Distinct rubrene/CsPbI2Br interfacial energetics on spin-coated and vacuum evaporated perovskite films

Understanding the interfacial energetics between metal halide perovskites and organic charge transport layers is critical for optimizing charge transport and achieving high-performance optoelectronic devices. While significant progress has been made in improving device efficiency, the fundamental interfacial electronic structure, particularly the influence of fabrication methods on energy level alignments, remains insufficiently explored. In this study, we compare CsPbI₂Br films fabricated via spin coating and vacuum co-evaporation, using rubrene as a model hole-transporting layer. Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) reveal that spin-coated CsPbI₂Br films contain surface iodine vacancies and dangling bonds, which facilitate chemical interactions with rubrene. This results in the emergence of a new state below the valence band maximum and a relatively large hole injection barrier of ∼ 0.6 eV. In contrast, vacuum-evaporated CsPbI₂Br films exhibit smoother, defect-less surfaces that interact physically with rubrene. The resulting interfacial electron transfer induces a band bending like effect, along with a reduced hole injection barrier of ∼ 0.4 eV, favoring more efficient hole collection. These findings highlight the critical role of fabrication techniques in modulating interfacial energetics and charge injection barriers through structural and electronic modifications, offering essential insights into interface engineering strategies for optimizing the performance of perovskite-based optoelectronic devices.