Gamma–ray irradiation of lead iodide precursor for enhanced perovskite crystalline properties

Abstract

We describe an effective method for tuning the structure of lead iodide (PbI2) via high-energy gamma (γ)-ray irradiation. The chemistry of the precursor used in preparing the solution critically determines the quality of the perovskite films and the photovoltaic performance. We investigated the dependence of the precursor crystal structure and morphology on the γ-ray irradiation dose without by-products. The crystal orientation of PbI2 gradually changed when PbI2 was exposed to γ-ray radiation, causing it to form high-valent iodoplumbates with organic solvents because of the increase in the Pb oxidation number required to maintain a planar structure. The iodoplumbates suppress rapid crystallization and limit the space available for the grains to grow, thereby improving perovskite crystallinity. We also analyzed the optical and electrical properties of a perovskite film containing the irradiated precursor and compared them with those of a film containing the pristine PbI2 precursor. The detailed analysis of the crystal structure of the film revealed the effects of γ-ray irradiation. The PSC devices produced with γ-irradiated precursor material displayed improved performance. The direct treatment of precursors with high energy sources, such as γ-rays, which does not involve fabrication, is efficient in improving perovskite structures.