The mechanism of the isostructural phase transition in C(NH2)3PbI3 as a guide for understanding the properties of the new phase

Abstract

Hybrid organic-inorganic perovskites (HOIPs) have attracted considerable attention, especially organometal trihalide perovskite, as promising materials for high-efficient solar cells. An interesting organic cation that can be incorporated in perovskite structure is the guanidinium (GUA) cation. Therefore, a number of investigations have been performed on the structure, stability and phase transitions of GUAPbI3. Herein, a study of the isostructural phase transition that is for the first time detected in GUPbI3, as well as some properties of the phase related to this transition, are presented. The existence of a new phase was deduced by the appearance of the temperature dependent isosbestic point at 47–48 °C in the infrared spectra, and the results obtained by the Raman spectroscopy. According to the powder X-ray diffraction (PXRD) patterns analysis, it was concluded that this phase transition is not accompanied by a change in the space group of the perovskite structure making it an isostructural one, and consequently, no additional peak at this temperature on differential thermal analysis (DTA) was detected. In order to relate the existence of this phase to the application of GUAPbI3 in solar cells, electrical measurements were undertaken from 24 to 71 °C. Thin films of GUAPbI3 on glass substrate were also prepared. The Ultra-violet and visible (UV/Vis) spectra of the corresponding phases were recorded and the band gaps were calculated.