The self-trapping of holes with the formation of a molecular X2– anion is a well-established process in metal halide (MX) crystals, but V-center (2X– + h+ → X2–) and H-center (X– + Xi– + h+ → X2–) defects have not yet been confirmed in halide perovskite semiconductors. The I2– split-interstitial defect is predicted to be a spin radical in CH3NH3PbI3 with an optically excited state in the semiconductor band gap.
The Crespo-Otero Research Group 