Indirect Bandgap Emission of the Metal Halide Perovskite FAPbI₃ at Low Temperatures

In this work, we provide a picture of the band structure of FAPbI₃ by investigating low-temperature spin-related photophysics. When the temperature is lower than 120 K, two photoluminescence peaks can be observed. The lifetime of the newly emerged low-energy emission is much longer than that of the original high-energy one by two orders of magnitude. We propose that Rashba effect-caused spin-dependent band splitting is the reason for the emergence of the low-energy emission and verify this using the magneto-optical measurements.