Origin of Defects and Positron Annihilation in Hybrid and All-Inorganic Perovskites

Emerging metal-halide perovskites (MHPs) have shown advanced charge transport properties suitable for application in solar cells, photodetectors, and many more. While the past decade witnessed tremendous progress in MHPs, very little is known about the origin of defects and their effect on carrier lifetime. In this study, we compare hybrid and all-inorganic MHPs prepared by inverse temperature solution and high-temperature melt growth to explore the influence of material preparation on the formation of defects. The presence of a low concentration of vacancies was shown in all MHPs regardless of their synthesis method demonstrated by the interaction of positron particles with vacancies and lattices of MHPs and explained by ab initio simulation of positron annihilation. We combined the Raman, Fourier transform infrared (FTIR), and positron annihilation spectroscopy methods to establish the nature of imperfections in MHPs grown using different methods. Our Raman and FTIR results reveal that only the solution-grown crystals are prone to the incorporation of a solvent in bulk during synthesis. In vast majority of studies, the charge carrier lifetime is explored using photoluminescence (PL) spectroscopy as it is a readily available method. However, PL is very sensitive to both bulk and surface recombination phenomena. Combining current waveform time-of-flight and time-resolved photoluminescence spectroscopy methods, the bulk recombination differs by a factor of 2 from crystals grown by solution versus high-temperature melt. The results propose that solvent trapping matters, not intrinsic defects. The study also suggests potential pathways for further improvement of hybrid and all-inorganic MHPs.