Ghada Abdelmageed

Reliability, scalability, and excellent film properties with large crystals and low grain boundaries are essential for successfully commercializing perovskites in optoelectronic applications. Our previous reports introduced meniscus-guided blade coating, or shearing, which is referred to as one-step blade coating in the present study, as a promising method for depositing scalable perovskite films with millimetre-sized crystals, fulfilling two of the essential criteria. As a subsequent study, we investigated the stability of the films in response to humidity by employing a readily accessible hydrophobic molecule, oleic acid (OA), through surface passivation. We compared the quality of the surface treatment on films produced via one-step and two-step deposition methods utilizing spin and blade coating techniques while subjecting them to continuous exposure to high humidity levels. Initially, we applied OA to the films using spin-coating, which is the standard method for surface passivation. Our results prove that the film properties resulting from the deposition technique determine the effectiveness of the passivation process. A quick surface treatment using OA via spin coating can be highly effective for perovskite films with smooth surfaces and smaller grain sizes, in contrast to textured films with larger crystal sizes. By tailoring the surface treatment method from spin coating to dip coating, we demonstrated that OA can prolong the stability of perovskites for months under continuous high-humidity exposure.

Organometal halide perovskites are highly promising materials for photovoltaic applications, yet their rapid degradation remains a significant challenge. Here, the light-induced structural degradation mechanism of methylammonium lead iodide (MAPbI₃) perovskite films and devices is studied in low humidity environment using X-Ray Diffraction, Ultraviolet-Visible (UV-Vis) absorption spectroscopy, Extended X-ray Absorption Fine Structure spectroscopy, Fourier Transform Infrared spectroscopy, and device measurements. Under dry conditions, the perovskite film degrades only in the presence of both light and oxygen, which together induce the formation of halide anions through donation of electrons to the surrounding oxygen. The halide anions generate free radicals that deprotonate the methylammonium cation and form the highly volatile CH₃NH₂ molecules that escape and leave pure PbI₂ behind. The device findings show that changes in the local structure at the TiO₂ mesoporous layer occur with light, even in the absence of oxygen, and yet such changes can be prevented by the application of UV blocking layer on the cells. Our results indicate that the stability of mp-TiO2-MAPbI₃ photovoltaics can be dramatically improved with effective encapsulation that protects the device from UV light, oxygen, and moisture.