The efficacy of oleic acid treatment in passivating MAPbI ₃ films

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 <i>via</i> 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 <i>via</i> 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.