Band gap engineering and optoelectronic properties of all-inorganic Ruddlesden-Popper halide perovskites Cs2B(X1-uYu)4 (B = Pb, Sn; X/Y = Cl, Br, I)

In this article two-dimensional Ruddlesden-Popper (2DRP) halide perovskites Cs2B(X1-uYu)4 where B = Pb, Sn; X/Y = Cl, Br, I; and u = 0, 0.25, 0.5, 0.75, 1 are investigated for potential applications in optoelectronic, photoemission and photovoltaic devices. In these compounds the corner sharing B-centered [BX2Y4]4- units build the 2D [BX2Y2]n2n− plane, where the halides occupy the in-plane bridging and out of plane apical site respectively, while the spacer cation (Cs+) balancing the charge and separate the octahedral layers. These compounds have direct band gaps and spin orbit (SOC) calculations split Pb/Sn p-orbital and reduce the band gaps. The wide (1.04–3.45) and direct band gaps enable these materials for futuristic applications in optoelectronics, high speed ultrathin transistors and photodetectors. The anti-bonding lone-pair Pb/Sn-s orbital at the valence band edge is excellent for light absorption and photovoltaic performance. These compounds are good dielectric and optically functional materials for photovoltaic and energy storage devices due to their small values of charge carrier effective masses and large exciton binding energies. Therefore, the optical coefficients like dielectric function (real and imaginary), absorption coefficient and index of refraction are calculated.