Publication date: 22nd July 2026
Metal halide perovskites are mixed ionic–electronic semiconductors in which vacancy-like defects formed during crystallization can influence phase stability, hysteresis, and degradation. Here I will discuss flash infrared annealing (FIRA) as a sub-second processing and diagnostic platform to access non-equilibrium defect landscapes in formamidinium lead iodide (FAPbI3) thin films [1–3].
FIRA replaces conventional minute-scale thermal annealing by millisecond-to-sub-second infrared pulses, allowing the perovskite conversion pathway to be driven far from quasi-equilibrium. Using high-speed optical imaging, X-ray diffraction/GIWAXS, positron annihilation lifetime spectroscopy (PALS), and first-principles calculations, we correlate crystallization history with alpha-phase retention and vacancy-like positron trapping signatures. In our latest FAPbI3 series, chemically and thermally modified films show a clear hierarchy in the PALS long-lifetime intensity ratio, with I2/I1 increasing from Cs-modified and fast-ramp FAPbI3 (~0.16–0.19) to TEMPO-modified films (~0.33) and long-ramp references (~0.47). First-principles positron calculations give a bulk lifetime close to the experimental short component and support the assignment of the long component to vacancy-like trapping environments, consistent with previous PALS/DFT studies of vacancy defects in lead halide perovskites [4]. These trends co-vary with the alpha-phase fraction obtained from XRD screening, indicating that the annealing pathway leaves a measurable defect fingerprint relevant to ionic stability.
This work positions FIRA not only as a scalable low-thermal-budget fabrication route, but also as a controlled perturbation method to study how crystallization kinetics, additive chemistry, and thermal history define vacancy populations that can later mediate ion migration, hysteresis, and degradation [5,6].
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