Decisive Influence Of Amorphous Pbi2-X On The Photodegradation Of Halide Perovskites

Capturing the photolysis process of archetypal perovskite materials (such as methylammonium lead triiodide, MAPbI(3)) into metallic Pb-0 is fundamentally important to understand the photodegradation pathway of organic-inorganic hybrid perovskites (OIHPs). In this study, the photodecomposition pathway of a MAPbI(3) film in an atmospheric argon (Ar) gas environment was quasi-in situ studied comprehensively. Under light illumination, the decomposition of the perovskite film is first triggered at the grain boundaries, along with an obvious generation of metallic lead (Pb-0) nanoparticles. Then, the degradation sites extend into the inner MAPbI(3) grains. By calculating the growth kinetics of the Pb-0 enriched nanoparticles, we can find that it strictly obeys an interfacial diffusion-controlled growth model. Atomic resolution high angle annular dark-field (HAADF) characterization confirms that the Pb-0 enriched nanoparticles are with Pb@PbI2-x (x approximate to 0.4) core-shell structures, while the interface between crystalline MAPbI(3) and amorphous PbI2-x controls the photodegradation pathway of perovskite films. To the best of our knowledge, this is the first time to directly observe the photolysis process of perovskite films in a practical environment (Ar gas and light illumination), particularly with nano or even atomic-scale resolution. Furthermore, the discovery of the interfacial-controlled photodegradation pathway of MAPbI(3) into amorphous PbI2-x and then into Pb@PbI2-x aggregates has never been elucidated before.