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

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 mu m and a length of 4.2 mu m 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 degrees, 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 Omega to 13.5 Omega under an applied voltage of 1 V and from 18 Omega to 15.5 Omega 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.