Temperature dependency of excitonic effective mass and charge carrier conduction mechanism in CH3NH3PbI3-xClx thin films

Impact of Residual Strains on the Carrier Mobility and Sability of Perovskite Films

Solution-based inorganic-organic halide perovskites are of great interest to researchers because of their unique optoelectronic properties and easy processing. However, polycrystalline perovskite films often show inhomogeneity due to residual strain induced during the film's post-processing phase. In turn, these strains can impact both their stability and performance. An exhaustive study of residual strains can provide a better understanding and control of how they affect the performance and stability of perovskite films. In this work, we explore this complex interrelationship between residual strains and electrical properties for methylammonium CH3NH3PbI3-xClx films using grazing incidence X-ray diffraction (GIXRD). We correlate their resistivity and carrier mobility using the Hall effect. The sin2(ψ) technique is used to optimize the annealing parameters for the perovskite films. We also establish that temperature-induced relaxation can yield a significant enhancement of the charge carrier transports in perovskite films. Finally, we also use Raman micro-spectroscopy to assess the degradation of perovskite films as a function of their residual strains.

Physically Detachable and Operationally Stable Cs2 SnI6 Photodetector Arrays Integrated with µ-LEDs for Broadband Flexible Optical Systems

With the surge in perovskite research, practical features for future applications are desired to be secured, but the reliability of the materials and the use of hazardous Pb are longstanding problems. Here, an air-stable Cs₂ SnI₆ (CSI) is prepared via diluted hydriodic acid solvent-based precursor optimization during scalable hydrothermal growth. Materials characterization is performed using various elemental peak analyses and crystallographic identification. The resulting CSI exhibits long-term operating stability over 6 months, i) at elevated temperatures, ii) in ambient air, and iii) under light illumination from UV to near-infrared. More importantly, to demonstrate an intriguing class of applications up to system level, physically detachable CSI photodetector arrays (PD-arrays), integrated with micro-light-emitting-diodes (μ-LEDs) arrays, are successfully fabricated. In addition, 3 × 3 flexible CSI PDs are fully operational, even in air, and their spatial uniformity in pixels is quantitatively evaluated. The charge-transport mechanisms of the CSI PDs under light and elevated temperature are assessed via temperature-dependent characterization from 148 to 373 K, implying the involvement of 3D variable-range hopping. Multicycle evaluation of the CSI PD-arrays confirms their operational stability in AC and DC modes, demonstrating this platform's potential benefit for wireless optical interconnection in advanced Si technology.

Evaluation of the Thermoelectric Properties and Thermal Conductivity of CH3NH3PbI3-x Cl x Thin Films Prepared by Chemical Routes

The thermoelectric properties and thermal conductivity of mixed-phase CH₃NH₃PbI_3-x Cl _x thin films have been reported as a function of temperature, ranging from room temperature (RT) to 388 K. Thermoelectric study confirms that CH₃NH₃PbI_3-x Cl _x is a p-type material and the charge carrier transport in CH₃NH₃PbI_3-x Cl _x is governed by polarons and the thermal scattering process. The Peltier function and power factor are found to decrease initially up to ∼325 K, after which they increase with increasing temperature. The position of (E _F - E _V) of all samples drops down sharply to zero level around 325 K. The avalanches of thermoelectric properties at ∼325 K indicate the existence of tetragonal-cubic phase transition in CH₃NH₃PbI_3-x Cl _x . The calculated thermal conductivity is very low, as desired for thermoelectric materials, due to strong anharmonic interactions. Both the figure of merit (ZT) and device efficiency increase with increasing temperature. However, ZT remains small with temperature. Despite the limitations on the operating temperature range due to phase complexity and small ZT, CH₃NH₃PbI_3-x Cl _x exhibits reasonable thermoelectric power and low thermal conductivity. This signifies the possibility of CH₃NH₃PbI_3-x Cl _x as a prospective thermoelectric material.