Ligand-Mediated Revival of Degraded α-CsPbI to Stable Highly Luminescent Perovskite.

Although α-CsPbI is regarded as an attractive optical luminophore, it is readily degraded to the optically inactive δ-phase under ambient conditions. Here, we present a simple approach to revive degraded ("optically sick") α-CsPbI through "medication" with thiol-containing ligands. The effect of different types of thiols is systematically studied through optical spectroscopy. The structural reconstruction of degraded α-CsPbI nanocrystals to cubic crystals in the presence of thiol-containing ligands is visualized through high-resolution transmission electron microscopy and supported by X-ray diffraction analysis. We found that 1-dodecanethiol (DSH) effectively revives degraded CsPbI and results in high immunity towards moisture and oxygen, hitherto unreported. DSH facilitates the passivation of surface defects and etching of degraded Cs PbI phase, thus reverting them back to the cubic CsPbI phase, leading to enhanced PL and environmental stability.