Organic-inorganic lead halide perovskite phases segregate (and their structures degrade) under illumination, exhibiting a poor stability with hysteresis and producing halide accumulation at the surface.In this work, we observed structural and interfacial dissociation in methylammonium lead iodide (CH NH PbI ) perovskites even under dark and vacuum conditions. Here, we investigate the origin and consequences of self-degradation in CH NH PbI perovskites stored in the dark under vacuum. Diffraction and photoelectron spectroscopic studies reveal the structural dissociation of perovskites into PbI , which further dissociates into metallic lead (Pb ) and I ions, collectively degrading the perovskite stability. Using TOF-SIMS analysis, AuI formation was directly observed, and it was found that an interplay between CH NH , I , and mobile I ions continuously regenerates more I ions, which diffuse to the surface even in the absence of light. Besides, halide diffusion causes a concentration gradient between Pb and I and creates other ionic traps (PbI , PbI ) that segregate as clusters at the perovskite/gold interface. A shift of the onset of the absorption band edge towards shorter wavelengths was also observed by absorption spectroscopy, indicating the formation of defect species upon aging in the dark under vacuum.

We have presented a detailed analysis of the phase transition kinetics and binding energy states of solution processed methylammonium lead iodide (MAPbI3) thin films prepared at ambient conditions and annealed at different elevated temperatures. It is the processing temperature and environmental conditions that predominantly control the crystal structure and surface morphology of MAPbI3 thin films. The structural transformation from tetragonal to cubic occurs at 60 °C with a 30 minute annealing time while the 10 minute annealed films posses a tetragonal crystal structure. The transformed phase is greatly intact even at the higher annealing temperature of 150 °C and after a time of 2 hours. The charge transfer interaction between the Pb 4f and I 3d oxidation states is quantified using XPS.

Tin-based perovskite materials have the drawbacks of high density of Sn vacancies, structural deformations of SnI 6 − octahedra, and oxidation of unstable Sn 2+ states, resulting in poor chemical stability processed at inert and open atmosphere. In this work, we demonstrate the temperature effects on reduction of Sn vacancies (V sn ) in polymorphic CsSnI 3 perovskite solar cells. Evidence of light-induced I − ion diffusion and an interplay between iodide and Sn vacancies were briefly presented. We have observed by X-ray photoelectron spectroscopy that the formation of iodide vacancies (V I ) are highly activated at 60 °C, contributing to the reduction of acceptor defects, mainly Sn vacancies (V sn ). The formation of SnO − and SnO 2 − at high temperature mitigates the Sn−I interaction and eventually increases the trap density at Au/CsSnI 3 interfaces. We have observed by time-of-flight secondary ion mass spectrometry that the delocalized I − ions are accumulated near the metal contacts and form AuI − ions which diffuse through the material, inhibiting the exciton transport.

We employed simple shear-force-dominated planetary ball milling to prepare graphene on a large scale (200 g per cycle) with less structural defects.