Two-Dimensional Halide Perovskite Materials Featuring 2‑(Methylthio)ethylamine Organic Spacers for Efficient Solar and Thermal Energy Harvesting

Two-dimensional (2D) halide-based hybrid perovskites are recognized as emerging materials for solar cells and thermoelectric applications. Here, we report on the electronic, optical, and thermoelectric properties of the 2-(methylthio)ethylamine (MTEA)-based 2D perovskites (MTEA)2PbI4 and (MTEA)2(MA)Pb2I7 using density functional theory calculations. The Rashba-splitting strength is observed to lie between 0.41 and 0.65 eV Å at four positions of the band structure of (MTEA)2(MA)Pb2I7. The strong sulfur–sulfur interaction between MTEA spacers results in a noticeable shift in the onset of the absorption spectrum. For (MTEA)2(MA)Pb2I7, a larger theoretical limit in the power conversion efficiency (29%) is calculated compared to (MTEA)2PbI4, which can be attributed to the absorption coefficient difference in both structures. The considered structures show very small effective electron masses, which results in an exceptionally high electron carrier mobility. The calculations yield an extremely large thermoelectric power factor of 42.3 mW/mK2 for (MTEA)2(MA)Pb2I7 at 300 K, which is even higher than that of 3D and 2D perovskites reported so far. The present work suggests that the (MTEA)-based 2D perovskites are promising candidates for application in solar- and thermal-energy harvesting

Enhancing the electronic and phonon transport properties of two-dimensional hexagonal boron nitride through oxygenation : A first principles study

Thermoelectric (TE) materials have gathered much attention due to their ability to harvest waste heat energy. To fulfill the goal of sufficient efficiency conversion two important parameters are required (1) low thermal conductivity and (2) high power factor (PF). Two dimensional (2D) hexagonal boron nitride (h-BN) is isostructural with graphene and composed of excellent opto-electronic properties, high mechanical and chemical stability, further exhibiting wide range of applications in diverse areas. Insulating nature of 2D h-BN can be tuned by different approaches such as functionalization, doping or hybrid structures. Therefore, present work focuses on the oxygenation of h-BN, i.e. BNO, for optimization of electronic and phonon transport properties using the state-of-the-art density functional theory (DFT) and Boltzmann transport equation. The presence of oxygen in out-of-plane direction leads to the buckling in h-BN resulting in 65% decrement in the lattice thermal conductivity of BNO (103.66 W/mK) at room temperature. Further, the giant reduction (from 4.63 to 0.7 eV) in electronic bandgap after oxygenation in h-BN is found, leading to the nine times larger electrical conductivity as compared to h-BN. The calculated power factor is almost double in case of BNO. Present study suggests, BNO might have promising utilization in high temperature thermoelectric applications