ABSTRACT
Calcium titanium oxide has emerged as a highly promising material for optoelectronic devices, with recent studies suggesting its potential for favorable thermoelectric properties. However, current experimental observations indicate a low thermoelectric performance, with a significant gap between these observations and theoretical predictions. Therefore, this study employs a combined approach of experiments and simulations to thoroughly investigate the impact of structural and directional differences on the thermoelectric properties of two-dimensional (2D) and three-dimensional (3D) metal halide perovskites. Two-dimensional (2D) and three-dimensional (3D) metal halide perovskites constitute the focus of examination in this study, where an in-depth exploration of their thermoelectric properties is conducted via a comprehensive methodology incorporating simulations and experimental analyses. The non-equilibrium molecular dynamics simulation (NEMD) was utilized to calculate the thermal conductivity of the perovskite material. Thermal conductivities along both in-plane and out-plane directions of 2D perovskite were computed. The NEMD simulation results show that the thermal conductivity of the 3D perovskite is approximately 0.443 W/mK, while the thermal conductivities of the parallel and vertical oriented 2D perovskites increase with n and range from 0.158 W/mK to 0.215 W/mK and 0.289 W/mK to 0.309 W/mK, respectively. Hence, the thermal conductivity of the 2D perovskites is noticeably lower than the 3D ones. Furthermore, the parallel oriented 2D perovskites exhibit more effective blocking of heat transfer behavior than the perpendicular oriented ones. The experimental results reveal that the Seebeck coefficient of the 2D perovskites reaches 3.79 × 102 µV/K. However, the electrical conductivity of the 2D perovskites is only 4.55 × 10-5 S/cm, which is one order of magnitude lower than that of the 3D perovskites. Consequently, the calculated thermoelectric figure of merit for the 2D perovskites is approximately 1.41 × 10-7, slightly lower than that of the 3D perovskites.
ABSTRACT
This study investigates the effects of Rb doping on the Rb-formamidinium-methylammonium-PbI3 based perovskite photodetectors. Rb was incorporated in the perovskite films with different contents, and the corresponding photo-response properties were studied. Doping of few Rb (~2.5%) was found to greatly increase the grain size and the absorbance of the perovskite. However, when the Rb content was greater than 2.5%, clustering of the Rb-rich phases emerged, the band gap decreased, and additional absorption band edge was found. The excess Rb-rich phases were the main cause that degraded the performance of the photodetectors. By space charge limit current analyses, the Rb was found to passivate the defects in the perovskite, lowering the leakage current and reducing the trap densities of carriers. This fact was used to explain the increase in the detectivity. To clarify the effect of Rb, the photovoltaic properties were measured. Similarly, h perovskite with 2.5% Rb doping increased the short-circuit current, revealing the decline of the internal defects. The 2.5% Rb doped photodetector showed the best performance with responsivity of 0.28 AW-1 and ~50% quantum efficiency. Detectivity as high as 4.6 × 1011 Jones was obtained, owing to the improved crystallinity and reduced defects.
ABSTRACT
: In this study, a glass/indium tin oxide (ITO)/formamidinium-methylammonium-cesium (FA-MA-Cs) tri-cation lead iodide perovskite/poly(methyl methacrylate (PMMA)/Al memory device with a controlled composition of (FA0.75MA0.25)1-xCsxPbI3 (x = 0-0.1) is demonstrated to exhibit bipolar resistive switching behavior. The tri-cation organic-inorganic metal halide perovskite film was prepared by a one-step solution process in which the amount of Cs was varied to modify the property of FA0.75MA0.25PbI3. It was found that the microstructure and defect properties of films are highly dependent on the contents of FA, MA, and Cs in the perovskite. The results found that 5% CsI doping is the optimized condition for improving the quality of FA0.75MA0.25PbI3, forming a high quality tri-cation perovskite film with a smooth, uniform, stable and robust crystalline grain structure. The resistive switching on/off ratio of the (FA0.75MA0.25)0.95Cs0.05PbI3 device is greater than 103 owing to the improved thin-film quality. Moreover, for the 5% CsI doped FA0.75MA0.25PbI3 films, the endurance and the stability of retention are better than the non-doped film. The improved microstructure and memory properties are attributed to the balance stress of FA/MA/Cs with different ionic size. It suggests the potential to achieve a desired resistive memory property of tri-cationic perovskite by carefully adjusting the cation ratios.
