Mobility Driven Thermoelectric and Optical Properties of Two-Dimensional Halide-based Hybrid Perovskites: Impact of Organic Cation Rotation

The pivotal impact of organic cation rotation may result in structural complexity in two-dimensional (2D) halide-based hybrid perovskites. The crucial role of the orientation of the organic cation (MA = CH3NH3+) in the 2D Ruddlesden-Popper phase (2DRP) is explored using density functional theory (DFT) calculations. Our results propose that the MA cation rotation imposes the structural distortion in the PbI6 network, which is further responsible for the changes in nature and value of the electronic bandgap, charge density and optical absorption. The spin-orbit coupling effect results in a wide range of Rashba splitting parameters being obtained from 0.04 to 0.278 eV Å. The simulated optical absorption spectra suggest that absorption edge for the alignment of the MA molecule along the X-axis (having unidirectional hydrogen bonds) is higher than that of the alignment of the MA cation in the z-direction. Furthermore, the unidirectional hydrogen bonds between the MA cation and Pb-I framework significantly help to achieve the highest mobility of charge carriers up to ∼1437 cm2 V-1 s-1. Such high mobility leads to supremacy in the thermoelectric transport properties, which are investigated for the first time with the rotation of the MA cation. The calculated thermoelectric power factor at room temperature shows exceptionally high values (up to 2.04 mW m-1 K-2), leading to desired applications in thermoelectric devices. The rotation of the MA cation might be utilized as a useful tool for variation in optical absorption and transport coefficients. Therefore, our results spark the idea to develop 2D perovskites for real-time perspective in solar and heat energy utilization.