Influence of A site cation on nonlinear band gap dependence of 2D Ruddlesden-Popper A2Pb1-xSnxI4 perovskites

Ruddlesden-Popper phase (RPP) perovskites of the form A1(n-1)A2(2)B(n)X(3n+1) show great promise in stable photovoltaic (PV) devices or as light emitting diodes (LEDs). In particular, n = 1, monolayer RPPs of the form A(2)BX(4) have also shown great progress as the passivating layer for 3D perovskite PVs. We study the electronic behaviour of mixed B site A(2)Pb(1-x)Sn(x)I(4) where A = PEA or MA to investigate if the size of the A site cation indirectly affects the nonlinear band gap dependence of a 2D monolayer RPP layer. Both perovskites show a nonlinear behaviour primarily due to the relative energy difference between the Sn 5s-I 5p antibonding states and the Pb 6s-I 5p antibonding states, though the extent of the nonlinearity is reduced relative to 3D bulk perovskites due to the reduced dimensionality of these 2D structures. We also discuss the influence on band gap nonlinearity due to the structural distortions induced by the differences between the A site cation. This research presents a strategy to the design of mixed solid state 2D perovskites by tuning the structural parameters as well as metal and halide composition.