Photoelectronic mechanism investigation of the structural transformation of CH3NH3PbI3 perovskites from a subnanosheet to a microwire

Abstract

In this work, a subnanosheet CH₃NH₃PbI₃ perovskite with a side length of 260 nm was successfully structurally transformed into a microwire shape with a radius of 1.8 μm and a length of 4.2 μm via temperature tuning and solvent effects. The photoelectronic characteristics of both types of CH₃NH₃PbI₃ perovskite were investigated, and the structural transformation mechanism was demonstrated. TEM results showed that the crystal distance increased from 0.254 nm to 0.325 nm when the subnanosheet structure CH₃NH₃PbI₃ perovskite transformed into the microwire shape. The rotation angle of the covalent bond decreased by 3.92°, based on the TEM results, which was attributed to the subnanosheet having a 0.03 eV lower energy than that of the microwire shape, as characterized by the fluorescence spectrum. Further analysis of the structural transformation was performed by employing a DC constant power source and a laser source at a wavelength of 446 nm. Experimental results showed that the resistance of the subnanosheet decreased from 14 Ω to 13.5 Ω under an applied voltage of 1 V and from 18 Ω to 15.5 Ω under an applied voltage of 5 V, which has the largest reducement ratio of resistance reaching 12.5% when it transformed into a microwire. Compared to the microwire-shaped CH₃NH₃PbI₃ perovskite, the power absorption of the subnanosheet was 25% to 50% higher when the incident power ranged from 1.15 W to 0.25 W. This study provides insight into the characteristic differences of CH₃NH₃PbI₃ upon structural transformation and offers suggestions for choosing a suitable perovskite structure for an application.