Positron Annihilation Spectroscopic Investigation on the Origin of Temperature-Dependent Electrical Response in Methylammonium Lead Iodide Perovskite.

Organic-inorganic hybrid perovskite has appeared as one of the leading materials for realizing solution-based high-performing optoelectronic devices. The charge transport properties in this class of material are quite intriguing and still need to be carefully investigated. The temperature-dependent electrical property of methylammonium lead iodide (CHNHPbI) has been investigated by employing positron annihilation spectroscopy (PAS), which unambiguously reveals the gradual formation of open volume defects with the enhancement in temperature. The high-temperature ionic conductivity is due to the generation of both cationic (CHNH) and anionic (I) vacancies, possibly because of the elimination of methylammonium iodide (CHNHI) as identified from the coincidence Doppler broadening (CDB) of the positron annihilation spectroscopy. Further, the evolution of temperature-dependent defect density and corresponding electrical responses has been correlated with the structural phase transitions of CHNHPbI. This is the first ever report of temperature-dependent PAS measurement on hybrid lead halide perovskites to understand the nature and the origin of its electrical characteristics arising due to the variation in temperature.