant\ncontributions of the dominant organic cation to the conduction band\nminimum. This contribution becomes more pronounced with increasing\nGe/Sn doping. The presence of Ge/Sn dopant atoms in the substituted\n2D (3-AMPY)<sub>4</sub>Pb<sub>4</sub>I<sub>16</sub> perovskite showed\nimproved photovoltaic performance compared to that of the pristine\nsystem. This study should form a basis for realizing a more benign\nphotovoltaic perovskite-based system.