Impact of Spacer Cation on the Properties of Two-Dimensional Monolayer Hybrid Halide Perovskites

Poor long-term stability of hybrid halide perovskites has severely inhibited their large-scale commercial applications. Recently emerging low-dimensional hybrid halide perovskites have much more enhanced long-term stability, but their wide bandgap and strong quantum well confinement severely hinder various optoelectronic applications. How to tackle these issues without sacrificing long-term stability, therefore, has been emerging as a crucial materials science concern. Based on the first principal calculations, we have investigated the impact of spacer cation on the properties of 2D monolayer hybrid halide perovskites in depth. Our simulations reveal that strong interactions of spacer cation with each other and with MX{_6}{^4–} backbone not only enhance the thermo stability of MX{_6}{^4–} backbone and protect it against water molecules, but also modulate the electronic properties via altering the crystalline structure. More importantly, the delocalized orbitals and relatively high dielectric constants of spacer cation resulting from the conjugated benzene ring weaken the quantum well confinement and potential barrier well, thus allowing the efficient electron-hole separation and photo-generated carrier out-of-plane transport. The comprehensive effect of spacer cations on the properties of 2D monolayer hybrid halide perovskites observed here, thereby, clearly demonstrates the importance of finely selected spacer cations in adopting their photophysical properties.