Interface Energy Alignment between Lead Halide Perovskite Single Crystals and TIPS-Pentacene

Abstract

At present, there is a huge development in optoelectronic applications using lead halide perovskites. Considering that device performance is largely governed by the transport of charges across interfaces and, therefore, the interfacial electronic structure, fundamental investigations of perovskite interfaces are highly necessary. In this study, we use high-resolution soft X-ray photoelectron spectroscopy based on synchrotron radiation to explore the interfacial energetics for the molecular layer of TIPS-pentacene and lead halide perovskite single crystals. We perform ultrahigh vacuum studies on multiple thicknesses of an in situ formed interface of TIPS-pentacene with four different in situ cleaved perovskite single crystals (MAPbI 3 , MAPbBr 3 , FAPbBr 3 , and Cs x FA 1−x PbBr y I 3−y ). Our findings reveal a substantial shift of the TIPSpentacene energy levels toward higher binding energies with increasing thickness, while the perovskite energy levels remain largely unaffected regardless of their composition. These shifts can be interpreted as band bending in the TIPS-pentacene, and such effects should be considered when assessing the energy alignment at perovskite/organic transport material interfaces. Furthermore, we were able to follow a reorganization on the MAPbI 3 surface with the transformation of the surface C 1s into bulk C 1s.

Composition dependence of X-ray stability and degradation mechanisms at lead halide perovskite single crystal surfaces

“…To obtain reliable results, it is crucial to identify and minimize any degradation from the measurement process itself. For example, PES is extensively used to study surfaces and interfaces of lead halide perovskites 9,10 and to investigate causes for their degradation when exposed to environmental stressors like humidity or heat. 3,11,12 However, the interpretation of the results becomes more challenging if X-ray induced initial shifts in binding energy position, 13 or the formation of metallic lead (Pb 0 ) are present.…”

“…3 To avoid these external factors, single crystal surfaces instead of thin film surfaces can be studied. We have shown that clean surfaces of perovskite single crystals can be prepared in vacuum through cleaving, 10,11,24 which enables us to study intrinsic behaviors of the material. Therefore, to take our previous study further and to gain insight into the behavior of lead halide perovskite surfaces with X-rays without the effects of grain boundaries, we decided to use perovskite single crystals in the work presented here.…”